Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 170245
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1045 PM EDT THU APR 16 2015

.SYNOPSIS...
AN AREA OF COOL HIGH PRESSURE WILL REMAIN OVER THE REGION INTO
FRIDAY MORNING. ONCE THIS WEDGE BREAKS...TEMPERATURES WILL WARM
BACK INTO THE 70S. TEMPERATURES WILL DROP AS RAIN CHANCES
INCREASE WITH THE PASSING OF A COLD FRONT ON SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 1030 PM EDT THURSDAY...

COOL DAMP CONDITIONS LIKELY THROUGH FRIDAY MORNING AS SHALLOW
WEDGE OF HIGH PRESSURE REMAINS LOCKED IN PLACE ALONG EASTERN
SLOPES OF THE APPALACHIANS. OCCASIONAL DRIZZLE AND FOG WILL BE
MOST PRONOUNCED ALONG THE EASTERN SLOPES OF THE BLUE RIDGE WHERE
SHALLOW ISENTROPIC LIFT WILL BE THE GREATEST.

VERY LITTLE CHANGE IN TEMPERATURES IS EXPECTED OVERNIGHT WITH
TEMPERATURES REMAINING IN THE U40S-M50S. FRIDAYS HIGH TEMPERATURES
HOWEVER...WILL BE A LITTLE TRICKY...ESPECIALLY IN AREAS WHERE THE
WEDGE HANGS ON. TEMPERATURES FOR LOCATIONS OUTSIDE OF THE WEDGE
COULD SEE HIGH TEMPERATURES IN THE LOW TO MID 70S. THOSE AREAS
REMAINING IN THE WEDGE MAY ONLY SEE TEMPERATURES WARMING INTO THE
LOW TO MID 60S WITH A LATE DAY SURGE IF THE WEDGE BREAKS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
AS OF 330 PM EDT THURSDAY...

SOUTHWEST FLOW ALOFT WILL TRANSITION TO NORTHWEST FLOW ALOFT AT
THE BEGINNING OF THE SHORT TERM AS AN UPPER SHORT WAVE MOVES OFF
THE MID-ATLANTIC COAST. ANY LINGER SHOWERS ACROSS THE BLUE RIDGE
SHOULD MOVE OUT OF THE REGION QUICKLY AFT 00Z SAT. UPPER-LEVEL
SHORT WAVE RIDGING WILL EVOLVE ACROSS THE OH/TN VALLEY SUNDAY AS
THE FLOW AMPLIFIES IN RESPONSE TO A DEEP UPPER TROUGH SHIFTING
SLOWLY EAST FROM THE CENTRAL/SOUTHERN PLAINS. THIS PATTERN WILL
BRING DRY/SEASONABLE CONDITIONS TO THE REGION SATURDAY.

