Friday, April 29, 2011

Brief recap of outbreak and glimpse into future

The tornadoes that occurred on Wednesday were very impressive due to both the amount of long-lived supercells as well as the viciousness of the tornadoes. My guess is that, synoptically, it was a once in a 15 to 20 year event based on tornado # / strength. However, what made it rarer, and the juice that feeds media in our country, is the death and destruction that it wreaked. If we looked at the number of deaths caused, it is more of a 1-in-40 year event (think back to 4/3/1974).

Another interesting note about the past event is to realize how impressive our technology has become ... For example, CIMMS Convective-initiation product (a real-time algorithm to sense for when boundary layer cumulus have reached the level of free convection) is now able to provide 15 to 20 minute lead times before a cell even shows up on radar.

Check it out here

Also, speaking of better technology, I've attached my 2 favorite images from Wednesday, and I'll admit that to get them, I actually took a picture of my TV as Greg Forbes was playing with his GRLevel 3 radar while I was eating dinner. Anyways, here they are: the first is the supercell that passed through Tuscaloosa and the second is a cross-section of that same cell that shows the core of the tornado as it extends well above the cloud base.

To finish up, I wanted to mention that we may be going into a prolonged lull for widespread severe weather. Even though I know long-range forecasts for severe weather are extremely risky business, ensembles have been showing the development of an Omega block with the axis of higher heights just east of the Rockies. The models have some skill at predicting blocks which is why I think we won't see a tornado west of the Mississippi river until ~May 15th or so ... Go ahead and start grilling me.

Here's an image from this morning's GFS ensembles. The contours show mean 500mb heights, the colors are the spread amongst the ensembles. Note that minimum in spread where many of the ensembles have a cut-off, blocking ridge, with two cutoff lows to the southeast and southwest.

Wednesday, April 27, 2011

April Tornadoes: Yes another plot!

Hey Chasers and Blog Followers,

As another follow up to Jake's and Dima's posts I saw that Greg Corbin (Warning Coordinating Meteoroligst for SPC) has put together a nice trend plot for April tornadoes. I figured I would add it to the page because he statistically shows what Dima was talking about and goes as far as to say, "More tornadoes are being reported, on average, than ever before and this appears to be due to secular/demographic changes in the reporting process." On this plot you can clearly see 1974, which was referenced by Dima, as the most signifcant Tornado April on record mainly due to several outbreaks that occured during that month.

Through yesterday (4/26/11) the April 2011 preliminary report total has swelled to 683 and again this number is sure to rise as more reports from yesterday are coming in as Storm Damage Surveys and radar studies are being conducted by the NWS offices. Today is also another HIGH Risk day with likely more potential than yesterday. I also wanted to throw out another couple of pretty impressive preliminary stats for this month: 16 of the 26 days thus far have had at least one documented tornado, 10 days with more than 20 tornado reports, 5 days with more than 50 reports, and 2 days with over 100 reports.

Dan aka Squall Line

Sunday, April 24, 2011

Follow up on storm reports

I am responding to Hailstone's previous post regarding tornado reports / records. First, let me state that April has been quite active. Do I think that it's the most active April on record? Sure, if you assume that reliable records started in say ~1990 when the nationwide radar system was upgraded. But, I think that 1974, due to the one outbreak on 4/3/1974 that had ~60 tornadoes F3 or stornger would've generated something like 500 reports in today's reporting system, so it's possible that on that one day alone, we could've overtaken the total for all of April 2011. Hailstone also mentioned the 4/1 report/ground truth ratio during the NC outbreak. It would be interesting to map out how this ratio changes for different parts of the country.

Here are a few other interesting things to consider ...

1. There has been 1 tornado report west of Oklahoma City all of this year. Hey, that must be another record! A record low, that is. What does that mean? All the other reports have been east of Oklahoma City, where the population density greatly increases. Even though the SPC's watches and NWS's warnings have been very impressive, people still died due to i) bad luck and ii) failure to heed the warnings.

2. One factor that affects reports is population density, the other may be the standards of the NWS in documenting tornadoes. I was on the NWS Milwaukee site reading about how the WI outbreak was also the most reports for April on record. When looking over the chart of path length, path width, etc., it seemed that the radar is of huge helping when picking out the short-lived tornadoes. I commend the NWS for becoming really, really good at documenting all the events that occurred, but with an increasing rigor to put every single event in the history books, it seems that the saying "records were meant to be broken" was never truer.

