Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 070457
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1157 PM EST SAT FEB 6 2016

.SYNOPSIS...
WEAK HIGH PRESSURE WILL REMAIN OVER THE AREA INTO TONIGHT. A
STORM SYSTEM DEVELOPING OFF THE SOUTHEAST COAST WILL MOVE
NORTHEAST BUT PASS WELL TO THE SOUTH AND EAST OF THE AREA SUNDAY
INTO SUNDAY NIGHT. A SECOND AREA OF LOW PRESSURE WILL MOVE
SOUTHEAST ACROSS THE MOUNTAINS FROM THE NORTHWEST EARLY NEXT
WEEK...RESULTING IN MUCH COLDER TEMPERATURES ALONG WITH SNOW
SHOWERS FOR MONDAY THROUGH WEDNESDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 940 PM EST SATURDAY...

JUST A FEW MINOR TWEAKS MADE IN THIS PACKAGE. ADJUSTED SKY COVER
BASED ON CURRENT IR OBSERVATIONS. FURTHER SLIGHT ADJUSTMENTS TO THE
TEMPERATURE VALUES BASED ON CURRENT CONDITIONS AT THIS HOUR...AND
BASED ON THE EXPECTED INCREASE IN THE MID CLOUD DECK MAINLY EAST OF
THE BLUE RIDGE MOUNTAINS BY MIDNIGHT.

PREVIOUSLY VALID DISCUSSION...

UPPER LOW ALONG THE NORTHERN GULF COAST CONTINUES TO HEAD EAST WITH
A RAPIDLY DEEPENING SURFACE SURFACE LOW PRESSURE HEADING NORTH
OFF THE FLORIDA COAST TO ALONG THE GULF STREAM BY MORNING. THIS
SHOULD CONTINUE TO FAN HIGH/MID CLOUDS NORTH ACROSS THE REGION
WITHIN THE SW FLOW ALOFT EARLY ON BEFORE THE SYSTEMS START TO
PHASE AND ATTEMPT TO LEAN DEEPER MOISTURE BACK INLAND. HOWEVER HOW
FAR TO THE NW THIS OCCURS REMAINS IFFY GIVEN SUCH DRY AIR IN PLACE
AND DEVELOPING SURFACE-7H NORTHERLY FLOW EAST OF THE BLUE RIDGE.
LATEST GUIDANCE KEEPS THE MAJORITY OF THE PRECIP WITHIN A TIGHT
DEFORMATION ZONE ON THE BACK OF THE COASTAL LOW JUST TO THE SE
THROUGH 12Z. HOWEVER THE GFS/CMC DO TOUCH THE FAR CORNER OF THE
PIEDMONT WITH A FLURRY/SPRINKLE WHILE THE HRRR AND LOCAL RNK-WRF
LOOK A BIT MORE OMINOUS IN BRINGING PRECIP JUST SOUTH OF THE CWA
LATE. SINCE THESE STILL APPEAR TO BE OUTLIERS ATTM WILL ONLY BEEF
UP CLOUDS SE LATE TONIGHT BUT STAY DRY FOR NOW PENDING LATER
TRENDS. OTRW WILL RUN WITH A PC FORECAST OVERALL FOR HIGH CLOUDS
THIS EVENING...THEN BECOMING MOSTLY CLOUDY SE THIRD OVERNIGHT.
LOWS AGAIN DEPENDENT UPON THE CLOUD CANOPY AS GIVEN LOW DEWPOINTS
COULD QUICKLY FALL BACK INTO THE 20S SOONER. THUS GOING ON THE
COLDER SIDE OF MOS OVERALL WHICH STILL SUPPORTS LOW/MID 20S
MOUNTAINS TO AROUND 30 SE.

