814
FXUS61 KRNK 071857
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
257 PM EDT TUE JUL 7 2020
SYNOPSIS
A SLOW MOVING AREA OF LOW PRESSURE WILL PROGRESS FROM THE SOUTHEAST
U.S., NORTHEAST ALONG THE EAST COAST THROUGH THURSDAY NIGHT. FOR
FRIDAY THROUGH MONDAY, A COUPLE OF DISTURBANCES WILL MOVE INTO AND
THROUGH THE REGION FROM THE GREAT LAKES REGION. BOTH OF THESE
PATTERNS WILL PROVIDE FOR MULTIPLE OPPORTUNITIES FOR THE AREA TO HAVE
SHOWERS AND STORMS IN THE FORECAST.
NEAR TERM /THROUGH WEDNESDAY NIGHT/
AS OF 230 PM EDT TUESDAY...
TONIGHT INTO WEDNESDAY WE WILL BE TRACKING AN UPPER LEVEL LOW OVER
THE SOUTHEAST U.S. THAT WILL SLOWLY TRACK NORTHEAST TO OVER THE
COAST OF THE CAROLINAS BY MID-DAY WEDNESDAY. THE COMBINATION OF
DIURNAL HEATING AND INCREASED EASTERLY MOISTURE CONVECTION OFF THE
ATLANTIC ON THE NORTH SIDE OF THE LOW, WILL ALLOW FOR THE
DEVELOPMENT OF SHOWERS AND STORMS. COVERAGE WILL BE GREATEST DURING
THE PEAK HEATING OF THE THIS AFTERNOON AND WEDNESDAY AFTERNOON
THROUGH THE EARLY EVENING OF EACH DAY. GIVEN THE EXPECTED SLOW
MOTION OF ANY SHOWERS AND STORMS THAT DEVELOP, TRAINING OF
CONSECUTIVE CELLS IS POSSIBLE, AND LEAD TO VERY LOCALIZED FLOODING.
GIVEN THE ISOLATED NATURE OF ANY POTENTIAL FLOODING, NO WATCH IS
WARRANTED AT THIS TIME. GIVEN THE STRONG INFLUX OF MOISTURE, DEW
POINTS ARE RUNNING HIGHER THAN NORMAL FOR THIS TIME OF THE YEAR.
THIS WILL ALLOW LOW TEMPERATURES TONIGHT TO LIKEWISE AVERAGE A FEW
DEGREES ABOVE NORMAL. HIGH TEMPERATURES WEDNESDAY WILL BE NEAR
NORMAL FOR THIS TIME OF YEAR.
CONFIDENCE IN THE ABOVE WEATHER SCENARIO IS MODERATE TO HIGH.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
AS OF 155 PM EDT TUESDAY...
THE SUB-TROPICAL LOW PRESSURE CENTER WILL SLOWLY LIFT FROM NEAR THE
CAROLINA COAST WED NIGHT NORTHEASTWARD UP TOWARD THE NEW ENGLAND
COAST BY LATE FRIDAY, THUS OUR REGION WILL REMAIN ON THE WEST SIDE
OF THIS THROUGH THE PERIOD, BUT IT IS NOT CLEAR HOW MUCH INSTABILITY
THERE WILL BE WITH THE LIGHT NORTHEAST FLOW AND DEGREE OF CLOUDINESS
ACROSS THE PIEDMONT AREAS.
THURSDAY MOST MODELS DO BRING AT LEAST SOME LIGHT SHOWER ACTIVITY
INTO THE FAR SOUTHEAST LATE THURSDAY BUT SEEM TO SUGGEST MORE
INSTABILITY THAN EXPECTED GIVEN LIKELY CLOUD COVER. MORE SUNSHINE IS
LIKELY IN MOUNTAINS BUT COULD ALSO BE SOME SUBSIDENCE TRYING TO
SUPPRESS CONVECTION. SOME LIFT ALONG THE RIDGES WITH LIGHT
EASTERLY FLOW MAY BE WHAT IT TAKES TO GET ANY CONVECTION TO
DEVELOP IN THE MOUNTAINS. SO AT THIS TIME STILL EXPECTING
HIGHEST POPS IN THE EAST EVEN THOUGH PROBABLY MAINLY LIGHT RAIN
AMOUNTS AND LIMITED DEEP CONVECTION, WITH MORE LOW TO MID CHANCE
POPS FAR WEST WITH POSSIBLE HEAVIER BUT MORE HIT AND MISS
SHOWERS/STORMS. HOWEVER, WOULD NOT BE SURPRISED IF THIS ENDS UP
BEING A MOSTLY DRY DAY FOR MUCH OF THE WESTERN HALF OF THE
FORECAST AREA WITH SUBSIDENCE WINNING.