Friday, April 22, 2011

April SPC Reports

Hey fellas -
I can't let all this hooplah go on about the April tornado reports without saying anything... On April 16th there were 106 reports in North Carolina....and according to the Raleigh office there were 28 confirmed Tornadoes....Thats almost a 4/1 tornado report ratio

There are a lot more chasers (none better than us though) and overall better communication which accounts for the Report inflation.... I'm not saying that in the past there weren't multiple reports on 1 tornado, but I am saying that comparing this month to past months could be misleading.... In terms of Fantasy Football...its like comparing Jerry Rice's 22TD catches in 12 games during the 1987 season, to Randy Moss's 23 in 16 games for 2007......

Thursday, April 21, 2011

Severe Weather Event #2 4/22/11:

Hey Chasers and Blog followers,

I had made a post back on 4/18/11 discussing the historical perspective on April '11 Severe weather and where it falls in the history books. Current updated April Tornado reports are at 491! Tuesday's outbreak across Missouri and Illinois definitely added to the total and there were a few nasty tornadoes to boot. In that Monday post I had mentioned 4 future severe weather events. I wanted to put a post up for tomorrows event for those curious and any one thinking of chasing. I unfortunately will not be able to chase tomorrow due to work and I have a marathon to run the next morning. So no pics/vids from my end. Besides, I am holding out for Monday (Severe Weather Event #3), but that post will come on Sunday. Seeing as tomorrow is a bit complicated and given I've been putting all this attention towards the potential breaking of the single monthly total for "tor" reports, I am just going to focus on tornado hot spots for tomorrow, so no in depth Synoptic and Mesoscale setup. Only the "Go Zone".

The Go Zone:
There looks to be two favored areas for tornadoes tomorrow. The first area is along the warm front, cold front, sfc low triple point across NC Missouri/SW Illinois. Here strongest upper level forcing will move over area of maximized CAPE, enhanced shear, and > mid 60s tds. Any elevated storms that go surface based near or along the warm front will be aided by backed flow with time and will undoubtedly be rotating as right movers will be favored. Closer to the cold front across east central missori, surface based convection in the warm sector will happen a little bit later and will be aided by 850mb-700mb confluence region across central Missouri. Convection should start out as discrete storms and ultimately grow upscale as boundary layer flow/properties are modified by down drafts/gust fronts. I'd favor SW Illinois as prime spot for tornadoes from discrete sfc based cells.

The second area, which is a little harder to make out in the model data appears to be across Southcentral/eastern OK into North Central Texas. The southwest portion of the Cold Front associated with larger system will stall out into a quasi stationary front. To the South of this frontal area dewpoints should reach the mid to upper 60s all the way South and West as the dryline in West Texas. This front will extend SW to Northcentral Texas where it will meet up with a secondary surface low. Here backed upslope flow at the surface from thermally induced heat low will aid in 0-1km and 0-3km enhanced helicity values. Surface based Storms that form along and south of the quasi stationary front will have sufficient CAPE > 3500 J/KG and enhanced low level shear to make up for lack of stronger mid level flow. Farther to the South along the Texas dryline a few supercells may be possible before/jsut after sunset. There a greater chance for Large Hail exists, but given backed flow at the surface and very large cape values, could see a "tor".

Should be an interesting day. I am extremely excited to see how it all shakes out. If a few things shift over the next 12hrs, these Go Zones could be total busts, lol. All in the fun though.

Fearless Fantasy Forecast: o/u 15.5 Tornado Reports

Dan aka Squall Line
P.S. It's been way too quiet on this blog recently, what gives??? I'm about ready to propose we rename this blog,"Where the Squall Line meets Convergence and Helicity"

Tuesday, April 19, 2011

TVS picked up in Sleet "Supercell?"

Yep, no joke. Here's the image from WeatherTap:

TVS marked as red storm track line east of Beloit, WI. This occurred ~2145 UTC (4/19/2011).
And a satellite image to compliment that cell...

How about this one, the "snake" squall-line? Squall-line, ever seen this feature before? Few bookend vorticies out there tonight, wouldn't be surprised to hear about some nighttime tors.

