Forecast Discussions mentioning ACARS, received at FSL on 01/20/00

...SNOW SPREADING RAPIDLY INTO THE NORTHWEST PIEDMONT... ...PROBLEMS OF THE NIGHT ARE TRANSITION ZONE LOCATION AND WHEN IT WILL OCCUR... AND ADJUSTMENT (IF ANY) TO LOCATION OF HEAVY SNOW...

00Z/20 DATA SHOWS A SNOW SOUNDING AT GREENSBORO WITH SIGNIFICANT DRY AIR AT 700 MB... INDICATING GOOD EVAPORATIVE COOLING ONCE SNOW STARTS. AIRCRAFT REPORTS SHOW LIGHT SNOW OVER CHARLOTTE AND SURFACE REPORTS SHOW SNOW AT ASHEVILLE. UPSTREAM SOUNDINGS (FFC,BNA) SHOW STRONG WARM AIR ADVECTION AT 850 MB ... 35 TO 45 KNOTS. 850 FRONT SEEMS TO BE SETTING UP WEST TO EAST ACROSS SOUTHERN NORTH CAROLINA. A BATTLE TONIGHT OF WARM AIR ADVECTION AND EVAPORATIVE COOLING TO SET UP TRANSITION ZONE. ANOTHER PROBLEM WILL BE SNOW ACCUMULATIONS IN THIS ZONE BEFORE THE CHANGEOVER. THE SNOW COULD BE HEAVY ENOUGH TO ACCUMULATE TO NEAR WARNING CRITERIA FROM ALBEMARLE TO RALEIGH BEFORE MIXING WITH RAIN.

CURRENT ZONE FORECAST LOOKS FINE AND SHOWS ACCUMULATING SNOW/RAIN TRANSITION ZONE FROM NEAR CHARLOTTE TO NEAR RALEIGH TO NEAR WILSON. HOWEVER... AN EVEN MORE WEST TO EAST (UNUSUAL TRANSITION ZONE CONFIGURATION) LOOKS LIKELY AS WARM AIR ADVECTION LIKELY GETS CUT OFF AS THE SECONDARY SURFACE LOW TAKES SHAPE TO OUR SOUTH. SO... AN EXTENSION OF THE FORECAST OF HEAVY SNOW (4 INCH AMOUNTS) WILL BE EXTENDED FARTHER EAST ALONG THE NC/VA BORDER TO ROANOKE RAPIDS. WAKEFIELD HAS COORDINATED THIS WITH US AND THEY PLAN TO INCLUDE NORTHAMPTON IN THE WARNING AS WELL.

RADAR TRENDS SHOW HEAVY SNOW TO SPREAD OUT OF THE BLUE RIDGE INTO THE NORTHWEST SHORTLY. WE WILL RAISE ACCUMULATIONS IN THE TRIAD AREA TO 4 TO 6 INCHES WITH AVERAGE QPF OF 0.50 EXPECTED.

THE TRANSITION ZONE WILL BE PROBLEMATIC AS SNOW IS EXPECTED AT THE ONSET AND IT WILL LIKELY BE HEAVY BEFORE SOME MIXING WITH RAIN. ANY MIXING WITH RAIN WOULD LIMIT SNOWFALL ACCUMULATIONS THUS THE ADVISORY.

WE HATE TO SPIT THE TRIANGLE... BUT IT LOOKS MORE LIKELY THAT PORTIONS OF DURHAM AND ORANGE COUNTY ...DEEPER INTO THE COLD AIR COULD SEE 4 INCHES OF SNOW.

IT WILL ALL BE OVER AROUND SUNRISE AS THE SURFACE LOW OFFSHORE TAKES OVER. BLUSTERY AND COLD WEATHER TO FOLLOW.

.RAH...WINTER STORM WARNING NORTHWEST AND NORTH PIEDMONT AND EXTREME NORTHERN COASTAL PLAIN... FROM DAVIDSON TO DURHAM TO HALIFAX COUNTIES. ADDITIONS INCLUDE DURHAM... ORANGE... GRANVILLE VANCE... WARREN AND HALIFAX.

WINTER WEATHER ADVISORY IN THE TRANSITION ZONE FROM STANLY TO LEE TO WAKE TO WILSON... 3 INCHES OF SNOW BEFORE A MIX WITH RAIN.

PWB

MAIN CHALLENGE WITH THIS FORECAST PACKAGE WILL BE THE TEMPERATURES AND WHEN THE CLOUDS WILL BEGIN CLEARING OUT.

LATEST WATER VAPOR LOOP SHOWING WELL DEFINED SHORTWAVE OVER CENTRAL OHIO SHOWING RAPID CYCLOGENISIS OUT AHEAD OF IT. MSAS DATA SHOWS THE SURFACE LOW HAS DEEPENED TO 1000 MB WHICH IS DEEPER THAN WHAT ALL THREE MODELS PROGGED. THIS MESS HAS EXITED OUR CWFA AND WILL CONTINUE TO SHIFT EAST TO THE ATLANTIC BY THIS EVENING. NOW ALL WE HAVE TO WORRY ABOUT IS THE GRADIENT WINDS BEHIND THIS SYSTEM AND THE AMOUNT OF COLD AIR ADVECTION THAT WILL ACCOMPANY IT. FOG IMAGERY SHOWS THE BACK EDGE OF THE LOW CLOUDS ARE NEAR THE MISSISSIPPI RIVER. THIS IS INITIALIZED WELL BY THE NGM AT THIS TIME SO WE WILL GENERALLY FOLLOW FAIRLY CLOSE TO ITS CLEARING TREND THROUGHOUT THE DAY. WE DECIDED TO BUMP UP THE WINDS ABOUT A CATEGORY IN MOST LOCATIONS DUE TO ACARS DATA SHOWING 40 KTS AROUND 3KFT. THESE WINDS SHOULD START DIMINISHING SOME THIS AFTERNOON...BUT THEY WILL STILL QUITE BREEZY. TEMPERATURES SHOULD ALSO START DESCENDING THIS MORNING AS THE COLD AIR STARTS POURING IN FROM CANADA. THUS...WE WENT FAIRLY CLOSE TO FWC NUMBERS.

