Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 011317
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
917 AM EDT SUN MAY 1 2016

.SYNOPSIS...
A COOL AIR WEDGE THIS MORNING WILL GIVE WAY TO A WARM FRONT THIS
AFTERNOON...THEN A COLD FRONT TONIGHT...BOTH OF WHICH WILL BRING
SHOWERS AND THUNDERSTORMS TO THE AREA. THE FRONT WILL STALL TO OUR
SOUTH MONDAY AS A WAVE OF LOW PRESSURE RIDES ALONG THE FRONT
MONDAY INTO TUESDAY. FOR WEDNESDAY THROUGH FRIDAY...AN UPPER LOW
WILL DRIFT SOUTHWARD INTO THE REGION FROM THE GREAT
LAKES...KEEPING AN UNSETTLED AND UNSEASONABLY COOL PATTERN
THROUGHOUT THE REGION.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 900 AM EDT SUNDAY...

WEDGE SLOWLY ERODING ACROSS THE FAR SW CWA WITH SUNSHINE STARTING
TO PEEK OUT IN THE NC MTNS INTO PORTIONS OF SW VA PER LATEST VIS
SATELLITE AND WEATHER CAMS. TWO AREAS OF HEAVIER SHOWERS THIS
MORNING...ONCE LEADING EAST OF THE BLUE RIDGE AND ANOTHER
STRETCHED FROM FAR SW VA/SE KY NORTHEAST TO THE ALLEGHANYS. HIGH-
RES MODELS ARE NOT HANDLING THIS TOO WELL...SLOWER THAN WHAT IS
GOING ON...THOUGH THE 00Z HIRES-ARW HAD A DECENT ENOUGH GRASP AT
12Z. WILL LEAN ON PERSISTENCE AND TRACKING THE NEXT FEW HOURS PER
RADAR TRENDS. HAVE ADDED SOME HEAVY RAIN AT TIMES...BUT OVERALL
AVERAGE RAINFALL THROUGH 18Z APPEARS TO BE UNDER AN INCH...WITH
LOCALLY HIGHER AMOUNTS. CELLS AND LINES ARE TRANSIENT AND MOVING
FAST ENOUGH SO FLASH FLOODING IS NOT A BIG CONCERN AT THE MOMENT.
WILL HAVE TO SEE IF ANY TRAINING OF CELLS OCCURS.

AS FAR AS SVR THREAT WILL HAVE TO MONITOR CLEARING...AS THE 6Z NAM
AND 00Z CMC ARE SHOWING CLEARING THIS AFTERNOON OVER THE SRN AND
SW CWA. IF THIS OCCURS...WILL SEE BETTER INSTABILITY. BETTER SHEAR
STILL EXISTS OVER KY AND THINK THE AREA OF GREATEST CONCERN SHOULD
BE FROM CENTRAL KY TO FAR SW VA INTO SRN WV THIS
AFTERNOON...POSSIBLY DOWN ACROSS THE NC PIEDMONT/FOOTHILLS.

PREVIOUS MORNING DISCUSSION...