And to play with model data 6 days out, it looks promising for a chase within range for those of us at UW...I'll eat crow when future runs have it 250 miles south, but thats fine. 

Helicity & Convergence

Monday, April 18, 2011

Severe Weather Outlook for the next 10 days:

Hey Chasers and Blog followers,

UPDATE 4/20/11:
After yesterdays powerful system and some updates to previous days, the official April '11 tornado report count is 481!!! 63 more tornado reports this month will break the old record of 543 in May '03. Again this is freaking insane considering the average number from April is around 150 reports historically!!! Stay tuned for more.

What a record breaking weekend for severe weather across the much of the central and southern portions of the country! All statistics, overinflation, and validity of every report aside, This past weekends three day severe weather event (tornado outbreaks) will likely go down in the history books as one of the most if not the most significant 3 day tornado outbreaks in history (even with the inflation of reports)and it has already gone down as the most deadly 3 day outbreak in history with 45 recorded deaths thus far. A three day running total of 267 tornado reports across 15 states and that number is still climbing. Here is an updated map from SPC of where we sit this year so far with Tornadoes:

That 501 total is after multiplying by 0.85 to address over counting (SPC also stresses this is raw data, subject to change). Total number of reports in 2011 thus far is 589. It is still early with 12 days left, but we are on our way to the most active Tornado month on record. As of 4/17/11 the April tornado report count was 371. After looking through various references, May 2003 was single most active tornado month on record at 543 reports.

I bring this point up because I believe there is a very real chance of breking this record when looking at the 10 day long range model output and that. Starting tomorrow, I count 4 upper level disturbances that will make their way across the heart of the country: 4/19/11, 4/22/11, 4/25/11, 4/27/11 each with significant potential to add to the April tornado total.

What I find fascinating is that each one of these upper level systems is following a simliar track off the Southern Rockies and then pushing NE across the Central Plains into the Central Midwest. Each system's upper level trough goes negatively tilted and has attendant surface Lows, fronts, rich moisture advection. I'll leave the stats/details/model output for another post. I know this pattern starts to become the norm as we get into May, but the fact that we have had such an active April already, the notion of breaking this record is something worth watching.

We are all witnessing weather history.

Dan aka Squall Line

Sunday, April 17, 2011

GO Zone shoveling edition

To comment further on the previous post, Convergence forgot the most important thing about forecasting this unfortunate April snow event...the GO ZONE!!!!

Based on the SREF forecast, Convergence's info, and my strong pessimism today, here is my snowfall GO ZONE:


Snow events: 1
Snow Precipitation: 2 inches
Frustration of Spring in WI (on scale of 1-10, where 10 is most frustrated): 7


Get your shovels ready!!!

I can't make this up, SREF, GFS and NAM all produce a swath of 2-4 inches over Madison between 7pm and 7am. Not sure how much will accumulate (Ground temperatures above 32F) on the ground but it certainly will snow for ~5hrs over night. At this point I am not even mad, just think it is hilarious, are we in late Feb or Mid April???

Here is the proof,

GFS 9z sounding from 12z run Sunday April 17th over Madison,
 NAM 9z sounding from 12z run Sunday April 17th

And the 3z run of the SREF Plumes...

The HRRR is not in range for the event and will be posted once its in.

Also, we should figure out the final name of the blog and organize the side bars a bit better. Welcome some suggestions.  I personally think just naming the blog, "Go Zone" would be great. That way there is no questioning who coined the term!


Wednesday, April 13, 2011

Severe Weather Southern Plains:4/14/11

Hey Chasers and blog Followers, Figured I would update everyone on the severe weathe situation forthcoming tomorrow afternoon/evening across the Central/Southern Plains. I realize that probably none of you will be able to chase this event tomorrow, but it does look like a quite favorable setup, even a classic type event.

