Recap of 4/12 & 4/14

Today was one heck of a day in Kansas. In retrospect, we can all probably say we should have gone there, but it's not clear why Nebraska was void of any significant tornadoes.

Anyways, I have a few quick videos from Thursday and today.

Thursday 4-12-2012:

I went up to Sterling, CO then east to Imperial and down towards McCook, NE. First, here's a video of hail east of Sterling. This was a nuisance because it created some thick hail fog and the temperature crashed from the mid 60's to the upper 40's in basically 10 minutes.



After this, I wandered along the warm front eastward, where the following picture recaps the common sight: towers getting choked and undercut by the cold air to the north that seemed to slosh north/south like a tide. I've heard people refer to these kind of towers as "turkey towers". The darker clouds are shallow stratus.

Finally, with the help of ours truly Squall Line, I was in position to take this footage a few miles north of Trenton, NE around 6pm. The video is bad quality (time to invest in a good camera), but at 0:45 seconds in, I think there's a funnel in the middle of the screen. This happened to coincide with the location and timing of the tornado report on the SPC reports.



Saturday 4-14-2012:

I was lazy today and paid the price. My goal was to head out to near Ogallala, NE as the 500-mb cold front was moving over the triple point. I like those situations as they always produce funnels/nados even though the cells are usually ugly looking on radar. I left too late though and was playing catch-up the whole time. I did manage to snag this cool video of a cell that later produced a few funnels near North Platte. The precip shaft in the middle is sweet.

Why Nebraska?

All of these ingredients will conveniently find themselves in a single location tomorrow afternoon...

• Nose of upper level jet
• strong diffluence 
• strong curvature from downstream ridge amplification over the course of the last 18 hours
• More than sufficient instability
• synoptic flow will keep morning warm frontal convection cirrus and debris from hampering afternoon destabilization
• Strong cyclogenesis
• bulging dryline and cold front
• pressure falls in region (Dima I know you like that parameter)
• Excellent vertical speed shear (ie bulk shear)
• lowest 1.5 km speed shear of 30 knots
• SSE wind at surface and SW at 850 (ie helicity)
• further enhanced shear from LLJ hour or two before sunset when storms are still coupled with BL

And this...

Hail but Not Much Else: Added thoughts

The image above is the sfc analysis at 2243Z yesterday as those three monster storms had just formed off of the dryline in northwest Kansas. the orange line is the dryline and the red line is the location of the warm front. The blue arrows depict the storm motion at the time. I think the biggest reason that there were no tornadoes ties in directly with what Dima (Dryline) was saying. The warm sector with temps above 70F and where the highest cape values (>2000 J/kg) was very modest in size. Each one of those supercells that formed off the dryline grew in a very favorable area to become tornadic; however based on storm motion they were not able to remain in the warm sector for very long before riding over the top of the retreating warm front and into much more stable boundary layer (Temps in the 50s/60s) even despite the strongly backed winds. Cape values to the north and east of the warm front where near 0 as Dima was saying and each one of those cells basically crapped out into a hail producer as they moved northeast into southwest Nebraska. The cells farther to the north seemed to be more dynamically driven and grew upscale as the shortwave was moving through (moving into more unidirectional shear) but again like the cells Dima was on to the south had no real chance at producing tornadoes.

It's tough to see such a favorable setup fail so hard. Storm motions would have had to have been much slower and more to the east, or if the cap could have broken earlier along the dryline while it was farther west across eastern Colorado. Anyways, I would say that was a pretty successful chase yesterday Dima and just a taste of whats to come for you the rest of this Spring into the upslope summer. Post some pictures when you get a chance.

Dan aka Squall Line

Hail, but not much else

After many promising cells (I counted chasing 4 or 5 65-dbz storms), I got hailed on 7 times, video to come later. Tornado wise, today was a letdown. I did not see well-developed wall clouds. All the rotation was on the scale of the whole thunderstorm with lots of unorganized turbulence producing funnels everywhere. Like I told Dan, who helped me catch the cell near Trenton, NE around 5-6pm, the report of a tornado looks to be an error because there were very low-lying clouds associated with the warm front the kept moving north/south after interaction with the passing cells.

Why the lack of tornadoes today? I would say instability. I measured low 60's over low 50's even south of the warm front, which was probably amounting to a few 100 worth of CAPE.

Still debating whether to head out Saturday. Looks like the show will be mostly after sunset. Anyone agree or disagree?

