Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 220040 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 840 PM EDT MON JUL 21 2014 .SYNOPSIS... A WEAK WEDGE OF HIGH PRESSURE ALONG THE MID ATLANTIC COAST WILL CONTINUE TO EXTEND INLAND ACROSS THE AREA TONIGHT INTO TUESDAY. EAST TO SOUTHEAST WINDS AROUND THE HIGH WILL COMBINE WITH DEEP MOISTURE LIFTING NORTH WITH A RESIDUAL FRONTAL BOUNDARY TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS INTO TUESDAY EVENING. A STRONGER COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST WEDNESDAY...AND PUSH THROUGH THE AREA THURSDAY...RESULTING IN MORE WIDESPREAD SHOWERS AND STORMS. && .NEAR TERM /THROUGH TUESDAY/... AS OF 840 PM EDT MONDAY... VERY FEW CHANGES WERE MADE TO THE FORECAST. WATER VAPOR SATELLITE SHOWS PSEUDO-TROPICAL MOISTURE ADVANCING NORTH TOWARD OUR REGION AROUND AN UPPER LEVEL LOW ACROSS THE SOUTHEAST U.S. 00Z/22 RNK SOUNDING CONTINUES TO SHOW AN EAST WIND AND MOIST AIRMASS IN THE LOWEST 3K FT AND BUFKIT FORECAST SOUNDINGS SUGGEST MOISTURE DEPTH DEEPENS OVERNIGHT WITH A LOW LEVEL EAST/SOUTHEAST FLOW. THIS WEAK UPSLOPE FLOW WILL LIKELY BRING A RETURN TO LOW CLOUDS/FOG AND EVEN SOME DRIZZLE ALONG THE BLUE RIDGE AS SHOWN BY MANY MESOSCALE MODELS AND SREF. NCEP RAPID REFRESH ENSEMBLE SYSTEM ALSO SUPPORTS THIS SCENARIO WITH LOWERING CEILINGS AND VISIBILITIES OVERNIGHT. AS A RESULT...CONTINUED THE IDEA OF RAMPING UP POPS...ESPECIALLY ALONG THE BLUE RIDGE OVERNIGHT. ALSO CANNOT RULE OUT WIDELY SCATTERED SHOWERS RE-DEVELOPING WITH A WEAK UPPER LEVEL SHORTWAVE LIFTING NORTH FROM NC. OTHERWISE...WITH BOTH THE GFS AND NAM MOS GUIDANCE SHOWING A RECENT STRONG COLD BIAS...KEPT LOW TEMPS ABOVE GUIDANCE VALUES. CUTOFF MID LEVEL LOW OVER THE SE WILL RETROGRADE OFF TO THE WEST ON TUESDAY LEAVING THE FAINT BOUNDARY TO LIFT NORTH INTO THE AREA BEFORE DISSIPATING WITH EVEN HIGHER PWATS AND MORE OF A SOUTHERLY TRAJECTORY LATE IN THE DAY. THIS SUPPORTS GOING WITH MORE DIURNAL COVERAGE OF STORMS THAN SEEN IN THE LAST COUPLE OF DAYS PER HIGHER FORECAST CAPES UNDER MORE INSOLATION. THIS SIMILAR TO THE LATEST GFS OUTPUT WITH BEST LOW LEVEL FOCUS SOUTHERN BLUE RIDGE AND OVER THE SW WHERE THE EDGE OF THE LEFTOVER FRONT WILL PIVOT NORTH INTO THE S/SE FLOW. THUS WILL RUN WITH A PERIOD OF LIKELY POPS THERE AFTER ANY MORNING COVERAGE FADES PER SOME MODEL CONSENSUS. ELSW MOSTLY MID TO HIGH CHANCES GIVEN SO MUCH MOISTURE AROUND BUT LIKELY LIMITED ACROSS THE NORTH/NE BY LINGERING DRY AIR ALOFT AND WEAK SUBSIDENCE. AGAIN WENT CLOSER TO THE SLIGHTLY COOLER MET MOS FOR HIGHS...BUT COULD SEE SOME SPOTS ZOOM CLOSER TO THE WARM MAV VALUES IF MORE SUN OCCURS EARLIER. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 400 PM EDT MONDAY... MODELS REMAIN IN GOOD AGREEMENT ON THE OVERALL SYNOPTIC PATTERN WITH A MAMMOTH (NEAR 600DM) RIDGE BUILDING ACROSS THE INTERMOUNTAIN WESTERN U.S....A SIMILAR RIDGE(NEAR 595DM) BUILDING ACROSS THE WESTERN ATLANTIC...AND AN UPPER TROUGH LINGERING ACROSS THE SOUTHEASTERN CONUS STUCK BETWEEN THE TWO AFOREMENTIONED UPPER RIDGES. THIS PATTERN WILL KEEP THE HOT WEATHER WELL TO OUR WEST. THE PERSISTENT SE CONUS TROUGH WILL DRIFT/RETROGRADE TO THE