BY FRIDAY AS THE LOW PRESSURE SYSTEM MOVES FARTHER UP THE COAST AND
AWAY, SUBSIDENCE AND NORTHEAST FLOW, POSSIBLY ALONG WITH LINGERING
CLOUD COVER COULD KEEP SHOWER AND STORM ACTIVITY TO A MINIMUM IN THE
EAST, BUT IN THE WEST WITH APPROACHING WEAK UPPER TROUGH AND LATE
RETURN OF WEAK WESTERLY FLOW AND RESULTANT CONVERGENCE THERE COULD
BE A BETTER CHANCE FOR SCATTERED SHOWERS AND STORMS FORMING LATE IN
THE DAY. THUS ULTIMATELY WENT HIGHER POPS FAR WEST, WITH
ADMISSION THAT CONFIDENCE IS STILL RELATIVELY LOW GIVEN
UNCERTAINTIES IN HOW QUICKLY THIS LOW WILL MOVE AWAY AND THE
DEGREE TO WHICH LINGERING CLOUD COVER AND BACK-SIDE SUBSIDENCE
COULD INFLUENCE AFTERNOON CONVECTION OR LACK THEREOF. IF THE LOW
SLOWS DOWN, BETTER PRECIP CHANCES COULD BE IN THE FAR NORTHEAST
WITH MINIMAL CHANCES IN THE WEST. MOST LIKELY HIGH TEMPS WILL
BE A BIT WARMER ON FRIDAY COMPARED TO THURSDAY, ESPECIALLY IN
THE EAST, BUT THIS WILL ALSO BE DEPENDENT ON HOW SOON THIS LOW
MOVES ON UP THE COAST.
LONG TERM /SATURDAY THROUGH MONDAY/
AS OF 125 PM EDT TUESDAY...
MOST GUIDANCE IN GOOD AGREEMENT THAT A SERIES OF SHORT WAVE
DISTURBANCES DROPPING IN FROM THE MIDWEST WILL HELP TO MAINTAIN A
WEAK LARGE SCALE TROUGH OVER THE APPALACHIAN REGION THROUGH AT LEAST
EARLY NEXT WEEK. THE FIRST AND WEAKER DISTURBANCE IS MOST LIKELY
OVER THE REGION ON SATURDAY, WITH THE SECOND AND STRONGER
DISTURBANCE DIGGING A DEEPER TROUGH OUT BY MONDAY AND POSSIBLY
LASTING INTO TUESDAY OR BEYOND. EXACT TIMING OF WHEN THESE WILL
RESULT IN THE MOST INSTABILITY GIVEN SLIGHTLY COOLER UPPER LEVELS
AND PERHAPS LOWER-LEVEL MOISTURE ADVECTION WITH MORE OF A SOUTHERLY
OR SW COMPONENT IS STILL UNCERTAIN, BUT THERE IS CURRENT SOME DEGREE
OF CONSENSUS THAT SATURDAY AND THEN MONDAY WOULD HAVE THE BETTER
CHANCES OF WIDER COVERAGE OF AFTERNOON/EVENING SHOWERS AND STORMS.
SUNDAY COULD SEE A RELATIVE BREAK IF BETWEEN WAVES, AND TUESDAY AS
WELL IF TROUGH IS PROGRESSIVE ENOUGH TO PUSH DEEPER MOISTURE EAST.
CONFIDENCE NOT HIGH ENOUGH THIS FAR OUT TO REFLECT ANYTHING LOWER
THAN LOW CHANCE POP VALUES ON THOSE TWO RELATIVE DOWN DAYS, BUT
KEEPING WITH HIGH CHANCE TO LOW LIKELY POPS ON SATURDAY AND MONDAY.
DESPITE WEAK TROUGH OVERHEAD MAX TEMPS EXPECTED TO BE NEAR OR A
LITTLE ABOVE SEASONABLE READINGS BUT WILL DEPEND ON AMOUNT OF CLOUD
COVER AND THUS COULD SEE MONDAY AND TUESDAY ENDING UP A LITTLE
COOLER THAN SATURDAY AND SUNDAY WITH DEEPER TROUGH OVERHEAD AND
PERHAPS MORE CLOUD COVER EARLIER IN THE DAY.
