Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 030308
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1008 PM EST MON MAR 2 2015

.SYNOPSIS...
HIGH PRESSURE WILL MOVE EAST INTO THE MID ATLANTIC REGION TONIGHT.
MEANWHILE...A WARM FRONT WILL PUSH NORTH THROUGH THE AREA LATE
TONIGHT INTO TUESDAY...THEN FOLLOWED BY A COLD FRONT TUESDAY NIGHT
INTO WEDNESDAY. COLD HIGH PRESSURE WILL RETURN FOR THURSDAY INTO THE
WEEKEND.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 1000 PM EST MONDAY...

1033 MB SURFACE HIGH WAS CENTERED OVER OHIO. THIS HIGH WILL
CONTINUE TO DRIFT EAST OVERNIGHT PROVIDING MAINLY DRY CONDITIONS.
A STATIONARY FRONT WAS OVER THE DEEP SOUTH...EXTENDING FROM
CENTRAL SOUTH CAROLINA SOUTHWEST TO JACKSON MS. THIS STATIONARY
FROM IS EXPECTED TO BEGIN MOVING NORTH OVERNIGHT AS A WARM
FRONT RESULTING IN THE RETURN OF LOW LEVEL MOISTURE TO THE AREA BY
DAYBREAK TUESDAY. QUESTION TO BE ANSWERED IS WHETHER THERE WILL BE
ENOUGH MOISTURE FOR PRECIPITATION. THE CLOSEST THING ON RADAR AT
THE MOMENT IS OVER THE SOUTHERN APPALACHIANS BETWEEN ASHVILLE NC
AND ATLANTA GA.

THE SURFACE HIGH WILL CERTAINLY BE IN A POSITION TO PROVIDE ENOUGH
COLD AIR FOR A WINTRY FORM OF PRECIPITATION TUESDAY MORNING. THE
QUESTION IS WHETHER THERE WILL BE ENOUGH DEPTH TO THE MOISTURE TO
PRODUCE PRECIPITATION. BOTH THE HRRR AND RNKWRF SUGGEST ONLY TRACE
AMOUNTS TO OCCUR BETWEEN NOW AND NOON TUESDAY WITH THE LARGER
SCALE MODELS PRODUCING A FEW HUNDREDTHS OF AN INCH. TRACE ICE IS
CERTAINLY ENOUGH TO BE A NUSCIANCE...BUT THIS IS NOT GOING TO BE
A WIDESPREAD EVENT.

THE MAIN PROBLEM WITH PRECIP PRODUCTION FOR TUESDAY IS THE LACK OF
UPPER LEVEL MOISTURE WITHIN THE M8-M12 DEG C DENDRITIC GROWTH ZONE.
FORECAST MODEL SOUNDINGS ARE DRY WITHIN THIS LAYER...ALL OF THE
SATURATION TAKING PLACE IN A LOWER LAYER BETWEEN +3 DEG C AND -3
DEG C. UNLESS THERE IS SOME SEEDER FEEDER PROCESS THAT DEVELOPS
INOF THE WARM FRONT...THE MODEL SOUNDINGS SUGGESTS THE PYTYPE WILL
BE EITHER DRIZZLE OR FREEZING DRIZZLE PENDING SURFACE TEMEPRATURE
AT THE TIME. THE CRITICAL WINDOW FOR THE FREEZING PRECIPITATION
WILL BE DURING THE MORNING...SO STILL SEE THE NEED FOR WINTER
WEATHER ADVISORIES TO ACCOUNT FOR THE POTENTIALLY LIGHT ICING THAT
MAY OCCUR...KEEPING IN MIND THAT EVEN A VERY LIGHT COATING OF ICE
ON AN UNTREATED SURFACE CAN POSE A TRAVEL/WALKING HAZARD.

