Thursday, April 12, 2012

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


4 comments:

  1. Excellent Post Criox...!!!
    I'm curious how the ST Jet is defined so far north. I'm guessing it is a direct result of that Monster Cyclone in the Pacific, but what about the high clouds associated with the ITCZ in the far southern part of the picture I sent you? My initial thought is the ST Jet would be along the interface of those cloud tops and the ribbon of dry air on the poleward side.

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  2. Next time I'll spell your name correctly....my bad Convergence

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  3. Couple of reasons. First and probably most important, the West Pacific Jet is essentially the STJ fueled by convection over the continent but also the Pacific and Indian Ocean basins. My hunch is that the strength of any given Indian monsoon has a significant impact on North American weather patterns (But that is an entirely different discussion). Any given SP that occurs in the Pacific that I have studied results from an equator migrating polar trough, such as what we are watching unfold. What this does is reduces the inertial stability on the polar edge of the Hadley cell allowing for the ITCZ or any other form of organized tropical convection to exhaust its outflow poleward. In this case the band of clouds that stretch from the occluded portion of the cyclone to around 14 degrees north provides the evidence of where it is easiest for convection to exhaust its outflow, resulting in a poleward surge of the tropics. That would be like having a cyclone over Madison that also has a footprint in Guatemala!

    There is a STJ, but very weak and restricted to its current latitude due to conservation of angular momentum in the region you highlighted. The organized convection could interact if the trough digs far enough south but that is unlikely keeping it restricted to the tropics.

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  4. This is fascinating stuff Convergence and a perfect thesis topic for you to get even more excited about as you grow closer to finishing and hopefully publishing. If possible it would be great to see some of your other results from the 3 cases that you're using for your research. I have more questions and some thoughts, but will email you about those later.

    I am eagerly looking forward to the rain and blowing dust this system is going to bring to central Arizona this afternoon (wind, causing blowing dust) and during the overnight hours (rain). April-May-June is our driest 3 month period climatologically speaking. The fact this system will bring rain to the desert makes it all the more interesting.

    As they say AZ, "Our wind events here during march-april-may season signals the onslaught of severe weather a day or two later across the Great Plains" - NWS employee (to remained un-named, :)

    -Squall Line

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