771
FXUS61 KLWX 150815
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
415 AM EDT SAT AUG 15 2026
WHAT HAS CHANGED
UPDATED KEY MESSAGE 2 REGARDING THE SEVERE/FLOOD THREAT SUNDAY.
ALSO UPDATED THE AVIATION SECTION AND KEY MESSAGE 1 (FOG).
KEY MESSAGES
- 1) DENSE RIVER VALLEY FOG EARLY THIS MORNING.
- 2) SEVERE THUNDERSTORMS AND SOME INSTANCES OF FLASH FLOODING
ARE POSSIBLE ON SUNDAY.
- 3) SEASONABLY WARM CONDITIONS AND DAILY SHOWER AND
THUNDERSTORM CHANCES ARE EXPECTED THROUGH MONDAY, BEFORE
ANOTHER ROUND OF STORMS ARE POSSIBLE ON THURSDAY.
DISCUSSION
KEY MESSAGE 1...DENSE RIVER VALLEY FOG EARLY THIS MORNING.
A COMBINATION OF CLEARING SKIES, ABUNDANT LOW-LEVEL MOISTURE IN
PART DUE TO RECENT RAIN, AND CALM WINDS IS RESULTING IN AREAS OF
FOG THIS MORNING IN THE RIVER VALLEYS OF WESTERN MD, EASTERN WV
AND INTO THE NORTHERN SHENANDOAH VALLEY IN VA. SOME OF THIS FOG
HAS BECOME DENSE WITH VISIBILITY DOWN TO ONE QUARTER MILE.
THE DENSE FOG ADVISORY HAS BEEN EXPANDED TO INCLUDE THE
NORTHERN SHENANDOAH VALLEY IN VA, MUCH OF EASTERN WV, AND INTO
NORTH-CENTRAL MD GIVEN INCREASING VISIBILITY OBS OF 1/4 MILE OR
LESS BOTH ON AWOS AND TRAFFIC CAMS.
FOG WILL SLOWLY BURN OFF THROUGH MID MORNING.
KEY MESSAGE 2...SEVERE THUNDERSTORMS AND SOME INSTANCES OF
FLASH FLOODING ARE POSSIBLE ON SUNDAY.
OVERNIGHT MODEL GUIDANCE HAS COME INTO A BROAD CONSENSUS
REGARDING THE SYNOPTIC EVOLUTION FOR SUNDAY.
IN THE UPPER LEVELS, A BELT OF SEASONABLY STRONG WESTERLIES
WILL PERSIST FROM THE UPPER GREAT LAKES ACROSS THE SAINT
LAWRENCE VALLEY INTO THE NORTHEAST AND CANADIAN MARITIMES. BROAD
ASCENT ON THE EQUATORWARD SIDE OF THIS JET WILL PERSIST MUCH OF
THE TIME FROM EARLY SUNDAY MORNING THROUGH LATE SUNDAY NIGHT.
MEANWHILE, A PAIR OF MID-LEVEL SHORTWAVES, LIKELY AUGMENTED BY
UPSTREAM CONVECTION OVER THE MIDWEST AND OHIO VALLEY, WILL TRACK
ACROSS THE MID-ATLANTIC ON SUNDAY. ALTHOUGH TIMING REMAINS A
BIT UNCERTAIN, MOST GUIDANCE NOW AGREES ON AN INITIAL WAVE AND
ATTENDANT ENHANCED LIFT/FLOW DURING THE MORNING. THIS INITIAL
WAVE MAY SLOW ON ITS EXIT DURING THE AFTERNOON, ONLY TO BE
FOLLOWED BY ANOTHER STOUT WAVE DURING THE LATE AFTERNOON AND
EVENING. W/NW FLOW IN THE 700-500 HPA LAYER INCREASES TO 30-40
KTS, POSSIBLY HIGHER DEPENDING ON HOW THESE WAVES ARE DEEPENED
BY CONVECTION THAT OCCURS TODAY/TONIGHT UPSTREAM.