LOW TEMPERATURES OVERNIGHT WILL RANGE FROM THE MID 20S IN THE
COLDEST VALLEYS TO THE LOWER 30S IN THE PIEDMONT. WARM AIR WILL
MOVE IN FROM THE SOUTHWEST TUESDAY CHANGING PRECIPITATION OVER TO
ALL LIQUID TUESDAY AFTERNOON. AREAS ACROSS THE NORTH AND
NORTHEAST WILL BE THE SLOWEST TO TRANSITION. HIGH TEMPERATURES
TUESDAY WILL RANGE FROM THE MID 30S IN THE NORTHEAST TO THE LOWER
50S IN THE SOUTHWEST.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 330 PM EST MONDAY...

COMPLICATED SHORT TERM FORECAST WITH MULTIPLE CONCERNS. TO BEGIN
TUESDAY NIGHT...ANY REMNANTS OF EARLIER WEDGE WILL BE LONG GONE TO
THE NORTHEAST WITH THE AREA SOLIDLY IN THE WARM SECTOR.
TEMPERATURES WILL BE WELL ABOVE FREEZING AND CONTINUING TO RISE
DURING THE OVERNIGHT HOURS ON THE HEELS OF A STRONG SOUTHWESTERLY
LLJ. CONSEQUENTLY...ANY ASSOCIATED WARM FRONTAL PRECIPITATION
WILL ALSO HAVE LIFTED WELL NORTHEAST OF THE REGION. NOW...THE
ATTENTION SHIFTS TO THE ARCTIC FRONT APPROACHING FROM THE WEST. A
BROAD UPPER RIDGE ACROSS THE CENTRAL/EASTERN GULF...590+ DM AT
THAT...WILL AMPLIFY INTO THE SOUTHEAST WHILE A DEEP UPPER TROUGH
DIGS INTO THE SOUTHERN PLAINS. A SIGNIFICANT SURGE OF ARCTIC AIR
WILL PLUNGE INITIALLY SOUTH INTO THE CENTRAL/SOUTH CENTRAL U.S. AS
THE ASSOCIATED ARCTIC FRONT SLOWS ITS PUSH INTO THE MID-
ATLANTIC/SOUTHEAST STATES THANKS TO THE AFOREMENTIONED UPPER RIDGE
AND THE APPALACHIAN MOUNTAINS. THIS HOLDS THE HEAVIEST RAINFALL
WEST OF OUR CWA THROUGH WEDNESDAY MUCH OF THE DAY
WEDNESDAY...MAINLY ACROSS THE OH/TN VALLEYS. FINALLY...WEDNESDAY
AFTERNOON/EVENING...THE FRONT WILL BEGIN A BETTER SOUTHEASTWARD
PUSH AS SHORT WAVE ENERGY KICKS OUT OF THE CENTRAL PLAINS. WOULD
EXPECT HEAVIER RAIN TO MOVE INTO THE WESTERN PARTS OF THE CWA BY
00Z WED...THEN BEGIN TO SPREAD EASTWARD OVERNIGHT.