COMPLICATED WEATHER PATTERN IN PLACE THROUGH THE NEXT 24 HOURS AS
A VARIETY OF SYSTEMS IMPACT THE REGION. TO START...A STRONG MID-
LEVEL DISTURBANCE WAS TRACKING FROM THE TN VALLEY NORTHEAST ACROSS
THE REGION THIS MORNING. A STRONG WEDGE WAS IN PLACE AT THE
SURFACE...EXTENDING AS FAR SOUTHWEST AS NORTHEAST GA. RAIN
CONTINUING TO FALL INTO THE WEDGE SERVES TO ENHANCE IT FURTHER.
BIG QUESTION TODAY IS WHEN WILL THE WEDGE BREAK. MOST MODELS...INCLUDING
THE HRRR...INSIST THAT IT WILL RAPIDLY RETREAT NORTHEAST BY MID-
DAY...LEAVING THE AREA IN A MUCH MORE UNSTABLE AND WARMER AIR MASS
BY AFTERNOON. THIS IS ALWAYS A BIG QUESTION IN THIS TYPE OF
SYNOPTIC SETUP. HOWEVER...WE HAVE SEEN SIMILAR RECENT EVENTS OVER
THE PAST COUPLE OF MONTHS...SO IT REMAINS A POSSIBILITY.
ALOFT...SOME OF THE BEST FORCING PASSES NORTHEAST OF THE AREA BY
MID-DAY. HOWEVER...THE AREA IS LEFT WITH SOUTHWEST FLOW ALOFT
THANKS TO A PERSISTENT BROAD AREA OF LOW PRESSURE IN THE SOUTHWEST
U.S. ADDITIONAL WEAK DISTURBANCES ARE EMBEDDED WITHIN THE UPPER
FLOW...ONE WHICH WILL HELP PUSH A NEW COLD FRONT INTO THE REGION
OVERNIGHT...WHICH WILL THEN STALL JUST TO OUR SOUTH BY MON. MANY
QUESTIONS REGARDING DEGREE OF INSTABILITY AND FORCING FOR THE
AFTERNOON. ECMWF/CANADIAN ARE VERY LACK LUSTER WITH INSTABILITY BY
AFTERNOON...HOLDING THE WEDGE IN MUCH OF THE AFTERNOON...WHILE THE
GFS IS ON THE OTHER END OF THE SPECTRUM SHOWING AN UNSTABLE AIR
MASS SUPPORTIVE OF MORE WIDESPREAD AND STRONGER CONVECTION. SPC
HAS PLACED MUCH OF THE CWA EXCEPT THE EXTREME E-NE PORTION IN A
MARGINAL RISK TODAY...NOTING AS I HAVE QUESTIONS REGARDING THE
DEGREE OF INSTABILITY AND FORCING. HAVE INCLUDED THUNDER ALL
AREAS...ESPECIALLY IN THE AFTERNOON...WITH EVEN A FEW RUMBLES
POSSIBLE THIS MORNING. BUT SEVERE FOR THIS AFTERNOON/EVENING IS A
BIG UNCERTAINTY AT THIS POINT. MODEL MOISTURE/QPF FIELDS ARE
EXTREMELY NOISY...MURKY...AND RATHER NON-DESCRIPT FOR THIS
AFTERNOON/EVENING...MAKING IT VERY DIFFICULT TO PINPOINT
SPECIFICALLY FAVORED AREAS. CATEGORICAL TO DEFINITE POPS ARE IN
ORDER FOR THE MORNING...WITH HIGH CHANCE TO LIKELY POPS ARE IN
ORDER FOR THE AFTERNOON

TEMPERATURES TODAY ALSO AN UNCERTAINTY AND HINGE ON WHEN/IF THE
WEDGE BREAKS. AGAIN...THE GFS IS ON THE WARM END OF THE SPECTRUM
SHOWING WIDESPREAD MID 70S ACROSS MUCH OF THE CWA BY 18Z. ECMWF IS
ON THE COOL END OF THE SPECTRUM WITH HIGHS MAINLY IN THE 60S EAST
OF THE ALLEGHANY FRONT. HAVE LEANED TOWARD THE COOLER ECMWF AS
CONFIDENCE IN THE WEDGE COMPLETELY BREAKING IS NOT THAT HIGH AT
THIS POINT. THIS IS AN INTENSE WEDGE...MORE SO THAN RECENT ONES.
HOWEVER...DO FEEL THAT WHATEVER IS LEFT OF THE WEDGE IN EASTERN
SECTIONS WILL FINALLY ERODE OVERNIGHT INTO MONDAY
MORNING...ALLOWING TEMPERATURES TO CONTINUE TO MODERATE WITH
MINIMAL COOLING OVERNIGHT. AREAS EAST OF THE BLUE RIDGE MAY SEE
MIN TEMPS MONDAY MORNING CLOSE TO MAX TEMPS THIS AFTERNOON.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 530 AM EDT SUNDAY...