BY SUNDAY...THE AFOREMENTIONED UPPER TROUGH BEGINS TO LIFT OUT OF
THE MID-SOUTH INTO THE MID-ATLANTIC REGION...WHILE TAKING ON A
STRONG NEGATIVE TILT. ANTECEDENT SURFACE HIGH PRESSURE WILL MOVE
OFF THE MID-ATLANTIC COAST INTO YET AGAIN ANOTHER FAVORABLE WEDGE
POSITION. STRONG PVA/ISENTROPIC LIFT WILL ENSUE QUICKLY OVER THE
SHALLOW WEDGE SUNDAY BRINGING WIDESPREAD RAIN...SOME HEAVY DURING
THE AFTERNOON/EVENING...INTO THE WEDGE AIR MASS. THE WEDGE WILL BE
REINFORCED WITH THE PRECIPITATION...HOLDING HIGH TEMPERATURES
SUN AFTERNOON POTENTIALLY IN THE 50S. RAINFALL IN EXCESS OF 1 INCH
ACROSS MUCH OF THE CWA APPEARS LIKELY WITH THIS EVENT. THE GOOD
NEWS IS THAT THE SYSTEM IS MOVING VERY QUICKLY AS A NORTHERN
STREAM UPPER LOW QUICKLY DIGS INTO THE NORTHERN PLAINS HELPING TO
PUSH THE SOUTHERN STREAM UPPER TROUGH NORTHEAST OF THE REGION BY
SUN NIGHT/EARLY MON. THIS SHOULD CONFINE THE PERIOD OF HEAVY RAIN
TO ABOUT 12 HOURS OR LESS...WHICH SHOULD HELP LIMIT ANY POTENTIAL
FLOOD ISSUES. WILL CONTINUE TO HIGHLIGHT IN THE HWO AS THE GROUND
IS WELL SATURATED NOW FROM ALL OF THE RECENT RAINFALL. IT STILL
APPEARS THAT THE HEAVIEST RAINFALL WILL FALL ALONG THE EAST FACING
SLOPES OF THE BLUE RIDGE WITH PRONOUNCED SOUTHEAST FLOW IN THE
WEDGE AIR MASS AS THE STRONG NEGATIVELY TILTED UPPER SHORT WAVE
TRAVERSES THE REGION LATE SUN/SUN NIGHT. CANNOT RULE OUT A FLOOD
WATCH AS WE GET CLOSER TO THAT PERIOD. WE WILL NEED TO ALSO
WATCH...AS NOTED BEFORE...STRONG SOUTHEAST WINDS ARRIVING ACROSS
THE USUAL AREAS OF SOUTHEAST WV/SOUTHWEST VA...EARLY SUN PRIOR TO
THE HEAVIER RAIN MOVING INTO THE REGION. BOTTOMLINE...THIS WILL BE
A SIGNIFICANT RAIN EVENT...BUT TIME DURATION SHOULD LIMIT
PROBLEMS. THE SEVERE THREAT APPEARS TO BE NIL WITH MUCH OF THE CWA
IN A STRONG WEDGE AND VERY STABLE. HAVE OPTED NOT TO INTRODUCED
THUNDER AT THIS POINT.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 345 PM EDT THURSDAY...

A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER APPEARS TO
EVOLVE THROUGH THE MID AND LATER PART OF NEXT WEEK AS A DEEP UPPER
TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. IN THE WAKE OF THE
STRONG UPPER SHORT WAVE ON SATURDAY. PRIOR TO THE ARRIVAL OF THE
COLDER AIR MON NIGHT/TUE...A WARM SECTOR WEDGE SURGES INTO THE
REGION DURING PEAK HEATING MON AFTERNOON. CAPE VALUES EXCEED 1000
J/KG ACROSS AREAS EAST OF THE BLUE RIDGE AND ARE NOTABLE IN MOST
OF THE CWA MON AFTERNOON. THE SIGNIFICANT SVR PARM RISES TOWARD
20000 ACROSS THE PIEDMONT WITH LIS DROPPING INTO THE -4C RANGE ON
SOME MODELS. THUS...MON AFTERNOON APPEARS TO BE THE BEST CHANCE
FOR THUNDERSTORM ACTIVITY...AND POTENTIALLY EVEN A FEW
STRONG/APPROACHING SEVERE LIMITS ACROSS EAST OF THE BLUE RIDGE.

BY TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB
TEMPS PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK.
ANTICYCLONIC FLOW WILL KEEP VARIABLE CLOUDINESS AND POTENTIALLY
UPSLOPE SHOWERS IN PLACE ACROSS THE MOUNTAINS. THE CLOUDS AND
CYCLONIC FLOW WILL HOLD MAX TEMPS INTO THE 50S ACROSS THE
MOUNTAINS THROUGH MUCH OF THE LATER HALF OF NEXT WEEK...WHILE 60S
TO 70S PREVAIL TO THE EAST WITH DOWNSLOPE NORTHWEST FLOW AND
SIGNIFICANTLY GREATER AMOUNTS OF SUNSHINE. EMBEDDED SHORT WAVES
ROTATING THROUGH THE UPPER TROUGH MAY ENHANCE CLOUD AND RAIN
SHOWERS AT TIMES...ESPECIALLY ACROSS THE MOUNTAINS...BUT NO
SIGNIFICANT RAINFALL EVENTS APPEAR THROUGH THIS PERIOD WITH DEEP
CYCLONIC NORTHWEST FLOW IN PLACE.