MEANWHILE...PART OF THE UPPER TROUGH LAGS BEHIND AND SURFACE LOW
PRESSURE DEVELOPS ACROSS THE SOUTHEAST STATES IN RESPONSE. THIS
WILL FURTHER DELAY THE PUSH OF THE PRECIPITATION INTO/THROUGH THE
CWA...BUT PERHAPS NOT THE SHALLOW COLD ARCTIC AIR ONCE IT MANGES
TO CROSS THE APPALACHIANS. QUITE A VARIETY OF SOLUTIONS PRESENTED
BY THE MODELS AND WPC AS TO THE WINTER WEATHER THREAT THURSDAY
GIVEN THAT THIS IS FAR FROM A NORMAL SYNOPTIC SITUATION FOR A SNOW
EVENT IN THIS REGION. THE BIG QUESTION IS NOT WHETHER OR NOT THERE
WILL BE PRECIPITATION...BUT HOW QUICKLY WILL THE COLD AIR SPREAD
INTO THE REGION BEHIND THE FRONT...BEFORE THE HEAVIER
PRECIPITATION MOVES OUT...AND HOW QUICKLY WILL THE COLD AIR BECOME
DEEP ENOUGH TO CHANGE THE PRECIPITATION TO SNOW. AM INCLINED AT
THIS POINT TO THROW OUT RAIN TO FREEZING RAIN SCENARIOS...NOT ONLY
BECAUSE IT IS NOT CLIMATOLOGICALLY OR SYNOPTICALLY FAVORABLE IN
THIS SITUATION...BUT THINKING IS THAT COLD AIR WILL BECOME DEEP
ENOUGH QUICKLY ENOUGH TO CHANGE RAIN OVER TO SNOW...OTHER THAN A
BRIEF PERIOD OF SLEET ALONG THE LEADING EDGE OF THE CHANGEOVER.
FURTHERMORE...GROUND TEMPS WILL NOT SUPPORT FZRA AT THE CHANGEOVER
TIME AS THE SOUNDING COLUMN COOLS ISOTHERMALLY. FINALLY...THIS IS
YET AGAIN A SIGNIFICANT ARCTIC AIR MASS...SO ONCE IT ENTERS THE
REGION...COOLING WILL BE QUICK...ESPECIALLY WEST OF I-81. FOR SNOW
AMOUNTS...A PRELIMINARY ESTIMATE...FAIRLY CONSISTENT WITH WPC
WWD...IS 4-5 INCHES NORTH...2-4 INCHES CENTRAL/WESTERN AREAS...1-2
INCHES VA PIEDMONT...LITTLE TO NONE NC PIEDMONT.

SEE THE HYDROLOGY SECTION BELOW FOR FURTHER DETAILS ON THE FLOOD
THREAT ASSOCIATED WITH COMBINED RAINFALL AND SNOW MELT. DID
ADVERTISE A PERIOD OF MODERATE RAIN WEDNESDAY EVENING FROM WEST TO
EAST...BUT HAVE REDUCED THE TIME PERIOD OF SUCH COMPARED TO
PREVIOUS FORECAST PACKAGES.

TEMPERATURE WISE...A LOT OF NON-DIURNAL TEMPERATURE TRENDS THROUGH
THIS FORECAST PERIOD. TEMPERATURES CONTINUING TO RISE TUESDAY
NIGHT/WEDNESDAY MORNING AND REMAINING MILD/ABOVE FREEZING UNTIL
THE ARCTIC FRONT ARRIVES IN THE WEST WEDNESDAY NIGHT. THE PIEDMONT
WILL LIKELY REMAIN ABOVE FREEZING FROM TUESDAY AFTERNOON UNTIL
THURSDAY MORNING. LIKEWISE...A NON-DIURNAL COOLING TREND EXPECTED
THROUGHOUT THE DAY THURSDAY AS ARCTIC AIR SPREADS INTO THE REGION.
THE GFS IN PARTICULAR SHOW SFC TEMPS BELOW ZERO IN OUR WESTERN
COUNTIES BY FRIDAY MORNING. GIVEN THAT IT IS EARLY MARCH AND THE
850MB TEMPS ARE ONLY AROUND -16C...AS COMPARED TO -26C A COUPLE OF
WEEKS AGO...I FIND THIS SOMEWHAT EXTREME. NONETHELESS...IT IS A
VERY COLD AIR MASS AND WELL BELOW NORMAL FOR THIS TIME OF YEAR.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 145 PM EST MONDAY...

HIGH PRESSURE WILL BUILD OVER THE REGION ON FRIDAY...AND BE IN
CONTROL OF OUR WEATHER PATTERN THROUGH AT LEAST SATURDAY NIGHT. THE
HIGH WILL GRADUALLY BUILD INTO THE AREA FROM THE WEST...AND MAKE ITS
WAY TO THE COAST BY SATURDAY. THIS WILL ALLOW FOR A TREND TOWARD
MILDER CONDITIONS AS THE LOW LEVEL FLOW ACROSS THE AREA BECOMES
GRADUALLY MORE SW-W...WHILE A SHORTWAVE RIDGE AND RISING 850 TEMPS
TAKE PLACE.

