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High Plains Drifter


disclaimer:  "The meteorological views/forecast thinking expressed are those solely of the author of this blog
and do not necessarily represent those of official National Weather Service forecast products,
therefore read and enjoy at your own risk and edification!"

December 19, 2006

SW KS Winter Storm Dec 19-20 [post 1]

Filed under: Dec 19-20, 2006,General Weather & Forecasting — Mike U @ 1:54 am

The first major winter storm of the 2006-07 winter season is approaching Southwest Kansas.  As for Dodge City where I live, it will be very close to a mostly freezing rain versus "plain" rain event as the 30-32°F line will be very close to Dodge City for a bulk of the event.  The QPF (quantative precipitation forecast) values from the models are really impressive for a storm in December in Southwest Kansas.  Below is a storm-total QPF from the December 19th 00z (6pm CST) NAM model run:

60-hr total QPF from the NAM model 

Below is the Area Forecast Discussion I wrote at work yesterday concerning the approaching event. 

..SIGNIFICANT ICE EXPECTED OVER PORTIONS OF SOUTHWEST KANSAS  
  
MAIN CHALLENGE IN THE FORECAST CENTERS AROUND SURFACE  
TEMPERATURES...AND DEGREE OF WARM LAYER ALOFT WITH RESPECT TO  
PRECIPITATION TYPE. THERE IS A LARGE DEGREE OF CONFIDENCE IN  
WIDESPREAD 0.75 TO 1.25 INCH TOTAL LIQUID EQUIVALENT PRECIPITATION.  
  
UPPER LOW WILL BEGIN INTERACTING WITH VERY RICH LOW LEVEL MOISTURE  
CURRENTLY RESIDING ACROSS MUCH OF TEXAS PER 295K ISENTROPIC  
ANALYSIS WITH 14-16C H85 DEWPOINTS PREVALENT. INGREDIENTS ARE  
COMING TOGETHER FOR SIGNIFICANT ICE PROBLEMS...LARGELY BECAUSE OF  
A) TREMENDOUS RESERVOIR OF MOISTURE ACROSS TEXAS...B) PROLONGED  
SOURCE OF LIFT WITH INTERACTION BETWEEN QUASI-GEOSTROPHIC FORCING AND  
MESOSCALE FRONTOGENETIC FORCING...ESSENTIALLY "TRAINING" OVER  
SOUTHWEST KANSAS FOR 12 TO 18 HOURS...C) SURFACE HIGH IN PLACE  
KEEPING COLD ENOUGH TEMPERATURES AND VERY DRY LOW LEVEL AIR AT THE  
ONSET OF THE EVENT FOR WET-BULB COOLING EFFECTS TO KEEP SURFACE  
TEMPS IN THE 28-31F RANGE.  
  
THE MOST SIGNIFICANT MODEL DISCREPANCY BETWEEN THE GFS AND THE NAM  
IS THE MAGNITUDE OF THE WARM AIR ALOFT CENTERED AROUND 750MB. THE  
NAM SUGGESTS THE ADVECTION OF +2 TO +3C AS FAR NORTHWEST AS  
JOHNSON AND SYRACUSE THROUGH MUCH OF THE EVENT. CURRENT THINKING  
NOW IS THAT AN ALL-SNOW SCENARIO LOOKS MUCH LESS LIKELY OVER EVEN  
THE NORTHWEST SECTION OF THE CWA. THINK EVEN IN HAMILTON COUNTY  
THERE WILL BE A SIGNIFICANT PERIOD OF SLEET MIXED WITH FREEZING  
RAIN...THEN BECOMING SLEET MIXED WITH SNOW. SNOW ACCUMS OF 1-3  
INCHES ARE POSSIBLE IN THESE AREAS. THE NEXT CONCERN IS THEN  
SURFACE TEMPERATURES FOR THE REST OF THE CWA...BECAUSE WITH SUCH A  
PRONOUNCED WARM LAYER ALOFT...THINK THAT ALL SNOW FALLING THROUGH WARM  
LAYER WILL COMPLETELY MELT...THUS WOULD TAKE A VERY COLD SURFACE  
LAYER TO RE-FREEZE AS SLEET...SO THE THINKING IS THAT A MAJORITY  
OF THE EVENT WILL BE FREEZING RAIN WEST OF A LINE FROM DODGE-  
NESS-WAKEENEY ALL THE WAY WEST TO LAKIN-ULYSSES-HUGOTON. MODEL QPF  
FIELDS ARE IMPRESSIVE WITH LARGE MODEL CONSISTENCY IN 1 TO 1.50  
INCH QPF. THINK THAT A LARGE PART OF THE FORECAST AREA WEST OF  
DODGE-NESS-WAKEENEY WILL SEE THREE-QUARTERS OF THE EVENT AS  
FREEZING RAIN AND CONFIDENCE IS QUITE HIGH IN THIS SCENARIO. THUS  
WILL GO WITH A WINTER STORM WARNING...PRIMARILY FOR UP TO A HALF  
INCH OR MORE OF ICE ACCUMULATION ON TREES/POWERLINES. WEST OF THE  
DOMINANT FREEZING RAIN AXIS...A NARROW CORRIDOR OF MAINLY SLEET  
FOR THE EVENT SHOULD EXIST...REALLY TOUGH TO PIN THIS DOWN OF  
COURSE AT 30-42 HOURS...HOWEVER UP TO AN INCH (OR MORE) OF SLEET  
MAY ACCUMULATE ESPECIALLY IN THE FAR WESTERN COUNTIES.  
  
COLD AIR CENTERED AROUND THE 750MB LAYER WILL EVENTUALLY FILTER  
EASTWARD BUT NOT UNTIL A BULK OF THE PRECIPITATION IS OVER  
WITH...HOWEVER THINK THAT SNOW MAY BE QUITE HEAVY FOR A BRIEF  
PERIOD OF TIME WEDNESDAY MORNING AS IT MOVES SOUTHWEST TO  
NORTHEAST ACROSS THE CWA.  
  
WEDNESDAY...AS UPPER LOW WINDS UP TO OUR NORTHWEST...DRY INTRUSION  
WILL WORK IN FAST AND THE EVENT WILL BE OVER WITH FOR SOUTHWEST  
KANSAS. WE SHOULD EVEN BREAK OUT INTO DECENT SUNSHINE IN THE  
SYNOPTIC DRY SLOT.  

 

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