Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 261645
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1245 PM EDT SAT JUL 26 2014

.SYNOPSIS...
A WEAK WARM FRONT LIFTS NORTHEAST ACROSS THE AREA THIS AFTERNOON
ALLOWING A MORE WEST TO SOUTHWEST TRAJECTORY TO DEVELOP. THUNDERSTORMS
WILL DEVELOP ALONG THIS FRONTAL BOUNDARY IN THE OHIO VALLEY BY
EVENING AND SPREAD SOUTHEAST TOWARD OUR AREA BY EARLY SUNDAY. A
STRONG COLD FRONT SHOULD MOVE ACROSS THE MID ATLANTIC AND SOUTHERN
APPALACHIANS BY MONDAY...WITH COOLER WEATHER INTO THE MIDDLE OF
NEXT WEEK.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 940 AM EDT SATURDAY...

MID LEVEL WAVE PASSING TO THE NE HAS ALLOWED A GOOD PUNCH OF DRY
AIR INTO THE AREA FROM THE WEST THIS MORNING PER VAPOR LOOP. THIS
ALSO SEEN VIA MORNING RAOBS WITH VERY DRY AIR ALOFT CAPPED BY A
MID LEVEL INVERSION AND DEEP WEST TO NW FLOW THROUGH THE COLUMN.
LATEST PWATS OFF RAOBS AND THE LOCAL IPW ALSO SHOW SOME DECREASE
IN MOISTURE WITH THE PASSAGE OF THE WAVE WHICH SUPPORTS A MAINLY
DRY AFTERNOON WITH NEXT ROUND OF LIFT WELL TO THE NW. THIS IN LINE
WITH MOST SHORT TERM SOLUTIONS SHOWING LITTLE CONVECTION THROUGH
EARLY THIS EVENING. HOWEVER CANT TOTALLY RULE OUT SOMETHING
ISOLATED POPPING FAR SOUTH-SE WHERE THE AXIS OF HIGH LOW LEVEL
THETA-E PER MSAS...AND THE WARM FRONT MAY INTERACT WITH CAPES
AROUND 2K J/KG LATER ON. FOR NOW GIVEN WEAK SUBSIDENCE AND LACK OF
SHRA OFF THE 12Z NAM WILL LEAVE OUT POPS AND RUN MAINLY SUNNY
UNDER A DEVELOPING CU FIELD ONCE THE CURRENT PATCHY FOG FADES.
SURGE IN 85H TEMPS TO BACK OVER +20C AND WEST/SW FLOW UNDER STRONG
HEATING SUPPORTS HIGHS REACHING THE LOW 90S PIEDMONT...AND 85-90
BLUE RIDGE...WITH ONLY THE FAR WESTERN ELEVATIONS STAYING IN THE
LOW/MID 80S.

TONIGHT...WILL BE WATCHING UPSTREAM AS MCS IS EXPECTED FOR THE
OHIO VALLEY AND MODELS SHIFT THIS AREA EAST AND SOUTH TOWARD SE
WV/FAR SW VA BY SUNDAY MORNING. MODELS IN DECENT AGREEMENT THROUGH
12Z SUNDAY IN HITTING SRN OHIO TO ERN KY AND WRN WV WITH BEST
COVERAGE...WITH HIGHER THETA-E RIDGE SITUATED ACROSS THIS REGION.
GIVEN THAT SYSTEMS TEND TO BE FASTER THAN MODEL FORECAST WILL HAVE
POPS UP TO LIKELY IN THE FAR WEST BY MORNING TAPERING TO SLIGHT
CHANCE TO THE BLUE RIDGE AND NORTH OF LYH. CONVECTION IS LIKELY TO
BE WEAKENING TOWARD MORNING GIVEN LACK OF THERMAL INSTABILITY BUT
WIND FIELDS ARE FAVORABLE FOR A FEW STRONG GUSTS. THE STORM
PREDICTION CENTER IS KEEPING THE MAIN THREAT OUT OF OUR AREA UNTIL
AFTER 12Z SUNDAY...WHICH IS COVERED IN THE NEXT SECTION OF THIS
DISCUSSION.

LOWS TONIGHT WILL BE MUGGY AS DEWPOINTS INCREASE...MAINLY IN THE
60S CWA WIDE....AROUND 70 SOUTHEAST.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
AS OF 240 AM EDT SATURDAY...

