Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 280126 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 926 PM EDT WED MAY 27 2015 .SYNOPSIS... HIGH PRESSURE OFF THE SOUTHEAST COAST WILL MAINTAIN A BROAD SOUTHERLY FLOW OF MOISTURE INTO THE REGION THROUGH THE REMAINDER OF THIS WEEK. A WEAK UPPER LEVEL DISTURBANCE AND ASSOCIATED FRONTAL BOUNDARY WILL SLIDE INTO THE REGION EARLY THURSDAY. THIS WEATHER FEATURE IN COMBINATION WITH DAYTIME HEATING AND INSTABILITY WILL RESULT IN PERIODIC ROUNDS OF SHOWERS AND STORMS OVER THE NEXT FEW DAYS. && .NEAR TERM /THROUGH THURSDAY/...
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AS OF 926 PM EDT WEDNESDAY... SHOWERS AND THUNDERSTORMS LOCATED TO OUR SOUTHEAST FROM RALEIGH NORTH CAROLINA TO EMPORIA VIRGINIA WHICH DEVELOPED ALONG OUTFLOW BOUNDARIES AND IN THE AREAS OF RICHER CAPE ABOVE 1K AND STRONG THETAE/ADVECTION ARE MOVING NORTHEAST AND WILL MISS THE EASTERN COUNTIES OF OUR FORECAST AREA DURING THE NEXT HOUR OR TWO. ISOLATED SHOWERS HAVE FORMED IN THE WESTERN MOUNTAINS AND ENDED QUICKLY WITH THE MORE STABLE AIR. WE WILL HAVE TO WATCH NEXT COUPLE OF HOURS TO SEE IF ANY CONVECTION TO OUR WEST IN EASTERN TENNESSEE AND KENTUCKY SURVIVES ITS MARCH EASTWARD INTO THE STABLE AIR ACROSS THE WESTERN MOUNTAINS. HOWEVER...WITH THE LOSS OF SOLAR HEATING MOST OF THE CONVECTION WILL WEAKEN AND DISSIPATE THIS EVENING INTO TONIGHT. UNDER PARTLY CLOUDY SKIES EXPECT ANOTHER MILD OVERNIGHT WITH LOW TEMPERATURES FROM THE UPPER 50S IN THE MOUNTAINS TO THE MID 60S IN THE PIEDMONT. LINGERING BOUNDARIES AND MCVS FROM UPSTREAM CONVECTION SHOULD PROVIDE FOR BETTER COVERAGE OF CONVECTION THURSDAY AFTERNOON. THE SWODY2 (CONVECTIVE OUTLOOK DAY 2 FOR SEVERE POTENTIAL) KEEPS OUR AREA IN THE GENERAL THUNDERSTORMS. WITH WEAK STEERING FLOW AND WELL ABOVE AVERAGE PRECIP WATER VALUES EXPECTED...LOCALLY HEAVY RAIN WILL BE POSSIBLE WITH TRAINING OR STORMS LOCKED ON TERRAIN. HIGH TEMPERATURES WILL RANGE FROM THE MID 70S IN THE MOUNTAINS TO THE UPPER 80S IN THE PIEDMONT. AS OF 630 PM EDT WEDNESDAY... MADE SOME ADJUSTMENTS TO POPS FOR THIS EVENING INTO TONIGHT. USED A BLEND OF HRRR AND RNK WRFARW. DRIER AIR PUSHING IN FROM THE WEST...WAS HINDERING THUNDERSTORM DEVELOPMENT. GIVEN LIMITED INSTABILITY EXPECTED CONVECTION TO DIMINISH WITH THE LOSS OF SOLAR HEATING THIS EVENING. LOW TEMPERATURES WILL BE MILD OVERNIGHT WITH READINGS FROM AROUND 60 DEGREES IN THE MOUNTAINS TO THE MID 60S IN THE PIEDMONT. AS OF 350 PM