973
FXUS61 KLWX 121912
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
312 PM EDT SUN JUL 12 2026
WHAT HAS CHANGED
NO MAJOR CHANGES HAVE BEEN MADE TO THE FORECAST THIS AFTERNOON.
WE CONTINUE TO MONITOR SHOWERS AND THUNDERSTORMS CURRENTLY DEVELOPING
ACROSS THE AREA.
KEY MESSAGES
- 1) SHOWERS AND A FEW THUNDERSTORMS ARE EXPECTED THIS AFTERNOON
INTO THIS EVENING.
- 2) HEAT AND HUMIDITY RETURN FOR THE MIDDLE AND SECOND HALF OF
THE WEEK.
- 3) SCATTERED THUNDERSTORM DEVELOPMENT IS ANTICIPATED DURING
THE THE SECOND HALF OF THE WEEK IN A MODERATELY UNSTABLE AND
SHEARED ENVIRONMENT.
DISCUSSION
KEY MESSAGE 1...SHOWERS AND A FEW THUNDERSTORMS ARE EXPECTED
THIS AFTERNOON INTO THIS EVENING.
THE FRONT THAT MOVED THROUGH OVERNIGHT HAS NOW STALLED OUT
ACROSS NORTHERN NC AND SOUTHWESTERN VA. WINDS HAVE TURNED
OUT OF THE EAST TO NORTHEAST TO THE NORTH OF THE FRONT. A WARM,
HUMID AIRMASS REMAINS IN PLACE AT LOW-LEVELS, WITH SURFACE
DEWPOINTS STILL IN THE UPPER 60S AND LOWER 70S. SHOWERS AND
THUNDERSTORMS HAVE STARTED TO POP UP ACROSS THE AREA, WITH THE
GREATEST COVERAGE CURRENTLY FROM DC SOUTHWARD ALONG THE I-95
CORRIDOR, AND THEN WESTWARD INTO CENTRAL VIRGINIA AND THE
CENTRAL SHENANDOAH VALLEY. THE MOST WELL DEVELOPED AREA OF
SHOWERS AND STORMS IS LOCATED OVER THE POTOMAC AT THE MOMENT,
AND WILL CONTINUE TO DRIFT WESTWARD OVER TIME, PRIMARILY
IMPACTING CENTRAL VIRGINIA, AND THEN EVENTUALLY THE CENTRAL
SHENANDOAH VALLEY.
THE 12Z IAD SOUNDING SHOWS NEAR SATURATION UP TO ABOUT 650 HPA,
WITH DRIER AIR IN THE MID TO UPPER LEVELS OF THE ATMOSPHERE. IN
CONTRAST, THE 12Z RNK SOUNDING SHOWS NEAR SATURATION ALL THE WAY
THROUGH THE DEPTH OF THE TROPOSPHERE (HIGHLIGHTING THE MORE
FAVORABLE ENVIRONMENT FOR SHOWERS AND STORMS TO THE SOUTH).
MODEL GUIDANCE ALSO SHOWS THIS GRADIENT IN MID- UPPER LEVEL
MOISTURE FROM NORTH TO SOUTH ACROSS THE FORECAST AREA. THUS FAR,
SHOWERS HAVE PROGRESSED FROM EAST TO WEST WITHIN THE LOW- LEVEL
EASTERLY FLOW. THERE IS A BIT OF WEST TO NORTHWESTERLY FLOW AT
HIGHER LEVELS OF THE ATMOSPHERE, SO IF STORMS WERE TO DEEPEN,
THEY MAY ACTUALLY SLOW DOWN, WITH MOST MODEL SOUNDINGS AND THE
12Z IAD SOUNDING SHOWING LCL-EL MEAN WINDS OF LESS THAN 5 KT.
DEEPER CONVECTION, AND BY PROXY SLOWER STORM MOTIONS, MAY BECOME
MORE FAVORED TO THE SOUTH (ACROSS CENTRAL VIRGINIA AND THE
CENTRAL SHENANDOAH VALLEY), WHERE THE DEEPER MOISTURE MAY
PROMOTE STORMS GROWING TALLER AND TAPPING INTO THE WEST TO
NORTHWESTERLY FLOW ALOFT, WHICH WOULD COUNTER LOW-LEVEL
EASTERLIES AND CREATE SLOWER STORM MOTIONS. THE DEEPER MOISTURE
WOULD ALSO LIMIT COLD POOL DEVELOPMENT AND ASSOCIATED
PROPAGATION COMPARED TO STORMS FURTHER TO THE NORTH. WITH THE
AROUND 1000 J/KG OF MLCAPE, SLOW STORM MOTIONS, AND DEEP WARM
CLOUD LAYERS (AROUND 14K FT) HEAVY RAINFALL SHOULD BE THE
PRIMARY THREAT WITH STORMS TODAY. THERE COULD POTENTIALLY BE AN
ISOLATED INSTANCE OR TWO OF FLASH FLOODING FROM THE CENTRAL
SHENANDOAH VALLEY TO CENTRAL VIRGINIA TODAY, ESPECIALLY IF ANY
STORMS ARE ABLE TO ANCHOR TO HIGHER TERRAIN IN THE LIGHT
EASTERLY UPSLOPE FLOW. HOWEVER, BACKGROUND DROUGHT CONDITIONS
AND RESULTANT HIGH FLASH FLOOD GUIDANCE VALUES COULD POTENTIALLY
BE LIMITING FACTORS. WPC CURRENTLY HAS FAR SOUTHWESTERN
PORTIONS OF THE FORECAST AREA (CHARLOTTESVILLE, STAUNTON AREA)
OUTLOOKED IN A SLIGHT RISK (LEVEL 2 OF 4) FOR EXCESSIVE
RAINFALL, WITH A MARGINAL RISK (LEVEL 1 OF 4) EXTENDING
NORTHEASTWARD TO A LINE ROUGHLY FROM FREDERICKSBURG TO CULPEPER
TO PETERSBURG. CHANCES FOR SHOWERS AND THUNDERSTORMS SHOULD WIND
DOWN LATER THIS EVENING WITH LOSS OF DAYTIME HEATING. PRIMARILY
DRY CONDITIONS ARE EXPECTED OVERNIGHT.
