614
FXUS61 KRNK 172323
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
723 PM EDT WED OCT 17 2018
SYNOPSIS
A DRY COLD FRONT ASSOCIATED WITH A COLDER AIR MASS WILL PROGRESS
ACROSS THE REGION EARLY TONIGHT. HIGH PRESSURE IS EXPECTED TO
SETTLE OVER THE AREA TOMORROW INTO FRIDAY. ANOTHER COLD FRONT WILL
BRING A RETURN OF WET WEATHER INTO SATURDAY. TEMPERATURES WILL BE
BELOW NORMAL THROUGH THE NEXT FIVE DAYS.
NEAR TERM /THROUGH THURSDAY/
AS OF 710 PM EDT WEDNESDAY...
WINDS ARE DIMINISHING IN THE PIEDMONT, BUT FORECAST TAKES
DEWPOINTS TO THE MID 30S BY DAWN WITH TEMPS IN THE UPPER 30S,
AND AT THE MOMENT CONFIDENCE IS LOW ON ENOUGH FROST FOR ADVISORY
CRITERIA, BUT WOULD NOT BE SURPRISED IF SOME OUTLYING RURAL
AREAS WILL SEE PATCHY FROST AT DAWN THURSDAY. AT THE SAME TIME
CIRRUS WILL BE MOVING IN, BUT SHOULD NOT INHIBIT ANY FROST
FORMATION IN THE WESTERN VALLEYS WHERE WINDS SHOULD FALL OFF
LATE.
PREVIOUS DISCUSSION FROM EARLY AFTERNOON...
THE CENTRAL/SOUTHERN APPALACHIANS AND PIEDMONT IS ENTRENCHED IN
POST-FRONTAL DRY CONDITIONS THIS AFTERNOON. AIR MASS HAS DRIED
OUT SIGNIFICANTLY WITH DEWPOINTS COMMONLY IN THE 30S TO LOWER
40S. IT REMAINS BLUSTERY AT TIMES IN THE WESTERN HALF OF THE
FORECAST AREA AND PARTICULARLY AT ELEVATION, AS STRONG
INSOLATION HAS BOOSTED TEMPS IN THE 60S TO NEAR 70. STEEPENING
OF LOW-LEVEL LAPSE RATES HAS ALLOWED TO TAP INTO A ROBUST 35-40
KT NORTHWESTERLY JET. THUS FAR, WIND GUSTS BETWEEN 25 TO 35 MPH
HAS BEEN COMMON TENDING HIGHER AT ELEVATION. A SECONDARY AND DRY
COLD FRONT ALOFT IS EXPECTED TO CROSS THE REGION LATE THE
AFTERNOON, WHICH WILL ALLOW FOR THE BEST COLD ADVECTION INTO THE
EARLY-EVENING HOURS, OFFSET FROM PEAK HEATING. LOOK FOR
NORTHWESTERLY WIND GUSTS TO INCREASE ANOTHER 5 MPH OR SO THROUGH
SUNSET. EFFECTS OF COLD ADVECTION AND PRESSURE RISES WILL KEEP
BREEZY CONDITIONS GOING WELL INTO THE FIRST PART OF THE EVENING,
THOUGH WIND GUST SPEEDS WILL TEND TO DECREASE.