**UPDATE 7:30am 4/14/11**
After looking at latest data and model guidance have shifted my target area to get to this afternoon a bit farther South and East. I will be working until 2:30pm CST and then plan to head out right after. Will be taking Rachel with me as she is a good luck charm, and can drive. This way I should be able to get better video and continue to analyze latest obs, radar, etc. Back up base support would still be great if anyone has some time in the 3pm-6pm time frame. Yesterday I had mentioned the Wichita, KS area and while I still think storms will initially fire in that area Surface dryline/encroaching coldfront will occlude with warm front faster to the West, will plan to target the Neodesha, KS/Coffeyville, KS, Nowata, OK area. Would like to get to > 60s Td and be South of the leading edge of warm front area. Will update again one more time this afternoon before I head out if things change. Can already here the Twister theme song playing in my head, :)

Synoptic Setup:
A potent 30omb negatively tilted trough will dig its way Southeast across the Central Rockies late this evening into tomorrow afternoon over the SW Great Plains region. Attendant riggourous 500mb shortwave will eject over the region between 18z-00z tomorrow afternoon/evening. GFS, ECMWF, and WRF are all pretty much in line with the upper level pattern yielding a broad area of synoptic ascent from exit region of 100kt 300mb jet leading the upper level trough axis. A very focalized area of upper level diffluence resultant of the negatively tilted trough should also aid in strong upper level forcing over the region in question (This is exactly what I look for at upper levels in a classic severe weather outbreak setup). At mid levels SW flow at 700-850mbs will advect a strong EML with > 8K/Km lapse rates out ahead of the system across the dryline region of the Southern Plains this afternoon/evening into tomorrow morning. At low levels a deepening sfc low will develop to the Lee of the Southern Rockies and trek across Southern CO/Northern NM later this evening into tomorrow morning. As this system strengthens strong southerlies out ahead of the sfc low will pull low level moisture up across the Red River valley into Central OK and Southern KS. A distinct warm front and dryline setup will be in place across the region by 12Z-18Z tomorrow with lagging cold front drapped back across eastern CO.

Mesoscale Setup and Severe Parameters:
This pattern will promote the classic Sfc Low, Dryline, Warm Front triple point severe weather setup. Sfc forcing associated with deepening low and warm frontal lift will aid in elevated convection developing in the early to late morning hours across Eastern CO, Western KS, and SW NE. Afternoon heating and subsequent mixing out of BL should cause afternoon bulging/advancing dryline to act as the initial focal point for surface based convection to form. Uppper level cooling and forcing will further help to destabilize warm sector by later afternoon. Forecast ML CAPES across the warm sector should be 1000-1500 J/kg over South Central KS to > 2,000 J/kg across central OK. 0-6km bulk shear values over 40kts across the area in question will promote the development of Supercells. Backed flow at the surface and veering profiles with height will promote right movers as storms split and move ne into very favorable conditions for rotating updrafts and potential tornadoes. Look at any progged sounding in the warm sector and you will easily see what I'm talking about.

The "GO ZONE":
Based on what I mentioned above, my game plan is to head down to the Wichita area to be on the dryline for initiation) and wait for surface based storms to develop and move into the more favored zone for tornadic development. I think there will be a pretty large area for severe weather extending South along the dryline and eventual cold front overtaking, but want to focus on storms along the OK/KS border that will move into my favored area in red above. My main concern with tomorrow is BL moisture. Given the lack of time for return flow from off the gulf, I think > mid 60's Tds will be very difficult to get all the way into Central KS. 12z Model guidance shows a narrow tongue extending up from Central OK into Extreme Southern KS by 00z. Hoping Td depressions will not be too large to get ground circulations. That being said though, steep lapse rates and adequate CAPE values will lead to large hail potential with most storms especially as you head south, but also will promote very strong downdrafts due to the EML. Thinking that may be enough to overcome moisture shortcomings and get some of these funnels to the ground.

Fearless Fantasy Forecast: o/u 12 tornado reports, 45 hail reports, 30 wind reports

Let the games begin and I'll do my best to keep the "tor" streak alive and get some great pictures/videos for the blog. I'd love to hear anyones thoughts on the setup for tomorrow and I'm pretty sure SPC is going with a MOD risk as well. It's always good when we can agree on potential.

Happy Hunting,

Dan aka Squall Line

Tuesday, April 12, 2011

April 10, 2011 West / Central WI Chase *Updated*

Update: I have the video now uploaded to youtube:

Keep in mind that I wanted to document the entire chase, so this starts from LaCrosse and ends in Coloma. Few times in the video it really looked like a few of the cells were going to produce, but I still call the chase a success given the terrain we had to deal with and very fast storm motions. Enjoy!

Hey everyone!

