Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 300835
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
435 AM EDT SAT APR 30 2016

.SYNOPSIS...
A FRONTAL BOUNDARY WILL MOVE JUST SOUTH OF THE AREA TODAY AS AN
AREA OF LOW PRESSURE APPROACHES FROM THE WEST THIS AFTERNOON AND
TONIGHT. THE FRONT WILL MOVE NORTH OF THE AREA SUNDAY AFTERNOON AS
A WARM FRONT. A STRONGER COLD FRONT WILL THEN MOVE THROUGH THE
REGION BY MIDWEEK. EXPECT SEVERAL DAYS OF UNSETTLED WEATHER WITH
WIDESPREAD RAIN...WITH SOME THUNDERSTORMS SUNDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AS OF 430 AM EDT SATURDAY...

WEDGE FRONT VERY WELL DEPICTED IN THE LAPS ANALYSIS AND GOES-R
PROVING GROUND MVFR/IFR GRAPHIC...NOW NEAR A LWB-PSK-UKF. LOW
CLOUDS SPREAD INTO THE REGION VERY QUICKLY BEHIND THE FRONT WITH A
SHARP LINE NOTED FROM JUST OVC250 CIGS AT BCB/BLF/LWB TO CIGS AOB
010 ROA/DAN/LYH...AND WITHIN THE LAST COUPLE OF HOURS BCB. MODELS
CONTINUE TO MOVE WEDGE FRONT WEST THROUGH THE REST OF THE CWA BY
THE 12Z-15Z TIME FRAME...LIKELY STALLING SOMEWHERE NEAR THE
VA/TN...NC/TN BORDER BY EVENING. AS THE WEDGE DEEPENS AND MID-
LEVEL MOISTURE BEGINS TO SPREAD OVER TOP OF THE SHALLOW
WEDGE...WOULD EXPECT -DZ TO EVOLVE...ESPECIALLY IN UPSLOPE AREAS
ALONG THE BLUE RIDGE AND ALLEGHANY FRONT. MEANWHILE...A PERSISTENT
BROAD UPPER LOW REMAINS IN THE SOUTHWEST U.S...AND WILL INTO EARLY
NEXT WEEK. A NORTHERN STREAM SHORT WAVE WILL DROP SOUTHEAST FROM
THE GREAT LAKES TONIGHT AND COMBINE WITH A SHORT WAVE EMANATING
FROM THE SOUTHWEST U.S. UPPER LOW TO BRING WIDESPREAD OVERRUNNING
RAINFALL TO THE AREA AFT 00Z...POTENTIALLY ARRIVING IN WESTERN
AREAS LATE AFTERNOON/EARLY EVENING. ELEVATED THUNDER IS POSSIBLE
AFTER 00Z MAINLY WEST-SOUTHWEST OF A BLF-MKJ-UKF LINE. WIDESPREAD
BENEFICIAL RAINFALL IS EXPECTED ACROSS THE ENTIRE REGION FROM WEST
TO EAST OVERNIGHT INTO EARLY SUNDAY. RAINFALL AMOUNTS SHOULD
AVERAGE FROM ABOUT 1-1.25 INCH WESTERN AREAS TO ABOUT 1/2 INCH
EASTERN AREAS THROUGH THIS TIME FRAME. SPC HAS INDICATED A
MARGINAL RISK FOR SEVERE IN THE FAR WESTERN AREAS FOR DAY 1. AT
THIS TIME...HAVE NOT MENTIONED ANY SEVERE IN THE GRIDS THROUGH 12Z
SUN AS INSTABILITY PARAMETERS ARE MARGINAL AT BEST WITHIN THE
WEDGE AREA. SOME CONCERN NEAR THE WEDGE BOUNDARY...BUT FEEL THAT
WILL BE A MORE SIGNIFICANT PROBLEM LATER IN THE DAY SUNDAY.

