475
FXUS61 KLWX 181404
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1004 AM EDT FRI JUL 18 2025
SYNOPSIS
A STATIONARY FRONT MEANDERS OVER THE AREA TODAY, BEFORE RETURNING
NORTHWARD AS A WARM FRONT ON SATURDAY. A STRONGER COLD FRONT MOVES
THROUGH SUNDAY NIGHT, WITH LOWER RAIN CHANCES AND LOWER HUMIDITY TO
START NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
MID-MORNING UPDATE: NO MAJOR CHANGES HAVE BEEN MADE TO THE
PREVIOUS FORECAST THIS MORNING. CURRENT SATELLITE IMAGERY SHOWS
A BROAD ZONE OF CLOUD COVER EXTENDING FROM NEAR BALTIMORE
WESTWARD THROUGH THE OHIO VALLEY INTO INDIANA. SOME DEEPENING
CONVECTIVE CORES ARE EVIDENT FROM SOUTHEASTERN INDIANA EASTWARD
ACROSS SOUTHERN OHIO AND NORTHERN KENTUCKY INTO WESTERN WEST
VIRGINIA. THESE STORMS ARE DEVELOPING IN THE VICINITY OF A
SURFACE BOUNDARY WHICH EXTENDS WESTWARD ACROSS THE OHIO VALLEY.
THE SAME SURFACE BOUNDARY ARCS SOUTHEASTWARD ACROSS OUR
FORECAST AREA FROM FAR WESTERN MD INTO THE VIRGINIA PIEDMONT,
ALBEIT WITH A BIT WEAKER LOW-LEVEL CONVERGENCE IN THE VICINITY
OF THE FRONT. A MID-LEVEL SHORTWAVE IS ALSO EVIDENT ACROSS
INDIANA/OHIO, AND IS ACTING TO APPLY SOME SYNOPTIC SCALE LIFT
ATOP THE FRONTAL BOUNDARY. COVERAGE OF SHOWERS AND STORMS SHOULD
GRADUALLY INCREASE LATER THIS MORNING INTO THIS AFTERNOON AS
LARGE SCALE ASCENT ASSOCIATED WITH THE MID-LEVEL SHORTWAVE
STARTS TO OVERSPREAD THE STATIONARY BOUNDARY. PREVIOUS
DISCUSSION FOLLOWS...
EARLY MORNING RAP AND OBSERVATIONS ANALYSIS SHOWS A STALLED FRONTAL
BOUNDARY DRAPED ALONG THE PA/MD BORDER, STRETCHING WESTWARD ACROSS
THE OH VALLEY. THIS REGION AND THE MID-ATLANTIC ARE SANDWICHED
BETWEEN THE BERMUDA HIGH (WHICH IS WELL WEST OF ITS NORMAL CLIMO
POSITION IN THE WESTERN ATLANTIC) AND A WEAKER SURFACE HIGH OVER THE
UPPER GREAT LAKES. ABUNDANT HIGH LEVEL CLOUDS THIS MORNING ARE
EXPECTED TO PERSIST ALL DAY, WITH BUILDING LOW LEVEL CLOUDS ONCE
MIXING STARTS SHORTLY AFTER SUNRISE. THIS IS GOING TO KEEP HIGHS
LOWER TODAY, MAINLY IN THE LOW TO MID 80S. PEAK HEAT INDICES REACH
THE MID TO UPPER 90S IN CENTRAL VA.
SOUTHERLY FLOW INTO THE STALLED BOUNDARY CONTINUES TO ADVECT DEEP
TROPICAL MOISTURE INTO THE REGION, SO EXPECT PWATS TO JUMP WELL OVER
2" ONCE AGAIN THIS AFTERNOON. ALOFT, A WELL TIMED SHORTWAVE TROUGH
LOOKS TO MOVE ACROSS OUR AREA DURING PEAK HEATING AND THE MAIN
CONVECTIVE TIME WINDOW THIS AFTERNOON TO EARLY EVENING. MODEST DEEP-
LAYER WESTERLY SHEAR AROUND 30 KNOTS WILL BE ENOUGH TO SUPPORT
ORGANIZED DEEP CONVECTION, ESPECIALLY OVER THE SHENANDOAH VALLEY AND
CENTRAL VA. MORE THAN ENOUGH INSTABILITY IS GOING TO BE PRESENT IN
THIS HOT AND HUMID AIRMASS, WITH SBCAPE VALUES OF 1000-2000 J/KG.