SURFACE LOW RAPIDLY DEEPENS HEADING ALONG THE GULF STREAM SUNDAY AS THE
UPPER LOW CATCHES UP AND HELPS SLOW THE SYSTEM DOWN. GUIDANCE AGAIN
DEPICTS AN INTENSE BUT VERY COMPACT SYSTEM OFFSHORE WITH A TIGHT
GRADIENT BETWEEN CLOUDS AND DEFORMATION PRECIP ON THE NW SIDE OUT EAST.
HOWEVER STILL APPEARS THAT BETWEEN DRY AIR IN PLACE AND SOME EASTWARD
BOOT VIA THE NEXT UPSTREAM SHORTWAVE KICKER THAT MOST DEEP MOISTURE
SHOULD AGAIN STAY JUST TO THE SOUTH AND EAST SUNDAY MORNING BUT
SOMETHING STILL TO WATCH. THEREFORE PLAN TO STAY DRY WITH MORE SUN WEST
AND CLOUDS GIVING WAY TO MORE SUN DURING THE DAY EAST AS THE MID DECK
CANOPY SLOWLY FADES AND SHIFTS EAST. WINDS MAY TURN GUSTY AS WELL
SUNDAY OUT EAST ON THE PERIMETER OF THE CYCLONE WHILE OVERALL WARMING
ALOFT TAKES PLACE. THIS SUPPORTS HIGHS BACK INTO THE 40S WEST AND
PERHAPS SOME 50S JUST IN THE LEE OF THE BLUE RIDGE ON THE EDGE OF THE
EASTERN CLOUD SHIELD PENDING HOW FAST IT EXITS.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 225 PM EDT SATURDAY...

AN UPPER LEVEL SHORT WAVE TROUGH IN THE SOUTHERN STREAM WILL CROSS
OVER THE CAROLINAS ON SUNDAY NIGHT...WHICH WILL SPIN UP AN INTENSE
LOW PRESSURE SYSTEM OFF THE COAST. THE MODELS KEEP THE CWA DRY...BUT
SOME CLOUD COVER MAY LINGER OVER THE PIEDMONT. AS THE COASTAL LOW
EXITS ON MONDAY...A BROAD UPPER LEVEL TROUGH IN THE NORTHERN STREAM
WILL DIG SOUTHWARD FROM THE GREAT LAKES TOWARD THE MID ATLANTIC. A
POTENT CLIPPER SYSTEM ALONG THE LEADING EDGE OF THIS TROUGH SHOULD
PROVIDE LIGHT SNOW WEST OF THE BLUE RIDGE DURING MONDAY. THE 12Z
ECMWF SEEMS TOO SLOW WITH THE PROGRESS OF THE CLIPPER SYSTEM AND THE
APPROACHING ARCTIC AIR...WHILE THE 12Z GFS MAY BE TOO BULLISH WITH
QPF. PRECIPITATION TYPE BECOMES MORE PROBLEMATIC IN THE
PIEDMONT...AS FLURRIES BEGIN OVER THE PIEDMONT BEFORE CHANGING TO
RAIN WITH TEMPERATURES RISING INTO THE 40S. THE RAIN WOULD CHANGE
BACK TO FLURRIES BY MONDAY EVENING AS TEMPERATURES DROP.