AT THIS ANY THREAT OF SIGNIFICANT OR WIDESPREAD IMPACTS FROM
ANY STORMS APPEARS LOW THROUGH THE SATURDAY TO TUESDAY TIME
FRAME, WITH THE POSSIBLE EXCEPTION ON MONDAY DEPENDING ON HOW
STRONGLY THE TROUGH DIGS AND TIMING OF WHEN ANY SURFACE
BOUNDARY OR EMBEDDED WAVE MOVES THROUGH.
AVIATION /19Z TUESDAY THROUGH SUNDAY/
AS OF 145 PM EDT TUESDAY...
CLOUD COVER IS BOTH ADVECTING NORTHWARD INTO THE REGION, AND
DEVELOPING WITH THE HEATING OF THE DAY. WITH SURFACE DEW POINT
DEPRESSIONS BETWEEN 10 AND 15 DEGREES F, LCL VALUES HAVE BEEN
PLACING NEW DEVELOPED CLOUDS IN THE HIGH END OF MVFR AND LOW END
OF VFR ACROSS THE AREA. ISOLATED SHOWERS WERE ALSO DEVELOPING
OVER OR MOVING INTO THE SOUTHERN PARTS OF THE REGION. ISOLATED
THUNDERSTORMS ARE ALSO POSSIBLE. AS THE AFTERNOON PROGRESSES,
WE EXPECT THE SHOWER ACTIVITY TO EXPAND AND SPREAD NORTHWARD,
AND FOR CEILING HEIGHTS TO INCREASE SLIGHTLY AS THE SURFACE
WARMS AND LCLS INCREASE A BIT.
THIS EVENING AND INTO THE OVERNIGHT, SHOWER AND STORM ACTIVITY
WILL DECREASE, BUT CLOUD COVER WILL REMAIN RATHER ROBUST OVER AT
LEAST THE SOUTHERN THIRD OF THE REGION, WITH DECREASING COVERAGE
HEADING NORTH ACROSS THE FORECAST AREA. WE ARE EXPECTING ANOTHER
NIGHT WITH THE DEVELOPMENT OF IFR/MVFR FOG, ESPECIALLY IN THE
RIVER AND MOUNTAINS VALLEYS, AND ANY LOCATION THAT GETS AT LEAST
A FEW HUNDREDTHS OF AN INCH OF RAIN THIS AFTERNOON OR EVENING.
CEILINGS WILL TREND LOWER THROUGH THE NIGHT INTO THE IFR/MVFR
RANGE FOR MOST OF THE REGION.
FOR WEDNESDAY, WE ARE EXPECTING ADDITIONAL SHOWERS TO DEVELOP OR
MOVE INTO THE AREA IN ASSOCIATION WITH AN AREA OF LOW PRESSURE
THAT WILL BE HEADING SLOWLY NORTHEAST ALONG THE SOUTHEAST COAST
OF THE U.S. CEILINGS WILL IMPROVE TO MVFR OR LOW END VFR BY THE
CONCLUSION OF THE VALID TAF PERIOD, 18Z/2PM WEDNESDAY.
WINDS THROUGH THE FORECAST PERIOD WILL BE MAINLY CALM OR LIGHT
AND VARIABLE.
CONFIDENCE IN THIS AVIATION SCENARIO IS MODERATE.
EXTENDED AVIATION DISCUSSION...
THE SLOW MOVING UPPER LOW ALONG THE EAST COAST WILL HELP
MAINTAIN THE PATTERN OF MAINLY DIURNAL SHOWERS AND STORMS ACROSS
THE REGION THROUGH AT LEAST THURSDAY OR THURSDAY NIGHT. POCKETS
OF SUB-VFR CONDITIONS ARE EXPECTED, ESPECIALLY UNDER THE HEAVIER
SHOWERS AND STORMS, AND THEN THROUGH THE OVERNIGHT HOURS AS
MOISTURE IS TRAPPED UNDER THE DEVELOPING NOCTURNAL INVERSION.
ADDITIONAL SHOWERS AND STORMS ARE POSSIBLE WILL FRIDAY THROUGH
SUNDAY THANKS TO A SERIES OF NORTHWEST FLOW SHORTWAVE TROUGHS
CROSSING THE AREA. COVERAGE WILL LIKELY BE GREATEST ACROSS THE
MOUNTAINS. CEILINGS HAVE A GREATER POTENTIAL OF BEING SUB-VFR
ACROSS THE MOUNTAINS AS COMPARED TO THE PIEDMONT REGION.
RNK WATCHES/WARNINGS/ADVISORIES
VA...NONE.
NC...NONE.
WV...NONE.
SYNOPSIS...DS
NEAR TERM...DS
SHORT TERM...SK
LONG TERM...SK
AVIATION...DS
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