WEST WITH TIME IN RESPONSE TO THE BUILDING WESTERN ATLANTIC UPPER RIDGE. THIS SYSTEM HAS SOME PSEUDO TROPICAL CHARACTERISTICS WITH PWATS NEAR 2.0 INCHES IN THE ASSOCIATED AIR MASS. AS THIS SPREADS NORTHWEST TUE-WED...EXPECT AN INCREASE IN DEEP CONVECTION...ESPECIALLY ALONG THE EAST FACING SLOPES OF THE BLUE RIDGE FROM NW NC NORTHEASTWARD INTO SOUTHWEST/SOUTH CENTRAL VA. WITH SUCH HIGH PWS AND WEAK STEERING CURRENTS ALOFT...THE THUNDERSTORMS WILL BE VERY EFFICIENT RAIN PRODUCERS AND AS SUCH COULD RESULT IN LOCALIZED POOR DRAINAGE FLOODING. FORTUNATELY...MUCH OF THE CWA IS IN A MILD DROUGHT...SO THE RAINFALL WILL BE WELCOME. BUT IN THE MOUNTAINOUS TERRAIN...AN INCH OR TWO IN AN HOUR CAN BECOME PROBLEMATIC RATHER QUICKLY. ATTM DO NOT ANTICIPATE NEED FOR FLASH FLOOD WATCH DUE TO THE LOCALIZED NATURE OF THE EXPECTED THUNDERSTORMS. HOWEVER...A MENTION OF LOCALIZED HEAVY RAIN IN THE HAZARDOUS WEATHER OUTLOOK IS CERTAINLY WARRANTED. AS FOR A SEVERE THREAT...THE PROBABILITY IS MUCH LOWER THAN THE FLASH FLOOD THREAT DUE TO THE TROPICAL NATURE OF THE AIRMASS AND VERY WEAK WINDS ALOFT. CAN`T TOTALLY RULE OUT AN ISOLD WET DOWNBURST...BUT NOT ENOUGH CONFIDENCE TO EVEN MENTION IN THE HWO AT THIS POINT. BY THURSDAY THE STEERING FLOW INCREASES AS A COLD FRONT MOVES INTO THE REGION FROM THE NORTHWEST. MODELS REMAIN IN GENERALLY GOOD AGREEMENT WITH THE FRONT MOVING THROUGH THE AREA DURING THE DAY. THE EXPECTATION IS FOR THIS FRONT TO INTERACT WITH THE TROPICAL MOISTURE THAT IS ALREADY IN PLACE...RESULTING IN NUMEROUS SHOWERS AND THUNDERSTORMS. AGAIN...THE MAIN CONCERN WITH THIS FRONT WILL BE LOCALIZED HEAVY RAINFALL AS IT INTERACTS WITH THE VERY MOIST AIR MASS IN PLACE ACROSS THE REGION. OVERALL PROGGED INSTABILITY AND SHEAR SUGGEST THAT THE SEVERE THREAT IS MINIMAL AND CURRENTLY SPC DOES NOT HAVE ANY AREAS OUTLOOKED. EVEN SO...USUALLY THE DYNAMICS/BETTER FORCING EVIDENT ALONG A FRONT OFFER AT LEAST A SLIGHT INCREASE IN THE SEVERE THREAT. TEMPERATURES FOR MID WEEK WILL CREEP UP SLIGHTLY PRIOR TO THE FRONTAL PASSAGE. 85H TEMPS ARE PROGGED IN THE +18C RANGE AS 500MB HEIGHTS RISE TOWARD 590DM. HOWEVER...INCREASING MOISTURE CONTENT...ABUNDANT CLOUD COVER...AND SCT-NMRS SHRA/TSRA EACH AFTERNOON SHOULD KEEP TEMPERATURES FROM BECOMING OPPRESSIVELY HOT. HOWEVER...HUMIDITY LEVELS WILL BE NOTABLY HIGHER THAN RECENT DAYS...SO EVEN WITH HIGHS MOSTLY IN THE 80S WEST TO NEAR 90 PIEDMONT...DEWPOINTS OF 65 TO 70 WILL LOWER THE COMFORT FACTOR. WEDNESDAY SHOULD BRING THE WARMEST TEMPERATURES TO THE REGION IN ADVANCE OF THE FRONT...ESPECIALLY ACROSS THE PIEDMONT...WHICH SHOULD SEE A SLIGHT DECREASE IN CONVECTION AT THAT TIME...THUS POTENTIALLY SEEING MAX TEMPS TOUCHING 90 LYH-DAN AND VICINITY. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 445 PM EDT MONDAY... FRONTAL SYSTEM SHOULD SHIFT JUST SOUTH OF THE REGION FRI...ALTHOUGH ALWAYS UNCERTAINTY IN MID-SUMMER REGARDING AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING. WITH STRONG UPPER RIDGE TO THE WEST AND STRONG NW FLOW ALOFT ACROSS OUR REGION AS A RESULT...FEEL IT WILL AT LEAST GET FAR ENOUGH SOUTH OF THE CWA TO ENSURE ONE MOSTLY DRY DAY. HAVE HELD ONTO SLIGHT CHC POPS ACROSS THE FAR SE COUNTIES...MAINLY THE NC COUNTIES...TO ACCOUNT FOR THE SLIGHTLY LESS SOUTHWARD MOVEMENT ADVERTISED BY SOME OF THE MODELS. DRYING AND COOLING BEHIND THE FRONT COMPARED TO THE PAST TWO SUCH EVENTS IS MINOR AND WE SHOULD STILL SEE HIGHS IN THE 80S...70S MOUNTAINS. HUMIDITY LEVELS/DEWPOINTS WILL DROP SLIGHTLY...BUT WITH PWATS STILL NEAR 1.5 INCHES...SIGNIFICANT DRYING IS NOT EXPECTED WITH THIS FRONTAL PASSAGE. FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL CONUS UPPER RIDGE. THERE ARE SEVERAL SUCH STRONG DISTURBANCES NOTED IN THE MODELS DURING THIS TIME FRAME...THE MOST NOTABLE ON SUN...THAT COULD BRING THUNDERSTORMS BACK INTO THE AREA. HAVE RETAINED EXISTING CHC POPS THAT WERE ADVERTISED WITH EARLIER FORECAST PACKAGES...BUT CLEARLY THESE COULD POTENTIALLY BECOME LIKELY AT SOME POINT AS THE DEVELOPMENT OF AN UPSTREAM MCS BECOMES MORE APPARENT. BY EARLY THE FOLLOWING WEEK...MODELS IN GOOD AGREEMENT ON THE UPPER TROUGH REAMPLIFYING ACROSS THE EASTERN CONUS...WHICH SHOULD KEEP CONDITIONS UNSETTLED WITH NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES WHILE THE EXTREME HEAT REMAINS WELL TO OUR WEST AND WELL AWAY FROM OUR PART OF THE COUNTRY. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... AS OF 720 PM EDT MONDAY... AVIATION CONDITIONS WILL AGAIN DETERIORATE TONIGHT...WITH CIGS FORECAST TO LOWER TO IFR CONDITIONS AT ALL TAF SITES EXCEPT BLF. WIDELY SCATTERED SHOWERS...BRINGING LOCALLY HEAVY RAIN WILL WANE THIS EVENING...BUT NOT COMPLETELY DISSIPATE. UPSLOPE FLOW WITH LIGHT SOUTHEAST WINDS TONIGHT WILL HELP LOWER CIGS AND GENERATE AREAS OF -DZ BR ALONG THE BLUE RIDGE. AREAS OF FOG REDUCING VSBYS TO MVFR/IFR LEVELS WILL ALSO BE FOUND ACROSS MUCH OF THE FORECAST AREA OVERNIGHT. WEDGE WILL WEAKEN A BIT MORE ON TUESDAY AS THE LOW LEVEL FLOW TURNS A LITTLE MORE SOUTHERLY PERHAPS ALLOWING LOW CIGS TO IMPROVE A BIT FASTER TO VFR THAN THE LAST COUPLE OF DAYS. HOWEVER ANY BREAKS WILL ONLY LEAD TO QUICKER DEVELOPMENT OF SHRA/TSRA BY TUESDAY AFTERNOON WITH DECENT COVERAGE LIKELY ESPCLY BLUE RIDGE...AND POINTS WEST ON TUESDAY...BUT MAINLY AFTER THE VALID TAF PERIOD. EXTENDED AVIATION DISCUSSION... UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL CUTOFF AND SHIFT WESTWARD INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD FRONT FOR THURSDAY. HOWEVER LEFTOVER DEEP MOISTURE WITH THE OLD FRONT AROUND WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION WEDNESDAY AFTERNOON WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF VFR...THEN PERIODIC MVFR IN CLOUDS/TSRA. A COLD FRONT LOOKS TO PUSH THROUGH ON THURSDAY WITH BETTER COVERAGE OF MVFR/IFR PRODUCING SHOWERS AND STORMS. IMPROVED AVIATION CONDITIONS ARE EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO NO PRECIPITATION INTO SATURDAY. && .EQUIPMENT... AS OF 500 PM EDT MONDAY... KFCX RADAR IS DOWN. TECHNICIANS HAVE ORDERED THE PARTS NEEDED FOR REPAIR. RADAR WILL BE DOWN THROUGH TONIGHT AND AT LEAST PART OF THE DAY ON TUESDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/NF NEAR TERM...JH/PH SHORT TERM...PM/RAB LONG TERM...PM/RAB AVIATION...JH/PH EQUIPMENT...CF/JH

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.