THE BROAD UPPER LEVEL TROUGH WILL BE OVERHEAD BY TUESDAY...AS A DEEP
ARCTIC AIR MASS SPILLS OVER THE CWA. WITH 500 MB HEIGHTS APPROACHING
520 DAM AND MODEL SOUNDINGS PORTRAYING A NEARLY SATURATED CLOUD
LAYER UP TO -30 C FROM MONDAY EVENING THROUGH MOST OF TUESDAY...THE
UPSLOPE SNOW MACHINE WILL BE HUMMING AT FULL POWER ALONG THE WESTERN
SLOPES. WINTER WEATHER HEADLINES APPEAR LIKELY FOR THESE AREAS
DURING MONDAY AND TUESDAY...SO IT HAS BEEN MENTIONED IN THE HWO.
AREAS TO THE EAST MAY STILL A FEW FLURRIES FLYING IN THE NORTHWEST
WIND...BUT NO ACCUMULATION WILL BE REALIZED AFTER THE CLIPPER SYSTEM
DEPARTS OFFSHORE BY MONDAY NIGHT. TEMPERATURES WERE HELD BELOW MOS
GUIDANCE THROUGHOUT THIS PERIOD DUE TO PERSISTENT COLD AIR
ADVECTION. ONE LAST CONCERN COULD BE THE WIND CHILL ON TUESDAY
NIGHT...AS THESE VALUES MAY DIP INTO THE SINGLE DIGITS WEST OF THE
BLUE RIDGE BY DAWN...AND POSSIBLY HIT ZERO ALONG THE WESTERN SLOPES.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 245 PM EST SATURDAY...

A DEEP ARCTIC AIR MASS SHOULD REMAIN ENTRENCHED OVER THE MID
ATLANTIC DURING WEDNESDAY AND THURSDAY. PERSISTENT NORTHWEST FLOW
SHOULD KEEP THE UPSLOPE SNOW MACHINE IN ACTION THROUGH WEDNESDAY
ALONG THE WESTERN SLOPES...BUT THE PIEDMONT SHOULD STAY DRY FROM THE
DOWNSLOPE FLOW. ALTHOUGH THE SNOWFALL THREAT WILL DECREASE LATER IN
THE WORK WEEK...THE THREAT FOR LOW WIND CHILL VALUES WILL INCREASE.
THE LONG RANGE MODELS PROJECT THAT THE WIND CHILL VALUES SHOULD
APPROACH WIND CHILL ADVISORY CRITERIA OF -5 F IN THE WESTERN
MOUNTAINS ON EARLY WEDNESDAY MORNING...AND EVEN LOWER TO -10 F BY
THURSDAY MORNING. WITH LOW TEMPERATURES DIVING INTO THE TEENS AND
UPPER SINGLE DIGITS AND A DECENT NORTHWEST BREEZE...THE WIND
CHILL THREAT IS WORTHY ENOUGH TO NOTE IN THE HWO.

TEMPERATURES SHOULD MODERATE A LITTLE BY FRIDAY AS THE UPPER LEVEL
TROUGH PUSHES EASTWARD...BUT THE MODELS SIGNIFICANTLY DIVERGE BEYOND
THIS POINT. THE 12Z GFS TRIES TO DEVELOP ANOTHER BAND OF LIGHT SNOW
FROM A SUBTLE SHORT WAVE DURING FRIDAY AFTERNOON THROUGH SATURDAY
MORNING...BUT THE 12Z ECMWF KEEPS ANY MOISTURE FURTHER TO THE
SOUTHEAST AND OUT OF THE CWA. WITH SO MUCH UNCERTAINTY AT THIS
POINT...ONLY SLIGHT CHANCE TO LOW CHANCE POPS WERE INTRODUCED.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 1150 PM EST SATURDAY...

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF VALID PERIOD. A DEEP
COASTAL LOW PRESSURE SYSTEM WILL BE DEVELOPING WELL TO OUR
SOUTHEAST THROUGH THE PERIOD...THEN TRACKING NORTHEAST OFF THE
SC/NC COAST. THIS SYSTEM WILL SPREAD SOME MID/HIGH CLOUDS ACROSS
AREAS ALONG AND EAST OF THE BLUE RIDGE THROUGH THE
PERIOD...ESPECIALLY OVERNIGHT/EARLY SUNDAY...BUT ANY CIGS BELOW
MUCH BELOW 10KFT ARE EXPECTED TO REMAIN EAST OF THE RNK TAF
SITES. TO THE WEST...A DEEPENING LOW WILL BE TAKING SHAPE ACROSS
THE WESTERN GREAT LAKES AND MOVING SOUTHEAST. HOWEVER...THIS
SYSTEM WILL NOT APPROACH OR IMPACT THE RNK CWA UNTIL JUST BEYOND
THE TAF VALID PERIOD...ALTHOUGH MID/HIGH CLOUDS WILL BE
APPROACHING WESTERN AREAS TOWARD THE END OF THE TAF VALID PERIOD.
NO PRECIPITATION IS EXPECTED AT ANY TAF SITES THROUGH THE TAF
VALID PERIOD. THE AIR MASS IS EXTREMELY DRY...SO VISIBILITIES WILL
REMAIN VFR.

