Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 171745
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
145 PM EDT WED SEP 17 2014

.SYNOPSIS...
A COOL WEDGE OF HIGH PRESSURE SETTLES IN FROM THE NORTH THIS
AFTERNOON BEFORE WEAKENING OVERNIGHT INTO THURSDAY. ANOTHER
LARGER AREA OF HIGH PRESSURE WILL STRENGTHEN TO THE NORTH OF THE
REGION FRIDAY INTO SATURDAY BEFORE PASSING OFFSHORE ON SUNDAY. A
COLD FRONT WILL CROSS THE AREA FROM THE NORTHWEST ON MONDAY
BRINGING A BETTER CHANCE OF SHOWERS TO START THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 115 PM EDT WEDNESDAY...

MADE ADJUSTMENTS TO SKY COVER BASED ON SAT TRENDS AND MODEL
TRENDS. NOT REALLY SEEING GOOD SIGNALS FOR RAIN SHOWERS THIS
AFTERNOON...EXCEPT FOR INCREASING THETA-E AT THE SFC WITH SOME
CONVERGENCE OVER THE MOUNTAINS OF NC/SW VA. KEPT SPOTTY POPS IN
THE SOUTHERN CWA THIS AFTERNOON BUT NOT REALLY SEEING A LOT OF
COVERAGE AT THIS POINT. TEMPS WERE BUMPED A LITTLE MORE WHERE MORE
SUN HAS ALLOWED THEM TO RISE ABOVE FORECAST.


PREVIOUS VALID DISCUSSION...

WEAK WAVE ALOFT SHOULD PASS TO THE SOUTH TODAY AS WELL WITH
ANOTHER NEARING THE WESTERN SLOPES THIS EVENING.

WEAK WEDGE LINGERS ESPCLY EAST OVERNIGHT WITH ADDED CLOUDS WEST
AHEAD OF ANOTHER SHORTWAVE DIVING SE IN THE NW FLOW ALOFT. HOWEVER
SETUP NOT TOTALLY IDEAL FOR GOOD WEDGING GIVEN WEAKENING OF THE
MID ATLANTIC SURFACE HIGH AND MORE NORTH/NW FLOW JUST ABOVE THE
BOUNDARY LAYER MOIST LAYER. THIS ALONG WITH PLENTY OF DRY AIR
ALOFT SUPPORTS LITTLE MORE THAN CLOUDS/PATCHY DRIZZLE EASTERN
SLOPES LATE ALONG WITH SOME FOG IN SPOTS SO TRIMMED POPS. LOWS
MAINLY 50S UNDER THE LOW LEVEL COOL POOL WITH SOME 40S POSSIBLE
VALLEYS ESPCLY IF MORE CLEARING DEVELOPS.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 400 AM EDT WEDNESDAY...

A WEAK SHORT WAVE WILL MOVE THROUGH THE REGION EARLY THU. THE TRACK
WILL TAKE THE BEST LIFT/MOISTURE FROM EASTERN KY/EASTERN TN TOWARD
FAR SW VA/NW NC. AT THIS POINT ONLY EXPECTING SOME MID CLOUDS AND
POSSIBLY A PASSING SPRINKLE...BUT NOT ENOUGH SUPPORT TO INCLUDE ANY
-SHRA IN THE GRIDS AT THIS POINT. FOLLOWING THIS TROUGH...THE BROAD
UPPER LOW ANCHORED OVER HUDSON BAY WILL DEEPEN BRIEFLY. A STRONG
CANADIAN SFC HIGH WILL TRANSLATE EASTWARD TOWARD NEW ENGLAND BY
EARLY FRI AND INTO A VERY FAVORABLE WEDGE POSITION. AS THE SFC HIGH
STRENGTHENS TOWARD 1030MB...DEEPENING EASTERLY FLOW WILL SPREAD DOWN
THE EAST SIDE OF THE APPALACHIANS INTO THE SOUTHEAST STATES.
GFS/ECMWF/NAM ALL IN GOOD AGREEMENT ON UPSLOPE WINDS ALONG THE BLUE
RIDGE/ALLEGHANY FRONT LIKELY SQUEEZING OUT -DZ FRI MORNING...WHICH
TRANSLATES FURTHER W-SW BY AFTERNOON TOWARD THE VA/TN/NC BORDER
REGION. ABUNDANT LOW CLOUDS...ESPECIALLY BLUE RIDGE WESTWARD...WILL
HOLD TEMPS BELOW NORMAL. BY SAT...THE FLOW QUICKLY BECOMES MORE
ZONAL AS HEIGHTS RISE IN RESPONSE TO A BROAD UPPER RIDGE BUILDING
ACROSS THE SOUTH CENTRAL/SOUTHEAST STATES. MEANWHILE...ANOTHER SHORT
WAVE DIGS SOUTHWARD THROUGH THE GREAT LAKES WITH THE ASSOCIATED
FRONTAL SYSTEM REACHING THE REGION BY SUN. THUS...WITH THE WEDGE
ERODING QUICKLY SAT AND SW FLOW DEVELOPING IN ADVANCE OF THE NEXT
SHORT WAVE...WE SHOULD SEE WARMER TEMPERATURES AND MORE SUNSHINE
THAN WILL BE THE CASE FRI.