EDT WEDNESDAY... CONVECTION STRUGGLING TO GET GOING SO FAR THIS AFTERNOON AND WILL LIKELY REMAIN ISOLATED THROUGH THIS EVENING...MAINLY IN MTNS AND FOOTHILLS...GIVEN LIMITED INSTABILITY AND DRIER AIR PUSHING IN FROM THE WEST BEHIND THE WEAK SHORT WAVE THAT HAS LIFTED NORTHEAST OVER THE NORTHEAST U.S. ANY WIDELY SCATTERED CONVECTION THAT DOES MANAGUA TO DEVELOP THE REMAINDER OF THE AFTERNOON SHOULD DIMINISH QUICKLY WITH LOSS OF HEATING. WILL NEED KEEP AN EYE ON MORE ORGANIZED CONVECTION WELL TO THE WEST AS IT MOVES INTO EASTERN KY AND TN...BUT ALL INDICATIONS ARE THAT THIS WILL DIE QUICKLY WELL BEFORE IT REACHES WESTERN SLOPES OF APPALACHIANS...WHICH WOULD BE NEAR MIDNIGHT IF IT DID SURVIVE. KEEPING A SLIGHT CHANCE POP IN THE WEST FOR THIS SMALL POSSIBILITY... AS WELL AS ALONG BLUE RIDGE MAINLY IN NW NC GIVEN SOME LINGERING INSTABILITY AND CONVERGENCE PER THE HRRR...BUT OTHERWISE DROPPING POPS AFTER MIDNIGHT. SOME SUGGESTION IN THE GUIDANCE THAT PATCHY FOG MAY BE MORE LIKELY LATE TONIGHT...BUT WITH GENERAL LACK OF RAINFALL EXPECTED REMAINDER OF THE DAY...AND SOME RESIDUAL MID DECK OVERNIGHT...THINK THIS IS NOT LIKELY AND HAVE CHOSEN NOT TO INCLUDE IT. FOR THURSDAY...WE FINALLY HAVE SOME INGREDIENTS COMING TOGETHER TO SUPPORT MORE WIDESPREAD COVERAGE OF CONVECTION...WITH WEAK UPPER WAVE MOVING INTO APPALACHIANS EARLY IN THE DAY AND ASSOCIATED WEAK FRONTAL BOUNDARY...OR REALLY MORE OF A TROUGH AXIS...WHICH WILL ADD TO SOME WEAK CONVERGENCE ALREADY GEOGRAPHICALLY FAVORED NEAR THE BLUE RIDGE. MODELS SUGGEST MODEST INSTABILITY IN PART BECAUSE OF WARMER AFTERNOON TEMPS EXPECTED...BUT STILL NOTHING SUPER IMPRESSIVE...AND PERHAPS ENOUGH DRY AIR AT MID LEVELS TO SUPPORT SOME GUSTY DOWNDRAFTS. AT THIS POINT THINK SEVERE POTENTIAL IS LIMITED...BUT MUCH BETTER THAN THE LAST COUPLE OF DAYS. HOWEVER WITH WEAKER STEERING FLOW AND WELL ABOVE AVERAGE PRECIP WATER VALUES EXPECTED...LOCALLY HEAVY RAIN WILL BE THE MAIN CONCERN. GIVEN DRY ANTECEDENT CONDITIONS...NOT ALL THAT CONCERNED ABOUT A FLASH FLOOD THREAT...BUT STILL SOMETHING TO KEEP AN EYE ON WITH ISOLATED AREAS IF ANY STORMS BECOME LOCKED ON TERRAIN. THIS WILL STILL MAINLY BE OVER THE MOUNTAINS...WITH COVERAGE JUSTIFYING SOME LIKELY POPS...BUT STORMS MAY DRIFT INTO THE PIEDMONT BY LATE AFTERNOON...SO MID CHANCE POPS BY LATE IN THE DAY THERE AS WELL.