Central Pacific Cyclone and Downstream Consequences

Fellow Chasers and avid weather followers, 


If you like interesting, high impact weather then you are in for a treat. Included below are a few snippets of dialogue from a wide selection of text products from the NWS. Notice an over arching theme, strong wording multiple days out, model confidence, model agreement and a robust synoptic feature as the main ingredient for this 4-5 days of active weather in the US. Also, not to be over looked, this is only the 11th time a Moderate Risk has been issued for the day 3 outlook!

THE COMBINATION OF MOISTURE ASSOCIATED WITH THE LOW AND THE AFOREMENTIONED COLDER AIR COULD RESULT IN APPRECIABLE SNOW ACCUMULATION ACROSS THE SERN TWO THIRDS OF OUR CWA DURING THIS TIME FRAME.

THESE FACTORS COMBINED WITH FAST STORM MOTIONS SUGGEST THE POTENTIAL FOR LONG-TRACKED...STRONGTORNADOES OCCURRING FROM THE AFTERNOON THROUGH THE EVENING /INCLUDING AFTER DARK/.

GFS/ECMWF ARE IN FAIRLY GOOD AGREEMENT THROUGH D4/SUN AS THE STRONG PACIFIC TROUGH EXPECTED TO REACH CO/NM BY 12Z SUN

BOTH THE ECMWF AND GFS ARE SHOWING A FAIRLY SIGNIFICANT DISTURBANCE RIDING NEWD ALONG THE FRONT ACROSS THE MIDWEST SUNDAY NIGHT INTO MONDAY.

A POTENT UPPER LEVEL TROUGH WILL EJECT OUT OF THE FOUR CORNERS REGION SUNDAY WITH THE SURFACE LOW RAPIDLY DEEPENING ACROSS WESTERN IOWA/EASTERN NEBRASKA.


Currently this feature, which is a superposition of  the Polar and Sub-Tropical jet, is getting organized in the Central Pacific Ocean. A superposition of the POLJ and STJ is when, using an objective identification scheme, both the POLJ and STJ are present in the same, vertically integrated column.


Below in red is where the POLJ has been identified at a given grid point and the white indicates where the STJ has been identified. The second image, indicated by the yellow dots, there are 4 present, show where the POLJ and STJ are present in the same vertical grid column.

A few consequences of a Superposition from recent research:

• Superposition associated with high impact sensible weather events (April 2011, Oct 2010, May 2010)

• Intensified lower stratospheric and upper tropspheric frontal zones and attendant vertical circulations

• Intensified horizontal circulation 

• Single, amplified tropopause that separates tropical and polar tropopause

And a few images below provide satellite perspectives of the 984mb low that allowed for a migration of the tropics poleward and a Superposition to occur. 

And courtesy of Jake.

The down stream consequences of this feature will not go unnoticed as discussed above. Saturday is shaping up to exhibit wide spread severe weather as the nose of this jet streak reaches the central and southern plains with cyclogenesis taking hold over Colorado. With strong dynamic forcing and unstable air mass in place it is not a matter of if but rather when severe weather will occur. With many of the hodographs looking similar to this one near Wichita, KS the shear profiles are supportive of discrete supercells capable of producing strong and possible long track tornadoes.  

Moving our attention to Sunday and Monday, severe weather will still be present. It appears at this point however that the setup favors discrete cells initially with upscale growth likely, as indicated by the shear profiles but also the precipitation distribution for both days. Another clue is the pulsing nature of the jet aloft which indicates organized convection (squall line or MCS) at night will enhance the jet just down shear. Also taking place as the cyclone tracks NE will be an increased region of baroclinicity in the upper midwest. With cooler temperatures in place it looks likely that a decent swath of snow will line up across MN and WI.  Below is the 850mb temp, height and winds highlighting the enhanced baroclinicity and cold air in place for mostly snow on the N and W side of the cyclone. 

Tuesday and Wednesday warrant further monitoring as the upper wave moves east but that will be saved for further discussion. 

-Convergence

Triple Point Fun

Hey there fellow chasers,

Myself (Dryline aka Dima) and fellow UW chaser Chris Rozoff will be snooping around the KS/CO/NE border area tomorrow looking for tornadoes around the triple point. You guys know how it goes with those triple points: guaranteed Hel-to-the-icty (no, not Zak) but also more dynamics which could yield clouds that put a damper on the surface heating. Currently optimistic since upslope flow is present and looks like we can get mid 50's dewpoints all the way to McCook, NE. I will hopefully post again tomorrow.

Dima