975
FXUS61 KLWX 170748
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
348 AM EDT THU SEP 17 2026
WHAT HAS CHANGED
MODELS HAVE TRENDED EASTWARD WITH STORM COVERAGE TODAY WHICH
COULD BRING THIS ACTIVITY TO NEAR I-95 BY THE 4-9 PM TIME
PERIOD. THE LACK OF WIND SHEAR AND STORM ORGANIZATION SHOULD
LIMIT ANY SEVERE WEATHER POTENTIAL. UNCERTAINTY REMAINS HIGH FOR
THE SUNDAY INTO EARLY NEXT WEEK PERIOD GIVEN THE POSITION OF A
MEANDERING BOUNDARY WILL IMPACT THE TEMPERATURE AND
PRECIPITATION FORECAST.
KEY MESSAGES
- 1) WARM AND HUMID, WITH THUNDERSTORM CHANCES TODAY BEFORE
TURNING COOLER INTO THE FIRST HALF OF THE WEEKEND.
- 2) UNSETTLED WEATHER CONDITIONS RETURN AGAIN SUNDAY AND INTO
NEXT WEEK.
DISCUSSION
KEY MESSAGE 1...WARM AND HUMID, WITH THUNDERSTORM CHANCES TODAY
BEFORE TURNING COOLER INTO THE FIRST HALF OF THE WEEKEND.
AS CANADIAN HIGH PRESSURE HAS EDGED TOWARD THE ATLANTIC
COASTLINE, RETURN FLOW AROUND THE WEST SIDE OF THIS ANTICYCLONE
HAS YIELDED A MILDER AND MORE MOISTURE-LADEN AIR MASS. RELATIVE
TO 24 HOURS, CURRENT TEMPERATURES AND DEW POINTS HAVE INCREASED
BY ABOUT 8 TO 12 DEGREES. CONSEQUENTLY, THIS PLACES 07Z/3 AM
TEMPERATURES IN THE MID 60S TO LOW 70S, WITH DEW POINTS MAINLY
RANGING BETWEEN 62 AND 68 DEGREES. A SOUTHEASTERLY ONSHORE COMPONENT
TO THE WIND FIELDS HAS LED TO THE DEVELOPMENT OF A MID-LEVEL
CLOUD DECK ALONG/EAST OF I-95. OFF TO THE WEST, SCATTERED
SHOWERS CONTINUE TO CHURN EASTWARD ACROSS EASTERN OHIO INTO
WESTERN PENNSYLVANIA. LIKE MUCH OF THE LAST 3 TO 6 HOURS, ANY
APPROACHING SHOWERS QUICKLY WEAKEN GIVEN THE NOTABLE CONVECTIVE
INHIBITION (CIN) AT AROUND 50 TO 100 J/KG. AS A RESULT, WILL
KEEP ONLY ISOLATED SHOWERS IN THE FORECAST THROUGH DAYBREAK
ACROSS WESTERN MARYLAND.
UNLIKE PREVIOUS DAYS, DIURNAL SHOWERS AND THUNDERSTORMS RETURN
TO THE PICTURE. THE CURRENT PLAYERS ARE: (1) AN EXPANSIVE AND
ANOMALOUS MID/UPPER RIDGE STRETCHING ACROSS SOUTHERN U.S./GULF
COAST UP INTO THE OHIO VALLEY AND MID-ATLANTIC STATES, (2) A
SHARPENING TROUGH CROSSING WESTERN ONTARIO, AND (3) AN AREA OF
DISTURBED WEATHER JUST NORTH OF THE BAHAMAS. IN TIME, THE HIGH-
LATITUDE TROUGH IS EXPECTED TO ERODE THE NORTHERN EXTENT OF THE
RIDGE. ALTHOUGH HEIGHT ANOMALIES REMAIN AROUND 1.5 TO 2 SIGMA
ABOVE MID-SEPTEMBER CLIMATOLOGY, THE SUBTLE HEIGHT FALLS SHOULD
BE ENOUGH TO SUPPORT INCREASED LIFT THIS AFTERNOON. THIS SHIFT
IN THE SYNOPTIC PATTERN ALLOWS A STALLED FRONT ALONG I-70 IN
OHIO/INDIANA TO PUSH SOUTHEASTWARD LATER TODAY. THE COLD FRONT
IS NOT EXPECTED TO CROSS THE ENTIRE REGION UNTIL LATE TONIGHT
INTO EARLY FRIDAY MORNING. THUS, THE PRE-FRONTAL AIR MASS WILL
SUPPORT SCATTERED CONVECTION THIS AFTERNOON AND EVENING.
