Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 251730
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1230 PM EST THU DEC 25 2014

.SYNOPSIS...
A COLD FRONT WAS MOVING EAST TOWARD THE COAST THIS MORNING. HIGH
PRESSURE OVER THE GULF COAST WILL THEN BUILD ACROSS THE EASTERN
UNITED STATES TODAY AND REMAIN OVER THE REGION THROUGH SATURDAY.
ANOTHER COLD FRONT ARRIVES BY SUNDAY WITH THE NEXT CHANCE OF
PRECIPITATION.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 930 AM EST THURSDAY...

FORECAST IS IN QUITE GOOD SHAPE THIS CHRISTMAS MORNING SO JUST
SOME MINOR ADJUSTMENTS TO WORK LATEST OBS INTO GRIDS. LATEST SAT
IMAGES AND AREA RADAR LOOPS SHOW THAT NWLY WINDS ACROSS THE
REGION ARE GIVING US THE TRADITIONAL UPSLOPE CLOUDS/LIGHT PCPN
WEST OF THE BLUE RIDGE WITH DOWNSLOPE CLEARING TO THE WEST. WITH
PARENT LOW CONTINUING TO PULL WELL INTO CANADA...LOW LEVEL
MOISTURE WILL BE ERODING QUICKLY THIS AFTERNOON AND WINDS WILL
BACK AROUND A BIT AS HIGH PRESSURE BUILDS IN FROM THE LOWER
MISSISSIPPI VALLEY...ALLOWING FOR STEADY IMPROVEMENT WEST OF THE
RIDGE. WINDS HAVE BEEN BLUSTERY THIS MORNING BUT BELOW ADVSY
CRITERIA AND LOW LEVEL FLOW WILL BE SLACKENING FROM HERE ON OUT.

PREVIOUS AFD... COLD FRONT WAS JUST EXITING THE FAR EASTERN
COUNTIES OF THE FORECAST AREA. THE WESTERN EDGE OF THE FRONTAL
PRECIPITATION EXTENDED FROM CHARLOTTESVILLE TO DANVILLE. LATEST
HRRR HAS THIS PRECIPITATION EXITING THE EASTERN COUNTY WARNING
AREA AROUND 10Z/5AM. WILL KEEP CHANCE OF SHOWERS IN THE WESTERN
UPSLOPE AREAS THIS MORNING. MOISTURE ABOVE 700 MB MOVES OUT OF THE
FORECAST AREA THIS MORNING ALONG WITH THE COLD FRONT. MODELS ERODE
THE LOW LEVEL MOISTURE THIS EVENING. WILL KEEP SOME CLOUD COVER IN
THE NORTHWEST THROUGH THIS EVENING. LOCATIONS TO THE EAST WILL
CLEAR OUT THIS MORNING.

SURFACE HIGH PRESSURE WAS OVER THE GULF COAST. THE HIGH MOVES ACROSS
THE SOUTHEAST UNITED STATES TODAY AND WILL BE CENTERED OVER THE
FORECAST AREA BY FRIDAY MORNING. SURFACE DEW POINTS DROP INTO THE
20S BY LATE TODAY. WITH THE DRY AIR MASS THAT WILL BE IN
PLACE...DIURNAL VARIATION IN TEMPERATURES WILL BE 20 TO 25 DEGREES.
EXPECT VALLEYS TO DECOUPLE THIS EVENING. WILL KEEP LOW TEMPERATURES
AT OR BELOW GUIDANCE TONIGHT.

MSAS SHOWED BEST PRESSURE RISES OVER THE GREAT LAKES EXTENDING INTO
NORTHERN VIRGINIA. 850 WINDS WILL BE AROUND 50 KNOTS FROM THE WEST
EARLY THIS MORNING...BUT WILL STEADILY DIMINISH TO BELOW 20 KNOTS
TONIGHT.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 300 AM EST THURSDAY...

HIGH PRESSURE WILL KEEP THE REGION DRY THROUGH SATURDAY.
TEMPERATURES WILL MODERATE AS THE CENTER OF THE HIGH SHIFTS EAST AND
INCREASING SOUTHWEST WINDS USHER IN A WARM AIR ADVECTION PATTERN
ACROSS THE REGION.