THIS IS WHERE SPC HAS A SLIGHT RISK (LEVEL 2 OF 5) FOR SEVERE STORMS
TODAY, WITH DAMAGING WIND GUSTS AS THE MAIN THREAT. THE THREAT FOR
THUNDERSTORMS REALLY DROPS OFF QUICKLY NORTH/EAST OF THE POTOMAC
RIVER, WITH THE BALTIMORE METRO TO NE MD LIKELY TO STAY CLEAR FOR
THE MOST PART TODAY.
THE MAIN THREAT IS GOING TO BE FLASH FLOODING, WHICH COULD BE VERY
SIGNIFICANT IN PARTS OF THE SHENANDOAH VALLEY. THE TROPICAL AIRMASS
WILL EASILY SUPPORT RAINFALL RATES OF 1-2+" IN 30 MINUTES, WITH
HOURLY RAINFALL RATES OF 3-4" POSSIBLE IN THE HEAVIEST
THUNDERSTORMS. ANY AREA THAT SEES EITHER MULTIPLE ROUNDS OR TRAINING
THUNDERSTORMS IS LIKELY TO EXPERIENCE SOME FLOODING.
PARTICULARLY WORRYING IS THE RRFS ENSEMBLES SHOWING UP TO 40PCT
CHANCE OF SEEING 100YR RI RAINFALL AMOUNTS (WHICH EQUATES TO ROUGHLY
5" OR MORE OF RAIN) IN THE CENTRAL SHENANDOAH VALLEY. THE HREF MAX
QPF ALSO INDICATES THE HIGH-END POTENTIAL OF 4-7" OF RAIN. NOW THESE
EXTREME AMOUNTS WON'T BE WIDESPREAD AND MIGHT NOT OCCUR, BUT THE
POTENTIAL IS DEFINITELY THERE FOR WORST-CASE SCENARIO FLASH
FLOODING. AS A RESULT, A MODERATE RISK OF FLASH FLOODING HAS BEEN
COORDINATED WITH WPC FOR THE CENTRAL SHENANDOAH VALLEY, BLUE RIDGE
MOUNTAINS, AND PORTIONS OF THE CENTRAL VA PIEDMONT. ELSEWHERE, A
SLIGHT RISK OF FLASH FLOODING EXTENDS NORTH/EAST TO AROUND THE
POTOMAC RIVER. A (FLASH) FLOOD WATCH HAS BEEN ISSUED.
SCATTERED SHOWERS AND THUNDERSTORMS COULD LINGER LATE INTO THE
EVENING. SOME CAMS INDICATE OUTFLOW BOUNDARIES GENERATING ADDITIONAL
CONVECTION INTO THE DC METRO AND SOUTHERN MD LATE INTO THE EVENING.
MUGGY CONDITIONS CONTINUE TONIGHT AS TEMPS SETTLE IN THE UPPER 60S
TO MID 70S. LOW CLOUDS AND PATCHY FOG ARE POSSIBLE LATE TONIGHT.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
THE BEGINNING OF A CHANGE IN THE SYNOPTIC PATTERN GETS GOING THIS
WEEKEND, THOUGH WE STILL ARE LOOKING AT WIDESPREAD SHOWERS AND
THUNDERSTORMS EACH AFTERNOON TO EVENING. HOT AHD HUMID CONDITIONS
PERSIST, WITH HIGHS IN THE MID TO UPPER 80S SATURDAY, AND LOW 90S
SUNDAY. HEAT INDICES PEAK ON SUNDAY BETWEEN 98-103.