SUNDAY INTO MONDAY A GENEROUS AMOUNT OF VARIATIONS IN THE MODELS
TAKE PLACE. WHILE BOTH THE GFS AND THE NAM EVENTUALLY COME INTO
AGREEMENT OF A LONG WAVE TROUGH OVER THE EASTERN THIRD OF CONUS BY
MONDAY OR TUESDAY OR NEXT WEEK...HOW THE SOLUTIONS COME TO BE THAT
WAY HAVE NOTABLE DIFFERENCES. THE GFS IS MORE PROGRESSIVE IN
ESTABLISHING THE TROUGH IN THE EAST BY SUNDAY...AND ANY SOUTHERN
STREAM SYSTEMS EASILY BYPASS OUR REGION EXITING THE U.S. NEAR THE
GA/FL BORDER. THE ECWMF IS NOT A QUICK TO ESTABLISH AN EAST COAST
TROUGH...AND A SUCH...SOUTHERN STREAM SYSTEMS HAVE A BETTER
OPPORTUNITY TO PROGRESS NORTHEAST THROUGH OUR REGION ON THE EAST
SIDE OF AN APPROACHING SHORTWAVE TROUGH.

OUR FORECAST FOR SUNDAY INTO MONDAY WILL BE A CONSENSUS OF THESE
TWO...WITH IT RESEMBLING A WATERED DOWN VERSION OF THE ECWMF IN
TERMS OF PRECIPITATION POTENTIAL ON SUNDAY AND SUNDAY NIGHT...AND
ALSO STAYING ON MORE OF THE MILD SIDE THAN COLD IN REGARDS TO
MONDAY.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
AS OF 630 PM EST MONDAY...

VFR CONDITIONS WILL CONTINUE ACROSS THE ENTIRE REGION THROUGH
ROUGHLY 04Z/11PM. AFTER THIS TIME...MVFR CIGS WILL START
PROGRESSES NORTHEAST ACROSS THE REGION IN CONJUCTION WITH A WARM
FRONT HEADING TOWARD THE AREA. ALONG WITH THE FRONT WILL COME
LIGHT WINTRY PRECIPITATION IN THE FORM OF PATCHY LIGHT FREEZING
RAIN AND SLEET. BY DAYBREAK TUESDAY...MANY AREAS WILL HAVE LOWERED
TO LIFR/IFR CIGS AND MVFR VSBYS DUE TO THE PRECIPITATION AND
MIST. THE BULK OF THE WINTRY PRECIPITATION WILL BE CONFINED TO
NORTH A LINE FROM KBLF-KROA-KLYH DURING THE LATE MORNING. BY THE
AFTERNOON...SURFACE TEMPERATURES SHOULD BE MILD ENOUGH FOR A
WIDESPREAD AREA OF PLAIN RAIN. LIFR/IFR CIGS AND IFR/MVFR VSBYS
WILL BE THE NORM DURING THE DAY TUESDAY.

WINDS WILL REMAIN LIGHT THROUGH THE NIGHT AND GRADUALLY VEER NORTH
TO SOUTHEAST. ON TUESDAY...WINDS WILL INCREASE DURING THE DAY FROM
THE SOUTHWEST...AND WINDS AT 850 MB WILL INCREASE TO AROUND 45 TO
50 KTS. LOW LEVEL WIND SHEAR WILL BE POSSIBLE DURING THE
AFTERNOON...ESPECIALLY AT TERMINALS AT HIGHER ELEVATION.

MEDIUM CONFIDENCE IN CEILINGS...VISIBILITIES AND WINDS DURING THE
PERIOD.

EXTENDED FORECAST...

