Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 290501
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1201 AM EST THU JAN 29 2015

.SYNOPSIS...
HIGH PRESSURE OVER THE OHIO VALLEY THIS EVENING WILL MOVE
SOUTHEAST...REACHING THE CAROLINAS ON THURSDAY MORNING. LOW
PRESSURE WILL TRACK FROM NEBRASKA INTO ONTARIO BY THURSDAY
EVENING. THIS SYSTEM WILL PUSH A STRONG COLD FRONT THROUGH THE MID
ATLANTIC REGION ON THURSDAY NIGHT.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 715 PM EST WEDNESDAY...

WILL MAKE MINOR CHANGES TO GRIDS TO INCORPORATE MOST RECENT OBS
BUT NO SIGNIFICANT CHANGES NEEDED. IR SATELLITE SHOWS THIN CIRRUS
SPILLING OVER THE TOP OF THE UPPER RIDGE TO OUR WEST. MODELS DO
SHOW THE CIRRUS ADVANCING BUT INDICATIONS ARE THAT IT WILL REMAIN
THIN AND SHOULD NOT IMPEDE RADIATIONAL COOLING WITH OTHERWISE
CLEAR SKIES AND LIGHT WINDS...SO LOW TEMP FORECAST STILL LOOKS TO
BE ON TRACK.

PREVIOUS AFD...

UPPER RIDGE PASSES OVER THE REGION TONIGHT INTO THURSDAY MORNING.
850 MB TEMPERATURES MODERATE TONIGHT AND WILL BE JUST ABOVE ZERO
BY THURSDAY AFTERNOON. SURFACE HIGH PRESSURE WILL PASS OVER THE
REGION TONIGHT SO WINDS WILL DECOUPLE. WITH SUCH LOW SURFACE DEW
POINTS AND WITH ONLY A FEW HIGH CLOUDS COMING OVER THE RIDGE
TONIGHT... TEMPERATURES WILL PLUMMET THIS EVENING. WILL STAY
CLOSER TO COLDER MAV GUIDANCE FOR MINIMUM
TEMPERATURES...ESPECIALLY IN THE VALLEYS.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 400 PM EST WEDNESDAY...

SERIES OF SHORT WAVES SHARPENS UPPER TROF WITH A 500MB LOW CLOSING
OFF OVER NEW YORK BY LATE FRIDAY. FORECAST AREA WILL BE IN FAVORABLE
LEFT EXIT REGION OF UPPER JET ON THURSDAY NIGHT. FIRST SURGE OF MUCH
COLDER 850 MB AIR COMES IN THURSDAY NIGHT AND IS RE-ENFORCED ON
FRIDAY. ALONG WITH THE COLD AIR ADVECTION...LOW LEVEL JET COMES
AROUND TO THE NORTHWEST ON THURSDAY NIGHT WITH SPEEDS OF 45 TO 55
KNOTS INTO FRIDAY NIGHT. STRONG WINDS WILL BE ALONG THE SOUTHERN
APPALACHIANS THURSDAY NIGHT AND FRIDAY THEN WILL SHIFT TO THE
NORTHERN APPALACHIANS ON FRIDAY NIGHT AS THE SURFACE LOW DEEPENS
OFF THE COAST. NAM/GFS SHOWED PRESSURE RISES CLOSE TO 6MB/6HR FOR
THURSDAY NIGHT THROUGH FRIDAY. BUFKIT AND GUIDANCE CONTINUE TO
SUPPORT ADVISORY LEVEL WINDS BEHIND THE FRONT THURSDAY INTO FRIDAY
EVENING. THREAT WILL REMAIN HIGHLIGHTED IN HAZARDOUS WEATHER
OUTLOOK.

MOISTURE INCREASES ON THURSDAY AFTERNOON FROM THE WEST. WITH THE
DEEP NORTHWEST WINDS...WILL START TO SEE CLEARING EAST OF THE BLUE
RIDGE ON FRIDAY MORNING. THE REMAINING LOW LEVEL MOISTURE ON THE
WESTERN SLOPES ON FRIDAY WILL ERODE LATE IN THE DAY. SATURDAY
SURFACE AND LOW LEVEL WINDS WILL DIMINISH AND BACK MORE TO THE
WEST. HIGH CLOUDS WILL SPREAD OVER THE SOUTHERN COUNTY WARNING
AREA AHEAD OF THE SOUTHERN PLAINS SYSTEM.