KEY MESSAGE 2...HEAT AND HUMIDITY RETURN FOR THE MIDDLE AND SECOND
HALF OF THE WEEK.
UPPER HIGH CENTERED OVER THE DAKOTAS EARLY IN THE WEEK IS EXPECTED
TO EXPAND EASTWARD CRESTING OVER THE AREA TUE EVENING. THIS WILL
SUPPORT HIGH TEMPERATURES IN THE UPPER 90S, BUT DEWPOINTS WILL NOT
BE TERRIBLY TOO HIGH IN THE 60S. BY THU AND FRI, LOW LEVEL MOISTURE
RETURNS INTO THE AREA WITH DEWPOINTS IN THE UPPER 60S TO NEAR 70
RESULTING IN HEAT INDICES NEAR 100 DEGS WHICH IS STILL BELOW HEAT
ADVISORY CRITERIA. WHILE IT WILL BE HOT, IT WON'T BE AS HOT AS IT
WAS DURING THE FIRST WEEKEND OF JULY.
KEY MESSAGE 3...SCATTERED THUNDERSTORM DEVELOPMENT IS ANTICIPATED
DURING THE THE SECOND HALF OF THE WEEK IN A MODERATELY UNSTABLE AND
SHEARED ENVIRONMENT.
DURING THE SECOND HALF OF THE WEEK, THE UPPER RIDGE CENTERED OVER
THE DAKOTAS EARLY IN THE WEEK WILL BUILD WESTWARD WITH TIME WHILE
THE EASTERN CANADA TROUGH DIGS SOUTHWARD. THIS RESULTS IN MODERATELY
STRONG FLOW ALOFT ACROSS THE AREA WITH THE SYNOPTIC PATTERN BECOMING
FAVORABLE FOR THUNDERSTORM CLUSTERS OR MCSS TO FORM OVER THE UPPER
GREAT LKS AND UPPER MIDWEST TO TRACK SOUTHEASTWARD INTO THE OH
VALLEY AND MID-ATLANTIC STATES. THE EARLIEST WE COULD SEE
THUNDERSTORMS IT SEEMS TO BE THU, BUT WITH HIGHER PROBS OF
THUNDERSTORMS FRI INTO SAT AND LIKELY EXTENDING IT BEYOND THAT.
AVIATION /18Z SUNDAY THROUGH FRIDAY/
PREVAILING VFR CONDITIONS ARE EXPECTED THIS AFTERNOON, BUT THERE
WILL BE SHOWERS AND THUNDERSTORMS SCATTERED ABOUT THE AREA. CHO
STANDS THE GREATEST CHANCE TO SEE IMPACTS FROM SHOWERS AND
STORMS, BUT BRIEF DISRUPTIONS ALSO CAN'T BE RULED OUT AT IAD,
DCA, OR MRB. ANY SHOWERS OR STORMS SHOULD WIND DOWN SHORTLY
AFTER DARK. SOME MVFR CEILINGS OR FOG MAY BE POSSIBLE AT CHO
TONIGHT. THEREAFTER, VFR CONDITIONS ARE EXPECTED OVER THE NEXT
SEVERAL DAYS.
WINDS WILL GENERALLY BE OUT OF THE EAST TODAY, SOUTHEAST
TOMORROW, SOUTH TO SOUTHWEST ON TUESDAY, WEST ON WEDNESDAY, AND
NORTHWEST ON THURSDAY.
MARINE
WINDS WILL REMAIN OUT OF THE EAST THIS AFTERNOON. SCAS ARE IN
EFFECT LATER THIS AFTERNOON THROUGH TONIGHT FOR THE LOWER TIDAL
POTOMAC AND OUR SOUTHERNMOST BAY ZONES. ELSEWHERE, MWSS OR SMWS
MAY BE NEEDED AT TIMES AS SHOWERS AND THUNDERSTORMS MOVE OVER
THE WATERS. ANY SHOWERS OR THUNDERSTORMS SHOULD COME TO AN END
THIS EVENING SHORTLY AFTER SUNSET.
THEREAFTER, GREAT BOATING WEATHER IS EXPECTED MONDAY THROUGH
MID WEEK WITH NO THUNDERSTORM POTENTIAL. WINDS WILL GENERALLY
BE OUT OF THE SOUTHEAST TOMORROW, SOUTH ON TUESDAY, SOUTHWEST ON
WEDNESDAY, AND NORTHWEST ON THURSDAY.
TIDES/COASTAL FLOODING
ELEVATED WATER LEVELS WILL PERSIST FOR THE NEXT COUPLE OF DAYS
WITH MINOR COASTAL FLOODING BECOMING INCREASINGLY LIKELY MONDAY
INTO TUESDAY AS SOUTHERLY FLOW STRENGTHENS.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT MONDAY FOR ANZ534-537-543.
DISCUSSION...LFR/KJP
AVIATION...LFR/KJP
MARINE...LFR/KJP
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