Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 182333
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
633 PM EST THU DEC 18 2014

.SYNOPSIS...
HIGH PRESSURE OVER THE UPPER MIDWEST WILL GRADUALLY BUILD EAST
ACROSS THE AREA RESULTING IN OVERALL DRY WEATHER THROUGH FRIDAY
EVENING. A WEAK AREA OF LOW PRESSURE WILL EVENTUALLY DEVELOP ALONG
THE GULF COAST STATES FRIDAY NIGHT AND MOVE EAST-NORTHEAST OVER
THE CAROLINAS ON SATURDAY. THIS SYSTEM WILL BRING A PERIOD OF
LIGHT WINTRY PRECIPITATION SATURDAY MORNING...CHANGING TO RAIN
OVER THE PIEDMONT IN THE AFTERNOON.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 615 PM EST THURSDAY...

REALLY NOT MUCH TO UPDATE OVERALL IN THE FORECAST. SOME LIGHT
RETURNS ON RADAR OVER THE MTNS OF SE WV...MAY BRING A FLURRY/SNOW
SHOWERS...WITH LITTLE/NO ACCUMULATION THROUGH THIS EVENING.
OTHERWISE...CLOUDS WILL HANG TOUGH OVERNIGHT IN THE WEST AS FLOW
TURNS MORE NW...WHILE THE HIGHER CLOUDS OUT EAST THIN OUT.

PREVIOUS VALID DISCUSSION...

WAVE ALOFT PASSES EAST OVERNIGHT LEAVING WEAK SUBSIDENCE IN PLACE
AS HIGH PRESSURE TO THE NW NOSES BACK IN LATE.

CLOUDS THIS AFTERNOON KEPT TEMPERATURES COOL AND THIS SHOULD
TRANSLATE TO COOLER TEMPERATURES OVERNIGHT. WITH AFTERNOON DEW
POINTS MAINTAINING IN THE L/M 20S...ANY SUBSTANTIAL CLEARING WITH
LIGHT WINDS WILL ALLOW OVERNIGHT LOWS TO RADIATE DOWN COLDER THAN
FORECASTED. CURRENT THINKING IS TO HAVE SOME CLOUDS AND/OR MIXING
OVERNIGHT TO KEEP OVERNIGHT LOWS IN BETWEEN GFS AND NAM MOS.

FRIDAY LOOKS TO BE ON THE DRY SIDE AS HIGH PRESSURE STRETCHING
FROM THE GREAT LAKES THROUGH THE OHIO RIVER VALLEY REMAINS THE
MAIN FEATURE IN OUR WEATHER PATTERN. MOSTLY SUNNY SKIES AND LIGHT
NORTHWESTERLY DOWNSLOPE WINDS WILL ALLOW AFTERNOON TEMPERATURES TO
RANGE FROM THE MID 30S ALONG THE WESTERN RIDGES...TO AROUND 50
OVER THE SOUTHSIDE AND THE NORTH CAROLINA PIEDMONT.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 250 PM EST THURSDAY...

MODELS HAVE BEEN TRENDING QUITE A BIT WEAKER WITH THE SHORT WAVE
COMING OUT OF ARIZONA AND REACHING THE MID ATLANTIC REGION ON
SATURDAY. ISENTROPIC LIFT AND VORTICITY ADVECTION COME THROUGH ON
SATURDAY AND WILL BE EAST OF THE FORECAST AREA ON SATURDAY NIGHT.
MOST SIGNIFICANT CHANGE IN THE GUIDANCE IS WITH THE AMOUNT OF
MOISTURE. 12Z GUIDANCE NOW KEEPS BULK OF THE DEEPER MOISTURE SOUTH
OF THE FORECAST AREA...ESPECIALLY THE 12Z NAM. WILL FOLLOW THIS
TREND AND LOWER PROBABILITY OF PRECIPITATION IN ALL BUT THE
SOUTHERN THIRD OF THE COUNTY WARNING AREA. WILL ALSO CUT BACK ON
AMOUNT OF PRECIPITATION.