FOR TEMPERATURES...LESS IMPRESSED WITH THE POTENTIAL WEDGE SETUP FOR
THU...IF ANY. THE FIRST SFC HIGH IS VERY WEAK AND DISSIPATES AS
OVERALL NW FLOW ALOFT PREVAILS. HAVE REMOVED MENTION OF DRIZZLE FOR
EARLY THU AND ALSO WARMED TEMPERATURES SOMEWHAT THU IN ANTICIPATION
OF RETURNING SW SFC FLOW...OR AT LEAST SOUTHERLY FLOW...AND LIKELY
SOME SUNSHINE BY AFTERNOON WITH THE DISSIPATING WEAK WEDGE.
ADJUSTMENT TO MOS GUIDANCE WAS NEEDED FOR MAX TEMPS ALL THREE DAYS.
FOR MAX TEMPS THU...HAVE USED A COMPROMISE BETWEEN THE WARMEST MAV
MOS AND THE COLDEST MET MOS...THUS JUST A TAD WARMER THAN THE
ECMWF MOS. FOR FRI...HOWEVER...HAVE UNDERCUT ALL MODEL
GUIDANCE...ESPECIALLY THE MAV MOS WHICH IS WAY TO WARM AND IN
DISAGREEMENT WITH THE CLOUD FIELD AND -DZ/-RA IT GENERATES.
POTENTIALLY...SOME AREAS FRI MAY NOT GET OUT OF THE MID TO UPPER 60S
WEST OF THE BLUE RIDGE. BY SAT...SOUTHWEST FLOW...MORE
SUNSHINE...AND NOTABLY HIGHER HEIGHTS/TEMPERATURES ALOFT...585DM AT
500MB...SHOULD SUPPORT LOW 80S ACROSS THE PIEDMONT TO THE LOWER 70S
IN THE MOUNTAINS. AGAIN...GUIDANCE DOES NOT HAVE A GOOD HANDLE ON
THIS AND IS TOO COOL.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 400 AM EDT WEDNESDAY...

UPPER TROUGH WILL MOVE THROUGH THE REGION SUNDAY...ACCOMPANIED BY A
CHANCE OF SHOWERS. WITH PREVAILING NW FLOW...THE BEST CHANCE WILL BE
WEST OF THE ALLEGHANY FRONT ACROSS EASTERN WV. LATEST MODELS PROG
ENOUGH INSTABILITY TO CONSIDER THUNDER...ALSO GIVEN CURRENT EXPECTED
TIMING OF THE CONVECTION REACHING THE CWA LATE AFTERNOON/EARLY
EVENING. HOWEVER...OUR ONLY NEIGHBOR TO MENTION THUNDER AT THIS
POINT IS IN EAST TN...SO WILL LEAVE OUT AT THIS POINT. AT ANY
RATE...THIS WOULD APPEAR TO BE ONE OF THE MORE TYPICAL EVENTS WE
OFTEN SEE AS THE SYSTEM CROSSES THE MOUNTAINS WHERE MOST
PRECIPITATION WANES RATHER QUICKLY AFTER IT PASSES EAST OF THE
BLUE RIDGE.

