REGARDING THE UPCOMING WINTER STORM ALL PROGNOSTIC TOOLS ARE IN AGREEMENT WITH FORECASTED QPF AMOUNT OF AROUND 1.25 LIQUID EQUIVALENT. THE FORECAST MODELS PLACE THE FREEZING LINE ALMOST DIRECTLY OVER THE FA DURING THE TIME IN QUESTION. THAT BEING SAID...

SNOW SHOULD BEGIN TOMORROW MORNING SOMETIME AFTER DAYBREAK. WRF PRECIPIATION FORECASTS ARE SHOWING LIGHT PRECIPITATION SPREADING OVER THE FA AT 12Z. PRECIPIATATION MAY BEGIN A LITTLE LIGHTER THEN WRF FORECAST INDICATES. HOW QUICKLY THE STORM APPROACHES WILL DETERMINE HOW QUICKLY THE PRECIPIATION INTENSIFIES. DUE TO THE POTENCY OF THE INCOMING STORM AND THE MOISTURE ASSOCIATED WITH IT, ONCE SNOW DOES BEGIN CONDITIONS WILL GRADUALLY WORSEN. EXPECT LIGHT SNOW TO BEGIN FALLING DURING THE MORNING RUSH AND PROGRESS TOWRADS A HEAVIER SNOW BY MID AFTERNOON.

BY AROUND 20Z ON TUESDAY AFTERNOON SNOW SHOULD BE FALLING HEAVILY OVER THE FA WITH THE LP SYSTEM CENTERED OVER CENTRAL KENTUCKY WITH A SHEILD OF HEAVY PRECIPIATION EXTENDING NORTH AND EASTWARD. AT THIS TIME A SECONDARY AREA OF LP IS GOING TO BEGIN FORMING OFF OF THE COAST OF NORTH CAROLONA. THIS IS A SECOND FACTOR THAT WILL ANTAGONIZE HIGHER PRECIPIATATION AMOUNT IN THE FA. IF THIS LOW RAPIDLY DEEPENS MUCH OF THE MOISTURE FROM THE INITIAL LP WILL BE "ROBBED" THUS LOWERING OVERALL AMOUNTS.

BY TUESDAY EVENING THE LP SYSTEM WILL BE IN SO. WV AND THE ASSOCIATED FREEZING LINE IS GOING TO BE VERY NEAR THE FA. MOST MODELS AGREE ON THIS. THE FORECASTERS SEE TWO SCENARIOS RESULTING FROM THIS...

THE FIRST SCENARIO HAS THE LP SYSTEM PROGGING MORE TO THE SOUTH ALLOWING FOR A NE WIND TO SUSTAIN THROUGHOUT THE DAY.  A WINTRY MIX WILL OCCUR SOMEWHERE BETWEEN 02Z AND 06Z WEDNESDAY.  WITH ANY DRY AIR INTRUSION MIX PRECIP WILL CAUSE EVAPORATE COOLING WHICH WILL COOL THE LOWER LEVELS AND ALLOW FOR SNOWFALL TO BEGIN ONCE AGAIN.  WINTRY MIX IS EXPECTED THROUGH 06Z BEFORE SNOWFALL BEGINS.  UPPER LEVEL TROUGH WILL SUPPORT ANY CHANCE OF A STRONG BURST OF PRECIP.  HEAVIEST PRECIP IS EXPECTED TUESDAY NIGHT INTO THE MORNING.  MREF SUGGEST OVER 1.00 INCHES OF LIQUID PRECIP HOWEVER KEEPING THE 0F ISOTHERM TO OUR SOUTH MOST OF THE STORM PERIOD.  TUESDAY WILL SEE 3-6 INCHES OF SNOW BEFORE CHANGING OVER TO A WINTRY MIX.  FREEZING RAIN/SLEET CAN ACCUMULATE UP TO 0.25IN BEFORE TURNING TO SNOW.  WEDNESDAY MORNING INTO THE AFTERNOON WILL SEE AN ADDITIONAL 2-4 INCHES OF SNOW.  THIS WILL MEAN 36 HOUR STORM TOTALS WILL BE 5-10 INCHES OF SNOW WITH AN ADDITIONAL 0.25IN OF FREEZING RAIN/SLEET. 

THE SECOND SCENARIO HAS THE LP MOVING THROUGH KY INTO CENTRAL WV.  WITH SNOW AHEAD OF A WARM FRONT, INTENSITY SHOULD BE LIGHT TO MODERATE, ACCUMULATING 2-4" BEFORE CHANGEOVER.  WAA SHOULD BE SIGNIFICANT ENOUGH TO CAUSE 850 TEMPS TO WARM UP TO 0C TO 2C OVER THE FA, ALLOWING FOR ENOUGH MID-LEVEL WARMING TO MELT SNOW BEFORE REFREEZING PRIOR TO REACHING THE GROUND.  HOWEVER ENOUGH SFC COLD AIR SHOULD BE PRESENT TO FREEZE THE PRECIP INTO SLEET PELLETS BEFORE REACHING GROUND.  TIMING OF THE CHANGEOVER TO SLEET COULD OCCUR AS SOON AS 01Z WED BUT A LATER START COULD HAVE IT LAST THROUGH 11Z WED.  WITH THIS SCENARIO, SLEET ACCCUMULUATION COULD REACH AS HIGH AS 0.5" BEFORE CHANGEOVER BACK TO SNOW ALONG THE BACKSIDE OF THE REDEVELOPING COASTAL LP.  AFTER CHANGING BACK TO SNOW, THE FA SHOULD BE AT THE BACK EDGE OF THE STORM, ONLY ALLOWING FOR AN ADDITIONAL 1-2" OF SNOWFALL.  THIS WOULD GIVE US A TOTAL SNOWFALL OF 3-6" WITH UPWARDS OF 0.5" LAYER OF SLEET MIXED W/ MINIMAL FREEZING RAIN.

THE FORECAST MODLES AND THE FORECASTER ARE ALL IN AGREEMENT WITH THE TIMING AND PLACEMENT OF THE STORM. THE ISSUES IN DISAGREEMENT ARE THE EXACT LOCATION OF THE FREEZING LINE AND HOW LONG THE FREEZING RAIN AND SLEET PERSIST. THE OTHER KEY TO THIS STORM IS HOW QUCIKLY THE COASTAL LP BOMBS OUT AND BEGINS HOARDING MOISTURE FROM THE CONTINENTAL LP.

ALL IN ALL THIS SHOULD BE A SIGNIFICANT WINTER STORM. WITH THE AREA BEING UNDER A WINTER STORM WARNING PEOPLE SHOULD BE PREPARED FOR HAZARDOUS TRAVEL CONDITIONS WITH THE MOST DIFFICULT TIME FOR DRIVING BEING TUESDAY NIGHT AND EARLY WEDNESDAY MORNING. SOUTHWEST PA HAS THE MOST UNCERTAIN FORECAST FOR ANY AREA THAT WILL BE AFFECTED BY THIS WINTER STORM. WHILE THIS STORM COULD SEE AS LITTLE AS 4 INCHES OF SNOW AND A LIGHT ICE ACCUMULATION IT COULD SEE AS MUCH AS A FOOT OF SNOW IF PECIPIATION RATIOS ARE IN FACT AT 10-1 AS CURRENT GUIDANCE SUGGESTS. WE

THE CONSENSUS BETWEEN THE TWO FORECAST TEAMS IS 4-8 INCHES WITH A .25'' ICE ACCUMULATION. WILL BE UPDATING OUR FORECAST AS THE STORM APPROACHES.