IN THE LOW LEVELS, FLOW WILL ALSO INCREASE. THIS WILL ALLOW A
SHARP RISE IN THETA-E, WITH PWS RISING FROM AROUND 1.75" AT 09Z
TO NEAR 2.25" BY 15Z. FURTHER INCREASES ARE PROGGED INTO THE
EVENING. LOW-LEVEL/STEERING FLOW WILL LIE PARALLEL TO A SLOWLY
NORTHWARD LIFTING WARM FRONT EXPECTED TO BISECT THE AREA, SO
DESPITE THE INCREASED FLOW, BACKBUILDING/REPEATING CONVECTION
SEEMS PLAUSIBLE. TRAINING PLUS THE HIGH PW AIRMASS YIELDS A
THREAT FOR EXCESSIVE RAIN AND FLOODING, PERHAPS MITIGATED A BIT
BY ONGOING DROUGHT EAST OF THE APPALACHIANS.
AREAS THAT HAVE SEEN RECENT HEAVY RAIN, OR TYPICAL POOR
DRAINAGE/URBAN AREAS WOULD BE RATHER SUSCEPTIBLE TO ANY SUCH
EXCESSIVE RAINFALL AMOUNTS. OF NOTE, THE 00Z HREF 3-HR PMM HAS
50-70% CHANCE OF EXCEEDING 1" IN THE VICINITY OF WESTERN MD
EARLY SUNDAY MORNING AS A PRESUMABLY WEAKENING MCS TREKS INTO
THE REGION. THE PROBS FOR 3" ARE LESS THAN 10%, BUT RECENT HEAVY
RAIN IN THIS AREA COULD RAISE AT LEAST A CONDITIONAL FLOOD
CONCERN AS EARLY AS THE PREDAWN HOURS ON SUNDAY. PROBS FOR 1"
AND 3" IN 3 HOURS ARE NOTABLY HIGHER EAST OF THE BLUE RIDGE
DURING THE AFTERNOON HOURS. THE LATEST HREF ONLY GOES OUT UNTIL
EARLY SUNDAY EVENING, BUT GUIDANCE SUCH AS THE NAM AND EXTENDED
RAP SUGGEST A FURTHER INCREASE IN PWS, LOW-LEVEL FLOW, AND
SBCAPE SUNDAY NIGHT SUGGESTING A LINGERING HEAVY RAIN THREAT.
IN ADDITION TO ANY HEAVY RAIN THREAT IS THE POTENTIAL FOR BANDS
OF STRONG TO SEVERE THUNDERSTORMS. INCREASED FLOW DOWN INTO THE
LOW LEVELS WOULD BE FAVORABLE FOR ORGANIZED LINE SEGMENTS
CAPABLE OF MIXING DOWN DAMAGING WIND GUSTS IN ANY ORGANIZING
COLD POOLS. THE SATURATED PROFILES COULD RESULT IN WATER LOADING
DOWNDRAFTS, THOUGH THE LACK OF MID-LEVEL DRY AIR MAY KEEP DCAPE
LOW PUTTING A CEILING ON JUST HOW HIGH DAMAGING WIND GUSTS CAN
GET (MOST LIKELY IN THE 50-65 MPH RANGE). THE INCREASED LOW-
LEVEL FLOW AND SRH COUPLED WITH MOIST PROFILES COULD LEND TO THE
THREAT OF A FEW TORNADOES AS WELL.
ALTHOUGH THE PROSPECT OF EARLY MORNING CLOUDS AND PRECIP MAY AT
FIRST GLANCE SEEM TO PRECLUDE A HIGHER POTENTIAL FOR HEATING AND
SEVERE WEATHER LATER IN THE DAY, THE HIGH LOW-LEVEL MOISTURE
CONTENT COUPLED WITH STEADY HEIGHT FALLS ALOFT MEANS THAT
HEATING WILL NOT NEED TO BE AS ROBUST TO RESULT IN SUFFICIENT
CAPE FOR STRONG TO SEVERE CONVECTION, ESPECIALLY GIVEN THE SHEAR
THAT WILL BE PRESENT.
SOME SEVERE WEATHER OR FLOOD THREAT MAY PERSIST INTO THE NIGHT
GIVEN THE ABOVE LISTED FACTORS.
