Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 262005
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
405 PM EDT THU MAR 26 2015

.SYNOPSIS...
A STRONG COLD FRONT TO OUR WEST WILL TRAVEL EAST THIS EVENING AND
PUSH THROUGH THE AREA TONIGHT. MUCH COLDER AIR WILL BE MOVING IN
BEHIND THE COLD FRONT FOR THIS WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 400 PM EDT THURSDAY...

A STRONG COLD FRONT LOCATED JUST TO OUR WEST THIS AFTERNOON WITH
PREFRONTAL LINE OF CONVECTION AND ANAFRONT RAIN WELL BEHIND THE
FRONTAL BOUNDARY WILL MOVE EAST TONIGHT INTO FRIDAY. THE COLD AIR
WEDGE FINALLY ERODED THIS AFTERNOON WITH HEATING AND MIXING.
ANTICIPATING THAT ADDITIONAL CONVECTION WILL DEVELOP AHEAD AND ALONG
THE FRONT THIS AFTERNOON INTO TONIGHT AS IT MOVES EAST. SKINNY CAPE
AND INSTABILITY MAKES CONVECTION FORECAST PROBLEMATIC WITH THIS
BOUNDARY. USED A BLEND OF THE NAM AND HRRR FOR POPS THIS AFTERNOON
INTO TONIGHT. THERE IS SOME UNCERTAINTY IF CONVECTION DEVELOP EXACTLY
AS PROGGED ALONG BLUE RIDGE MOUNTAINS BY HIGHER RESOLUTION MODELS
LIKE THE RNKWRFARW...HRRR AND HIRESW-ARW. FOR THE WINDOW FOR
THUNDERSTORM DEVELOPMENT IS SMALL.

ANOTHER ISSUE IS WHETHER THE COLD AIR CATCHES FRONTAL MOISTURE
ASSOCIATED WITH THE FRONT SLOWED BY LOW PRESSURE WAVE MOVING ALONG
THE BOUNDARY LATE TONIGHT INTO FRIDAY. THE RATE OF FALL IS ALSO
IMPORTANT FOR LATE TONIGHT INTO FRIDAY MORNING FOR POTENTIAL COOLING
OF TEMPERATURES. BELIEVE THAT ENOUGH COLD AIR CATCHES SOME MOISTURE
LATE TONIGHT INTO FRIDAY TO CREATE SOME MOUNTAIN SNOW SHOWERS AND
SNOW FLURRIES. ANY SNOW ACCUMULATIONS WILL GENERALLY BE LIGHT AND
MAINLY IN THE WESTERN UPSLOPE FAVOR AREAS. THE STRONG COLD AIR
ADVECTION COMBINED WITH PRESSURE RISES OF 5 TO 10MB/6HRS WILL RESULT
IN GUSTY WINDS TONIGHT. LOW TEMPERATURES WILL DROP INTO THE MID 20S
IN THE NORTHWEST MOUNTAINS TO THE MID 40S IN THE PIEDMONT TONIGHT.

THE FRONTAL WAVES BEING DRIVEN BY UPPER LEVEL SHORT WAVE ENERGY WILL
KEEP RESIDUAL PRECIPITATION ACROSS THE EAST FRIDAY. MEANWHILE...
NORTHWEST WINDS WILL BE GENERATING UPSLOPE PRECIPITATION WEST OF THE
BLUE RIDGE AS MUCH COLDER COLDER AIR MOVES IN. SNOW ACCUMULATION IN
THE WESTERN MOUNTAINS WILL BE LIMITED BY THE STRENGTH OF THE SUN
THIS TIME OF YEAR AND WARM ANTECEDENT CONDITIONS. WPC IN DAY 1 PAINT
UP TO 2 INCHES POSSIBLE IN WESTERN GREENBRIER AND THE POTENTIAL UP
TO AN INCH IN THE WESTERN MOUNTAINS. HIGH TEMPERATURES FRIDAY WILL
RANGE FROM THE MID 30S IN THE NORTHWEST MOUNTAINS TO THE LOWER 50S
IN THE PIEDMONT.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
AS OF 340 PM EDT...