THE WEAK SURFACE HIGH OVER NY SLIDES OFFSHORE, CAUSING THE BERMUDA
HIGH TO RETREAT FROM ITS EXTENDED POSITION ACROSS THE WESTERN
ATLANTIC OCEAN. THIS CAUSES THE STALLED FRONTAL BOUNDARY OVER OUR
AREA TO LIFT NORTH AS A WARM FRONT. IN THE ZONAL FLOW ALOFT, THE
FIRST OF TWO SHORTWAVES ARRIVES SATURDAY AFTERNOON AND HELPS FUEL
HIGH CHANCES FOR SHOWERS AND THUNDERSTORMS. THE ONE CAVEAT FOR
SATURDAY IS AN OVERALL LACK OF FLOW AND NO STRONG FORCING, WHICH
MEANS LOCAL TERRAIN CIRCULATIONS, BAY/RIVER BREEZES, AND OUTFLOW
BOUNDARIES WILL RULE WHERE CONVECTION ULTIMATELY DEVELOPS.
A STRONGER SHORTWAVE TROUGH ALOFT, ACCOMPANIED BY A SURFACE COLD
FRONT LOOK TO CROSS THE AREA SUNDAY AFTERNOON INTO SUNDAY NIGHT. BY
THAT POINT THERE IS LIKELY TO BE DEEP WESTERLY FLOW IN PLACE, WHICH
SHOULD LIMIT COVERAGE OF CONVECTION SUNDAY. THIS IS EVIDENT BY LOWER
RAIN CHANCES SUNDAY AT 40-60PCT (COMPARED TO SATURDAY 50-80PCT).
BOTH DAYS COULD SEE A SEVERE THUNDERSTORM OR TWO CAPABLE OF
PRODUCING DAMAGING WIND GUSTS, AND THE THREAT FOR FLASH FLOODING DUE
TO VERY HEAVY RAIN RATES. CONSIDERATIONS FOR FLOOD WATCHES WILL BE
LOOKED AT FOR EACH DAY DURING THE EARLY MORNING FORECAST
UPDATES.
LONG TERM /MONDAY THROUGH THURSDAY/
THE MAIN STORY FOR THE PERIOD WILL BE THE SHIFT TO A DRIER PATTERN
AS A MID-LEVEL TROUGH DEPARTS TO THE NORTHEAST AND A STRONG 500MB
RIDGE BUILDS OVER THE SOUTHERN U.S. MONDAY BEGINS WITH THE PASSING
OF A SURFACE COLD FRONT, THAT FOR THE FIRST TIME IN SEVERAL WEEKS,
SHOULD ACTUALLY FULLY MOVE SOUTH OF THE REGION. FOLLOWING THE
CLEARANCE OF THE FRONT, THE LONG TERM APPEARS MOSTLY INFLUENCED BY
SURFACE HIGH PRESSURE OVER THE AREA THAT HELPS TO STIFLE CONVECTION
AND LOWER THE PRECIPITATION FORECAST. IF SHOWERS AND THUNDERSTORMS
WERE TO OCCUR, THE BEST COVERAGE WOULD BE OVER THE MOUNTAINS AND
SHENANDOAH VALLEY, BUT CURRENTLY POPS ARE KEPT BELOW 50%.
AS FAR AS TEMPERATURES ARE CONCERNED, MONDAY SHOULD BE A RELATIVELY
MILD SUMMER DAY WITH HIGH TEMPERATURES ONLY REACHING THE 70S IN THE
MOUNTAINS AND LOW-MID 80S ELSEWHERE. LOW TEMPERATURES TUESDAY
MORNING ACTUALLY LOOK MORE TYPICAL OF EARLY SEPTEMBER, WITH
WIDESPREAD 60S AND SOME OF THE COLDER LOCATIONS DIPPING INTO THE
UPPER 50S. AS THE WEEK PROGRESSES, BOTH HIGH AND LOW TEMPERATURES
WILL WARM BY A FEW DEGREES EACH DAY, REACHING ABOVE-NORMAL LEVELS
AGAIN BY THURSDAY (80S TO 90S HIGHS, 70S LOWS).
