129
FXUS61 KLWX 211829
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
229 PM EDT MON SEP 21 2026
WHAT HAS CHANGED
A SOLID LINE OF THUNDERSTORMS HAS DEVELOPED FROM NEAR CANAAN
VALLEY SOUTH TO GREENBRIER COUNTY IN WEST VIRGINIA AS OF 2 PM.
THIS LINE IS EXPECTED TO MOVE EAST AND WEAKEN WHILE CROSSING THE
MOUNTAINS THIS AFTERNOON. MEANWHILE, HAVE EXPANDED THE SMALL
CRAFT ADVISORY TO INCLUDE ALL ZONES STARTING AT 6 PM TONIGHT.
KEY MESSAGES
- 1) CLOUDY, DAMP, AND COOL THROUGH AT LEAST MID WEEK.
- 2) DRY CONDITIONS RETURN LATER THIS WEEK AND INTO THE WEEKEND.
DISCUSSION
KEY MESSAGE 1...CLOUDY, DAMP, AND COOL THROUGH AT LEAST MID WEEK.
A LINE OF THUNDERSTORMS CROSSING THE APPALACHIANS WILL RUN OUT
OF SBCAPE SHORTLY, BUT WILL HAVE SOME ELEVATED (MUCAPE)
INSTABILITY TO WORK WITH AS IT PROGRESSES DOWN THE I-64
CORRIDOR. THIS WILL BE ENOUGH FOR SOME DOWNPOURS AND LIGHTNING,
WITH ANY GUSTY WIND POTENTIAL LIKELY LIMITED TO 45 MPH OR LESS
AT THE HIGHER ELEVATIONS. SOME REPEAT THUNDERSTORM ACTIVITY IS
POSSIBLE WHERE INSTABILITY LINGERS NEAR THE MOUNTAINS INTO
TONIGHT WHICH COULD RESULT IN AN ISOLATED FLOOD THREAT.
CONFIDENCE WAS TOO LOW FOR A WATCH AS OF MID AFTERNOON, BUT WILL
MONITOR AS THE EVENING PROGRESSES.
OTHERWISE, HIGH PRESSURE ALREADY IN PLACE TO OUR NORTH ACROSS
SOUTHERN QUEBEC WILL RAPIDLY STRENGTHEN TO NEAR 1040 HPA BY
TUESDAY NIGHT. AS THIS OCCURS, NORTHEASTERLY FLOW WILL
STRENGTHEN AND THE CAD WEDGE IN PLACE TO THE EAST OF THE
APPALACHIANS WILL STRENGTHEN. LARGE SCALE FORCING FOR ASCENT
WILL ALSO GRADUALLY INCREASE FROM WEST TO EAST TONIGHT INTO
TUESDAY AS A SHORTWAVE TROUGH AND EMBEDDED UPPER LOW APPROACH
FROM THE OHIO VALLEY. AS LARGE SCALE FORCING FOR ASCENT
INCREASES, THE COVERAGE OF SHOWERS WILL INCREASE SUBSTANTIALLY
THROUGH TONIGHT, AND LIKELY PERSIST AT TIMES THROUGH WEDNESDAY
MORNING. THE PRECIPITATION MAY EVEN RESEMBLE MORE OF A
CONTINUOUS STRATIFORM RAIN SHIELD AS OPPOSED TO SHOWERS AS THE
CAD STRENGTHENS BY LATER TONIGHT.
THE FLOW PATTERN ACROSS THE CONUS OVER THE NEXT COUPLE DAYS WILL
BE EXTREMELY COMPLEX, WITH A SPLIT FLOW PATTERN AND A CLOSED
UPPER-LEVEL RIDGE BUILDING TO THE NORTH OF THE UPPER LOW OVER
THE OHIO VALLEY. SO WHILE THE BIG PICTURE OF THE FORECAST
TONIGHT THROUGH WEDNESDAY HAS HIGH CONFIDENCE (LOW CLOUDS, COOL,
AND RAINY), THERE IS STILL SOME FORECAST UNCERTAINTY REGARDING
THE FINER SCALE DETAILS. A FEW MODEL SOLUTIONS ATTEMPT TO
PRODUCE SEVERAL INCHES OF RAINFALL OVER LOCALIZED AREAS AS WE
BECOME POSITIONED IN THE RIGHT ENTRANCE REGION OF A STRONG JET
STREAK DEVELOPING OFF TO OUR NORTH AND EAST, BUT THERE IS LOTS
OF MODEL TO MODEL INCONSISTENCY AS TO IF THAT WILL OCCUR AND
WHERE. AS OF NOW, THE MOST LIKELY SCENARIO APPEARS TO BE FOR
MOST OF THE REGION TO RECEIVE 1-2 INCHES OF RAINFALL SPREAD OUT
OVER A PROLONGED PERIOD TIME TONIGHT THROUGH WEDNESDAY MORNING.