MAIN ISSUE FOR THE WEEKEND IS THE INFLUENCE OF THE DEEP UPPER TROUGH
AND ANOMALOUSLY COLD AIR MASS.  FIRST...LINGERING LIGHT ACCUMULATING
SNOW SHOWERS ON WESTERN SLOPES OF APPALACHIANS FOR FRIDAY NIGHT AND
PERHAPS INTO FIRST PART OF SATURDAY ASSOCIATED WITH COLD ADVECTION
AND AIDED BY SOME SLIGHTLY DEEPER LIFT WHEN THE UPPER VORTICITY MAX
AND TROUGH AXIS SWING THROUGH BETWEEN MIDNIGHT AND DAYBREAK
SATURDAY.  THEN WITH COLD AIR MASS IN PLACE...INCLUDING COLDER THAN
MINUS 10 C AT 850MB OVER MUCH OF THE AREA SATURDAY...HIGH TEMPS
SATURDAY WILL BE 15-20 F BELOW AVERAGE...AND WE COULD BE CLOSE TO
RECORD LOWS FOR SUNDAY MORNING THE 29TH...SEE CLIMATE SECTION BELOW.
WENT WITH COLDER MAV AND ECMWF GUIDANCE COMPARED TO MET...WHICH BOTH
KEEPING TRENDING DOWN...AND WAS TEMPTED TO GO EVEN COLDER THAN
GUIDANCE WITH THE URFACE HIGH RIGHT OVERHEAD SUNDAY MORNING.  ONE
CAUTION IS THAT WARM ADVECTION ALOFT BEGINS AGAIN AND THERE COULD BE
SOME THIN CIRRUS DRIFTING AHEAD OF WARM FRONT...MOST LIKELY ACROSS
THE WEST...SO WILL WAIT ANOTHER 24 HRS BEFORE DECIDING TO GO BELOW
GUIDANCE OR NOT.

ALSO WITH UPPER TROUGH OVERHEAD AND SOME WEAK MID LEVEL
INSTABILITY...SOME MODELS SHOWING VERY LIGHT SHOWERS ACROSS CENTRAL
THROUGH FIRST HALF OF SATURDAY...SO INTRODUCED A SLIGHT CHC POP
THERE.

TEMPS SHOULD MODERATE NICELY DURNG THE DAY SUNDAY WITH RETURN OF
WARM ADVECTION...BUT STILL BELOW NORMAL. COULD SEE HAVING TO TWEAK
THOSE UP A FEW DEGREES BETWEEN NOW AND SUNDAY.

NEXT CLIPPER SYSTEM MAY ARRIVE AS EARLY AS SUNDAY NIGHT IN WEST BUT
THINK GFS IS A BIT TOO FAST WITH THIS GIVEN POSITION OF LARGER
TROUGH STILL OFF EAST COAST...SO LEANING TOWARD SLOWER ECMWF AND
HOLDING OFF ON BEST PRECIP CHANCES UNTIL MONDAY...BUT DO HAVE LOW
CHANCE FAR WEST BY AFTER MIDNIGHT.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 355 PM EDT...

STILL SOME UNCERTAINTY IN TIMING OF THE CLIPPER SYSTEM AND AMOUNT OF
PRECIP GIVEN CURRENT MODEL DIFFERENCES...BUT ECMWF AND CANADIAN ON
SAME PAGE WITH MORE OF A DAYTIME MONDAY TIMING...AND ECMWF TRENDS
SHOWING LITTLE WETTER SOLUTION AND BETTER CHANCES FOR PRECIP TO
SPREAD INTO PIEDMONT AT SOME POINT...SO HAVE INCREASED POPS TO LOW
CHC FOOTHILLS AND SLIGHT CHC INTO ALL OF PIEDMONT...AND MAY
EVENTUALLY HAVE TO GO HIGHER IF TIMING HOLDS STEADY.

PLENTY MILD ENOUGH FOR ALL RAIN WITH THIS SYSTEM...WITH THE POSSIBLE
EXCEPTION OF HIGHEST TERRAIN IN WEST VIRGINIA MONDAY MORNING...BUT
DO NOT THINK THERE WILL BE ANY ISSUES WITH ACCUMULATING SNOW EVEN ON
HIGHEST RIDGES.