A WELCOME CHANGE FROM THE REST OF THE MONTH, FLASH FLOODING AND
SEVERE WEATHER CHANCES APPEAR TO BE NONEXISTENT IN THIS PATTERN AS
PWATS DROP BELOW 1.0" AND CAPE IS SHUNTED SOUTH AND WEST.
AVIATION /13Z FRIDAY THROUGH TUESDAY/
SHOWERS AND THUNDERSTORMS ARE IN THE FORECAST EACH DAY THROUGH THE
WEEKEND, THOUGH IMPACTS TO ANY TERMINAL WILL VARY BY DAY. FOR TODAY,
CHO LOOKS TO HAVE THE BEST OPPORTUNITY FOR IMPACTFUL THUNDERSTORMS
LATE THIS AFTERNOON, THEN ALL TERMINALS COULD BE IMPACTED ON
SATURDAY INTO SUNDAY. ANY THUNDERSTORM MOVING OVER A TERMINAL WILL
RESULT IN BRIEF PERIOD OF SUB-VFR CONDITIONS, ALONG WITH GUSTY WINDS
AND TORRENTIAL RAINFALL.
OUTSIDE OF SHOWER AND THUNDERSTORM ACTIVITY, EXPECT VFR CONDITIONS
TO PREVAIL. PATCHY DENSE FOG IS POSSIBLE EARLY THIS MORNING AROUND
CHO, AND AGAIN TONIGHT AT MOST TERMINALS (THOUGH ESPECIALLY CHO AND
MRB).
PREVAILING VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES NEXT WEEK.
THERE ARE LOW-END CHANCE POPS FOR KCHO ON MONDAY AND TUESDAY
AFTERNOON/EVENINGS, BUT MOST AREAS SHOULD REMAIN DRY. WINDS MONDAY-
THURSDAY WILL BE LIGHT, BELOW 10 KTS. MONDAY AND TUESDAY WILL
FEATURE NORTH AND NORTHEAST WINDS, SHIFTING TO SOUTH AND SOUTHEAST
WEDNESDAY-THURSDAY.
MARINE
VARIABLE WINDS AROUND 5 KNOTS ACROSS THE WATERS TODAY EVENTUALLY
BECOMES MOSTLY SOUTH TO SOUTHWEST AT 5-10 KNOTS TONIGHT THROUGH
SATURDAY. A COLD FRONT MOVES THROUGH SUNDAY NIGHT, THOUGH NO SCA
WINDS ARE EXPECTED THROUGH THE WEEKEND.
DAILY SHOWERS AND THUNDERSTORM ARE IN THE FORECAST TODAY THROUGH THE
ENTIRE WEEKEND, WITH SATURDAY HAVING THE HIGHEST RAIN CHANCES. ANY
THUNDERSTORM WILL POSE A THREAT TO MARINERS DUE TO STRONG WIND GUSTS
AND LIGHTNING STRIKES. SPECIAL MARINE WARNINGS ARE LIKELY NEEDED AT
TIMES EACH AFTERNOON TO EVENING AS THUNDERSTORMS MOVE ACROSS THE
WATERS.
WINDS THROUGH THE PERIOD WILL REMAIN SUB-SCA LEVELS. THE STRONGER
WINDS (10-15 KTS) OCCUR ACROSS THE SOUTHERN CHESAPEAKE AS SOUTHERLY
FLOW TAKES OVER TUESDAY-THURSDAY. SHOWERS AND THUNDERSTORMS ARE NOT
EXPECTED TO AFFECT MARINE AREAS.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...FLOOD WATCH THROUGH THIS EVENING FOR MDZ501-509-510.
VA...FLOOD WATCH THROUGH THIS EVENING FOR VAZ025>031-036>040-503-
504-507-508.
FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH THIS EVENING
FOR VAZ050-051-055-056-501-502-526-527.
WV...FLOOD WATCH THROUGH THIS EVENING FOR WVZ050-055-501>506.
MARINE...NONE.
SYNOPSIS...KRR
NEAR TERM...KJP/KRR
SHORT TERM...KRR
LONG TERM...CPB
AVIATION...CPB/KRR
MARINE...CPB/KRR
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