WITH HIGH TEMPERATURES RISING INTO THE MID 80S TO LOW 90S,
COUPLED WITH DEW POINTS REACHING THE UPPER 60S, AROUND 1,500 TO
2,000 J/KG OF SURFACE-BASED CAPE DEVELOPS. DEEP-LAYER SHEAR IS
SOMEWHAT MEAGER, GENERALLY AVERAGING AROUND 15 TO 20 KNOTS.
HOWEVER, FORECAST SOUNDINGS DO SHOW SOME MODEST DOWNDRAFT CAPE
AROUND 500 TO 700 J/KG. THIS WOULD BE ENOUGH TO PRODUCE SPOTTY
GUSTY WINDS IN ANY MORE ROBUST THUNDERSTORM. ALTHOUGH LOW-LEVEL
LAPSE RATES SIT IN THE 8 TO 8.5 C/KM RANGE, MID-LEVEL LAPSE
RATES ARE WEAK WHICH CASTS A DOUBT ON HOW TALL ANY STORM WILL
GET. CONVECTION IS EXPECTED TO FORM OFF THE HIGHER TERRAIN
BEFORE PUSHING TOWARD THE I-95 CORRIDOR DURING THE 4-9 PM
TIMEFRAME. SHOWER CHANCES SHOULD DIMINISH BY A COUPLE HOURS
AFTER DARK GIVEN THE LOSS OF INSTABILITY.
THE COLD FRONT SWEEPS THROUGH OVERNIGHT BEFORE REACHING THE
NORTHERN NECK OF VIRGINIA BY MIDDAY FRIDAY. WITH SOME RESIDUAL
FORCING CROSSING THE CENTRAL VIRGINIA PIEDMONT BACK INTO THE
POTOMAC HIGHLANDS, SOME AFTERNOON SHOWERS AND THUNDERSTORMS ARE
POSSIBLE. OVERALL, FORECAST HIGHS WILL BE IN THE UPPER 70S TO
MID 80S, WITH LOW/MID 70S FOR MOUNTAIN LOCALES. WINDS WILL
MAINLY BE OUT OF THE NORTH WITH GUSTS UP TO 15 TO 20 MPH. A
COOLER NIGHT LIES AHEAD AS HIGH PRESSURE CROSSES SOUTHERN QUEBEC
INTO NEW ENGLAND. FRIDAY NIGHT'S LOWS SHOULD BE IN THE UPPER 50S
TO MID 60S. THE INFLUENCE OF THIS RIDGE FAVORS NEAR AVERAGE
TEMPERATURES TO START THE WEEKEND ON SATURDAY. ALTHOUGH SKIES
SHOULD BE MOSTLY CLOUDY, IT IS A MAINLY DRY FORECAST WITH HIGHS
IN THE 70S TO LOW 80S WITH A REDUCTION IN HUMIDITY.
KEY MESSAGE 2...UNSETTLED WEATHER CONDITIONS RETURN AGAIN SUNDAY
AND INTO NEXT WEEK.
FROM SUNDAY AND INTO NEXT WEEK, MODEL GUIDENCE POINTS TO MORE
UNSETTLED WEATHER, AS A PERSISTENT UPPER RIDGE AXIS PUSHES TOWARDS
THE DEEP SOUTH. THIS ALLOWS MULTIPLE UPPER-LEVEL DISTURBANCES TO
MOVE ACROSS THE MID-ATLANTIC FROM THE GREAT PLAINS, DRIVING DAILY
CHANCES FOR SHOWERS AND THUNDERSTORMS. LONG-TERM ENEMBLE MODELS SHOW
A WIDE RANGE OF POSSIBILITIES REGUARDING THE TIMING AND LOCATION OF
THESE DISTURBANCES. WHILE WIDESPREAD CHANCES FOR SHOWERS AND
THUNDERSTORMS EXIST, THE EXACT TIMING, COVERAGE, AND NATURE OF THESE
STORMS REMAINS QUITE UNCERTAIN. IT WILL INTERESTING TO WATCH THE
EVOLUTION OF THESE DISTURBANCES IN THE COMING MODEL RUNS.
AVIATION /06Z THURSDAY THROUGH MONDAY/
CANADIAN HIGH PRESSURE HAS BEGUN TO PULL JUST OFF THE ATLANTIC
COAST WHICH HAS RESULTED IN A SHIFT TO LIGHT SOUTH TO
SOUTHEASTERLY WINDS. SOME SHOWERS AND THUNDERSTORMS EMERGE OFF
THE HIGHER TERRAIN THIS AFTERNOON. THE THREAT FOR THUNDER DOES
DROP OFF WITH EASTWARD EXTENT OF THESE STORMS. CONSEQUENTLY,
WILL ONLY MENTION 4SM SHRA WITHIN PROB30 GROUPS FOR LATE THIS
AFTERNOON INTO THE EARLY EVENING. ANY RESTRICTIONS SHOULD BE
LIMITED TO SUCH SHOWERS BEFORE VFR CONDITIONS RETURN INTO
TONIGHT.
