Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 010102
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
902 PM EDT SAT APR 30 2016

.SYNOPSIS...
HIGH PRESSURE TO THE NORTH WILL MAINTAIN A COOL WEDGE ACROSS THE
REGION OVERNIGHT AHEAD OF A WARM FRONT APPROACHING FROM THE SOUTH
LATE. THIS WARM FRONT WILL MOVE NORTH OF THE AREA SUNDAY
AFTERNOON...FOLLOWED BY A COLD FRONT MONDAY. A STRONGER COLD FRONT
WILL THEN MOVE THROUGH THE REGION BY MIDWEEK.
&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 840 PM EDT SATURDAY...

DEEPER MOISTURE HAS CONTINUED TO SLOWLY INCREASE FROM SW TO NE
THIS EVENING AS BACKING ALOFT OVER THE WEDGE HAS RESULTED IN
PROGRESSIVELY WETTER SOUNDINGS PER PWATS NOW OVER AN INCH. HOWEVER
THE LOW LEVEL CAD REMAINS FIRMLY ENTRENCHED WITH THE EVENING RNK
RAOB SHOWING EASTERLY FLOW UP TO ABOVE 9H WHILE GUIDANCE INDICATES
LITTLE EROSION UNTIL LATE AND MAINLY ACROSS THE SW PERIMETER. THIS
WILL CONTINUE TO SUPPORT BANDS OF CONVECTION DEVELOPING TO THE
SOUTH WITHIN MORE INSTABILITY...AND THEN RIDING OVER THE COOL
POOL IN ELEVATED FASHION OVERNIGHT IN CONJUNCTION WITH MORE ISENTROPIC
LIFT NATURE LIGHT RAIN FARTHER NORTH. LATEST HRRR SUPPORTS THIS
TREND OVER THE NEXT FEW HOURS WITH ANY CONVECTION WEAKENING BEFORE
RAMPING UP DURING THE EARLY MORNING HOURS WHEN THE WARM FRONT TO
THE SOUTH GETS CLOSER AND MOISTURE CONVERGENCE ENHANCES. APPEARS
COULD BE A COUPLE ROUNDS OF HEAVIER SHOWERS WITH ISOLATED TSRA
POSSIBLE MAINLY SOUTH/WEST AS WARMING ALOFT DEEPENS A BIT BUT
STILL UNCERTAINTY WITH THE DEGREE OF ANY PROLONGED HEAVY RAIN.

THUS WONT HOIST ANY FLOOD WATCHES ESPCLY GIVEN LIGHTER TOTALS SO
FAR AND LITTLE OUT EAST WHERE THE DEEPER WEDGE CONTINUES TO LIMIT
PRECIP. OTRW HAVE AGAIN TRENDED POPS LOWER EAST OF THE BLUE RIDGE
TO INIT BEFORE INCREASING TO LIKELY/CATEGORICAL OVERNIGHT AS
DEEPER MOISTURE FINALLY NUDGES EAST. FOG ALSO REMAINS AN ISSUE
ALONG THE BLUE RIDGE BUT WITH RAIN INCREASING EXPECTING SOME
IMPROVEMENT FROM SW TO NE. THUS STAYING WITH THE GOING SPS FOR
AREAS OF DENSE FOG WITHOUT HEADLINES FOR NOW. LOWERED TEMPS A
LITTLE MORE GIVEN CONTINUED LOW LEVEL COOL ADVECTION AND LIGHT
RAIN/DRIZZLE THROUGH THE COLUMN WHICH HAS COOLED MOST BACK INTO
THE CHILLY/DAMP LOW/MID 50S THIS EVENING.


UPDATE AS OF 620 PM EDT SATURDAY...