WE EXPECT TONIGHT TO BE THE FIRST FROST SINCE THE SPRING ACROSS
THE WESTERN THIRD OF COUNTIES. WE DO HAVE FREEZE WARNINGS
POSTED FOR BATH AND WESTERN GREENBRIER COUNTY, AND FROST
ADVISORIES FOR ALL OF SOUTHEASTERN WV, THE REST OF THE ALLEGHANY
HIGHLANDS AND INTO BLAND AND TAZEWELL COUNTIES. THESE
FROST/FREEZE HEADLINES TAKE EFFECT AT MIDNIGHT AND CONTINUE
UNTIL 9 AM THURSDAY. BASED ON TODAY'S FORECAST GUIDANCE, DIDN'T
SEE ENOUGH COMPELLING REASON TO EXPAND FROST OR FREEZE HEADLINES
FURTHER EAST. COMBINATION OF HIGH PRESSURE RIDGING INTO THE
REGION WITH CLEAR SKIES, THE VERY DRY AIR MASS IN PLACE AND
DECOUPLING AND EASING SURFACE WINDS SHOULD ALLOW FOR GOOD TO
NEAR-IDEAL RADIATIONAL COOLING. 850 MB TEMPERATURES ARE FORECAST
TO BE AT OR BELOW FREEZING (0 TO -2C) ACROSS THE ALLEGHANY
HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY HILLTOPS, WHICH
SUPPORTS FREEZE CONDITIONS MAINLY AT ELEVATION IN THE COUNTIES
UNDER THE FREEZE WARNING INTO THE PRE-DAWN HOURS. WHILE FORECAST
LOWS LOOK WARM ENOUGH TO PERMIT FROST IN THE PIEDMONT/FOOTHILLS
INTO THE ROANOKE VALLEY, DO EXPECT AT LEAST PATCHY AREAS OF
FROST IN THE MOUNTAIN EMPIRE, GREENBRIER VALLEY AND IN THE
DEEPER MOUNTAIN VALLEYS IN SOUTHEAST WV. PATCHY FROST COULD BE
OBSERVED IN THE NEW RIVER VALLEY, SMYTH/WYTHE COUNTY AND INTO
THE MOUNTAINS OF NORTHERN NC BUT EXPECTED FROST COVERAGE WASN'T
GREAT ENOUGH TO SUPPORT EXPANSION OF HEADLINES. MAY SEE SOME
SHALLOW MOISTURE BANK ITSELF AGAINST THE ALLEGHANY MTNS WHICH
COULD SUPPORT SOME SCATTERED STRATOCU THROUGH THE EASTERN WV
MOUNTAINS BUT THIS LOOKS MORE LIKELY TO OCCUR AFTER PEAK
NIGHTTIME COOLING. LOWS IN THE UPPER 20S TO NEAR 30 IN THE
MOUNTAINS OF BATH AND WESTERN GREENBRIER COUNTY, LOW TO MID 30S
IN THE AREAS IN THE FROST ADVISORY, MID/UPPER 30S FROM THE
SOUTHERN BLUE RIDGE INTO THE NEW RIVER VALLEY, AND LOW 40S EAST
OF THE BLUE RIDGE.
HIGH PRESSURE WILL CONTINUE TO BUILD SOUTHEASTWARD FROM THE
UPPER MIDWEST/OHIO VALLEY, ITS CENTER SETTLING INTO THE
ALLEGHANY MTNS TOWARD EARLY THURSDAY EVENING. PLENTIFUL SUNSHINE
EXPECTED AGAIN THURSDAY BUT 850 MB TEMPERATURES AROUND +1 TO
+5C WILL SUPPORT COOLER TEMPERATURES THAN TODAY BY SOME 5-10
DEGREES (MAINLY IN THE 50S TO NEAR 60, WITH MID/UPPER 40S IN THE
HIGHER ELEVATIONS IN THE BLUE RIDGE AND WESTERN GREENBRIER
COUNTY).
FORECAST CONFIDENCE IS HIGH, BUT SOME QUESTION ON HOW QUICKLY
WINDS SLACKEN LENDS MODERATE FORECAST CONFIDENCE ON FROST
POTENTIAL.
SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/
AS OF 339 PM EDT WEDNESDAY...
WEAK UPPER RIDGING ON FRIDAY THEN 500MB HEIGHTS FALL AS TROUGH
DEEPENS OVER THE EASTERN UNITED STATES. PIECE OF ENERGY FROM THE
UPPER LOW OVER THE SOUTHWEST UNITED STATES TRACKS EAST FRIDAY AND
SATURDAY. MEANWHILE DEEP TROUGHING DEVELOPS OVER THE NORTHEAST
UNITED STATES. FRIDAY MORNING SURFACE HIGH PRESSURE WILL BE CENTERED
OVER VIRGINA. THIS HIGH MOVES OFFSHORE FRIDAY NIGHT WHILE A COLD
FRONT WILL EXTEND FROM THE GREAT LAKES INTO THE CENTRAL PLAINS. THE
COLD FRONT WILL CROSS THE MID ATLANTIC REGION ON SATURDAY.
MODELS HAVE SLOWED THE RETURN OF DEEPER MOISTURE OVER THE CENTRAL
APPALACHAINS FROM THE SOUTHWEST. EVEN THE FASTER GFS DOES NOT HAVE
THE HIGH CLOUDS REACHING THE MOUNTAINS UNTIL FRIDAY AFTERNOON AND
LOW LEVELS DO NOT SATURATE UNTIL FRIDAY EVENING. WILL HAVE A
MAJORITY OF THE PRECIPITATION CROSSING THROUGH SOUTHWEST VIRGINIA,
NORTHWEST NORTH CAROLINA AND SOUTHEAST WEST VIRGINIA BETWEEN 03Z-15Z
SATURDAY/11PM FRIDAY TO 11AM SATURDAY.
