355
FXUS61 KLWX 181337
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
ISSUED BY NATIONAL WEATHER SERVICE STATE COLLEGE PA
937 AM EDT TUE AUG 18 2026
WHAT HAS CHANGED
SOME FOG MAY DEVELOP AT LEAST BRIEFLY EARLY THIS MORNING,
ESPECIALLY IN SHELTERED RIVER VALLEYS. A POP UP SHOWER OR
THUNDERSTORM IS POSSIBLE THIS AFTERNOON INTO EARLY EVENING IN
THE I-64 CORRIDOR TO AROUND SOUTHERN MARYLAND.
KEY MESSAGES
- 1) HIGH PRESSURE BUILDS IN THROUGH MID WEEK.
- 2) DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS RETURN
THURSDAY, THEN CONTINUE FRIDAY THROUGH SUNDAY.
DISCUSSION
KEY MESSAGE 1...HIGH PRESSURE BUILDS IN THROUGH MID WEEK.
LATE THIS MORNING, REGIONAL SATELLITE AND RADAR IMAGERY SHOWED
AN AREA OF ENHANCED/TEXTURED CLOUDINESS AND ISOLATED SHOWERS
COMING OFF THE BLUE RIDGE INTO SOME THE VALLEYS OF WESTERN AND
CENTRAL VA. THIS APPEARS TO BE TIED TO A WEAK MID-LEVEL IMPULSE
IN THE WESTERLY FLOW ALOFT. OVERALL, THE DEPTH OF MOISTURE HAS
DIMINISHED IN THE WAKE OF LAST NIGHT'S COLD FRONTAL PASSAGE, SO
AS THE AFOREMENTIONED SHORT-WAVE TRAVERSES THE REGION INTO EARLY
AFTERNOON, ITS MAIN IMPACT SHOULD BE RESTRICTED TO
ISOLATED/WIDELY SCATTERED SHOWERS AND GARDEN VARIETY
THUNDERSTORMS FOR PORTIONS OF VA AND FAR SOUTHERN MD. OUTSIDE OF
THAT, WE'RE LOOKING AT RAIN-FREE CONDITIONS FOR THE BALANCE OF
THE DAY, WITH SEASONABLE TEMPERATURES RANGING FROM THE 70S OVER
THE HIGHER TERRAIN OF THE ALLEGHENIES, TO THE MID-UPPER 80S
ACROSS THE METROPLEX.
SURFACE HIGH PRESSURE WILL BE THE PRIMARY CONTROLLING FACTOR, AS
IT BUILDS ACROSS THE MID-ATLANTIC INTO WEDNESDAY, WITH DRY
CONDITIONS EXPECTED. A COLD FRONT WILL APPROACH FROM THE GREAT
LAKES, BRINGING AN INCREASING CHANCE OF SHOWERS AND PERHAPS A
THUNDERSTORM BY LATE WEDNESDAY NIGHT.
KEY MESSAGE 2...DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS
RETURN THURSDAY, THEN CONTINUE FRIDAY THROUGH SUNDAY.
ALTHOUGH TIMING REMAINS A BIT UNCERTAIN, A COLD FRONT LOOKS TO
ENTER THE AREA THURSDAY MORNING, THEN SLOWLY CROSS THROUGH
THURSDAY NIGHT. QUESTIONS REGARDING EARLY DAY PRECIP AND CLOUD
COVER LEND TO UNCERTAINTY IN HOW MUCH INSTABILITY BUILDS
THURSDAY AFTERNOON, THOUGH A FEW STRONGER STORMS ARE CERTAINLY
POSSIBLE GIVEN INCREASED FLOW ALOFT AND LIFT ALONG THE FRONT.
MODEL GUIDANCE IS IN RELATIVELY GOOD AGREEMENT THAT THE LONGWAVE
PATTERN ACROSS THE CONUS WILL AMPLIFY SIGNIFICANTLY HEADING INTO
NEXT WEEKEND AS UNSEASONABLY DEEP TROUGHING DIGS ACROSS THE GREAT
LAKES AND OHIO VALLEY. WHILE THERE IS SOME SPREAD WITH RESPECT TO
JUST HOW DEEP THIS TROUGH WILL BE AND ITS EXACT EAST/WEST PLACEMENT,
NEARLY ALL SOLUTIONS PLACE US DOWNSTREAM OF THE TROUGH, WHICH WILL
KEEP US IN SOUTHWESTERLY FLOW ALOFT AND KEEP THE PATTERN ACTIVE.
DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS ARE EXPECTED WITHIN THE
ZONE OF LARGE SCALE ASCENT DOWNSTREAM OF THE LONGWAVE TROUGH
SHARPENING TO OUR WEST. DEPENDING ON HOW MUCH INSTABILITY DEVELOPS,
SOME OF THESE STORMS COULD POTENTIALLY BE ON THE STRONGER SIDE.
TEMPERATURES ARE FORECAST TO RUN SLIGHTLY BELOW NORMAL, WITH HIGHS
IN THE UPPER 70S AND LOW 80S, AND OVERNIGHT LOWS IN THE 60S.
MOST SOLUTIONS HAVE THE LONGWAVE TROUGH MAKING SOME EASTWARD
PROGRESS BY SUNDAY NIGHT INTO MONDAY, WHICH SHOULD RESULT IN A COLD
FRONT PASSING THROUGH. CONTINUED BELOW NORMAL TEMPERATURES AND DRIER
CONDITIONS ARE FORECAST BEHIND THE FRONT FOR MONDAY.
AVIATION /13Z TUESDAY THROUGH SATURDAY/
NW FLOW AS A COLD FRONT CROSSES ALONG WITH SOME MID/HIGH CLOUDS
WILL COMPETE WITH HIGH HUMIDITY FOR THE FORMATION OF SOME FOG
THROUGH EARLY THIS MORNING. THE MOST LIKELY TAF SITE TO SEE FOG
SEEMS TO BE KCHO WHERE RECENT RAIN PLUS MORE DISPLACEMENT FROM
THE LIGHT NW FLOW ASSOCIATED WITH THE APPROACHING COLD FRONT IS.
OTHERWISE, VFR CONDITIONS ARE EXPECTED AT THE TAF SITES THROUGH
MID WEEK (WEDNESDAY). ADDED A PROB30 FOR -SHRA AT KCHO 18-22Z,
THOUGH SOME TS OR SLIGHTLY LATER TIMING ARE POSSIBLE. RAIN MAY
APPROACH THE TAF SITES AHEAD OF A COLD FRONT LATE WEDNESDAY
NIGHT, WITH TS POSSIBLE THURSDAY AFTERNOON AND EVENING. LIGHT
N/NW FLOW IS EXPECTED THROUGH TONIGHT, BECOMING SW TO S
WEDNESDAY INTO WEDNESDAY NIGHT BEFORE POSSIBLY RETURNING TO NW
THURSDAY INTO THURSDAY NIGHT DEPENDING ON THE PLACEMENT OF THE
NEXT COLD FRONT.
PREVAILING VFR CONDITIONS ARE EXPECTED FOR BOTH FRIDAY AND SATURDAY,
BUT SHOWERS OR THUNDERSTORMS COULD LEAD TO TEMPORARY RESTRICTIONS
EITHER DAY. WINDS WILL BE LIGHT OUT OF THE NORTHEAST ON FRIDAY,
BEFORE TURNING OUT OF THE SOUTHEAST ON SATURDAY. THERE IS SOME
UNCERTAINTY IN THE WIND FORECAST DEPENDING ON THE PLACEMENT OF A
NEARBY FRONT AND WAVE(S) OF LOW PRESSURE.
MARINE
LIGHT WINDS ARE EXPECTED THROUGH THE END OF THE WEEK. WINDS
SHIFT TO THEN NORTH/NORTHWESTERLY TODAY BEFORE RETURNING TO
SOUTHERLY BY LATE WEDNESDAY. A FEW ENHANCEMENTS ARE POSSIBLE
ALONG THE CHESAPEAKE BAY DURING ANY OF THESE WIND SHIFTS DUE TO
CHANNELING, BUT PROSPECTS OF ADVISORY CONDITIONS ARE MARGINAL
AT BEST. A POP UP THUNDERSTORM IS POSSIBLE MAINLY SOUTH OF
ANNAPOLIS AND DAHLGREN THIS AFTERNOON OR EARLY EVENING. A COLD
FRONT MAY BRING ADDITIONAL THUNDERSTORMS THURSDAY INTO FRIDAY.
SUB-SCA LEVEL WINDS ARE EXPECTED FOR BOTH FRIDAY AND SATURDAY. WINDS
ARE FORECAST TO BE OUT OF THE NORTHEAST ON FRIDAY, BEFORE TURNING
OUT OF THE SOUTHEAST ON SATURDAY. AN AFTERNOON THUNDERSTORM CAN'T BE
RULED OUT EITHER DAY. THERE IS SOME UNCERTAINTY IN THE WIND
FORECAST DEPENDING ON THE PLACEMENT OF A NEARBY FRONT AND
WAVE(S) OF LOW PRESSURE.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
DISCUSSION...99
AVIATION...
MARINE...
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