THE COLD FRONT SHOULD PUSH EASTWARD OVER THE MID ATLANTIC ON
MONDAY...AND BRING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS. SPC
HIGHLIGHTS THE CWA FOR A MARGINAL RISK OF SEVERE WEATHER...AND THE
MODEL SOUNDINGS APPEAR FAVORABLE FOR CONVECTIVE DEVELOPMENT. HIGHS
FOR MONDAY REACH THE LOWER 70S TO THE LOWER 80S...WHICH WILL ALLOW
CAPE VALUES TO EXCEED 1000 J/KG BY THE AFTERNOON IN THE PIEDMONT. IF
ANY STRONGER STORMS MATERIALIZE AHEAD OF THE COLD FRONT...LARGE HAIL
AND DAMAGING WINDS WOULD BE THE MAIN THREATS. THIS FRONT IS
PROJECTED TO WEAKEN AND STALL DURING MONDAY NIGHT INTO TUESDAY...BUT
HOW FAR SOUTH IT CAN REACH BEFORE IT BECOMES STATIONARY REMAINS A
LITTLE QUESTIONABLE. REGARDLESS...IT WILL KEEP SCATTERED SHOWERS IN
THE FORECAST THROUGHOUT THIS TIME.

SEVERAL MORE WAVES OF LOW PRESSURE RIDE NORTHWARD ALONG THE STALLED
FRONTAL BOUNDARY DURING TUESDAY AND WEDNESDAY. WHILE THE CHANCE OF
SHOWERS SHOULD LINGER THROUGH THESE TWO DAYS...THE THREAT OF
THUNDERSTORMS APPEARS LIMITED TO MAINLY NORTHWEST NORTH CAROLINA ON
TUESDAY AFTERNOON DUE TO LINGERING INSTABILITY AND THE PROXIMITY OF
THE STALLED FRONT. HIGH TEMPERATURES ON TUESDAY SHOULD DIP FIVE TO
TEN DEGREES LOWER THAN ON MONDAY. THE CHANCE OF THUNDERSTORMS
DIMINISHES ON TUESDAY NIGHT...AS THE WAVES OF LOW PRESSURE
SUCCESSFULLY PUSH THE FRONTAL BOUNDARY TOWARD THE COAST BY
WEDNESDAY. THAT SITUATION SHOULD KEEP JUST A CHANCE OF SHOWERS
THROUGH WEDNESDAY...WITH HIGHS NEARLY THE SAME COMPARED TO TUESDAY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 545 AM EDT SUNDAY...

AS THE COLD FRONT FINALLY GAINS ENOUGH ENERGY TO LIFT OFFSHORE ON
WEDNESDAY NIGHT...A DEEP UPPER LEVEL TROUGH WILL MIGRATE FROM THE
HUDSON BAY IN CANADA TOWARD THE GREAT LAKES. THE TROUGH SHOULD REACH
THE APPALACHIAN MOUNTAINS BY THURSDAY...AND EVENTUALLY CUT OFF
OVERHEAD. MEANWHILE...ANOTHER CLOSED UPPER LEVEL LOW WILL ALSO CUT
OFF OVER THE ROCKY MOUNTAINS. IN BETWEEN THESE TWO LOWS...A STRONG
UPPER LEVEL RIDGE WILL RESIDE OVER THE PLAINS. THIS ATMOSPHERIC
PATTERN CREATES ANOTHER OMEGA BLOCK OVER THE UNITED STATES SIMILAR
TO WHAT WAS WITNESSED BACK IN MID APRIL...WHICH BOTH THE LATEST
ECMWF AND GFS MODELS DEPICT IN REASONABLY GOOD AGREEMENT.

UNLIKE THE LAST OMEGA BLOCK WHERE THE MID ATLANTIC ENJOYED
UNSEASONABLY WARM AND DRY CONDITIONS UNDER THE UPPER LEVEL
RIDGE...JUST THE OPPOSITE WILL OCCUR DUE TO BEING UNDER THE UPPER
LEVEL LOW...WITH COOL AND WET CONDITIONS EXPECTED THROUGH THE END OF
THIS WORK WEEK. HIGHS WILL ONLY REACH THE 50S AND 60S BY THURSDAY
AND FRIDAY. ON SATURDAY...THE OMEGA BLOCK GRADUALLY WEAKENS...WHILE
UPPER LEVEL RIDGING SLOWLY BEGINS OVERHEAD. IT APPEARS THAT WARMER
AND DRIER CONDITIONS COULD ARRIVE TOWARD THE END OF THIS WEEKEND.

&&

.AVIATION /13Z SUNDAY THROUGH THURSDAY/...
AS OF 800 AM EDT SUNDAY...