BY THE END OF THE WEEK...THE UPPER FLOW DEAMPLIFIES AND BECOMES
MORE ZONAL. AN EMBEDDED SHORT WAVE MAY BRING A MORE SIGNIFICANT
THREAT OF RAIN TO THE REGION THU NIGHT/FRI...SO HAVE RETAINED CHC
POPS TOWARD DAY 8 AS A RESULT. INSTABILITY MAY SUPPORT ISOLD
THUNDER...BUT HAVE NOT INTRODUCED JUST YET.

TEMPERATURES ARE EXPECTED TO BE BELOW NORMAL THROUGH MOST OF THE
PERIOD...WITH THE EXCEPTION OF MONDAY...WHEN SOME LOWER 80S ARE
POSSIBLE ACROSS THE PIEDMONT. CLOUDS AND WIND SHOULD PREVENT ANY
FROST/FREEZE CONCERN THROUGH THIS TIME FRAME.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
AS OF 720 PM EDT THURSDAY...

IFR TO MVFR CEILINGS WERE NOTED ACROSS THE MOUNTAIN TAF
SITES...INCLUDING KBCB...KLWB AND KBLF...AND EVEN AT KROA CIGS
WERE MVFR. AS LOW LEVEL WINDS TURN TO A MORE SOUTHERLY
DIRECTION...MOISTURE WILL ADVECT INTO THE REGION DURING THIS
EVENING AND OVERNIGHT HOURS. THIS MOISTURE ADVECTION IN
COMBINATION WITH A WEAK UPPER LEVEL DISTURBANCE MOVING OVER THE
AREA TONIGHT WILL KEEP LOW CLOUDS AND LIGHT PRECIP IN PLACE.
EXPECT FLYING CONDITIONS TO CONTINUE TO WORSEN TONIGHT WITH ALL
TAF SITES FALLING INTO IFR OR LIFR FLIGHT CATEGORIES THROUGH EARLY
FRIDAY.

ON FRIDAY...LOW LEVEL FLOW TURNS TO THE SOUTHWEST IN
ADVANCE OF A COLD FRONT. THIS SHOULD ALLOW CEILINGS TO RISE AND
EVEN BRING SOME CLEARING TOMORROW...ESPECIALLY BY AFTERNOON.
THIS MORE UNSTABLE AIRMASS WILL SPAWN WIDELY SCATTERED TO
SCATTERED SHOWERS AND STORMS...BUT THE COVERAGE IS NOT EXPECTED
TO BE GREAT ENOUGH TO ADD PRECIP AT ANY TAF SITES.

A COLD FRONT WILL PASS ACROSS THE AREA FRIDAY NIGHT...WITH DRIER
HIGH PRESSURE BUILDING IN BEHIND FOR SATURDAY.

EXTENDED AVIATION...

A COMPLEX STORM SYSTEM WILL BEGIN TO AFFECT THE REGION LATER IN
THE WEEKEND WITH A WARM FRONT BRINGING WIDESPREAD MVFR/IFR
CONDITIONS IN RAIN SUNDAY/SUNDAY NIGHT FOLLOWED BY ANOTHER COLD
FRONTAL PASSAGE MONDAY. THIS LIKELY TO KEEP PERIODS OF MVFR IN
PLACE UNTIL THE FRONT POSSIBLY CLEARS THE REGION LATER MONDAY.

&&

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

&&

$$
SYNOPSIS...RCS
NEAR TERM...PM/RCS
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...PH/RCS


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