SUNDAY INTO SUNDAY NIGHT CONTINUES TO LOOK LIKE A VERY ACTIVE
WEATHER DAY ACROSS AT LEAST THE WESTERN AND NORTHERN PARTS OF THE
REGION...WITH A POTENTIAL THUNDERSTORM COMPLEX ENTERING AND MOVING
THROUGH THE AREA DURING THE AFTERNOON AND EVENING HOURS. THE NEW DAY
2 CONVECTIVE OUTLOOK BY THE STORM PREDICTION CENTER HAS THE CENTER
OF A MODERATE RISK OF POTENTIAL SEVERE WEATHER NEAR THE KY/WV
BORDER...WITH THE EASTERN EDGE OF THE MODERATE AREA JUST TOUCHING
GREENBRIER COUNTY WV SOUTHWEST INTO TAZEWELL COUNTY VA. THE
REMAINDER OF THE FORECAST AREA IS WITHIN THE NEW DAY 2 SLIGHT RISK
AREA. DAMAGING WINDS AND LARGE HAIL ARE EXPECTED TO BE THE MAIN
THREATS ACROSS THE REGION...WITH AN ISOLATED TORNADO POTENTIAL
WITHIN THE MODERATE RISK AREA.

THIS SYSTEM WILL BE IN ADVANCE OF A SHORTWAVE TROUGH/LOW THAT WILL
HEAD SOUTHEAST THROUGH THE GREAT LAKES REGION SUNDAY NIGHT. IT WILL
BE THIS FEATURE THAT MERGES WITH A SOUTHEAST CANADIAN AREA OF LOW
PRESSURE THAT YIELDS A LONGWAVE TROUGH ACROSS MOST OF THE EASTERN
THIRD OF CONUS...CENTERED OVER OUR REGION...BY MONDAY AFTERNOON. A
DECENT GRADIENT WILL EXIST AROUND THE SOUTHERN WAVE FOR THIS TIME OF
YEAR TO PRODUCE 850 MB WINDS ON THE ORDER OF 35 TO 45 KTS ACROSS THE
AREA LATE SUNDAY...SUNDAY NIGHT...AND EARLY MONDAY TO ALLOW FOR
SURFACE GUSTS IN THE 20 TO 30 MPH RANGE AT HIGHER ELEVATIONS DURING
THIS PERIOD.

WEAK DISTURBANCES WITH IN THE FLOW OF THE PARENT LONGWAVE TROUGH
WILL PERIODICALLY PROGRESS TROUGH OUR AREA MONDAY INTO TUESDAY. THE
FIRST OF THESE WILL ALLOW FOR SOME SCATTERED SHOWER AND PERHAPS AN
ISOLATED THUNDERSTORM ON MONDAY...ESPECIALLY ACROSS THE MOUNTAINS. A
LEE TROUGH WILL DEVELOP THANKS TO STRONG W-NW FLOW. AFTERNOON
DEVELOPMENT WILL BE POSSIBLE JUST EAST OF THIS TROUGH WHERE LOW LEVEL
WINDS WILL BACK SOUTHWEST...AND YIELD A CONVERGENCE LINE ALONG THE
TROUGH.

MONDAY NIGHT...THE ACTIVE WILL SLOWLY WANE...BUT NOT COMPLETELY END
ACROSS THE MOUNTAINS WHERE LINGERING UPPER SUPPORT...AND A NORTHWEST
UPSLOPE FLOW WILL HELP MAINTAIN SOME ISOLATED SHOWERS.

ON TUESDAY...ANOTHER WEAK DISTURBANCE HEADS SOUTH THROUGH THE
AREA...BUT BY THIS TIME...SURFACE HIGH PRESSURE WILL ALSO BE ACROSS
THE AREA. WILL LIMIT PRECIPITATION COVERAGE TO ISOLATED SHOWERS
ACROSS MAINLY WESTERN AND SOUTHERN PARTS OF THE AREA. THIS ACTIVITY
IS EXPECTED TO END BY TUESDAY EVENING.

TEMPERATURES DURING THIS PORTION OF THE FORECAST WILL TREND COOLER
EACH DAY. TEMPERATURES BY TUESDAY AND TUESDAY NIGHT WILL BE SOME 10
TO 15 DEGREES COOLER THAN THOSE EXPECTED SUNDAY AND SUNDAY NIGHT.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 1230 PM EDT SATURDAY...