MODELS WERE IN SIMILAR AGREEMENT WITH THE TIMING OF THE SURFACE COLD
FRONT ON THURSDAY NIGHT. WILL BE TRIMMING BACK PROBABILITY OF
PRECIPITATION BEFORE 18Z/1PM THURSDAY. A BULK OF THE PRECIPITATION
ASSOCIATED WITH THE SYSTEM WILL BE ALONG AND WEST OF THE BLUE RIDGE
BUT EVEN THAT WILL NOT BE VERY HIGH AMOUNTS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 330 PM EST WEDNESDAY...

TEMPERATURES BELOW NORMAL THROUGH THE EXTENDED.

UPPER LEVEL PATTERN FOR THE EXTENDED WILL SEE A CHANGE AS SPLIT FLOW
WITH A SOMEWHAT SHALLOW EASTERN TROF BECOMES UNIFIED AS THE CLOSED
LOW OVER THE BAJA PENINSULA OPENS UP AND EJECTS EASTWARD LATE IN THE
PERIOD...LEAVING US WITH A WELL AMPLIFIED RIDGE AND A BROAD FLAT
EASTERN TROF EXTENDING FROM A CLOSED LOW WAY UP NEAR HUDSON BAY
IN CANADA. THIS SHOULD BE A FAIRLY PROGRESSIVE PATTERN WITH SURGES
OF SHORT WAVE ENERGY HEADING OUR WAY ON A FAIRLY REGULAR BASIS.

WE WILL START THE PERIOD UNDER HIGH PRESSURE SATURDAY NIGHT...BUT AS
THE HIGH PUSHES TO OUR EAST AND WAVES RIDE ALONG AN APPROACHING COLD
FRONT WE WILL SEE OUR CHANCES FOR PRECIPITATION INCREASE FOR SUNDAY
AND SUNDAY NIGHT. PTYPE WILL BE WINTRY MIX AT THE START THEN EXPECT
A MOSTLY RAIN EVENT...THEN BACK TO SOME UPSLOPE SNOW SHOWERS WEST OF
THE BLUE RIDGE AS WE GET ON THE BACK SIDE OF THE LOW MONDAY.

COLD HIGH PRESSURE THEN BUILDS AS UPSLOPE SNOW SHOWERS WIND DOWN
MONDAY NIGHT AND...AFTER A VERY COLD MORNING...QUIET WEATHER SHOULD
BE THE RULE FOR TUESDAY. HEADING INTO WEDNESDAY...THE REMNANTS OF
THE CLOSED UPPER LOW WILL BE EJECTING TOWARD US AS THE NRN AND SRN
STREAMS PHASE. LONG RANGE MODELS ARE INDICATING THE POTENTIAL FOR A
/MILLER A/ TYPE LOW TO DEVELOP OVER THE GULF COAST WEDNESDAY AND
TRACK THROUGH THE SOUTHEAST US AND OFF THE MIDDLE ATLANTIC COAST
WEDNESDAY NIGHT. TEMPERATURES ARE CURRENTLY EXPECTED TO BE
BORDERLINE AT BEST ACROSS OUR AREA FOR WINTRY WEATHER. NOTHING TO
GET EXCITED ABOUT AT THIS POINT...BUT WE WILL BE WATCHING TO SEE HOW
LATER MODEL RUNS HANDLE THE EVOLUTION OF THIS SYSTEM.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AS OF 1155 PM EST WEDNESDAY...