IF THIS WERE TO OCCUR, THE RAINFALL WOULD BE BENEFICIAL IN
NATURE GIVEN THE ONGOING DROUGHT CONDITIONS. HOWEVER, IF THE
SOLUTIONS THAT PRODUCE ISOLATED TOTALS OF 3-6 INCHES WERE TO
PLAY OUT, THERE COULD BE LOCALIZED ISSUES WITH FLOODING. EVEN IF
THE SOLUTION WITH HIGHER END TOTALS PLAYS OUT, INSTANTANEOUS
RAINFALL RATES WON'T BE OVERLY HIGH GIVEN THE LACK OF
INSTABILITY, SO IT WOULD BE MORE OF A PROLONGED SOAKING RAINFALL
LEADING TO AREAL FLOODING, AS OPPOSED TO THUNDERSTORMS
PRODUCING FLASH FLOODING. WE'LL CONTINUE TO MONITOR THIS
POTENTIAL AS WE MOVE FORWARD.
EITHER WAY, TUESDAY AND WEDNESDAY WILL FEATURE LOW CLOUDS,
GUSTY NORTHEASTERLY WINDS, AND WELL BELOW NORMAL TEMPERATURES.
TEMPERATURES LIKELY HOLD IN THE 60S ON TUESDAY, AND MAY EVEN
STRUGGLE TO GET OUT OF THE 50S ON WEDNESDAY AS THE CAD WEDGE
REACHES ITS PEAK STRENGTH.
BY THURSDAY, HIGH PRESSURE TO THE NORTH NUDGES SOUTHWARD ENOUGH
TO PUSH DRIER AIR INTO THE REGION AND SHUNT MOST RAIN CHANCES
SOUTH INTO THE CAROLINAS. CLOUD BREAKS LIKELY DEVELOP, THOUGH
TEMPERATURES REMAIN BELOW NORMAL.
KEY MESSAGE 2...DRY CONDITIONS RETURN LATER THIS WEEK AND INTO
THE WEEKEND.
SURFACE HIGH PRESSURE BUILDS NORTHWEST OF THE FORECAST AREA
BEGINNING ON FRIDAY AS A SURFACE LOW PRESSURE TRACKS NORTHWARD OFF
THE EAST COAST. PRIMARILY DRY CONDITIONS ARE EXPECTED, ALTHOUGH
A NEARBY LOW PRESSURE SYSTEM BRINGS INCREASED PRECIPITATION
CHANCES TO THE EASTERN PORTIONS OF THE FORECAST AREA.
UNCERTAINTY REMAINS ON THE TRACK AND TIMING OF THE LOW PRESSURE
SYSTEM, BUT RECENT GUIDANCE HAS IT TRACKING NORTH TOWARDS THE
NORTHEAST AWAY FROM THE MID-ATLANTIC, POSSIBLY MAKING A CYCLONIC
LOOP NEAR LONG ISLAND. THE MOST LIKELY IMPACT FROM THE NEARBY
SYSTEM WILL BE INCREASED WINDS DUE TO THE TIGHT PRESSURE
GRADIENT OVERHEAD. NORTH/NORTHWEST WINDS BLOW AROUND 15-20 MPH
FRIDAY AND SATURDAY BEFORE DECREASING SUNDAY AND INTO THE WORKWEEK.
IN ADDITION TO MAINLY DRY CONDITIONS AND GUSTY WINDS,
TEMPERATURES GRADUALLY WARM EACH DAY. ON FRIDAY, HIGHS WILL BE
IN THE 60S FOR MOST (50S MTNS) WITH OVERNIGHT LOWS DIPPING INTO
THE 40S AND 50S. BY THE END OF THE WEEKEND, HIGH TEMPERATURES
WILL BE IN THE 70S FOR MOST (60S MTNS) WITH MOST STAYING IN THE
50S OVERNIGHT.