WITH THE MAJORITY OF THE MEASURABLE RAINFALL MAINLY ACROSS THE FAR
NW AND EXTREME SW SECTIONS...UPDATED TO LOWER POPS BACK TO CHANCE
ELSEWHERE FOR A COUPLE HOURS INTO THIS EVENING. APPEARS MOST
SIGNIFICANT RAINFALL WILL OCCUR OVER THE NW NC MOUNTAINS/FOOTHILLS
WHERE CONVECTION DEVELOPING IN A MORE UNSTABLE ENVIRONMENT TO THE
SW PUSHES INTO/OVER THE WESTERN PERIPHERY OF THE WEDGE OVER THE
NEXT FEW HOURS. THIS WARM ADVECTION HAS ALSO CAUSED CLOUD BASES TO
LOWER ALLOWING FOR MORE WIDESPREAD DENSE FOG ALONG PARTS OF THE
SOUTHERN BLUE RIDGE. THIS TREND MAY DEVELOP FARTHER NORTH AS WARM
AIR ALOFT DEEPENS OVER THE WEDGE AND AIDED BY SATURATED LOW LEVELS
PER RAINFALL. ALSO LOWERING LOW TEMPS A FEW DEGREES MOST LOCATIONS
SINCE CLOSE TO CURRENT FORECAST VALUES OVERNIGHT ALTHOUGH NOT
EXPECTING VALUES TO FALL MUCH MORE AS RAINFALL INCREASES.


PREVIOUS DISCUSSION AS OF 330 PM EDT SATURDAY...

STRONG WEDGE IN PLACE THIS AFTERNOON WILL HOLD AS WE HEAD THRU THE
NIGHT. MEANWHILE...UPPER LEVEL DIVERGENCE AHEAD OF SHORTWAVE WILL
SET UP ACROSS THE CENTRAL AND SOUTHERN APPALACHIANS THIS EVENING
WITH RAINFALL OVERSPREADING THE MOUNTAINS. LOOKING AT OVERNIGHT WE
START TO SEE MODELS EMPHASIZE STRONG LOW LVL CONVERGENCE WITH UPPER
DIVERGENCE ACROSS THE SOUTHERN CWA...WITH ENHANCED RAINFALL AMOUNTS
IN THE SOUTHERN APPALACHIANS. ATTM...LOOKS LIKE AT LEAST MOST OF THE
AREA WILL SEE RAIN OVERNIGHT WITH ONE HALF TO THREE QUARTERS OF AN
INCH SETTING UP ACROSS THE SOUTHERN BLUE RIDGE. WILL NOT ISSUE A
FLOOD WATCH AT THIS POINT...BUT WILL BEAR MONITORING TO SEE IF ANY
DEEP CONVECTION DEVELOPS AND TRAINS ACROSS THIS AREA LATE TONIGHT.

WILL MAINTAIN ISOLATED FLOOD THREAT IN THE HWO.

AS FAR AS THUNDERSTORMS...AM KEEPING THEM OUT OF THE FORECAST
THROUGH TONIGHT GIVEN LACK OF INSTABILITY AND WEDGE. AS WE HEAD TO
SUNDAY WILL BE HARD PRESSED TO CLEAR SKIES IN THE NORTH AND EAST BUT
MODELS FAVOR QUICKER EROSION OF THE WEDGE. WILL BE SLOWER...THEN
INTRODUCE A CHANCE OF STORMS IN THE AFTERNOON. SPC CONTINUES TO
HIGHLIGHT MARGINAL RISK FOR MOST OF THE CENTRAL AND SOUTHERN
APPALACHIANS INTO THE PIEDMONTS OF NC/VA. QUESTION WILL BE IF
SUNSHINE CAN BREAK OUT. AT THE MOMENT SEEMS BEST CHANCE OF THIS WILL
BE IN WV/FAR SW VA AND ACROSS THE NW NC PIEDMONT...BUT THINK CLOUDS
WILL BE AROUND MOST OF THE DAY.

WITH FLOW TURNING SSW BY AFTERNOON WENT CLOSE TO MOS ON HIGHS...BUT
COULD SEE IT COOLER IN LYH TO HSP. MOST WILL SEE HIGHS IN THE LOWER
TO MID 70S.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 230 PM EDT SATURDAY...