KEY MESSAGE 3...SEASONABLY WARM CONDITIONS AND DAILY SHOWER AND
THUNDERSTORM CHANCES ARE EXPECTED THROUGH MONDAY, BEFORE ANOTHER
ROUND OF STORMS ARE POSSIBLE ON THURSDAY.
HIGH PRESSURE BUILDING ACROSS SOUTHERN QUEBEC DOWN INTO NEW
ENGLAND WILL FAVOR A MOSTLY QUIET DAY FOR THE AREA TODAY. AN
ONSHORE COMPONENT TO THE WINDS SHOULD FAVOR A MIX OF CLOUDS AND
SUN THROUGH THE DAY. HIGHS WILL RISE INTO THE MID/UPPER 80S WITH
ANY SHOWER/THUNDERSTORM CHANCES CONFINED TO THE POTOMAC
HIGHLANDS ACROSS THE CENTRAL SHENANDOAH VALLEY TOWARD I-64.
RECENT HIGH-RESOLUTION MODELS ARE SHOWING AN MCS RACING ACROSS
THE OHIO VALLEY LATE TODAY. SOME OF THIS COULD LEAK ACROSS THE
ALLEGHENIES, BUT CONFIDENCE REMAINS LOW.
AS SUNDAY'S COLD FRONT TRACKS OFFSHORE, UPPER-LEVEL ZONAL FLOW
BRINGING DRIER AIR FROM THE GREAT LAKES PERSISTS OVER THE MID-
ATLANTIC THROUGH MIDWEEK, CREATING A BREAK IN THE RAIN AND
THUNDERSTORMS. WHILE TEMPERATURES AND DEWPOINTS DROP A FEW
DEGREES BY TUESDAY IN THE WAKE OF THE FRONT, TEMPERATURES SHOULD
GRADUALLY INCREASE AGAIN IN THE LATTER HALF OF THE WEEK AS HIGH
PRESSURE BUILDS OVERHEAD. PRIOR TO HIGH PRESSURE BUILDING,
ADDITIONAL CONVECTION IS POSSIBLE MONDAY BUT WITH A LIKELY
LESSER THREAT OF SEVERE WEATHER OR FLOODING.
MEANWHILE, AN UPPER-LEVEL TROUGH WILL BEGIN TO FORM OVER THE
NORTHERN PLAINS AND THEN TRACK ACROSS THE GREAT LAKES LATE IN THE
WEEK, WITH A STRONG COLD FRONT POTENTIALLY MOVING THROUGH THE MID-
ATLANTIC BETWEEN THURSDAY AND FRIDAY. MEDIUM-RANGE ALGORITHMS ARE
ALREADY HIGHLIGHTING A POTENTIAL FOR SEVERE THUNDERSTORMS WITH THIS
SYSTEM. HOWEVER, SEVERE PROBABILITIES CURRENTLY VARY WIDELY ACROSS
MODELS, WITH CSU ML PROBABILITIES HIGHLIGHTING ONLY A MARGINAL 5%-
15% PROBABILITY AS OF THE 12Z MODEL RUNS WHILE THE WXNEXT2 MEAN AI
OUTLOOK IS ALREADY SHOWING A 30%-45% PROBABILITY. DETERMINISTICALLY,
THE GFS/ECMWF ALSO HAVE NOT QUITE ALIGNED ON THE TIMING AND
PLACEMENT OF THE TROUGH 7 DAYS OUT. SHOULD THIS SETUP
MATERIALIZE, STORMS CAPABLE OF HEAVY DOWNPOURS AND DAMAGING
WINDS WOULD BE POSSIBLE. AS DROUGHT CONDITIONS CONTINUE TO
IMPROVE AREA-WIDE, LOCALIZED FLOODING BECOMES MORE OF A CONCERN
WITH ANY THUNDERSTORMS THAT FORM IN THE REGION. FOR NOW, THIS
WILL BE A FEATURE TO CONTINUE TO MONITOR AS THE SYNOPTIC SETUP
BECOMES MORE DEFINED.