AVIATION /18Z MONDAY THROUGH SATURDAY/
CEILINGS WILL VARY BETWEEN MVFR AND VFR INTO THIS EVENING BEFORE
DROPPING MORE READILY TO IFR. AN AREA OF RAIN SHOWERS WILL MOVE
ACROSS THROUGH ABOUT 22Z, WITH EMBEDDED TSRA NEAR KCHO.
GUIDANCE IS IN BETTER AGREEMENT THAT CEILINGS WILL LOWER TO IFR
TONIGHT AS SHOWERS INCREASE IN COVERAGE ACROSS THE AREA. IFR
CEILINGS AND ON AND OFF SHOWERS THEN CONTINUE THROUGH THE DAY
WEDNESDAY. WINDS WILL BE OUT OF THE NORTHEAST THROUGH WEDNESDAY,
AND SHOULD GUST TO AROUND 15-25 KNOTS ON TUESDAY AND WEDNESDAY.
NORTHEAST WINDS ON THURSDAY SHIFT TO NORTH/NORTHWESTERLY ON FRIDAY,
GUSTING 15 TO 20 KNOTS EACH AFTERNOON. ON FRIDAY, METRO TERMINALS
GUST 20 TO 25 KNOTS. VFR CONDITIONS ARE EXPECTED BOTH DAYS UNDER
DRY CONDITIONS.
MARINE
EAST TO NORTHEAST WINDS INCREASE THROUGH MID WEEK, WITH GALES
POSSIBLY MAINLY AROUND SOUTHERN MARYLAND WEDNESDAY INTO
THURSDAY. PERIODS OF RAIN ARE ALSO EXPECTED, WHICH WILL REDUCE
VISIBILITY. PERSISTENT ONSHORE FLOW MAY RESULT IN WAVES AS HIGH
AS 3 TO 6 FEET IN THE WIDER WATERS OF THE CHESAPEAKE BAY OFF
SOUTHERN MARYLAND BY MID WEEK.
NORTHEAST WINDS ON THURSDAY BLOW 15 TO 25 KNOTS OVER THE WATERS WITH
GUSTS UP TO 35 KNOTS POSSIBLE. A GALE WATCH IS IN EFFECT UNTIL
THURSDAY AFTERNOON FOR THE MIDDLE PORTIONS OF THE CHESAPEAKE
BAY OFF SOUTHERN MARYLAND. ON FRIDAY, NORTH/NORTHWEST WINDS
BLOW 20 TO 30 KNOTS OVER THE WATERS WITH GUSTS UP TO 35 KNOTS
POSSIBLE. GALE CONDITIONS ARE POSSIBLE OVER THE SOUTHERN
PORTIONS OF THE WATERS WITH ADDITIONAL WATCHES POSSIBLE.
TIDES/COASTAL FLOODING
TIDES ARE EXPECTED TO SNAP BACK TO THE NORTH, WITH ANOMALIES
RAPIDLY RISING AGAIN LATER TONIGHT THROUGH THE DAY TUESDAY.
ELEVATED TIDE LEVELS ARE THEN EXPECTED THROUGH MUCH OF THE WEEK
AS A STRONG AREA OF HIGH PRESSURE BUILDS TO OUR NORTH, LEADING
TO PERSISTENT ONSHORE FLOW. THE WIND DIRECTION WILL BE CLOSER TO
NORTHEASTERLY RATHER THAN EASTERLY, SO THE TIDAL LEVELS ARE
EXPECTED TO INCREASE WITH SOUTHWARD EXTENT IN THE CHESAPEAKE
BAY. MANY LOCATIONS WILL LIKELY REACH MINOR FLOOD STAGE ON
TUESDAY AND WEDNESDAY, AND ANNAPOLIS COULD COME CLOSE TO
FLOODING TONIGHT AS WELL. MODERATE FLOODING CAN'T BE RULED OUT
AT SOME LOCATIONS, ESPECIALLY AT ANNAPOLIS BY MID WEEK. A
COASTAL LOW IS EXPECTED TO DEVELOP OFFSHORE LATER THIS WEEK,
POTENTIALLY PROLONGING COASTAL FLOOD CONCERNS.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 AM EDT
WEDNESDAY FOR ANZ530>543.
GALE WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT
FOR ANZ533-537-541-542.
GALE WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY AFTERNOON
FOR ANZ534-543.
DISCUSSION...DHOF/KJP/EST
AVIATION...DHOF/KJP/EST
MARINE...DHOF/KJP/EST
TIDES/COASTAL FLOODING...LWX
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