SURFACE HIGH PRESSURE OVER THE UPPER MISSISSIPPI VALLEY WILL
GRADUALLY MOVE EAST AND WILL BE OVER THE OHIO VALLEY ON SATURDAY.
THE HIGH CONTINUES SLOW PROGRESS TO THE EAST SATURDAY NIGHT AND BY
LATE SUNDAY THE RIDGE AXIS WILL BE OFFSHORE. THIS WILL BEGIN TO
BRING SURFACE AND LOW LEVEL WINDS AROUND TO THE SOUTH LATE IN THE
DAY. SURFACE REFLECTION OF THE SHORT WAVE ON SATURDAY WILL BE AN
INVERTED TROF OVER THE SOUTHERN APPALACHIANS. EXPECT CLOUDS AND
PRECIPITATION WILL KEEP MAXIMUM TEMPERATURES ON SATURDAY COOLER
THAN GUIDANCE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM EST THURSDAY...

A VERY ACTIVE WEATHER PATTERN EXPECTED DURING THE MEDIUM RANGE
WITH ENOUGH MODEL DIFFERENCES TO MAKE THE DETAILS OF THE SENSIBLE
WEATHER A GOOD CHALLENGE. AN AREA OF LOW PRESSURE SYSTEM WILL
DEVELOP ALONG THE GULF COAST SUNDAY NIGHT...PUSH MOISTURE
NORTHWARD AND INTRODUCING ANOTHER CHANCE OF RAIN...AND POTENTIALLY
FREEZING PRECIPITATION TO THE MOUNTAINS. UTILIZED THE TOPDOWN
APPROACH LEANING TOWARDS GFS FOR TEMPERATURE PROFILES. HELD LOW
TEMPERATURES A FEW DEGREES BELOW MOS WITH CLOUDS AND
PRECIPITATION. IN GENERAL...SUNDAY NIGHT LOWS WILL RANGE FROM THE
UPPER 20S IN THE MOUNTAINS TO THE LOWER 30S IN THE PIEDMONT.

FOR MONDAY...A WAVE OF LOW PRESSURE ALONG THE FRONTAL BOUNDARY
WILL BE LOCATED ALONG THE NORTH CAROLINA COAST WITH AXIS OF
MOISTURE/PRECIPITATION MOVING NORTH ASSOCIATED WITH INCREASING
WARM ADVECTION AHEAD OF THE DEVELOPING LONGWAVE TROUGH TO THE
WEST. HOW MUCH THE LOW CENTER DEEPENS...ITS ASSOCIATED
PRECIPITATION AND PTYPE REMAINS PROBLEMATIC FOR OUR REGION. EACH
MODEL HAS A DIFFERENT TAKE ON THE MAGNITUDE OF THE WARM NOSE OVER
OUR REGION. WILL MAINTAIN THE RAIN VERSUS FREEZING RAIN FORECAST
DURING MUCH OF MONDAY MORNING. THERMAL PROFILES SUGGEST SOME
POTENTIAL FOR LIGHT FREEZING RAIN OR SLEET ACROSS THE VIRGINIA
HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY. FELT THAT THERE WAS
ENOUGH SUPPORT TO RAISE POPS FROM SLIGHT INTO THE CHANCE LEVEL
MONDAY. KEPT HIGHS MONDAY COOLER THAN GUIDANCE WITH READINGS FROM
THE MID 30S IN THE WEST TO THE MID 40S IN THE EAST.

BY MONDAY NIGHT...LOW PRESSURE MOVES INTO THE MIDWEST WITH
TRAILING FRONTAL BOUNDARY SOUTH INTO THE MISSISSIPPI VALLEY. A
DEEP LONGITUDINAL TROUGH DEVELOPS SOUTH TO THE GULF OF MEXICO BY
TUESDAY AFTERNOON WITH INCREASING SOUTHERLY LOW LEVEL FLOW ACROSS
OUR REGION...ACCOMPANIED BY INCREASING MOISTURE ADVECTION. USING
SUPERBLEND FOR LOW TEMPERATURES MONDAY NIGHT PRODUCED READINGS
GENERALLY IN THE UPPER 20S AND LOWER 30S. TEMPERATURES WILL TREND
MILDER FOR HIGHS TUESDAY FROM THE MID 40S TO THE LOWER 50S.

