Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 270546
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
146 AM EDT MON APR 27 2015

.SYNOPSIS...
COOL AND UNSETTLED WEATHER WILL BE IN PLACE ACROSS THE
APPALACHIANS AND CENTRAL MID ATLANTIC REGION THIS WEEK... AS A
COOL UPPER LOW REMAINS ANCHORED OVER THE NORTHEAST UNITED STATES.
THE BEST CHANCE FOR PRECIPITATION WILL BE WEDNESDAY AND
THURSDAY...AS LOW PRESSURE DEVELOPS OVER THE SOUTHEAST AND TRACKS
JUST TO OUR SOUTH AND EAST...BEFORE MOVING OFF THE MIDDLE ATLANTIC
COAST THURSDAY NIGHT.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1245 AM EDT MONDAY...

MINOR CHANGES TO TEMPS/SKY/WX INTO EARLY MORNING BASED ON TRENDS.
MAINLY SEEING MID DECK IN THE SRN CWA AND EXPECT THE CLEARING
TREND TO CONTINUE INTO MORNING. FOG IN THE RIVER VALLEYS OF WEST
AND/OR PATCHY FROST TO OCCUR THRU DAWN.

AS OF 330 PM EDT SUNDAY...

THE WEDGE IS SLOWLY ERODING FROM THE NORTH AS LOW PRESSURE IS
PULLING AWAY AND ALLOWING DRIER AIR TO WORK IN. VISIBLE SATELLITE
IMAGES SHOW THE CLEARING AND OTHER BREAKS IN THE CLOUDS AND THIS
IS ALLOWING THE SUN TO GIVE TEMPS A BIT OF A LATE DAY BOOST. THE
CLEARING TREND IS EXPECTED TO SLOWLY CONTINUE THROUGH EARLY
TONIGHT AND THIS WILL ALLOW FOR SOME CHILLY TEMPERATURES
OVERNIGHT. THERE MAY BE SOME PATCHY FROST WEST OF THE BLUE RIDGE
AND IN SOME LOW SPOTS ACROSS THE PIEDMONT BUT DO NOT BELIEVE
CONDITIONS WILL BE WIDESPREAD ENOUGH FOR AN ADVISORY SO WILL
HIGHLIGHT THIS IN AN SPS FOR AREAS WEST OF THE BLUE RIDGE.

WE SHOULD BE IN FOR A BIT OF EARLY MORNING SUN TO START OFF ON
MONDAY...BUT WITH A POOL OF COLD AIR ALOFT AND A VIGOROUS SHORT
WAVE ROTATING AROUND THE UPPER LOW OVER THE NORTHEAST US...EXPECT
CLOUDS TO BLOOM BY LATE MORNING AND A CHANCE/SLGT CHC OF SHOWERS
WEST OF THE BLUE RIDGE BY THE AFTERNOON. ISOLATED THUNDER AND SOME
GRAUPEL IS NOT OUT OF THE QUESTION FROM THE GREENBRIER VALLEY
THROUGH THE ALLEGHANY HIGHLANDS. TEMPS TOMORROW WILL CONTINUE TO
RUN BELOW NORMAL WITH HIGHS GENERALLY MIDDLE 50S WEST OF THE RIDGE
TO MIDDLE 60S EAST. THE BOUNDARY LAYER WILL ALSO BE WELL MIXED SO
EXPECT A GOOD NORTHWEST BREEZE TO ADD TO THE CHILL.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 330 PM EDT SUNDAY...

TWO SYSTEMS WILL BE THE PRIMARY PLAYERS IN OUR WEATHER FOR THE FIRST
HALF OF THE WORK WEEK. THE FIRST IS A LARGE UPPER LOW OFF THE NEW
ENGLAND COAST...AND THE SECOND IS A SOUTHERN STREAM SYSTEM THAT
MOVES THROUGH THE SOUTHERN PLAINS INTO TENNESSEE VALLEY BY
WEDNESDAY.

WITH REGARD TO THE SECOND SYSTEM...MODEL ENSEMBLES SHOW THERE IS LOW
CONFIDENCE ON THE TIMING AND STRENGTH OF THIS SYSTEM. THE 12Z GFS IS
STRONGEST AND SLOWER...WHILE THE NAM APPEARS TO BE AN OUTLIER WITH
ITS FASTER SOLUTION. GENERALLY FOLLOWED THE 00Z ECMWF WITH THIS
SYSTEM...WHICH HAS SHOWN GOOD CONSISTENCY KEEPING THE SYSTEM CLOSED
THROUGH 00Z THURSDAY.

A SHORTWAVE PIVOTING AROUND THE LARGE NEW ENGLAND UPPER LOW EXITS
OUR AREA TO THE SOUTH BEFORE 12Z TUESDAY. LINGERING CONVECTIVE
SHOWERS UNDER THIS SYSTEM MONDAY EVENING SHOULD DIMINISH WITH THE
LOSS OF HEATING.  MEANWHILE...AT THE SURFACE...HIGH PRESSURE BEGINS
TO NOSE INTO WESTERN PORTION OF THE FORECAST AREA EARLY TUESDAY. IF
WINDS CAN SUBSIDE ENOUGH...TEMPS IN SOME OF THE HIGHER ELEVATIONS IN
SE WV MAY ALLOW FOR PATCHY FROST TO FORM.

TUESDAY APPEARS TO BE THE MOST TRANQUIL DAY OF THIS PERIOD...AS A
WEAK SHORTWAVE RIDGE BUILDS IN ADVANCE OF THE SOUTHERN STREAM SYSTEM
AND A BLEND OF THE BIAS CORRECTED MET/NAM MOS WAS USED FOR HIGHS.