LARGE SCALE PATTERN KEEPS SOME CLIPPER ENERGY HEADING TOWARD THE
APPALACHIANS AGAIN FOR TUESDAY OR TUES NIGHT...BUT THIS COULD REMAIN
TO THE NORTH...WHICH IS WHAT CURRENT ECWMF SOLUTION SUGGESTS...AND
THERE IS A TREND TO FLATTEN THE PATTERN A BIT SO EVEN THE WETTER GFS
MAY NOT BRING US MUCH OF ANYTHING...AND WOULD MOST LIKELY DO SO ONLY
ON WESTERN SLOPES. AFTER THAT NEXT BEST CHANCE FOR PRECIP COMES BY
WED NIGHT INTO THURSDAY WITH BETTER FRONTAL PASSAGE AND TAP OF SOME
GULF MOISTURE AS MODELS SHOWING SOME ATTEMPT TO PHASE A SOUTHERN
SHORT WAVE WITH YET ANOTHER COMING OUT OF THE NORTHERN PLAINS.  AT
THIS POINT...THINK THE GFS IS OVERDOING THE STRENGTH OF THE SOUTHERN
PIECE OF ENERGY GIVEN A LOT OF POTENTIALLY SPURIOUS CONVECTION NEAR
THE GULF COAST EARLIER WEDNESDAY...SO ONCE AGAIN WILL LEAN TOWARD
ECMWF WHICH IS SOMEWHAT DRIER AND NOT AS LIKELY TO SPREAD PRECIP
EAST.  OBVIOUSLY WITH THIS BEING 6 TO 7 DAYS OUT...THERE IS MUCH
UNCERTAINTY WITH DETAILS...AND WITH WARMING TREND THROUGHOUT THE
WEEK TOWARD OR ABOVE AVERAGE TEMPERATURES ONCE AGAIN...THIS MID WEEK
SYSTEM SHOULD NOT POSE ANY PRECIP TYPE ISSUES...NOR DOES IT LOOK TO
HAVE MUCH CHANCE OF GENERATING ANY SEVERE WEATHER GIVEN EITHER A
WEAK WEDGE IN PLACE IF GOING MORE WITH GFS...OR A VERY LIMITED
MOISTURE TAP IF GOING MORE WITH ECMWF.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
AS OF 150 PM EDT THURSDAY...

VFR AND MVFR CEILINGS WILL LOWER THIS AFTERNOON INTO TONIGHT.
MIXING HAS ERODED THE COLD WEDGE IN MOST AREAS EXCEPT A NARROW
PATCH ALONG THE SOUTHERN BLUE RIDGE. WITH HEATING AND MIXING THIS
AFTERNOON...LIGHT WINDS WILL BECOME GUSTY OUT OF THE SOUTHWEST
THIS AFTERNOON.

HIGH CONFIDENCE THAT A STRONG COLD FRONT WILL CROSS THROUGH THE
REGION JUST AROUND 00Z/7PM AT KLWB AND KBLF. THE FRONT IS
EXPECTED TO REACH KLYH AROUND 04Z/MIDNIGHT AND KDAN AROUND
05Z/1AM.

SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP ALONG AND BEHIND
THE FRONT. VISIBILITY MAY DROP TO MVFR LEVELS IN THE HEAVIER RAIN
SHOWERS. WINDS WILL BECOME NORTHWEST BEHIND THE FRONT WITH GUSTS
AT 20 TO 30 KNOTS.

SHOWERS AND GUSTY WINDS WILL CONTINUE THROUGH FRIDAY AS MUCH
COLDER AIR SURGES INTO THE REGION. SNOW SHOWERS AND SNOW FLURRIES
ARE LIKELY WITH MVFR CEILINGS AND VISIBILITIES IN THE WESTERN
UPSLOPE AREAS OF THE MOUNTAINS LATE TONIGHT THROUGH FRIDAY NIGHT.

MEDIUM TO HIGH CONFIDENCE IN CEILINGS...VISIBILITIES AND WINDS
DURING THE TAF PERIOD.

WINDS WILL DIMINISH SATURDAY WITH VFR CONDITIONS AS HIGH PRESSURE
BUILDS INTO THE AREA. SCATTERED MVFR SHOWERS ARE POSSIBLE SUNDAY
NIGHT INTO MONDAY. VFR WEATHER IS EXPECTED TUESDAY.

&&

.CLIMATE...
RECORD LOWS FOR MARCH 29:

ROA19
BCB17
LYH23
DAN23
BLF19
LWB18

&&

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

&&

$$
SYNOPSIS...KK
NEAR TERM...KK
SHORT TERM...SK
LONG TERM...SK
AVIATION...AMS/KK
CLIMATE...SK


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