THE PERIOD STARTS OFF WITH A COLD FRONT WELL OFF THE ATLANTIC COAST.
A 1020MB SURFACE HIGH OVER SE MO SHIFTS TO THE NE STATES THURSDAY
AND FRIDAY. AT THE MID LEVELS...A RIDGE WILL PERSIST ACROSS THE
WESTERN US...WHILE A TROUGH WILL PERSIST ACROSS THE EASTERN US. VERY
LITTLE MOISTURE IS AVAILABLE FOR WEDNESDAY AND THURSDAY. THE ONLY
PLACE THAT MAY BE ABLE TO SQUEAK OUT A SHOWER OR TWO IS ACROSS THE
FAR SW...OTHERWISE MUCH OF THE REGION WILL REMAIN DRY. MOISTURE AND
LOW LEVEL CONVERGENCE INCREASE FOR FRIDAY AND SATURDAY...THUS
INCREASING THE THREAT FOR SHOWERS AND THUNDERSTORMS. GREATEST CHANCE
POPS ARE ACROSS THE WEST WHERE THE CONVERGENCE IS MAXIMIZED.

850MB TEMPS OF +13-15C AND A PERSISTENT WEDGING EASTERLY WIND WILL
ALLOW SURFACE HIGH TEMPS TO BE 5-10 DEGREES BELOW NORMAL. THURSDAY
WILL BE THE COOLEST MORNING OF THE PERIOD WITH UPPER 40S POSSIBLE
ACROSS SOME OF THE MOUNTAIN VALLEY LOCATIONS. LOW TEMPS WILL
MODERATE FRIDAY THROUGH THE WEEKEND AS SURFACE DEWPTS INCREASE.
&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
AS OF 1220 PM EDT SATURDAY...

VFR EXPECTED TO PREVAIL THROUGH EARLY TONIGHT WITH BKN CU FIELDS
AROUND KDAN THIS AFTERNOON AND INCREASING HIGH CLOUDS OVER THE FAR
WEST.

MAIN AVIATION ISSUE WILL BE WITH A COMPLEX OF STORMS PROGGED TO
IMPACT THE KBLF/KLWB AREA BY 12Z/8AM SUNDAY. CONVECTION MAY BE
FASTER AND WIDESPREAD ENOUGH TO INCLUDE PREVAILING MVFR VSBYS/CIGS
AT BOTH SITES AROUND 10Z/6AM AND KBCB/KROA BEFORE 14Z/10AM BUT
LOWER CONFIDENCE THERE.

STORMS WILL DEFINITELY IMPACT THE KBLF/KLWB AND OVER TOWARD
ROA/KBCB/KLYH INTO EARLY AFTERNOON SUNDAY...AS MODELS ZIP THIS
FEATURE EAST WHILE WEAKENING UPON CROSSING EAST OF THE BLUE RIDGE.
THUS WILL ONLY INCLUDE A VCSH MENTION AT KLYH FOR NOW AND LEAVE
OUT OF KDAN AS APPEARS MOST CONVECTION WILL STAY JUST NORTH OF
THAT AREA. STILL AVIATION INTERESTS SHOULD BE WARY OF POTENTIAL
SUB VFR CIGS/VSBYS WITH HEAVY RAIN AND THUNDERSTORMS/WINDS ESPCLY
OVER THE MOUNTAINS SUNDAY MORNING. MAY SEE A LULL IN COVERAGE AS
THIS IMPULSE PASSES MID/LATE SUNDAY AFTERNOON WITH PERIODIC MVFR
CONDITIONS AFFECTING BOTH KBLF AND KLWB INTO THE EVENING WITH A
SECOND WAVE ALONG THE FRONT. ELSW MIXING AND WEAK SINKING MOTION
BEHIND THE INITIAL FEATURE MAY TREND MOST SPOTS TOWARD VFR DURING
THE AFTERNOON AS WE SLIP IN BETWEEN THE EARLY IMPULSE AND THE
UPSTREAM COLD FRONT THAT WONT ARRIVE UNTIL SUNDAY NIGHT.

THE SURFACE COLD FRONT WILL BE MOVING ACROSS BY SUNDAY NIGHT INTO
MONDAY...SO THREAT OF SUB VFR THROUGH MONDAY EXPECTED ACROSS SE
WEST VA PER NW FLOW...BUT LESS ELSEWHERE GIVEN DOWNSLOPE.

SOME GUSTY NW WINDS BEHIND THE FRONT LIKELY ESPCLY ALONG THE
RIDGES LATE SUNDAY NIGHT INTO MONDAY WITH DRIER AIR PUSHING IN FOR
TUE- WED...AND MAINLY VFR. CANNOT RULE OUT LATE NIGHT FOG
KBCB/KLWB BUT LOW LVLS MAY STAY DRY ENOUGH FOR LESS FOG COVERAGE.

&&

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

&&

$$
SYNOPSIS...JH/WP
NEAR TERM...JH/WP
SHORT TERM...DS
LONG TERM...CF
AVIATION...JH/WP



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