AVIATION /08Z SATURDAY THROUGH WEDNESDAY/
IFR CONDITIONS ARE LIKELY AT CHO AND MRB THROUGH AT LEAST 12Z OR
13Z. OTHERWISE, VFR CONDITIONS ARE EXPECTED FOR TODAY AS HIGH
PRESSURE BUILDS OVER NEW ENGLAND INTO SOUTHERN QUEBEC. ANY
SHOWER CHANCES ARE LIKELY CONFINED TO THOSE WEST OF THE BLUE
RIDGE AND SOUTH OF I-66. A DECAYING MCS COULD MOVE THROUGH LATE
TONIGHT, BUT THERE IS PLENTY OF UNCERTAINTY AT THIS POINT.
SUNDAY PRESENTS ITSELF AS A MUCH MORE ACTIVE WEATHER DAY WHICH
WOULD INCLUDE SOME CONVECTIVE-DRIVEN RESTRICTIONS. AHEAD OF THE
APPROACHING COLD FRONT, SOUTHERLY WINDS PICK UP IN STRENGTH WITH
AFTERNOON GUSTS TO AROUND 15 TO 20 KNOTS. CONVECTION COULD LOOM
INTO SUNDAY NIGHT AND MONDAY MORNING WHICH WOULD SUPPORT
ADDITIONAL SUB-VFR CONDITIONS. CONDITIONS TURN DRIER FOR LATER
IN THE DAY AS THE COLD FRONT MOVES OFF TOWARD THE SOUTHEAST.
PREVAILING VFR CONDITIONS ARE ANTICIPATED AT TERMINALS TUESDAY
THROUGH WEDNESDAY. LIGHT NORTHWEST WINDS SHIFT SOUTHERLY ON
WEDNESDAY.
MARINE
BACKGROUND WIND FIELDS REMAIN BELOW ADVISORY THRESHOLD THROUGH
EARLY SUNDAY. AHEAD OF A COLD FRONT, SOUTHERLY WINDS INCREASE IN
EARNEST WHICH WILL CARRY GUSTS TO AROUND 20 TO 25 KNOTS. THIS
LIKELY REQUIRES SMALL CRAFT ADVISORIES FROM SUNDAY AFTERNOON
INTO THE OVERNIGHT HOURS. ADDITIONALLY, THERE WILL BE AN
INCREASING RISK OF STRONG TO SEVERE THUNDERSTORMS, MANY OF WHICH
MAY NEED SPECIAL MARINE WARNINGS. SUNDAY LIKELY PRESENTS ITSELF
AS THE MOST HAZARDOUS DAY TO BE ON THE WATERS, PARTICULARLY
FROM THE AFTERNOON ONWARD. CONVECTION MAY CONTINUE INTO MONDAY
MORNING BEFORE THE STORM THREAT AND WINDS DROP OFF THROUGH THE
DAY.
WINDS STAY BELOW SCA THRESHOLDS ON TUESDAY. BEGINNING WEDNESDAY
AFTERNOON, WIND GUSTS PICK UP TO MARGINAL SCA THRESHOLDS BEFORE
DIMINISHING OVERNIGHT. NORTHWEST WINDS SHIFT SOUTHEAST BY WEDNESDAY
MORNING.
TIDES/COASTAL FLOODING
WATER LEVELS ARE LARGELY EXPECTED TO STAY BELOW ACTION STAGE
THROUGH SATURDAY. THE POTENTIAL EXCEPTION COULD BE ANNAPOLIS,
WHICH COULD REACH ACTION STAGE AT THE HIGHER OF THE DAILY TIDES.
WATER LEVELS WILL START TO INCREASE IN SOUTHERLY FLOW ON
SUNDAY, WITH ANNAPOLIS POTENTIALLY APPROACHING MINOR FLOOD
STAGE.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR MDZ003-501-
502-509-510.
VA...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR VAZ027>031.
WV...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR WVZ050>053-
055-502>504.
MARINE...NONE.
DISCUSSION...BRO/DHOF/CJL/SRT
AVIATION...BRO/DHOF/SRT
MARINE...BRO/DHOF/SRT
TIDES/COASTAL FLOODING...LWX
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