I'll be posting a link to the full video of our entire chase from LaCrosse to Coloma in the short term (tons of clips to edit together into a video... should be about 10 minutes long or better). In the meantime, enjoy some of the pictures and video that Keith Cavey was able to get.

Also, here's a link to a google map which depicts our exact chase route.

Link to unedited raw video from Keith's camera is on this page:

Monday, April 11, 2011

Sweet Lightning Video - 4/10/2011 Storm Chase

Hey all,

Check out this sweet lightning video from the backside of the supercell that ripped through north-central and northeast Wisconsin (I think it was the one that dropped tornado warnings in Appleton, but it could be the Oshkosh one).

Sorry about my face in part of it, I was dedicating the video to the owner of the camera.

I'll post some storm chasing pics as well later.


Sunday, April 10, 2011

4/9/2011 tornado pics and videos

Here are two videos showing the brief touchdowns near Onawa, Iowa along with gustnadoes and strong downdrafts. It then moves on to the multiple vorticies Mapleton tornado (as it was just starting out) and then as I travel get around the bluffs and make my way into the city. The second video is just the multiple vorticy touch down. Enjoy and maybe Ill get some of the other structure put together in some kind of video in the near future. Enjoy!

Dan aka Squall Line

Saturday, April 9, 2011

Update on Sunday 4/9

First of all, I should mention that one of our veteran members, Squall Line, was able to intercept a tornado today in West-central Iowa - nice job Squall Line. I nominate Squall Line for the 1st ever Chaser of the Month award, though he's got a bit of a home-court advantage...!

Now that I owe Squall Line a burrito because I lost our bet of under 2.5 tornado reports before dark, I want to point out something. I think severe weather forecasting has come a long way even within the past few years. For example, I was watching the weather channel today (which, if you hold an atmospheric degree, is illegal in some states), and the severe weather expert Greg Forbes, who was a grad students for the legend Ted Fujita, was pointing out how well SPC's "significant tornado parameter" coincided with the 3 or 4 supercells occuring around 8pm in Iowa and Nebraska: see image below. This location was under the gun from about 2 days out, and I would argue that it wouldn't have drawn a moderate risk based on the tools we had 5 years ago. Sure, some improvement is merely from increasing resolution, but that cannot explain all of it.

Anyways, enough with the flattery, we've got an impressive setup for severe weather tomorrow close to the good ol' Badger State. However, as always, there's uncertainty ... For tomorrow, in my mind, there are two uncertainties:

1. Evolution of nighttime convection, and it's impact (through mid & high-level cloud "debris") on surface heating tomorrow.
2. Whether it's worth chasing a potential tornado when you're dealing with the Mississippi River, hilly terrain and ~50mph storm motion.

My Go Zone forecast is below and here's the explanation for it: the surface cyclone, currently fairly broad will consolidate into one center by later tonight. The supercells and other small convective clusters look to merge into an MCS-looking blob and carry on north and east through the night. The GFS looks like it's suffering from a case of an underactive convective parameterization scheme and generates splotchy precip covering Iowa, Minn and Wisconsin for the next 18 hours straight. I think this model's out to lunch - I like the NAM a lot more.

At the surface, the cyclone's triple point will move northeast with the mean flow and will be positioned near Willmar, Mn at 18Z and Hayward, Wi at 00Z. Looks like convective initiation will be around 20Z west of the Mississippi and the storms may be discrete all the way down the cold front due to the high sfc-500mb shear and some veering even on the front itself. However, the best shot for discrete cells may be closer to the triple point, like today, which is why I'm thinking of going a bit north towards the warm front and backing surface winds.

Now it's time to figure out whether its worth braving the trees, hills and river crossings to chase...

Friday, April 8, 2011

Chasing update Saturday and Sunday

The amount of uncertainty for the severe weather threat on Saturday and Sunday seems to finally be subsiding, but there are still issues.

Let's start with Saturday, the map below shows a few key features that will dictate the Go Zone at 00Z Sunday (Saturday evening). First, let me state that we're only considering conditions during normal business hours (i.e. before sunset). The impressive trough currently in the west will crawl east so that by 00Z the best forcing is just coming off the Front range. There's also a decent upper-level ridge positioned just east of the Mississippi. The sfc low is around Sterling, CO with a diffuse occluded dryline/warm front boundary extending towards Hastings, NE where the triple point is positioned. My concerns are:

1) Forcing too far away to initiate storms before sunset (or even twilight, ahem, Squall Line).