THE MAIN STORY BEHIND THE UPPER TROUGH SATURDAY WILL BE A DEEPENING
TROUGH ACROSS EASTERN CANADA AND THUS DRASTICALLY LOWER
HEIGHTS/TEMPERATURES ALOFT ACROSS THE EASTERN U.S. THIS WILL
DOMINATE THE REGION THROUGH THE FIRST HALF OF NEXT WEEK AS IT SLOWLY
TRANSLATES TOWARD THE CANADIAN MARITIMES. A REINFORCING SHORT WAVE
WILL DRIVE WHAT APPEARS TO BE ONE OF THE COOLEST AIR MASSES OF THE
FALL SEASON SO FAR THROUGH THE REGION MON-TUE. 850MB TEMPS DROP INTO
THE +2C TO +6C RANGE BY TUE WITH MIN TEMPS POTENTIALLY INTO THE
30S IN THE MOUNTAINS AND 40S ELSEWHERE BY MID-WEEK NEXT WEEK. THE
GFS TENDS TO BE SLIGHTLY COLDER THAN THE ECMWF. PRECIPITATION BEYOND
SAT APPEARS TO BE PRETTY SCANT...BUT LIKELY EXTENSIVE UPSLOPE CLOUDS
ACROSS THE ALLEGHANYS WITH NW UPSLOPE FLOW AND STRONG CAA. STILL TOO
EARLY TO MENTION ANY -SHRA OR POTENTIALLY EVEN -SHSN AT THE HIGHEST
ELEVATIONS WITH THE COLD AIR MASS MID PART OF NEXT WEEK...ESPECIALLY
SINCE THE BEST UPPER SUPPORT REMAINS NORTH OF THE CWA WITH THE
SECONDARY REINFORCING UPPER TROUGH. THUS...HAVE NOT MADE ANY
SIGNIFICANT ADJUSTMENTS TO THE LONG TERM GRIDS AT THIS TIME.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 125 PM EDT WEDNESDAY...

CIGS HAVE BEEN RISING THROUGH THE DAY AND MOST LOCATIONS ARE VFR
OR HIGH END MVFR. THINK VFR WILL CARRY US INTO THIS EVENING WHEN
THE INVERSION SETS UP AGAIN WITH EAST-SE FLOW ALLOWING FOR SOME
STRATUS LAYER TO FORM. QUESTION IS HOW MUCH COVERAGE. MODELS ARE
FAVORING SUB VFR AT ALL SITES ALONG WITH FOG...SO MADE THE TAFS
SIMILAR TO THE PREVIOUS ISSUANCE AND WENT PESSIMISTIC ON VSBYS AT
ALL BUT ROANOKE.

WILL SEE SOME RECOVERY BACK TOWARD MVFR/VFR AFTER 12Z...WITH VFR
IN THE AFTERNOON THURSDAY AHEAD OF THE NEXT TROUGH.

EXTENDED AVIATION DISCUSSION...

TROUGH IN THE EAST LIFTS LATE THIS WEEK INTO SATURDAY BUT
WEAKNESS ALOFT TO LINGER OVER THE SOUTHEAST. HIGH PRESSURE AT THE
SFC WILL WEDGE SOUTHWEST INTO OUR AREA DURING THIS TIME. EXPECT
MAINLY VFR CONDITIONS OUTSIDE ANY FOG AT NIGHT AND POTENTIAL FOR
SOME STRATUS ALONG AND EAST OF ROA/BCB...THOUGH THE HIGH PRESSURE
SHOULD BE STRONG ENOUGH TO KEEP MOISTURE LIMITED.

NEXT UPSTREAM TROUGH AND FRONT EXPECTED TO ARRIVE BY EARLY NEXT
WEEK WITH A THREAT OF SHOWERS. MAY SEE SOME MVFR CIGS/VSBYS BUT
APPEARS MOST OF THE TIME WILL CONTINUE TO SEE VFR.



&&

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

&&

$$
SYNOPSIS...JH/WP
NEAR TERM...JH/WP
SHORT TERM...RAB
LONG TERM...AMS/RAB
AVIATION...JH/WP


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