BY TUESDAY NIGHT INTO WEDNESDAY...BOTH GFS AND ECWMF DEEPEN THE
UPPER LOW AND ASSOCIATED TROUGH AND NEGATIVELY TILT THE FEATURE SO
THAT THE TROUGH AXIS SHIFTS TO OFF THE NORTH CAROLINA
COAST...COINCIDENT TO THE POSITION OF THE ASSOCIATED SURFACE
OCCLUDED FRONT...WITH THE TRIPLE POINT PASSING SOMEWHERE NEAR OR
JUST SOUTH OF OUR REGION. AT THIS TIME...SPC DOES NOT HAVE ANY
THUNDERSTORMS IN ITS DAY 4-8 CONVECTIVE OUTLOOK. IT LOOKS
LIKE...THERE IS THE POTENTIAL FOR OUR REGION TO HAVE ACTIVE
WEATHER LATE TUESDAY NIGHT INTO WEDNESDAY WITH PLENTY OF
SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW THUNDERSTORMS.

COLD AIR PUSHES INTO THE REGION TUESDAY NIGHT INTO WEDNESDAY
MORNING...ALLOWING FOR SOME RAIN AND SNOW SHOWERS. IF ENOUGH COLD
AIR ARRIVES QUICKLY...THERE COULD BE SOME ACCUMULATING SNOW IN THE
WESTERN MOUNTAINS. KEPT THE HIGHEST POPS OF RAIN AND SNOW SHOWERS
IN THE WEST AS THE LOW CENTER MARCHES NORTHEAST PUSHES A COLD
FRONT TO THE COAST. IN THE WAKE OF THE COLD FRONT A COOLING TRENDS
WILL CONTINUE WEDNESDAY INTO THURSDAY...WITH WEST TO NORTHWEST
FLOW ALOFT. UPPER FLOW SHIFTS TO THE SOUTHWEST AS TROF CURVES OUT
IN THE CENTRAL US WITH SFC INFLECTION OF LOW PRESSURE DEVELOPS
OVER THE TENNESSEE VALLEY BY FRIDAY MORNING.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 625 PM EST THURSDAY...

VFR CIGS AT 5-9KFT THIS EVENING WILL SCATTER OUT EAST OF THE BLUE
RIDGE TOWARD DAWN. MEANWHILE...NW FLOW BEHIND THE UPPER WAVE WILL
INTRODUCE LOWER CIGS TO LWB/BLF OVERNIGHT WITH MVFR AT LWB BY
05Z...AND MVFR TO IFR AT BLF IN THE 04-07Z TIME FRAME. BCB WILL
STAY OUTSIDE THE LOWER CIGS...AND SCATTER OUT BY 14Z FRIDAY.

MODELS HAVE LOWER CIGS IN THE WEST SCATTERING OUT BY LATE FRIDAY
MORNING WITH VFR ALL SITES OVER MUCH OF THE AREA DURING THE
AFTERNOON.

EXTENDED DISCUSSION...

THE FRI NIGHT-SAT SYSTEM NOW HAS TRENDED WEAKER BUT WILL STILL
NEED TO BE WATCHED AS IT WILL LIKELY BRING A PERIOD OF SUB VFR
WINTRY WEATHER ESPECIALLY FROM THE BLUE RIDGE WEST SAT.

ON THE HEELS OF THIS FRIDAY/SATURDAY SYSTEM WILL BE ANOTHER
SYSTEM TO POTENTIALLY IMPACT MAINLY THE EASTERN PORTION OF THE
REGION SUNDAY NIGHT INTO MONDAY...WITH YET ANOTHER SYSTEM SLATED
FOR LATE TUESDAY INTO WEDNESDAY. THESE SYSTEMS ARE EXPECTED TO
BRING A PERIOD MAINLY RAIN BUT COULD BE SOME WINTRY WX AS WELL
ESPECIALLY IN THE MOUNTAINS. EXPECT POTENTIAL LOW LEVEL WIND SHEAR
AS WELL AND POOR FLYING WEATHER MONDAY.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

$$
SYNOPSIS...RCS
NEAR TERM...RCS/WP
SHORT TERM...AMS
LONG TERM...KK
AVIATION...JH/RCS/WP


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