Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 271149
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
749 AM EDT SAT SEP 27 2014

.SYNOPSIS...
HIGH PRESSURE...BOTH AT THE SURFACE AND ALOFT...WILL DOMINATE THE
AREA THROUGH THE WEEKEND. LOW PRESSURE DEVELOPING ALONG THE
CENTRAL GULF COAST WILL MOVE NORTHEAST LATE IN THE WEEKEND AND
EARLY NEXT WEEK...BRINGING WIDESPREAD RAIN TO THE REGION FOR THE
FIRST HALF OF NEXT WEEK. SEASONAL TEMPERATURES ARE EXPECTED TO
PREVAIL THROUGH THE FIRST PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 415 AM EDT SATURDAY...

BENIGN WEATHER EXPECTED THROUGH THE NEAR TERM AS HIGH PRESSURE...
BOTH AT THE SURFACE AND ALOFT...DOMINATES THE AREA THROUGH THE
WEEKEND. WITH SURFACE HIGH PRESSURE CENTERED TO THE NORTH OF THE
REGION THROUGH THE WEEKEND...NE-E FLOW WILL CONTINUE.
HOWEVER...THE DEEPEST MOISTURE HAS BEEN PUSHED INTO FAR SOUTHWEST
VA/NORTHWEST NC/EAST TN...AND WILL CONTINUE DRIFTING FURTHER SW
TODAY BEFORE STALLING ACROSS THE TN VALLEY. DRY AIR WILL CONTINUE
TO ADVECT SOUTHWEST FROM NEW ENGLAND AND THE NORTHERN MID-ATLANTIC
STATES. THE ONLY REAL WEATHER CONCERN THROUGH THE NEAR TERM IS
PATCHY DENSE FOG THIS MORNING AND THE POSSIBILITY OF SUCH AGAIN
SUNDAY MORNING. PESKY LOW CLOUDS PERSIST IN THE FAR SW PART OF THE
CWA...WHERE MKJ AND GEV ARE BOTH 1/4SM FG...LIKELY CLOUDS ON THE
RIDGE TOPS. THIS IS WHERE THE MOISTURE HAS POOLED/CONVERGED. IN
THE LOWER ELEVATIONS IN THESE AREAS...FOG WILL BE LESS OF A
PROBLEM BECAUSE OF THE STRATUS DECK. FURTHER NORTH...BATTLE
BETWEEN DRIER AIR TRYING TO ADVECT SOUTHWEST FROM THE REGION AND
MORE IDEAL RADIATIONAL CONDITIONS...BUT IN A FEW SPOTS THE
DECOUPLING WON OUT...E.G. LWB WITH 1/4SM FG. ANY PATCHY DENSE FOG
SHOULD DISSIPATE QUICKLY AFT 14Z AND OVERALL IT SHOULD TURN OUT TO
BE A SUNNY DAY EAST TO PARTLY SUNNY FAR SOUTHWEST. NOT TOTALLY
COMFORTABLE WITH MOSTLY SUNNY IN THE SOUTHWEST PART OF THE CWA.

MOS GUIDANCE SIMILAR TO MAX/MIN TEMPS. USED A BLEND BETWEEN THE
NAM/GFS/ECMWF FOR TODAYS MAX TEMPS WITH A BIAS TOWARD THE MET MOS.
FOR TONIGHTS MIN TEMPS...50/50 MODEL BLEND...WHICH RESULTED IN
SLIGHTLY WARMER TEMPS THAN PREVIOUSLY ADVERTISED. 850MB TEMPS
ALOFT ARE QUITE WARM...HOVERING AROUND +15C...FOR LATE SEPTEMBER.
NOT SURE AIR MASS IS DRY ENOUGH TO ALLOW IDEAL RADIATIONAL
COOLING.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
AS OF 400 AM EDT SATURDAY...