HAVE REFLECTED THE COOL AIR WEDGE IN THE TEMPERATURE GRIDS...WHICH
THE MET MOS REFLECTED BEST. THE ECMWF WAS TOO WARM AND NOT
PROPERLY REFLECTING THE WEDGE. TEMPERATURES WILL FALL LITTLE AFT
00Z...LIKELY ENDING UP ONLY A FEW DEGREES LOWER THAN MAX TEMPS
TODAY.

THE SYNOPTIC PATTERN DOES SUGGEST SOME POTENTIAL FOR GUSTY
SOUTHEAST WINDS LATE TONIGHT/EARLY SUNDAY IN THE
MERCER/TAZEWELL/SMYTH COUNTY REGION...BUT SHOULD BE FAR BELOW WIND
ADVISORY CRITERIA.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
AS OF 330 AM EDT SATURDAY...

A QUASI ZONAL UPPER PATTERN WILL BE TRANSITIONING TO A BROAD EASTERN
TROF THROUGH EARLY NEXT WEEK AND KEEP SYSTEMS FAIRLY PROGRESSIVE.

ON SUNDAY AS AN UPPER SHORT WAVE WILL DRIVE A SURFACE LOW FROM THE
MISSISSIPPI VALLEY INTO NEW ENGLAND THERE MAY BE ENOUGH PUSH TO NUDGE
THE WEDGE ALONG THE COAST A BIT FURTHER EAST...ALLOWING UNSTABLE AIR
AHEAD OF A COLD FRONT ASSOCIATED WITH THE LOW TO GENERATE SOME
THUNDERSTORMS ACROSS THE REGION. SEVERE PARAMETERS SUPPORT THE
CURRENT SPC MARGINAL OUTLOOK SO LONG AS THE WEDGE EXITS ON
SCHEDULE. THE RETREATING WEDGE FRONT WILL BE AN AREA TO WATCH FOR
ENHANCED SEVERE POTENTIAL. LOCALLY HEAVY RAIN WILL ALSO BE A
CONCERN WITH PWATS STILL RUNNING WELL OVER ONE INCH AND TRAINING
OF STORMS MAY CREATE SOME HYDRO ISSUES. AS THE FRONT SINKS TO OUR
SOUTH SUNDAY NIGHT CONVECTIVE PRECIPITATION WILL COME TO AN END
WITH SOME LINGERING SHOWERS IN UPSLOPE FLOW WEST OF THE BLUE
RIDGE.

MONDAY LOOKS TO BE QUIET WITH HIGH PRESSURE BRINGING A RESPITE FROM THE
RAINFALL...BUT THIS LOOKS TO BE A BRIEF BREAK AS MORE SHORT WAVE ENERGY
MOVING THROUGH THE DEVELOPING UPPER TROF STARTS TO DEVELOP A WAVES
ALONG THE FRONTAL BOUNDARY TO OUR SOUTH AND BRING A CHANCE OF SHOWERS
BACK TO THE FORECAST. GUIDANCE IS NOT OFFERING A FOCUSED SET OF
SOLUTIONS REGARDING HOW FAR NORTH THE WAVES WILL DRAG THE FRONTAL
BOUNDARY AND PRECIPITATION SO CONFIDENCE ON BEST TIMING/LOCATION OF
PRECIPITATION MONDAY NIGHT THROUGH TUESDAY IS RATHER LOW.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 300 PM EDT FRIDAY...

A COLD FRONT APPROACHES FROM THE WEST ON WEDNESDAY AND MOVES ACROSS
REGION ON WEDNESDAY INTO THURSDAY. WITH UNCERTAINTY...HELD ON TO THE
ISOLATED TO SCATTERED SHOWERS WITH THIS BOUNDARY. HIGHS ON WEDNESDAY
AND THURSDAY WILL BE IN THE LOWER TO MID 60S IN THE WEST TO THE
UPPER 60S TO LOWER 70S IN THE EAST. OVERNIGHT LOW TEMPERATURES
WILL DROP TO AROUND 40 IN THE MOUNTAINS TO NEAR 50 IN THE
PIEDMONT. DRIER AIR ARRIVE THURSDAY NIGHT INTO FRIDAY ON A WEST TO
NORTHWEST FLOW.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
AS OF 200 AM EDT SATURDAY...