WINDS WILL REMAIN CHAOTIC THROUGH THE PERIOD AS THE REGION FALLS
BETWEEN THE DEEPENING COASTAL LOW AND THE SYSTEM APPROACHING FROM
THE WEST. A GENERAL TENDENCY TOWARD NNW-NNE WINDS CAN BE EXPECTED
EAST OF THE BLUE RIDGE SEEING INFLUENCE FROM THE DEVELOPING
COASTAL LOW...WHILE LIGHT/VARIABLE TO LIGHT SW WINDS CAN BE
EXPECTED WEST OF THE BLUE RIDGE. EAST OF THE BLUE RIDGE...WINDS
WILL TRANSITION MORE TOWARD THE NNW-NW TOWARD THE END OF THE TAF
VALID PERIOD. WEST OF THE BLUE RIDGE...SPEEDS SHOULD BE MOSTLY
7KTS OR LESS THROUGH THE TAF VALID PERIOD. TO THE EAST...POTENTIAL
FOR 8-12KTS WITH GUSTS TO 20KTS KDAN-KLYH LATE TONIGHT THROUGH
SUNDAY AFTERNOON IN RESPONSE TO THE COASTAL LOW.

MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD.
HIGH CONFIDENCE IN VFR VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM
CONFIDENCE IN WIND SPEED/DIRECTION THROUGH THE TAF VALID PERIOD.

EXTENDED DISCUSSION...

FOR MONDAY INTO MID WEEK...A STRONG UPPER LEVEL LOW PRESSURE
SYSTEM WILL SINK SOUTHWARD FROM THE GREAT LAKES AND UPPER MIDWEST.
AN ASSOCIATED COLD FRONT WILL CROSS THE REGION MONDAY FOLLOWED BY
A SECOND SURGE OF ARCTIC AIR TUESDAY. NORTHWEST WINDS WILL
INCREASE WITH AN INFLUX OF VERY COLD AIR AND DEEP UPSLOPE
MOISTURE. SNOW SHOWERS WILL BEGIN MONDAY AND CONTINUE THROUGH
WEDNESDAY EVENING RESULTING IN VISIBILITY RESTRICTIONS ACROSS THE
MOUNTAINS IN ADDITION TO LOW CIGS. THIS SHOULD RESULT IN A
PROLONGED PERIOD OF MVFR TO IFR AT KBLF/KLWB AND POTENTIAL PERIODS
OF MVFR AT KBCB/KROA. ACCUMULATING SNOW IS LIKELY IN THE MOUNTAINS
WEST OF THE BLUE RIDGE. FLURRIES MAY OCCUR AS FAR EAST AS THE
PIEDMONT WHERE INTERVALS OF VFR TO MVFR CIGS WILL ALSO OCCUR.

CONDITIONS SHOULD BRIEFLY RETURN TO MAINLY VFR LATER WEDNESDAY
NIGHT ACROSS THE REGION BEFORE POSSIBLY RETURNING TO SUB-VFR AGAIN
OVER THE MOUNTAINS DURING THURSDAY WITH ANOTHER WEAK PASSING UPPER
IMPULSE.

&&

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

&&

$$
SYNOPSIS...JH/PM
NEAR TERM...JH/JM/MBS
SHORT TERM...PW
LONG TERM...PW
AVIATION...JH/PM/RAB


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