SATURDAY NIGHT THROUGH SUNDAY NIGHT A BAROCLINIC ZONE WILL ESTABLISH
ITSELF FROM NEAR THE MISSISSIPPI DELTA NORTHEAST INTO THE LOWER OHIO
VALLEY. A SERIES OF DISTURBANCES WILL TRACK ALONG THIS
BOUNDARY AND BRING MULTIPLE PERIODS OF RAIN ACROSS THE FORECAST
AREA. CONFIDENCE IS LOW REGARDING TIMING AND TRACK OF EACH OF THESE
SYSTEMS BASED UPON THE GENEROUS SPREAD IN MODEL SOLUTIONS OF THE
FEATURES. HOWEVER...BY THE DAY SUNDAY...IT IS LIKELY THAT RAIN WILL
OCCUR DURING SOME PERIOD OF THE DAY TIME HOURS...AND LIKEWISE DURING
THE SUNDAY NIGHT PERIOD.

TEMPERATURES WILL BE ABOVE NORMAL DURING THIS PERIOD OF THE FORECAST.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 300 PM EST WEDNESDAY...

LATE WEEKEND INTO MID NEXT WEEK LOOKS TO BE POTENTIALLY UNSETTLED
WITH LARGE SCALE TROUGH OVER THE WESTERN TWO THIRDS OF THE COUNTRY
KICKING SEVERAL SHORT WAVES OUT INTO SOUTHERN APPALACHIAN REGION.
MODELS OFFER SIGNIFICANT DIFFERENCES IN THE STRENGTH AND TIMING OF
THESE WAVES...AND AMOUNT OF GULF MOISTURE THEY ARE ABLE TO TAP.
ALSO RUN-TO-RUN INCONSISTENCIES ARE MAKING THIS OVERALL A RATHER
LOW CONFIDENCE FORECAST. AM CONCERNED THAT THE ECMWF IN PARTICULAR
HAS HAD A TENDENCY TO DIG THE SHORT WAVES A LITTLE TOO MUCH AND
THEN ULTIMATELY DRIVE A DEEPENING SFC WAVE TOO FAR NORTH UP THE
APPALACHIANS OR TO THE WEST OF US. THE FLATTER MORE PROGRESSIVE
GFS HAS BEEN BETTER AS OF LATE. LATEST 12Z ECMWF HAS TRENDED
TOWARD THE MORE SUBDUED GFS FOR THE FIRST SYSTEM HEADED UP OUR WAY
INTO MONDAY...WHILE CANADIAN NOW HAS A MUCH STRONGER SYSTEM
TRACKING JUST TO OUR SOUTH ON MONDAY AND MONDAY NIGHT. WILL LEAN
MORE TOWARD THE WEAKER/FLATTER IDEA ADVERTISED IN THE LATEST GFS
AND NOW ECMWF...AT LEAST THROUGH TUES. ECWMF IS A LITTLE STRONGER
WITH ANOTHER WAVE ON WEDNESDAY...WHILE GFS IS
FASTER...COLDER...AND GENERALLY KEEPS IT SOUTH OF US.

WHILE CONFIDENCE IN THE TIMING AND STRENGTH OF THESE SYSTEMS IS
QUITE LOW RIGHT NOW...THERE IS MORE CLARITY THAT THIS WILL AT THE
VERY LEAST BE A CLOUDY PERIOD...AND THAT LOW LEVEL TEMPS AND
THICKNESSES WILL GENERALLY BE WARM ENOUGH NOT TO HAVE ANY REAL
PRECIP TYPE CONCERNS...WITH THE POSSIBLE EXCEPT OF HIGHEST RIDGES
ACROSS THE FAR NORTH SUNDAY AND MONDAY...WITH ANY SYSTEM ON
WEDNESDAY THERE COULD BE ENOUGH DAMMING SETTING UP THAT
OVERRUNNING COULD BE SOME SORT OF WINTRY MIX...BUT NOT EVEN SURE
WE WILL HAVE PRECIP ON WED. ECMWF WOULD SUGGEST FREEZING RAIN.