WEDGE FRONT VERY WELL DEPICTED IN THE LAPS ANALYSIS AND GOES-R
PROVING GROUND MVFR/IFR GRAPHIC...NOW NEAR A LWB-ROA-MWK. LOW
CLOUDS SPREAD INTO THE REGION VERY QUICKLY BEHIND THE FRONT WITH A
SHARP LINE NOTED FROM JUST OVC250 CIGS AT BCB/BLF/LWB TO CIGS AOB
100 ROA/DAN/LYH. MODELS CONTINUE TO MOVE WEDGE FRONT WEST THROUGH
THE REST OF THE CWA BY THE 12Z-15Z TIME FRAME. AS THE WEDGE
DEEPENS AND MID-LEVEL MOISTURE BEGINS TO SPREAD OVER TOP OF THE
SHALLOW WEDGE...WOULD EXPECT -DZ TO EVOLVE...ESPECIALLY IN UPSLOPE
AREAS ALONG THE BLUE RIDGE AND ALLEGHANY FRONT. BONAFIDE -RA OR
-SHRA SHOULD BEGIN TO SPREAD INTO THE REGION LATER IN THE
AFTERNOON AS THE FIRST OF SEVERAL SHORT WAVES EMANATING FROM A
PERSISTENT UPPER LOW IN THE SOUTHWEST U.S. EJECT ENE-NE ACROSS THE
REGION. THE WEDGE COULD POTENTIALLY BREAK LATE IN THE DAY TOWARD
THE KBLF/KMKJ/KTNB AREA...BUT MOST LIKELY THIS WILL NOT OCCUR
UNTIL AFT 00Z.

CIGS STILL VFR AT KBLF/KLWB/KBCB. GIVEN THAT KROA IS ALREADY
LIFR...WOULD EXPECT KBCB TO TREND THAT WAY WITHIN THE NEXT TWO
HOURS. SHOULD TAKE UNTIL 08Z-10Z TO REACH KLWB...AND PROBABLY
12Z-13Z FOR KBLF. ONE THE WEDGE EVOLVES THE REGION FROM THE
EAST...EXPECT IFR-LIFR CIGS TO HOLD UNTIL 18Z OR SO...THEN BECOME
MOSTLY LOW END MVFR. VSBYS SHOULD DROP INTO THE MVFR CATEGORY BY
DAYBREAK...EXPECT POSSIBLY KBLF...WHICH SHOULD HOLD ONTO VFR UNTIL
LATER IN THE DAY. -DZ SHOULD EVOLVE IN UPSLOPE AREAS NEAR THE BLUE
RIDGE/ALLEGHANY FRONT BY EARLY TO MID-MORNING...THEN -RA OR-SHRA
BY 18Z AND BEYOND AS NOTED ABOVE. STILL DO NOT FORESEE MUCH WORSE
THAN MVFR VSBYS THROUGH THIS TAF VALID PERIOD.

WINDS LIGHT/VARIABLE WEST OF THE WEDGE. OTHERWISE...NORTHEAST
6-9KTS EAST OF THE BLUE RIDGE...EAST-SOUTHEAST TO SOUTHEAST
7-10KTS WEST OF THE BLUE RIDGE...WITH LOW END GUSTS DEVELOPING
DURING THE MORNING KBLF VICINITY...AND POSSIBLY OTHER
LOCATIONS...ESPECIALLY EAST OF THE BLUE RIDGE.

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

EXTENDED AVIATION DISCUSSION...

WIDESPREAD SHOWERS WITH MVFR INCLUDING LOCALLY IFR CONDITIONS
PERSIST OVERNIGHT INTO SUNDAY MORNING...LIKELY IMPROVING TO
MVFR/VFR BY AFTERNOON AS THE WEDGE ERODES...SHIFTS NORTHEAST AND
THE REGION MOVES INTO THE WARM SECTOR. 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. 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...RAB
NEAR TERM...RAB
SHORT TERM...MBS
LONG TERM...KK/MBS
AVIATION...DS/RAB/WP


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