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:
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.