ANOTHER LOW PRESSURE SYSTEM THAT WILL IMPACT ALL OF THE REGION
WILL TRACK FROM THE CENTRAL PLAINS INTO NEW ENGLAND TUESDAY NIGHT
INTO WEDNESDAY. THIS WILL RESULT IN SUB-VFR CONDITIONS WEDNESDAY
AND THURSDAY WITH WIDESPREAD RAIN AHEAD OF THE FRONT ON WEDNESDAY
AND WINTER PRECIPITATION BEHIND THE FRONT WEDNESDAY NIGHT AND
THURSDAY.

FRIDAY SHOULD SEE A RETURN TO HIGH PRESSURE AND VFR WEATHER.

&&

.HYDROLOGY...
AS OF 300 PM EST MONDAY

LIKELY TO SEE SOME SUBSTANTIAL RISES ON AREA RIVERS AND STREAMS IN
RESPONSE TO UPCOMING RAIN EVENT AND SNOWMELT IN THE
MOUNTAINS...QUESTIONS REMAIN ABOUT HOW SUBSTANTIAL. SIGNIFICANT SNOW
AMOUNTS ARE NOW CONFINED TO PARTS OF THE UPPER JAMES AND
GREENBRIER RIVER BASINS WHERE THE LATEST AVAILABLE ESTIMATES FROM
THE NATIONAL OPERATIONAL REMOTE SENSING CENTER SHOW ROUGHLY 1 TO 3
INCHES OF SNOW WATER EQUIVALENT WITH ISOLATED 4 INCHES IN THE
HIGHEST ELEVATIONS OF THE GREENBRIER. IN THE OTHER MAJOR RIVER
BASINS...NEW...ROANOKE/DAN AND TENNESSEE... MELTING OVER THE
WEEKEND AND TODAY HAS REDUCED THE SNOW TO LESS THAN 1 INCH OF SNOW
WATER AND IN MOST PLACES ZERO. THE OTHER ELEMENT OF COURSE IS THE
QPF. 12Z MODELS (INCLUDING LATEST EC) HAVE NUDGED THE HEAVIEST
QPF A LITTLE MORE TO THE WEST...REDUCING AMOUNTS IN THE JAMES AND
GREENBRIER SOME. IT STILL APPEARS AS IF 1 TO 2 INCHES COULD FALL
ACROSS THE WESTERN BASINS BY 12Z THURSDAY AND COMBINED WITH
SNOWMELT THIS COULD PRODUCE AT LEAST MINOR RIVER FLOODING ALONG
THE GREENBRIER AND POSSIBLY THE UPPER JAMES. GUIDANCE RECEIVED
FROM OHRFC THIS MORNING SUGGESTED MINOR FLOOD STAGE AT ALDERSON WV
ON THE GREENBRIER LIKELY BY EARLY THURSDAY WITH THE COMBINED
SNOWMELT AND QPF. HOWEVER...GIVEN THE CONTINUED UNCERTAINTIES WILL
HOLD OFF ON A FLOOD WATCH AT THIS POINT.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER WEATHER ADVISORY FROM 7 AM TO 1 PM EST TUESDAY FOR
     VAZ018>020-022>024-034-035-045>047.
     WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR VAZ007-009-
     010-012-015-016.
     WINTER WEATHER ADVISORY FROM 4 AM TO 1 PM EST TUESDAY FOR
     VAZ011-013-014-017-032-033-043.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR NCZ001-002-
     018.
WV...WINTER WEATHER ADVISORY FROM 7 AM TO 1 PM EST TUESDAY FOR
     WVZ507-508.
     WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR WVZ042.
     WINTER WEATHER ADVISORY FROM 4 AM TO 1 PM EST TUESDAY FOR
     WVZ043-044.

&&

$$
SYNOPSIS...KK/RAB
NEAR TERM...KK/PM
SHORT TERM...RAB
LONG TERM...DS
AVIATION...DS/KK
HYDROLOGY...PC



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