RESIDUAL LOW LEVEL MOISTURE AND UPSLOPE WIND ON SATURDAY NIGHT. WILL
HAVE LIGHT RAIN OR SNOW SHOWERS FROM SOUTHEAST WEST VIRGINIA INTO
TAZWELL COUNTY VIRGINIA. STRONGEST COLD AIR ADVECTION BEHIND THE
FRONT IS SATURDAY AFTERNOON INTO EARLY SUNDAY MORNING. STRONGEST
PRESSURE RISES ALSO FORECAST FOR LATE SATURDAY NIGHT INTO SUNDAY
MORNING, WHICH WILL LEAD TO GUSTY WINDS. WILL KEEP BELOW WIND
ADVISORY CRITERIA FOR NOW.
CONFIDENCE IS BELOW AVERAGE FOR LOWS THURSDAY NIGHT AND AVERAGE
FOR ALL OTHER ELEMENTS.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
AS OF 338 PM EDT WEDNESDAY...
AXIS OF LONG WAVE TROUGH MOVES OFF THE EAST COAST SUNDAY MORNING
FOLLOWED BY BROAD NORTHWEST FLOW. A SHORT WAVE TRACKS THROUGH THIS
FLOW REACHING THE MID ATLANTIC REGION ON TUESDAY ALTHOUGH THERE IS
SOME DIFFERENCE IN TIMING WITH THE DIFFERENT MODELS AND LIMITED
MOISTURE. THE ECMWF IS STILL MORE AMPLIFIED BY LATE WEDNESDAY THEN
THE OTHER LONG RANGE GUIDANCE, CLOSING OFF A 500MB LOW OFF THE
NORTHEAST COAST.
850MB TEMPERATURES BOTTOM OUT IN THE -1 TO -5 RANGE SUNDAY
AFTERNOON. OPERATIONAL GFS WAS WARMER THAN MOST OF THE GEFS MEMBERS
FOR LOWS SUNDAY NIGHT. WILL BE LEANING BELOW CLIMATOLOGY AND MAV
GUIDANCE. THE AIR MASS WARMS AHEAD OF THE TUESDAY SHORT WAVE THEN
COOLS AGAIN FOR WEDNESDAY BEHIND A COLD FRONT.
CONFIDENCE IS AVERAGE FOR ALL ELEMENTS.
AVIATION /23Z WEDNESDAY THROUGH MONDAY/
AS OF 715 PM EDT WEDNESDAY...
BESIDES SOME CIRRUS OVERNIGHT INTO EARLY THURSDAY, AIRMASS WILL
GET DRY AND CHILLY. THE THREAT OF LOWER CLOUDS AT BLF LOOK LESS
LIKELY NOW, SO REMOVED THEM FROM THIS SET OF TAFS.
NORTHWEST TO WEST WINDS WILL BE DIMINISHING THIS EVENING, AND
WILL BE LIGHT/VARIABLE THURSDAY.
FORECAST CONFIDENCE IS HIGH ON ALL ELEMENTS AND MEDIUM ON NO
STRATUS FORMING IN THE MOUNTAINS WEST OF BLF LATE TONIGHT.
EXTENDED DISCUSSION...
VFR UNTIL LATER FRIDAY EVENING AS A COLD FRONT WILL APPROACH
FROM THE WEST. THIS WILL BRING A RETURN OF RAINFALL TO THE AREA
FRIDAY NIGHT INTO SATURDAY WITH THE POTENTIAL FOR A GENEROUS
COVERAGE OF SUB- VFR CEILINGS AND LOCALIZED SUB- VFR
VISIBILITIES DURING THIS TIME FRAME. HIGH PRESSURE BUILDS IN
BEHIND THE FRONT ON SUNDAY WITH VFR RETURNING ACROSS THE REGION
AFTER ANY RESIDUAL LOW CLOUDS CLEAR THE NORTHWEST SLOPES. HIGH
PRESSURE WILL KEEP IT VFR INTO MONDAY.
RNK WATCHES/WARNINGS/ADVISORIES
VA...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT THURSDAY FOR
VAZ007-010-011-018-019.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT THURSDAY FOR
VAZ020.
NC...NONE.
WV...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT THURSDAY FOR
WVZ042>044-507.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT THURSDAY FOR
WVZ508.
SYNOPSIS...AL/JH
NEAR TERM...AL
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...AL/WP
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