A WEAK WAVE OF LOW PRESSURE WILL BE TRACKING NORTHEAST FROM THE OHIO
VALLEY TOWARD NEW ENGLAND OVERNIGHT SUNDAY DRAGGING A COLD FRONT
SLOWLY ACROSS THE REGION EARLY MONDAY. CHANCES FOR SHOWERS OVERNIGHT
WILL BE DECREASING DURING THE DAY AND SHOULD SEE SOME PARTIAL
CLEARING ESPECIALLY EAST OF THE MOUNTAINS LATER IN THE DAY. EXPECT
MILD TEMPS BEHIND THE FRONT ON MONDAY RANGING FROM NEAR 70 NORTHWEST
TO LOW 80S SOUTHEAST AS COOLING IS MODEST BEHIND IT..H85 TEMPS
DROPPING ONLY A FEW DEGREES BY LATE IN THE DAY. THIS BOUNDARY MAKES
ONLY SLIGHT PROGRESS TO THE SOUTHEAST BY LATE MONDAY LEAVING ENOUGH
CLOUDS TO HOLD TEMPS UP SOMEWHAT HIGHER MONDAY NIGHT...GENERALLY
UPPER 40S TO MID-50S. THE SAME FRONT WILL BECOME NEAR STATIONARY
ALONG COAST AND BECOME THE FOCUS FOR SHOWERS AND POSSIBLY SOME
THUNDERSTORMS ON TUESDAY AS SEVERAL WEAK WAVES TRAVERSE NORTHEAST
ALONG IT. MODELS DIFFER IN THE PLACEMENT OF THIS BOUNDARY STRENGTH
OF PERTURBATIONS ALONG IT WHICH WILL HAVE A SUBSTANTIAL IMPACT ON
PRECIPITATION CHANCES ON TUESDAY. WPC AND GFS SOLUTIONS CURRENTLY
FURTHER SOUTHEAST THAN EARLIER CMC OR ECMWF RUNS WHICH BOTH BRING
CONSIDERABLY MORE CLOUDS AND SHOWERS INTO OUR CWA. WENT WITH A MODEL
BLEND RETAINING CHANCE POPS ACROSS THE ENTIRE CWA BUT THE HIGHEST
OVER THE SOUTHEAST.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 230 PM EST SATURDAY...

LOW PRESSURE WILL CONTINUE TO LINGER ALONG THE SOUTHEAST COAST EARLY
WEDNESDAY WITH ASSOCIATED CLOUDS AND SHOWERS MAINLY CONFINED TO THE
COASTAL PLAIN AND EASTERN PIEDMONT DURING THE DAY BUT STILL
LINGERING POPS ACROSS OUR CWA BUT MAINLY SOUTHEAST. TEMPS WILL
REMAIN NEAR SEASONAL LEVELS WEDNESDAY WITH PARTIAL CLEARING DURING
IN THE DAY ESPECIALLY NORTHWEST. MEANWHILE ANOTHER FRONT OVER THE
UPPER PLAINS BEGINS TO DROP SOUTHEAST TOWARD THE AREA LATE WEDNESDAY
INTO THURSDAY AS NORTHERN STREAM TROUGH BEGINS TO AMPLIFY
SHARPLY.BOTH GFS AND EURO SHOW UPPER LOW CLOSING OVER THE EASTERN
CONUS BY LATE THURSDAY WITH EXACT POSITION UNCERTAIN AND LIKELY TO
HAVE CONSEQUENCES FOR SENSIBLE WEATHER BY THAT TIME. 00Z EURO IS THE
MOST AGGRESSIVE WITH DEEP COMPLEX SURFACE LOW MORE OR LESS MERGING
WITH THE EXISTING COASTAL SYSTEM AND ACTUALLY BACKING IN TOWARD THE
MID-ATLANTIC COAST. GFS/CMC NOT QUITE AS FAR SOUTH AND DEEP WITH
UPPER TROUGH AND SURFACE REFLECTION WHICH SEEMS MORE
CLIMATOLOGICALLY PLAUSIBLE BUT WENT WITH BLEND TO ACCOUNT FOR
SIGNIFICANT UNCERTAINTY. EITHER WAY A PERSISTENT DEEP NORTHWEST FLOW
WILL EXIST FRIDAY INTO SATURDAY WITH COOL TEMPS AND PLENTY OF CLOUDS
ESPECIALLY ACROSS THE MOUNTAINS. HIGHS FRIDAY WILL STRUGGLE TO REACH
60 OVER THE MOUNTAINS...CLOSE TO 10F BELOW NORMAL. SLOWLY RISING
HEIGHTS SATURDAY WILL ALLOW FOR SLOWLY IMPROVING CONDITIONS.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
AS OF 740 PM EDT SATURDAY...