TONIGHT THE SURFACE HIGH TRIES TO MAKE ITS WAY INTO THE REGION AND PROVIDE THE CWFA WITH CLEARING SKIES. WE ARE A LITTLE UNCERTAIN HOW MUCH WE WILL DECOUPLE SO WE ONLY WENT A CATEGORY COOLER THAN THE CONSERVATIVE FWC NUMBERS. FAN SEEMED A BIT TO COLD BUT IF WE DECOUPLE WE COULD BE IN THE SINGLE DIGITS.

TOMORRROW LOOKS TO BE A SLIGHT WARMUP AS THE SURFACE HIGH SHIFTS EAST...BUT WE WILL MOST LIKELY NOT REACH THE FREEZING MARK IN MOST LOCATIONS DUE TO A COOL START IN THE MORNING. PLUS...THE MODELS SHOW THE WARM AIR ADVECTION NOT REALLY KICKING IN UNTIL LATE IN THE DAY. WE MAY SEE SOME HIGH CLOUDS OUT AHEAD OF THE NEXT WAVE...BUT THAT WILL BE IT.

.SDF...NONE COX

SHORT TERM DISCUSSION: UPPER LEVEL RIDGE BUILDING OVER THE AREA TODAY...WITH ONLY SOME HIGH LEVEL MOISTURE TO CONTEND WITH. THE INCREASE IN MID LEVEL MOISTURE AND THUS ANY CHANCE OF MOUNTAIN SNOW WILL HOLD OFF UNTIL TONIGHT. MAIN QUESTION IS AMOUNT OF HIGH LEVEL CLOUDINESS AND THUS RESULTANT TEMPS.

SURFACE FLOW HAS ALREADY SHIFTED AROUND TO SOUTHERLY...AND PRESSURE FALLS INCREASING EAST OF THE ROCKIES. THEREFORE...TEMPS SHOULD RESPOND QUITE NICELY TO ANY SUNSHINE...ESPECIALLY CONSIDERING WARM TEMPS JUST ABOVE SURFACE AS SHOWN BY LOCAL ACARS SOUNDINGS WITH +6C AT 812 MB. NOT TERRIBLY IMPRESSED YET WITH THICKNESS OF WAVE CLOUD SO THERE SHOULD BE AT LEAST A COUPLE HOURS OF SUNSHINE. WILL GO WITH PARTLY CLOUDY FOR NOW...BUT IF WAVE CLOUD THICKENS DAY SHIFT CAN UPDATE TO MOSTLY CLOUDY.

BARJENBRUCH

LONG TERM DISCUSSION: MODELS ALL AGREE THAT WEAK UPR LVL RIDGING OVR CO TDA WL BE GIVING WAY TO MORE ZONAL FLOW BY FRI AND SAT. MODELS ALSO SHOW AND SATELLITE PICTURES VERIFY THAT MID AND UPR LVL MSTR WL ALSO BE EMBEDDED IN THE WLY FLOW. MAIN EFFECTS OF THESE FEATURES WILL BE FELT IN THE MTN ZONES WITH SNOW EXPECTED TO DEVELOP BY TONIGHT. AVN SHOWS A SUB-TROPICAL JET DEVELOPING AND MOVING ONSHR ACRS THE SWRN U.S. BY FRI AND SAT. SATELLITE PICTURES ALSO BACK THIS UP. INITIALLY...SINCE THE MSTR WL BE PRETTY HIGH BASED...DO NOT EXPECT TOO MUCH SNOW ACCUMULATION IN THE MTNS. AS MORE SUB-TROPICAL MSTR ARRIVES ON SAT...MORE APPRECIABLE SNOW MAY DVLP. ON THE PLAINS...THE WESTERLY FLOW ALOFT WL CONT THE DRY CONDS THAT WE HAVE SEEN PLENTY OF RECENTLY. MILD TEMPS FOR THIS TIME OF YEAR WL ALSO CONT.

LOOKING INTO THE EXTENDED...THE NEW MRF AT 120 HRS LOOKS NOTHING LIKE YDA'S 144HR FCST...EXCEPT ON THE MSLP CHART. AT 500 MB THE BLOCKINESS OVR THE PAC NW AT 120 HRS LOOKS VERY ODD...BUT THE PATTERN ON THE CURRNT SATELLITE PICTURES OVR THE GULF OF ALASKA IS STARTING TO LOOK A BIT BLOCKED UP WITH THE SHARP RIDGE MOVG ACRS THE DATELINE. THE MRF'S RUN TO RUN INCONSISTENCY COMBINED WITH THE IMMINENT CHANGE IN THE LARGE SCALE PATTRN MAKE IT VERY TRICKY TO SAY WHAT IS GOING TO HAPPEN ON DAY 5...OR BEYOND. THERE MAY END UP BEING PCPN IN ERN CO ON MON...BUT THE SCENARIO MAY NOT BE THE ONE THAT WAS OUTLINED BY YDA'S MODEL RUN. CONFIDENCE LEVEL IN ANY FCST SCENARIO FOR MON IS VERY LOW...SO WL STAY THE COURSE AND LV THE EXTENDED ALONE. KDRBY

.DEN...NONE.