HIGH PRESSURE WILL WEDGE DOWN THE APPALACHIANS SUNDAY. A DISTURBANCE
WILL DEVELOP ALONG THE GULF SUNDAY AFTERNOON AND WILL TRAVEL
NORTHEAST INTO SUNDAY NIGHT...EVENTUALLY OVERRUNNING THE SURFACE
WEDGE BRINGING RAIN INTO THE FORECAST AREA. RAIN WILL START IN THE
SOUTHWEST PORTIONS OF THE FORECAST AREA AND SPREAD NORTHWARD INTO
SUNDAY NIGHT. PLAYED HIGH TEMPERATURES SUNDAY CLOSE TO THE COOLER
ADJMAVBC WITH READINGS FROM THE MID 60S IN THE MOUNTAINS TO THE
UPPER 70S IN THE PIEDMONT.

AS THE TROUGH SWINGS EASTWARD OVER THE OHIO AND TENNESSEE
VALLEYS...RAIN WILL ENCOMPASS MOST OF FORECAST AREA SUNDAY NIGHT
INTO MONDAY. THE NAM AND ECMWF ARE SIMILAR WITH THE EASTERN
ADVANCE OF THE RAIN...WHILE THE GFS IS SLOWER BECAUSE OF THE LESS
AMPLIFIED TROUGH. LOW TEMPERATURES SUNDAY NIGHT WILL VARY FROM THE
MID 50S IN THE WEST TO THE LOWER 60S IN THE SOUTHEAST.

THE QPF FORECAST CAN BE PROBLEMATIC WITH POTENTIAL FOR A CSTAR
SCENARIO IF CONVECTION WITH THE LOW TRACKS EAST...LIMITING RAINFALL
FROM ADVANCING TO THE NORTH. INCREASED POPS AND SLOWED DOWN THE EXIT
OF THE DEER MOISTURE ON MONDAY. EXPANDED THE NORTHERN EXTEND OF
LIKELY POPS MONDAY WITH THE RAIN. LOWERED HIGH TEMPERATURES MONDAY
WITH RICH CLOUD COVER AND RAIN. HIGHS MONDAY WILL VARY FROM THE
UPPER 50S IN THE MOUNTAINS TO THE LOWER 70S IN THE EAST.

THE MAIN DISTURBANCE WILL MOVE SLOWLY EAST MONDAY NIGHT INTO TUESDAY.
LOW TEMPERATURES MONDAY NIGHT WILL GENERALLY BE IN THE 50S. TAPER
OFF POPS FROM WEST TO EAST TUESDAY INTO TUESDAY NIGHT. HOWEVER...LOW
CLOUDS AND PATCHES OF DRIZZLE MAY LINGER. USED THE SUPERBLEND FOR
HIGHS ON TUESDAY WITH VALUES GENERALLY IN THE UPPER 60S AND LOWER
70S. ALLOWED FOR SOME LIGHT POPS IN THE FAR EAST TUESDAY NIGHT WITH
LOW TEMPERATURES FROM THE LOWER 50S IN THE WEST TO AROUND 60 DEGREES
IN THE EAST.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 400 AM EDT SATURDAY...

SURFACE HIGH PRESSURE OVER THE CANADIAN MARITIMES RIDGING DOWN THE
EASTERN SIDE OF THE APPALACHIANS INTO THURSDAY. MOIST EASTERLY FLOW
MAY RESULT IN LOW CLOUDS AND DRIZZLE. A COLD FRONT APPROACH FROM THE
WEST ON FRIDAY. THIS FRONT SHOULD TRAVEL ACROSS OUR REGION FRIDAY
NIGHT INTO SATURDAY.

WITH ANOTHER COOL WEDGE OF HIGH PRESSURE OVER THE REGION...TEMPERATURES
WILL RUN COOLER THAN NORMAL. THE WARMEST DAY WILL BE FRIDAY AND/OR
SATURDAY...AHEAD OF THE FRONT. BEHIND THE FRONT...MUCH COOLER
TEMPERATURES EXPECTED FOR THE WEEKEND.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
AS OF 740 AM EDT SATURDAY...

