641
FXUS61 KRNK 240512
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
112 AM EDT THU JUL 24 2008
SYNOPSIS
A COLD FRONT WILL CONTINUE TO SWEEP EAST THROUGH THE REGION
OVERNIGHT. COOLER AND DRIER AIR IS EXPECTED TO OVERSPREAD THE
REGION THURSDAY AS HIGH PRESSURE BUILDS IN OVER THE OHIO VALLEY.
THE CHANCE OF RAIN WILL RETURN TO THE REGION BY FRIDAY NIGHT AND
WILL CONTINUE THROUGH THE REST OF THE WEEKEND.
NEAR TERM /UNTIL 6 AM THIS MORNING/
SENDING A QUICK UPDATE TO REMOVE THE GOING SVR WATCH 739 AND LOWER
POPS OVER THE WEST AS THE ACTUAL COLD FRONT EDGES ACROSS THE
MOUNTAINS. THINK COULD SEE ANOTHER COUPLE HOURS OF HEAVY RAIN
PRODUCING SHRA/TSRA OUT EAST BEFORE LOSS OF HEATING CAUSES THE
CONVECTION TO FINALLY WEAKEN. TWEAKED TEMPS A BIT AS WELL OTRW
MAIN UPDATE AT THIS POINT TO REMOVE THE SVR MENTION.
WATER VAPOR SHOWS A VERY STRONG SHORT WAVE FOR THE END OF
JULY...DEEPENING THE TROUGH IN THE EAST AND PUSHING A SFC COLD
FRONT SOUTHEASTWARD ACROSS WESTERN WV...EXTREME EASTERN KY AND
EASTERN TN. THERE IS A LINE OF SHOWERS/SCT TSTMS AHEAD OF THE
FRONT MOVG INTO THE WESTERN CWA AT THIS TIME. THE AIRMASS IS
MODERATELY UNSTABLE...WITH CAPES OF AROUND 1500 J/KG. SHEAR IS
INCREASING AS THE SHORT WAVE APPROACHES. WEST WIND SHAVE BECOME
LIGHT AHEAD OF THE LINE...AND HAVE BACKED TO THE SOUTH OR
SOUTHWEST EAST OF THE BLUE RIDGE. DEWPOINTS REMAIN IN THE MID 60S
TO AROUND 70. I SEE NO REASON WHY THE THE LINE WILL NOT CONTINUE
MOVING EAST...AND AS THE SHORT WAVE ROUNDS THE BASE OF THE TROUGH
THIS EVENING IT THE FRONT BECOMES MORE PARALLEL TO THE UPPER FLOW
AND SHOULD SLOW. THIS WILL OCCUR IN THE NC/VA PIEDMONT...CLOSE TO
THE EASTERN CWA. FOR NOW...HAVE KEPT THE HEAVY RAIN...GUSTY WINDS
AND FREQUENT LIGHTNING WORDING THROUGH THE EVENING OUT THAT WAY.
FFG IS HIGH ENOUGH THAT WE DO NOT THINK A FLASH FLOOD WATCH IS
NEEDED. THERE IS A POTENTIAL FOR VERY HEAVY RAIN ACROSS THE
PIEDMONT THOUGH. SEVERE THREAT WILL LAST THROUGH THE EVENING...BUT
DECREASING WEST TO EAST...AS WELL. STAYED CLOSE TO MAV GUIDANCE
LOWS- JUST A LITTLE WARMER IN THE EAST WHERE THE FRONT WILL SLOW
AND CLOUD COVER WILL LINGER THE LONGEST.
SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/
BY 12Z THURSDAY MORNING HIGH PRESSURE WILL BE CENTERED OVER
INDIANA AND COLD FRONT WILL BE FAR ENOUGH EAST THAT DRIER AND MORE
STABLE AIR WILL BE COMING INTO THE COUNTY WARNING AREA. 850 MB
TEMPERATURES DROPS SLIGHTLY IN THE MORNING BUT THEN START
RECOVERING THURSDAY NIGHT AND FRIDAY. STAYED CLOSE TO A BLEND OF
MAV/MET GUIDANCE...WITH TYPICAL ADJUSTMENTS FOR MODEL BIAS AT LWB.
BY FRIDAY AFTERNOON LOW LEVEL WINDS HAVE COME BACK AROUND TO THE
SOUTHWEST. THIS WILL HELP INCREASE THE INSTABILITY AHEAD OF THE
REMNANTS OF AN MCS THAT WILL BE CROSSING FROM THE MID MISSISSIPPI
VALLEY INTO ILLINOIS/INDIANA/KENTUCKY/TENNESSEE BY FRIDAY MORNING.
BY FRIDAY AFTERNOON AND EVENING THE OUTFLOW OR ANY CONVECTIVELY
INDUCED VORTICITY FROM THIS FEATURE WILL BE CLOSE ENOUGH TO THE
WESTERN COUNTY WARNING AREA TO KEEP A CHANCE OF RAIN IN THE
FORECAST.
NO REAL ORGANIZED SYNOPTIC SCALE SUPPORT EXPECTED ON SATURDAY...JUST
TYPICAL SCATTERED AIRMASS TYPE THUNDERSTORMS.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
LONG WAVE PATTERN STILL SHOWING AN UPPER RIDGE IN THE CENTRAL
UNITED STATES WITH A TROF IN THE EAST. HPC IS FAVORING A SLOWER
FRONTAL PASSAGE SIMILAR TO THE ECMWF WHICH HAS THE FRONT COMING
THROUGH OUR FORECAST AREA SUNDAY AND MONDAY. HAVE KEPT
TEMPERATURES...ESPECIALLY OVERNIGHT LOWS CLOSER TO THE WARMER
GUIDANCE NUMBERS AHEAD OF THE FRONT. HAVE ALSO GRADUALLY BROUGHT
IN DRY WEATHER BEHIND THE FRONT ON TUESDAY AND WEDNESDAY.
AVIATION /06Z THURSDAY THROUGH MONDAY/
DEW POINT FRONT SLOW TO MOVE THROUGH THE AREA OVERNIGHT AND WITH
CLEARING SKIES AND SATURATED GROUND...FOG DEVELOPMENT IS LIKELY IN
MOUNTAIN VALLEYS AND PIEDMONT SITES. MVFR FOG COULD BE WIDESPREAD
ACROSS THE AREA WITH IFR/LIFR CONDITIONS IN MOUNTAIN
VALLEYS...PARTICULARLY LWB. VFR CONDITIONS ARE EXPECTED AFTER
SUNRISE WITH NORTHWESTERLY WIND...POSSIBLY AS HIGH AS 10 KNOTS.
SERIES OF SHORT WAVE TROUGHS ARE EXPECTED TO PASS EAST THROUGH THE
SOUTHERN MID ATLANTIC REGION LATER FRIDAY AND INTO THE
WEEKEND...EACH OF WHICH WILL REINTRODUCE THE THREAT OF WIDELY
SCATTERED SHOWERS OR THUNDERSTORMS ALONG WITH LOCALIZED MAINLY MVFR
RESTRICTIONS TO VISIBILITY AND/OR CEILING.
OTHERWISE...EXPECT TO SEE GENERAL VFR CONDITIONS TO PREVAIL FOR MOST
OF THE TIME AT ALL TERMINAL FORECAST SITES FROM TODAY THROUGH THE
UPCOMING WEEKEND.
RNK WATCHES/WARNINGS/ADVISORIES
VA...NONE.
NC...NONE.
WV...NONE.
SYNOPSIS...JH/WERT
NEAR TERM...JH/JJ
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...RCS
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