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... AS OF 330 PM EDT WEDNESDAY... UPPER PATTERN WILL BE IN TRANSITION DURING THE SHORT TERM WITH FLATTENING OF THE EAST COAST RIDGE AND A TROF DEVELOPING INTO A CLOSED LOW OVER THE MISSISSIPPI VALLEY. THIS WILL KEEP US IN A WEAKLY FORCED WARM/MOIST/UNSTABLE ENVIRONMENT WITH A DIURNAL TREND AND MOUNTAIN BIAS FOR SHOWERS/THUNDERSTORMS. A WEAK COLD FRONT WILL BE APPROACHING FROM THE NORTHWEST BY THE WEEKEND BUT UNCERTAINTY WILL BE INCREASING AS GUIDANCE DIFFERS IN HANDLING THE SPEED OF THIS FEATURE. BELIEVE THE SCENARIO WILL LEAD TO INCREASING CHANCES FOR FOR CONVECTION DURING THE LATTER PORTION OF THE WEEKEND. BIGGEST CONCERN WILL BE THE POSSIBILITY OF LOCALLY HEAVY RAIN GIVEN PRECIPITABLE WATER VALUES OF 1.0 TO 1.5 INCHES ACROSS THE REGION. TEMPERATURES WILL REMAIN ABOVE NORMAL WITH READINGS TRENDING UP A FEW DEGREES THROUGH THE WEEKEND... GENERALLY LOOKING FOR MID/UPPER 80S EAST OF THE BLUE RIDGE LOWER 80S WEST WITH THE USUAL COOLER READINGS AT THE HIGHER ELEVATIONS. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 330 PM EDT WEDNESDAY... BY SUNDAY NIGHT THE UPPER PATTERN WILL BE WELL ON ITS WAY TO DEVELOPING A SPLIT FLOW REGIME ACROSS THE NORTHERN TIER OF STATES AS A CLOSED LOW DEVELOPS OVER THE MISSISSIPPI VALLEY AND SLOWLY SINKS SOUTHWARD THROUGH THE MIDDLE OF NEXT WEEK. SOME RIDGING WILL ALSO BE TAKING PLACE OVER THE MID ATLANTIC REGION AND SET UP A SLUGGISH BLOCKY PATTERN. AT THE SURFACE HIGH PRESSURE WILL BUILD THROUGH THE NORTHEAST AND WEDGE DOWN THE EASTERN SEABOARD...BRINGING COOLER/NEAR NORMAL TEMPERATURES TO THE REGION. HOWEVER...THE PATTERN WILL KEEP US MOIST WITH DEEP SOUTHEASTERLY FLOW AND EXPECT ENOUGH FORCING BETWEEN OROGRAPHIC UPSLOPE AND DIURNAL EFFECTS TO KEEP SOME SHOWER ACTIVITY...AND POSSIBLY A THUNDERSTORM... IN THE FORECAST THROUGH THE PERIOD. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... AS OF 745 PM EDT WEDNESDAY... GENERALLY VFR CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD...WITH SOME CAVEATS TO CONSIDER. FIRST ISSUE IS POTENTIAL FOR OVERNIGHT CLOUDS AND FOG. WITH RESPECT TO CLOUDS...UPSTREAM CONVECTION LINGERS ACROSS KY ASSOCIATED WITH NEXT UPSTREAM DISTURBANCE AS UPPER TROUGH REMAINS BACK IN THE MIDWEST. ADDITIONAL STRONG CONVECTION EVIDENT ACROSS AL/MIDDLE TN...MOVING ENE. THIS SHOULD BRING CONVECTIVE DEBRIS MID/HIGH CLOUDS ACROSS THE REGION LATER TONIGHT...SO HAVE INDICATED SO IN THE TAFS...ALL VFR. NEXT ISSUE IS FOG. MODELS ARE VERY ROBUST IN GENERATING IFR- LIFR FOG TONIGHT AT MOST TAF SITES. SYNOPTICALLY...THIS DOES NOT MAKE SENSE. EVEN THOUGH THE AIR