WE START TO EXPERIENCE THE EFFECTS OF THE SOUTHERN STREAM SYSTEM
TUESDAY NIGHT AND WEDNESDAY AS CLOUDS TUESDAY NIGHT AND LIGHT RAIN
ARRIVES AS EARLY AS WEDNESDAY MORNING IN THE NW NC MOUNTAINS. WE
COULD POTENTIALLY SEE A BIG DROP OFF IN TEMPS IN THE NORTHERN PORTION
OF OUR FORECAST AREA EARLY BEFORE CLOUDS ARRIVE LATE TUESDAY NIGHT.
WITH DEW POINTS IN THE 40S...IT MAY TAKE SOME TIME FOR THE
ATMOSPHERE TO SATURATE TO ALLOW RAIN TO REACH THE GROUND.

WEAK UPSLOPE FLOW SHOULD HELP FOCUS THE LIGHT PRECIP FROM THE
SOUTHERN BLUE RIDGE INT THE NW NC MOUNTAINS AND FOOTHILLS WEDNESDAY.
KEPT HIGH TEMPS BELOW GUIDANCE WITH EXPECTED WIDESPREAD
CLOUDINESS.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 330 PM EDT SUNDAY...

WHILE THERE ARE STILL DIFFERENCES IN TIMING...THE LONG RANGE MODELS
SHOW A SIMILAR SOLUTION OF LIFTING THE DEEP EASTERN U.S. TROF TO
THE EAST AND SLOWLY BUILDING AN UPPER RIDGE ACROSS THE OHIO VALLEY
BY THE END OF THE WEEKEND.

THE GFS APPEARS OVERDONE AND TOO FAR NORTH WITH ITS PLACEMENT OF THE
AXIS OF HEAVY RAIN IN OUR FORECAST AREA. OBVIOUSLY THIS WILL NEED TO
BE MONITORED...BUT LEANED TOWARD THE ECMWF AND CANADIAN SOLUTIONS OF
KEEPING THE AXIS OF HEAVIEST RAIN CLOSER TO THE FORECAST POSITION OF
THE SFC LOW IN THE SOUTHERN CAROLINAS.

WRAP AROUND MOISTURE WILL KEEP CLOUDS...MUCH COOLER THAN NORMAL
TEMPS...AND LIGHT PRECIP THROUGH THURSDAY AND THURSDAY NIGHT. WITH
THE DEEPENING COASTAL SFC LOW...AND PASSING OF A WEAK UPPER VORT
LOBE ON THE WEST SIDE OF THE UPPER TROF AXIS...BUMPED UP WINDS LATE
THURSDAY AND FRIDAY...BUT NOTHING THAT APPEARS TO WARRANT HEADLINES
ATTM.

AS THE DEEP SFC LOW CONTINUES TO MOVE NORTHEAST...WE SHOULD FINALLY
SEE SOME CLEARING FRIDAY...THEN TEMPS CLOSER TO AVERAGE FOR EARLY
MAY BY THE WEEKEND.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 125 AM EDT MONDAY...


HIGH PRESSURE ENTERING FROM THE NORTH SENDING DRIER AIR SOUTH INTO
THE REGION. SHOULD SEE ANY MID CLOUDS IN THE DANVILLE VICINITY
CLEAR OUT THIS MORNING. ISSUE WILL BE ANY FOG OVER THE RIVER
VALLEYS...WITH WET GROUND. BUT THE DRIER AIR WILL WORK TO RACE THE
TEMPS SUCH THAT DEWPOINT DEPRESSION WILL STAY ENOUGH TO PREVENT
DENSE FOG AT LEAST AT TAF SITES. WILL HAVE MVFR AT LYH/DAN/LWB AND
BCB AT TIMES EARLY...TEMPO OVER BCB/LWB FOR IFR. CONFIDENCE IS
MEDIUM OF THIS OCCURRING.

ANY FOG WILL BE GONE AFTER 12Z WITH NW WINDS PICKING UP A BIT.
SOME GUSTS TO 25 KTS POSSIBLE AT ROA/BCB. NW FLOW AND EMBEDDED
SHORTWAVE WILL BRING CLOUDS INTO THE MTNS BY MIDDAY/EARLY
AFTERNOON. CANNOT RULE OUT A SHOWER OVER BLF/LWB BUT COVERAGE IS
LOW TO KEEP OUT OF TAFS. KEPT THINGS VFR THROUGH THE DAY INTO THIS
EVENING.

WINDS WEAKEN TONIGHT THOUGH THE HIGHER TERRAIN COULD SEE SOME
GUSTS OVER 15 KTS.

EXTENDED AVIATION DISCUSSION...
VFR CONDITIONS ARE EXPECTED THROUGH EARLY WEDNESDAY BEFORE
CONDITIONS WORSEN ONCE AGAIN WEDNESDAY AFTERNOON INTO
THURSDAY...AS A LOW PRESSURE SYSTEM PASSES ACROSS THE SOUTHEAST
STATES. CONFIDENCE IS GROWING THAT THIS SYSTEM WILL RESULT IN
RAIN INTO MOST OF THE FORECAST ALONG WITH SUB VFR CIGS/VSBYS. SO
MUCH DISCREPANCIES IN THE MODELS ATTM FOR FRIDAY THAT WX COULD BE
CLEARING OUT ECMWF OR SUB VFR WITH SFC LOW SITUATED OVER THE MID
ATLANTIC COAST.

&&

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

&&

$$
SYNOPSIS...MBS
NEAR TERM...CF/MBS/WP
SHORT TERM...PH
LONG TERM...PH/RAB
AVIATION...MBS/RCS/WP


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