A STRONG COOL WEDGE REMAINS IN PLACE ACROSS THE REGION THIS
MORNING. ALL MODELS INDICATE THAT IT WILL ERODE FROM THE SOUTHWEST
BY EARLY TO MID-AFTERNOON. NOT TOTALLY POSITIVE THAT THIS WILL
OCCUR AS QUICKLY AS THE MODELS INDICATE...BUT IT SHOULD AT LEAST
ERODE IN WESTERN AREAS BY AFTERNOON. EQUALLY IN QUESTION IS THE
POTENTIAL FOR ADDITIONAL ROBUST CONVECTION THIS AFTERNOON/EVENING.
A STRONG SHORT WAVE WAS MOVING THROUGH THE REGION THIS MORNING
WITH WIDESPREAD RAIN AND A FEW THUNDERSTORMS. THIS SYSTEM WILL
MOVE EAST OF THE CWA BY 18Z. DEGREE OF WARMING/INSTABILITY WILL
DEPEND ON HOW QUICKLY THE WEDGE ERODES. UPPER SUPPORT IS MINIMAL
DURING PEAK HEATING...BUT ENOUGH TO WARRANT MENTION OF
THUNDERSTORMS...ESPECIALLY WESTERN AREAS. ANY UPPER SUPPORT FOR
THUNDERSTORMS WILL MOVE EAST OF THE REGION AFTER MIDNIGHT AWAITING
THE NEXT STRONGER UPPER IMPULSE APPROACHES THE REGION LATER
MONDAY AFTERNOON.

OTHERWISE...EXPECT IFR-LIFR CIGS TO PERSIST THROUGH AT LEAST MID-
MORNING...THEN IMPROVE TO MVFR AND EVENTUALLY VFR BY MID-LATE
AFTERNOON IN THE WEST...WITH LOCALLY MVFR-IFR IN HEAVIER SHRA/TSRA
DURING THE LATE AFTERNOON/EARLY EVENING. NOT CONFIDENT THAT WEDGE
WILL COMPLETELY ERODE IN EASTERN AREAS VSBYS...WHICH COULD ALLOW
LOCATIONS EAST OF THE BLUE RIDGE TO SEE IFR-LIFR CIGS/VSBYS AFTER
06Z MON IN DENSE FOG.

WINDS MOSTLY E-SE 5-7KTS...BECOMING SW KBLF/KLWB THIS
MORNING...THEN SW ELSEWHERE AFT 18Z...WITH SPEEDS INCREASING
7-10KTS WITH LOW END GUSTS WEST OF THE BLUE RIDGE. IT MAY TAKE
UNTIL MID OR LATE AFTERNOON FOR ANY SOUTHWEST WINDS TO REACH
KLYH/KDAN. WINDS WILL DIMINISH AND BACK TOWARD THE SSW AFT
00Z...FURTHER AIDING THE DEVELOPMENT OF POTENTIAL LOW CLOUDS AND
FOG AFTER MIDNIGHT...ESPECIALLY WITH WET GROUND IN PLACE ALL
AREAS.

LOW TO MEDIUM CONFIDENCE IN CIGS AND VSBYS THROUGH THE TAF VALID
PERIOD.
MEDIUM CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD.

EXTENDED AVIATION DISCUSSION...

THE AFOREMENTIONED LOW PRESSURE SYSTEM SHOULD CROSS OVER THE MID
ATLANTIC DURING SUNDAY NIGHT...BUT THE BOUNDARY WILL STALL
OVERHEAD BY MONDAY. MORE WAVES OF LOW PRESSURE WILL MOVE ALONG
THE STALLED BOUNDARY FROM TUESDAY THROUGH THURSDAY...WHICH SHOULD
HELP PUSH THE BOUNDARY OFFSHORE. A DEEP UPPER LEVEL TROUGH IS
PROJECTED TO DIVE SOUTHWARD OVER THE APPALACHIAN MOUNTAINS BY
WEDNESDAY INTO THURSDAY. OVERALL...FLYING CONDITIONS APPEAR RATHER
POOR THROUGH MOST OF THIS WEEK DUE TO THE LIKELIHOOD OF LOW
CLOUDS...PERIODS OF RAIN...AND PATCHY FOG.

&&

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

&&

$$
SYNOPSIS...RAB
NEAR TERM...RAB/WP
SHORT TERM...PW
LONG TERM...PW
AVIATION...PW/RAB


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