MASS IS MOIST WITH PWATS AROUND 1.35...WE HAVE HAD LITTLE TO NO RAIN FOR SEVERAL DAYS AND MID- LEVEL DRYING FURTHER DRIED OUT THE AIR MASS TODAY ALLOWING FOR ABUNDANT INSOLATION AND A LARGE T/TD SPREAD AT MOST SITES. IF ANY FOG DEVELOPS...CANNOT SEE MUCH WORSE THAN 4-5SM BR...MAINLY AT LWB/BCB/LYH...BUT FOR NOW HAVE LEFT OUT OF THE TAFS. FOR THU...LINGERING BOUNDARY AND MCVS FROM UPSTREAM CONVECTION SHOULD PROVIDE FOR BETTER COVERAGE OF CONVECTION BEGINNING AROUND 17Z. GFS LOOKS OVERDONE...BUT CERTAINLY WOULD EXPECT MORE THAN WE SAW TODAY. HAVE INTRODUCED VCSH/VCTS AT MOST TAF SITES WITH STILL MVFR CIGS AT THIS POINT. NOT ENOUGH CONFIDENCE TO INCLUDE TEMPO OR PROB30 JUST YET...AND NOT ENOUGH CONFIDENCE TO SAY THAT ONE SITE WILL BE MORE FAVORED THAN ANOTHER...OTHER THAN KDAN...WHICH SHOULD SEE THE LEAST CONVECTION AT THIS POINT...BUT EVEN THERE IT IS A POSSIBILITY. AGAIN...BRIEF PERIODS OF MVFR-IFR VSBYS/CIGS POSSIBLE IN TSRA...BUT NOT ENOUGH CONFIDENCE TO ADVERTISE THIS FAR OUT. WINDS LOOK VERY CHAOTIC THROUGH THE TAF VALID PERIOD AND CONFIDENCE IN ANY ONE SOLUTION IS VERY LOW. SW WINDS EARLY WILL DIMINISH TO NEAR CALM AND POTENTIALLY BECOME LIGHT SE EARLY THU...BUT MODEL SOLUTIONS ARE ALL OVER THE COMPASS AND WITH SFC HIGH PRESSURE GENERALLY SITUATED OVER THE AREA...THIS SCENARIO IS POSSIBLE. A PREPONDERANCE OF THE MODEL WIND GUIDANCE IS SOUTHEAST...SO HAVE LEANED IN THAT DIRECTION AFT 13Z. STILL...SPEEDS MOSTLY 7KTS OR LESS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. LOW CONFIDENCE IN WIND DIR...MEDIUM TO HIGH CONFIDENCE IN WIND SPD THROUGH THE TAF VALID PERIOD. LOW TO MEDIUM CONFIDENCE IN THUNDERSTORM POTENTIAL THU AFTERNOON. EXTENDED AVIATION DISCUSSION... FOR THE REMAINDER OF THE PERIOD...A MOIST UNSTABLE AIR MASS REMAINS ACROSS THE REGION WITH WEAK TRIGGERING MECHANISMS AND DYNAMICS. A FRONTAL SYSTEM WILL APPROACH FROM THE NORTH BY THE WEEKEND...BUT WILL LIKELY REMAIN WELL NORTH OF THE CWA THROUGH SUNDAY. THUS...NO CHANGE IN AIR MASS OR THE OVERALL SYNOPTIC PATTERN IS EXPECTED THROUGH THE PERIOD. EARLY MORNING LOW CLOUDS/FOG AND ASSOCIATED IFR-LIFR CIGS/VSBYS BECOME INCREASINGLY MORE LIKELY THROUGH THE PERIOD...ESPECIALLY FOLLOWING ANY LATE DAY RAINFALL. OTHERWISE...EXPECT MOSTLY VFR-MVFR CIGS OUTSIDE HEAVIER SHOWERS/THUNDERSTORMS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM/SK NEAR TERM...KK/SK SHORT TERM...MBS LONG TERM...MBS AVIATION...PM/RAB/SK

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