THE LARGE SFC HIGH NOSES IN MORE AND MORE AND EACH DAY LOOKS A
LITTLE COOLER THAN THE PREVIOUS ONE WHICH IS REFLECTED IN THE
TEMPERATURE FORECAST. WHILE I HAVE LOWERING POPS EACH
DAY...LARGELY DUE TO INCREASING UNCERTAINTY...AM KEEPING A LOW CHC
TO SLIGHT CHC IN THROUGH THE PERIOD WITH MORE INDICATION OF SOME
WINTRY PRECIP AS WE GET INTO TUES NIGHT AND WED.
OVERALL...FORECAST REALLY REFLECTS A VERY BROAD BRUSH RATHER THAN
GOING EXACTLY WITH ANY ONE SOLUTION...AND EXPECT THERE WILL BE
QUITE A FEW CHANGES TO THE EARLY WEEK FORECAST AS WE GET INTO THE
WEEKEND. NOT MUCH CHANCE FOR A MAJOR STORM DURING THIS
PERIOD...AND AFTER SUNDAY ITS POSSIBLE THAT DRY BUT COOL HIGH
PRESSURE MANAGES TO DOMINATE...BUT BEST GUESS FOR NOW IS SOMETHING
IN BETWEEN. AS ALWAYS...STAY TUNED!

&&

.AVIATION /17Z THURSDAY THROUGH MONDAY/...
AS OF 1220 PM EST WEDNESDAY...

NWLY WINDS WILL SLACKEN THIS AFTERNOON AS HIGH PRESSURE BUILDS IN
FROM THE LOWER MISSISSIPPI VALLEY. THIS WILL YIELD VFR CONDITIONS
EAST OF THE BLUE RIDGE WITH FEW CLOUDS. HOWEVER WITH ANTECEDENT
WET CONDITIONS AND GOOD RADIATIONAL COOLING AS THE HIGH BUILDS IN
TONIGHT...BELIEVE THERE IS THE POSSIBILITY FOR SOME GROUND FOG
TOWARD DAYBREAK. WILL NOT MENTION ANY FOG AT KROA SINCE THEY LOOK
TO KEEP A LIGHT WIND OVERNIGHT...BUT WILL INCLUDE A TEMPO MVFR
VISIBILITY RESTRICTION FOR KLYH/KDAN SINCE THEY SHOULD DECOUPLE
AND HAVE THE BEST CHANCE FOR FOG DEVELOPMENT.

FURTHER WEST...MOISTURE IS SLOWER TO PULL OUT THAN EARLIER THOUGHT
AND KLWB MAY NOT BREAK LOSE THEIR CIG. FURTHERMORE...THERE ARE
INDICATIONS THAT LOW LEVEL MOISTURE TRAPPED UNDER THE SUBSIDENCE
INVERSION WILL YIELD A RESURGENCE OF LOW MVFR CLOUDS FOR A WHILE
OVERNIGHT. WILL NOT SHOW A CIG AT KBCB BUT WILL REINTRODUCE AN
MVFR CIG AT KBLF FOR SEVERAL HOURS. WITH ONLY SCT CLOUDS FOR KBCB
THERE MAY BE ENOUGH RAD COOLING FOR SOME FOG HERE AS WELL...AND
KLWB LOOKS TO FINALLY CLEAR OUT TOWARD DAYBREAK AND THIS MAY
PROVIDE ENOUGH TIME FOR A BRIEF PERIOD OF FOG TO FORM.

TOMORROW LOOKS LIKE A FINE VFR DAY WITH LIGHT WINDS AND ONLY SOME
MID OR HIGH CLOUDS.

EXTENDED DISCUSSION...

HIGH PRESSURE SHOULD BUILD OVER THE SOUTHEAST...WHICH WILL
PROVIDE VFR WEATHER WITH LIGHTER WINDS THROUGH FRIDAY NIGHT.

ANOTHER COLD FRONT WITH ASSOCIATED LOW PRESSURE WILL APPROACH THE
REGION SATURDAY AND BE OVER OR JUST WEST OF THE AREA SUNDAY. BOUNDARY
MAY LINGER OVER OR JUST SOUTH OF THE REGION EARLY NEXT WEEK WITH
POSSIBLE RETURN TO VFR MONDAY AFTERNOON.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...MBS/AMS
SHORT TERM...DS
LONG TERM...SK
AVIATION...MBS/AMS



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