VFR CONDITIONS EXPECTED 14Z - 04Z...WITH LOCAL IFR-LIFR BR/FG PRIOR
TO 14Z AND AFT 04Z SUN MORNING.

LESS STRATUS EXPECTED THROUGH THIS TAF VALID PERIOD COMPARED WITH
RECENT DAYS AS DRIER AIR HAS WORKED ITS WAY SOUTHWEST THROUGH THE
REGION FROM HIGH PRESSURE CENTERED ACROSS NY/PA. HOWEVER...THE
CLEARING LED TO MORE EFFECTIVE SFC COOLING AND PATCHY DENSE
RADIATIONAL FOG IN WESTERN AREAS WHERE THE BL MOISTURE IS DEEPER.
LWB AND BCB HAVE BOTH FLIRTED SINCE 04Z WITH LIFR FG AND
ATTENDANT VV CIGS. WOULD EXPECT FAIRLY RAPID IMPROVEMENT IN THESE
LIFR-IFR CONDITIONS TO VFR AFT 14Z. AREAS EAST OF THE BLUE RIDGE
HAVE DROPPED TO MVFR AT WORSE. THE ONLY AREA WHERE ANY CLOUDS ARE
EXPECTED TO LINGER TODAY WOULD BE IN FAR SOUTHWEST VA.
OTHERWISE...CANNOT COMPLETELY RULE OUT SCT STRATUS...BUT MODEL
CROSSSECTIONS DO NOT SUPPORT MUCH IN THE WAY OF CLOUDS OTHER THAN
HIGH CIRRUS THROUGH THE TAF VALID PERIOD. MOSTLY CLEAR SKIES AND
EFFICIENT COOLING WITH SLIGHTLY DRIER AIR SUN MORNING SHOULD YIELD
AS MUCH IF NOT GREATER POTENTIAL FOR IFR-LIFR FG FOR BCB/LWB...AND
PERHAPS MVFR TO BRIEFLY IFR BR FOR LYH/DAN. THE AIR IS DRIER EAST
OF THE BLUE RIDGE...SO FOG MAY BE MORE DIFFICULT TO COME BY IN
THAT AREA. OTHERWISE...VFR TODAY AND TONIGHT. WINDS REMAINING NE-
ESE THROUGH THE TAF VALID PERIOD AT SPEEDS OF 5-9KTS. WILL NOT
INCLUDE ANY MENTION OF GUST TODAY.

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

EXTENDED AVIATION DISCUSSION...

AFTER THE FOG BURNS OFF SUN MORNING...EXPECT MAINLY VFR
CONDITIONS EXPECTED SUN. THE NEXT POTENTIAL FOR WIDESPREAD SUB-
VFR CONDITIONS WILL COME WITH A DISTURBANCE THAT IS PROGGED TO
MOVE OUT OF THE GULF OF MEXICO AND ACROSS THE SOUTHEAST STATES
EARLY NEXT WEEK. THIS COULD BRING MVFR-IFR CIGS TO MUCH OF THE
REGION MON-WED. THERE IS ALSO GOOD POTENTIAL FOR A WEDGE DEVELOP
IN THE WAKE OF THE EARLY WEEK SYSTEM...PROMOTING CONTINUATION OF
LOW CIGS/VSBYS IN STRATUS...FOG...AND DRIZZLE THROUGH THE LATER
HALF OF THE WEEK. A STRONG COLD FRONT IS PROGGED TO MOVE THROUGH
THE REGION LATE IN THE WEEK WITH A GOOD CHANCE OF SHOWERS AND
COOLER WEATHER...BUT UNTIL THAT TAKES PLACE...WE MAY BE LOOKING AT
AN EXTENDED PERIOD OF FAIRLY POOR AVIATION CONDITIONS NEXT WEEK.

&&

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

&&

$$
SYNOPSIS...RAB
NEAR TERM...AMS/RAB
SHORT TERM...KK
LONG TERM...KK/RCS
AVIATION...RAB


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