HIGH PRESSURE WILL DRIFT OVER THE REGION TONIGHT. HIGH CLOUDS WILL
INCREASE FROM THE WEST...MAINLY ACROSS NORTHERN PORTIONS OF THE
CWA...IN ADVANCE OF AN ALBERTA CLIPPER...THE MAIN DYNAMICS OF
WHICH WILL REMAIN NORTH OF OUR CWA. SCT-BKN250 WILL DEVELOP FROM
WEST TO EAST OVERNIGHT...THE MAJORITY OF WHICH WILL STAY NORTH OF
U.S. 460...BUT CIGS WILL REMAIN VFR. NOT EXPECTING ANY PROBLEMS
WITH VISIBILITY OVERNIGHT EITHER AS THE SFC AIR MASS IS VERY DRY.
DURING THE DAY THU...THE CLIPPER WILL RACE ACROSS THE GREAT LAKES
INTO WESTERN NEW YORK/QUEBEC. A NARROW BAND OF PRECIPITATION
ACCOMPANIES THE ASSOCIATED FRONT...MAINLY NORTH OF U.S. 460 AND
WEST OF I-81. MOISTURE IS EXPECTED TO BE TOO LIMITED FOR MUCH MORE
THAN CLOUDS TO THE SOUTH. PRECIPITATION WILL BE FALLING FROM MID-
BASED CLOUDS AND LIGHT...SO VISIBILITY WILL NOT BE AN
ISSUE...EXPECT POSSIBLY AT BLF/LWB WHERE DYNAMICS/LIFT ARE BETTER
AND CLOUD CIGS COULD LOWER TO LOW END VFR OR HIGH END MVFR DURING
THIS ACTIVITY...POTENTIALLY REDUCING VSBY THEN TO MVFR CATEGORY IN
-SHRA. SFC/850MB TEMPS SHOULD REMAIN WARM ENOUGH FOR ALL LIQUID
THROUGH THIS 00Z. BEHIND THE COLD FRONT...ROUGHLY FROM 02Z FAR
WEST TO AFT 06Z FAR EASTERN PIEDMONT...THERE WILL BE AN INCREASING
THREAT FOR UPSLOPE -SHSN ACROSS THE ALLEGHANYS...INCLUDING
LWB/BLF. AT THIS POINT...CIGS WILL ALSO DROP INTO THE MVFR RANGE
AND VISIBILITY POTENTIALLY INTO THE MVFR RANGE AT TIMES AS WELL.

WINDS WILL BECOME THE MAIN CONCERN LATE IN THE TAF VALID PERIOD
AS THE CLIPPER MOVES EAST OF THE REGION AND VERY STRONG NORTHWEST
WINDS IMPACT AREAS WEST OF THE BLUE RIDGE. THROUGH THE TAF VALID
PERIOD...HOWEVER...EXPECT CALM OR LIGHT/VARIABLE WINDS
OVERNIGHT...BECOMING SOUTHEAST 5-8 KTS AROUND DAYBREAK...THEN SSE-
SSW THROUGH THE DAY THU INCREASING TO 8-12KTS WITH LOW END GUSTS
TO AROUND 20KTS WEST OF THE BLUE RIDGE. AFT THE FRONTAL PASSAGE
WITHIN THE TIME FRAME NOTED ABOVE...MAINLY AFT 00Z...EXPECT WNW
WINDS 10-15KTS WITH GUSTS 25-30KTS. IT STILL APPEARS THE STRONGEST
WINDS WILL COME AFT 06Z AND ESPECIALLY DURING THE DAY FRIDAY.

MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD.
HIGH CONFIDENCE IN VSBYS THROUGH 12Z...THEN MEDIUM TO HIGH
CONFIDENCE AFT 12Z.
MEDIUM TO HIGH CONFIDENCE IN WIND DIR/SPD THROUGH THE TAF VALID
PERIOD.

EXTENDED DISCUSSION...

BEHIND THE COLD FRONT...MVFR CIGS LIKELY TO LINGER OVER THE
MOUNTAINS INTO FRIDAY WITH STRONG NW WINDS ALSO PERSISTING INTO
FRIDAY EVENING. GUSTS UP TO 40 KNOTS ARE POSSIBLE IN THE HIGHER
ELEVATIONS. CLOUDS WILL BEGIN TO CLEAR OUT EAST OF THE BLUE RIDGE
ON FRIDAY MORNING...SO KLYH AND KDAN WILL IMPROVE BACK UP TO VFR.

ANOTHER AREA OF HIGH PRESSURE SHIFTS EAST INTO THE AREA SATURDAY
WITH VFR EXPECTED FOR BOTH SATURDAY AND SATURDAY NIGHT. THE NEXT
LOW PRESSURE SYSTEM HEADING OUT OF THE SW STATES WILL BRING A
RETURN OF CLOUDS AND SOME PRECIPITATION ON SUNDAY AND MONDAY WITH
WIDESPREAD MVFR TO IFR LIKELY.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS/MBS
SHORT TERM...AMS
LONG TERM...MBS
AVIATION...AMS/RAB



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