SURFACE WEDGE WILL CONTINUE TO HOLD FAST IN THE EASTERN PART OF
THE REGION OVERNIGHT. LOW LEVEL WINDS WILL CONTINUE TO INCREASE IN
ADVANCE OF AN APPROACHING SYSTEM. MOISTURE ADVECTION WILL BE
STRONG WITHIN THESE WINDS. EXPECT LIGHT PRECIPITATION TO INCREASE
ACROSS THE REGION FROM WEST TO EAST DURING THE OVERNIGHT
HOURS...WITH COVERAGE GREATEST IN THE WEST. CIGS WILL LOWER TO
INTO THE LIFR/IFR RANGE WITH VSBYS MAINLY IFR/MVFR. THE STRONG LOW
LEVEL WINDS ABOVE THE WEDGE WILL ALLOW FOR A FEW HOURS OF LOW
LEVEL WIND SHEAR LATE TONIGHT INTO EARLY SUNDAY MORNING.

RAIN WILL CONTINUE ACROSS THE REGION SUNDAY MORNING...WITH ONLY
MINOR IMPROVEMENTS TO FLIGHT CATEGORIES. THE PRECIPITATION WILL
START TO BECOME MORE SHOWERY IN THE WEST BY THE LATE MORNING.

CIGS/VSBYS IMPROVING TO MVFR/VFR BY SUNDAY AFTERNOON AS THE WEDGE
ERODES. SUNDAY AFTERNOON BRINGS THE POTENTIAL FOR SCATTERED
CONVECTION...SOME POSSIBLY STRONG TO SEVERE AS SHORT WAVE ENERGY
TRACKS NORTHEAST ACROSS THE REGION IN THE WARM/UNSTABLE AIR MASS.
SITUATION APPEARS SOMEWHAT SIMILAR TO WHAT WAS OBSERVED THURSDAY
ACROSS THE REGION...BUT PERHAPS MORE ACTIVITY NORTH-WEST OF THE
BLUE RIDGE THIS TIME AROUND THAN WHAT WAS OBSERVED SUNDAY.

EXTENDED AVIATION DISCUSSION...

SFC LOW PRESSURE TRACKS NORTHEAST ACROSS GA/SC/NC SUN NIGHT-
TUE...LIKELY PROLONGING SUB-VFR CIGS AND POTENTIALLY LEAVING SOME
LIGHT PRECIPITATION ACROSS THE REGION...ESPECIALLY EAST OF THE
BLUE RIDGE. FOR THE MID AND LATER PART OF NEXT WEEK...A DEEP UPPER
LOW IS EXPECTED TO DROP DOWN ACROSS THE GREAT LAKES INTO THE
APPALACHIANS AND MID-ATLANTIC REGION...WHICH WILL LEAVE THE REGION
WITH VARIABLE CLOUDINESS...SHOWERS...AND PERIODS OF SUB-VFR
CONDITIONS.

&&

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

&&

$$
SYNOPSIS...JH/WP
NEAR TERM...JH/WP
SHORT TERM...PC
LONG TERM...PC
AVIATION...DS/WP


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