WINDS SHIFT TO NORTHERLY ON FRIDAY BEHIND AN EARLY MORNING COLD
FRONT. AFTERNOON GUSTS COULD REACH 15 TO 20 KNOTS DEPENDING ON
THE CALIBER OF BOUNDARY LAYER MIXING. SOME SHOWERS OVER CENTRAL
VIRGINIA MAY IMPACT KCHO, BUT CONFIDENCE IS LOW AT THIS TIME. AS
HIGH PRESSURE PASSES OFF TO THE NORTH, WINDS TURN EAST TO
SOUTHEASTERLY ON SATURDAY, BUT WITH CONTINUED VFR CONDITIONS.
SOUTHERLY WINDS ON SUNDAY WITH GUSTS UP TO 15-25 KNOTS ARE
POSSIBLE. IN GENERAL, EXPECT PREDOMINANTLY VFR CONDITIONS TO
PERSIST, BUT FLIGHT CONDITIONS COULD DETERIORATE AS SHOWER AND
THUNDERSTORM POTENTIAL INCREASE LATE IN THE WEEKEND AND INTO
EARLY NEXT WEEK. WEATHER CONDITIONS EARLY NEXT WEEK REMAIN
UNCERTAIN.
MARINE
WITH CANADIAN HIGH PRESSURE EDGING OFF THE ATLANTIC COAST, A
RETURN SOUTH TO SOUTHEASTERLY FLOW IS EVIDENT IN MARINE
OBSERVATIONS THIS MORNING. AHEAD OF THE COLD FRONT MOVING IN
FROM THE OHIO VALLEY, A FURTHER UPTICK IN THESE SOUTH TO
SOUTHEASTERLY WINDS IS POSSIBLE DURING THE AFTERNOON/EVENING
HOURS. THIS MAY EVEN NEAR SMALL CRAFT ADVISORY LEVELS,
ESPECIALLY ACROSS THE CHESAPEAKE BAY, WHICH MAY REQUIRE ISSUING
SUCH PRODUCTS. A FEW STORMS COULD REACH THE MARINE WATERS, BUT
CONFIDENCE IS LOW WHETHER THESE WOULD NECESSITATE SPECIAL MARINE
WARNINGS.
WINDS SHIFT TO NORTHERLY ON FRIDAY MORNING BEHIND THE COLD
FRONT. SOME NORTHERLY CHANNELING EFFECTS ARE POSSIBLE ON FRIDAY
MORNING INTO THE AFTERNOON DUE TO THE FRONTAL SURGE. SMALL CRAFT
ADVISORIES MAY BE NEEDED FOR SUCH AN EVOLUTION. AS HIGH PRESSURE
PASSES BY TO THE NORTH, WINDS SHIFT FROM NORTHEASTERLY TO EAST-
SOUTHEASTERLY ON SATURDAY. THIS COULD BRING A FEW GUSTS TO NEAR
20 KNOTS WHICH COULD APPROACH ADVISORY LEVELS.
SOUTHERLY WINDS ON SUNDAY WITH GUSTS OVER THE WATERS MEETING OR
SURPASING SCA LEVELS ARE POSSIBLE THROUGH MONDAY. WEATHER CONDITIONS
EARLY NEXT WEEK REMAIN UNCERTAIN.
TIDES/COASTAL FLOODING
WITH WINDS REMAINING OUT OF THE SOUTH TO SOUTHEASTERLY DIRECTION,
THIS FLOW REGIME HAS KEPT TIDAL ANOMALIES AROUND 0.50 TO 0.75
FEET. THIS HAS BEEN ENOUGH TO PUSH A FEW OF THE MORE SENSITIVE
LOCATIONS INTO THE ACTION STAGE. UNTIL THE COLD FRONT MOVES
THROUGH EARLY FRIDAY, WATER LEVELS WILL REMAIN SOMEWHAT
ELEVATED. ALTHOUGH NO TIDAL SITE IS SHOWN TO EXPERIENCE ANY
COASTAL FLOODING, IT WILL NEED TO BE MONITORED. THIS IS
PARTICULARLY THE CASE AT ANNAPOLIS, ESPECIALLY DURING THE HIGHER
OF THE TWO ASTRONOMICAL HIGH TIDES. EXPECT ANOMALIES TO DROP ON
FRIDAY INTO SATURDAY BEHIND THE MENTIONED COLD FRONT.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
DISCUSSION...BRO/KVH
AVIATION...BRO/KVH
MARINE...BRO/KVH
TIDES/COASTAL FLOODING...BRO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page