2) Models have large discrepancy in precip output. In fact, only two models generate precip before 00Z: the GFS and the NMM. The NMM's precip is in areas with dewpoint depressions of 10 C and higher, making this a good shot for isolated, great looking supercells, but not a good tornadic threat. The GFS's precip output basically summarizes my best guess for a pre-sunset Go Zone. Initiation would be ~6pm with any storms that do go quickly becoming tornadic. However, the chance of precip, based on the GFS ensembles and SREF is <25%, making me guesstimate a pre-sunset tornado threat of 2-5%. My over/under for daytime tornadoes Saturday is 1.5.

Now moving on to Sunday afternoon: much more interesting the past few runs. All models have been slowly the progression of the low, now the position at 00Z Monday is near Albert Lea, MN. There is a high probability of elevated nighttime convection Saturday night, which may actually provide a few strong tornadoes initially as the cells are still surface-based, say 9-11pm in western Iowa? This elevated convection will very slowly crawl east because the upper-wave is moving NNE making it difficult to sustain any MCS that move towards the east. South of the residual cloud cover from the morning MCS should see ample heating, with a nicely veering wind profile, good speed shear, good BL moisture and forcing coming into the area by 00Z. Initiation of discrete supercells should be earlier than Sunday, say 4pm with my Go Zone being MSP south to Tripoli, Iowa. Because the frontal boundary will be crawling along, we may see a prolonged discrete threat. Over-under for daytime tornadoes is 15.

4/9 & 4/10 Severe Weather Update ***Updated***

Updates coming this afternoon once ARW and NMM are available...

Alright since Dima did a pretty good layout of the forecast based on the 12z runs this morning I'll focus on a few other areas we may have over looked. How and why has the entire system slowed down over the past 3 days in the models and now the evolution goes from a positively tilted trough off in Cali to a negatively tilted trough in MN?

First of all since there are no observations off the west coast the model does not know the strength or location of the subtropical jet. Once it moves on shore where radiosondes are launched a much different evolution occurs. Due to the location of the upper trough from the mid latitudes this allows for the angular momentum to be reduced allowing for the subtropical jet to be further north (Due to the angular momentum typically out flow from tropical convection struggles to make it past ~20N). This allows the unstable tropical air to get wrapped up in the upper wave producing a much higher tropopause! What are the implications of this higher tropopause? Simple really, greater instability! Lets look at some observation and forecast soundings...

First 12z from this morning
The air above 200mb is the first we see of this tropical air being included into the wave. Below is another look at it from a forecast sounding 6hrs later in the same region.
It appears the tropopause begins at 250 but then the thermal profile suggest there is something else present...
Here is what a cross section through the area would look like...
Once these two jet structures "phase together" (for lack of a better term) the tropopause is consequently higher, moving the EL closer to 150mb. All the while the subtropical jet has been destabilizing the air out ahead of the upper wave at 500mb, setting the stage for 2,500+ J/kg of CAPE, seen below.

Then, as a result of this destabilization convection occurs, transportating low PV air near the surface upward and eastward, enhancing the jet along the ridge, amplifying it, enhancing the dynamics and the entire upper wave in just 48hrs goes from this...
to this...
Pretty crazy? And now the jet structure has a greater depth, with the subtropical and polar jet vertically stacked, enhancing the upper level dynamics and forcing...Sounds like a moderate and potentially major tornadic outbreak set up to this guy.

Did I say, "Can't Wait!"?


Thursday, April 7, 2011

This is getting ridiculous, SPC storm reports

Hey folks, I was just going back to look at the monster wind outbreak from Monday across the Gulf Coast and Southern MS/OH Rivery Valleys and noticed how the total number of reports has swelled to 1444!!!! That's toally insane!!! However I also would like to point out how absolutely disgusting the duplicate reports and (should be) non-reports were. Below the map you can see just a simple taste of the last 4 tornado reports. Three of them are the exact same and the final one should not even be a report as its for a "possible funnel cloud"





We all know that these storm report totals are preliminary and we also all know how bloated these will tend to be on any given event especially with sheriffnadoes ans what not, but this is just ridiculous. Getting slightly annoyed I went to search around the SPC webpage and very quickly came across this statement on the main page:

Note: On March 8, 2011, the SPC removed space/time filtering on incoming National Weather Service (NWS) Local Storm Reports (LSRs). This filtering had been used by SPC in an attempt to reduce duplicate reports and limit artificially inflated initial estimates of severe weather events when many reports arrived for the same event. Space/time filtering is no longer being applied to decoded NWS LSRs and this approach is consistent with NWS storm-based verification methods. However, identical reports should still be removed from SPC logs and should not appear on the preliminary maps and lists.

Now much more annoyed......I take a deep breath put together this post as I wait for the 12z products to come in and wonder how this data gets used for Severe Weather Storm Climatology products (Yes, it really does eventually).

Tuesday, April 5, 2011

Active End of the Week ***Updated***

Forecast sounding just west of Cedar Rapids 0z Sunday.

Alright, TON of uncertainty leading up to the severe weather Thursday-Sunday...

Starting with Saturday a very strong jet will be located over the southern plains with an impressive 120 knot jet. When looking long range, a good indicator for severe weather, as I have noticed for the past couple of years is where the winds change direction coming out of the trough. This has little proof, but holds some merit, blow in the highlighted region is where this wind shift occurs.  Often times this is where the upper level support is maximized with upward vertical motion through the jet axis due to the 4 quadrant jet model and curvature.
The GFS has sped up the entire pattern, which has decreased my confidence. The biggest question mark and least confidence I have is how far north the 60+ surface dewpoints reach. As was the case this past week the models way over did the surface dew points resulting in mostly a hail and wind show. Below are the sfc dew points valid at 0z Sun.
Without spitting out to many details as the models are likely to have variability in the coming days, below is my "Go Zone" for Saturday. Red arrows are 700mb flow with blue sfc. Saturday 700mb winds 45-55 knots and Sunday 50+ knots.

...and Sunday

To sum it all together, convection will be on going Friday night along and north of the warm front, warm sector destabilizies during the day with central Iowa as the best chance for Tors. Mostly due to the SE'erly component of the surface winds closer to the low center, better forcing aloft and the highest dew points or smallest dew point depressions. Saturday night there is on going convection with squall line feature that tracks across Iowa, WI and Ill leaving 15-21z or so for the best chance for descrete cells occuring earlier in the day Sunday.  Sunday destabilization will occur early in the day as surface dewpoints will already be in the 50s and 60s across WI and ILL.

Again, this is all based on the 12z run, I would expect the pattern to lag behind what is currently shown by the GFS and influenced where I put out Day 4 and 5 "Go Zones". The models will probably show little consistency and all this analysis will blow up in my face!!!

And a little humor with a NWS fail...

Monday, April 4, 2011

Severe Weather Outbreak potential for this weekend (4/8-4/10)

Chasers, 4/5/11 UPDATE: Wow, so 00z model runs from last night have complicated things a bit more with the GFS being a bit more progressive than the ECMWF. Even more difficult, is the fact that the ECMWF has the 300mb trough getting cutoff from the main flow for a 18-36hr period (Icky). Both models show timing issues with upper level support for earlier in the weekend and have lost the negatively tiled feature to the upper level trough, :( . However, Sunday is still looking very favorable across the lower Midwest/Mississippi river valley. Madison will not be a bad place to be starting from if these solutions hold. This setup is looking strangely similar to yesterdays system with multiple modes of severe convective activity but shifted to the West a few hundred miles. Given model discrepancies to the evlolution of the upper level system, I'll be hanging out along the dryline until further notice and holding off making a "Go Zone" (want to see SREF, 1st), lol. Come on ECMWF solution!!!! Anyone else care to take an early crack on Saturday and Sunday? 4-4-11: I've been watching the models very closely for the last 3-5 days for this upcoming weekend and it appears there could be several rounds of severe weather days with Sunday being the prime day (very good shot of a tornado outbreak) across the Mid Mississippi Valley. This evening I will post my thoughts on this coming weekend and speculate on how it could shake out complete with model output. Details to follow in a couple of hours. Dan aka Squall Line

For those who are fans of hail...

NWS Milwaukee has a short summary of some of the hail events in SE WI yesterday:

While no tornado reports yesterday, there was 2.5 inch hail in Middleton, WI!