746  
FXUS61 KLWX 221426  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
1026 AM EDT TUE AUG 22 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE IS CENTERED WELL OFF THE NORTH CAROLINA COAST. A  
COLD FRONT OVER MICHIGAN WILL TRACK ACROSS THE EASTERN GREAT  
LAKES TODAY, BEFORE PUSHING ACROSS THE MID-ATLANTIC TONIGHT INTO  
WEDNESDAY MORNING. THE FRONT COULD STALL JUST OFFSHORE THE  
DELMARVA PENINSULA WEDNESDAY. REINFORCING UPPER LEVEL ENERGY  
WILL HELP TO PUSH THE FRONT OFFSHORE AND ALLOW FOR HIGH  
PRESSURE TO BUILD IN FROM THE NORTHWEST THURSDAY INTO FRIDAY.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
THEAT AND HUMIDITY CONTINUE TODAY. DEWPOINTS REMAIN IN THE MID  
70S. HIGH TEMPERATURES ARE EXPECTED TO REACH THE LOWER TO MID  
90S EAST OF THE BLUE RIDGE. WE EXPECT TO SEE HEAT INDEX VALUES  
OF 100 TO LOWER 100S IN A LARGE AREA EAST OF THE MOUNTAINS.  
 
CLOUDS WILL INCREASE FROM NORTHWEST LATE THIS AFTERNOON THROUGH  
TONIGHT AS A STRONG COLD FRONT PUSHES ACROSS THE EASTERN OHIO  
VALLEY AND INTO THE MID-ATLANTIC REGION. SHOWERS AND  
THUNDERSTORMS WILL INCREASE IN COVERAGE AND INTENSITY FROM  
WESTERN MARYLAND TOWARD NORTHERN VIRGINIA AND THE I-95 CORRIDOR  
LATE THIS AFTERNOON AND EVENING. THERE IS A SLIGHT RISK FOR  
SEVERE THUNDERSTORMS IN WESTERN MARYLAND AND PARTS OF THE  
EASTERN WEST VIRGINIA PANHANDLE. THE MARGINAL RISK EXTENDS FROM  
THE MOUNTAINS OF HIGHLAND COUNTY IN WESTERN VIRGINIA TO  
DC/BALTIMORE. THE MAIN THREATS WITH THE STRONGEST THUNDERSTORMS  
WILL BE DAMAGING WINDS IN WET MICROBURSTS. GIVEN PWATS OF CLOSE  
TO 2" VERY HEAVY RAINFALL IS POSSIBLE WITH STORMS.  
 

 
   
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
 
 
WEDNESDAY BEGINS WITH A COLD FRONTAL PASSAGE ACROSS OUR REGION.  
AS WE GET INTO THE MIDDAY HOURS, THE FRONT COULD SHOW SIGNS OF  
STALLING JUST TO OUR SOUTHEAST AS CLOUDS AND WIDELY SCATTERED  
SHOWERS LINGER ALONG THE FRONT AND JUST TO THE NORTH. WITH ADDED  
DAYTIME HEATING AND SOME BACKING OF WINDS WITH HEIGHT WITH  
FRONTAL PASSAGE, ADDITIONAL SHOWERS AND A FEW THUNDERSTORMS  
COULD FORM AND BE SCATTERED THROUGHOUT THE EASTERN PIEDMONT OF  
VIRGINIA, SOUTHERN MARYLAND AND A LARGE PORTION OF THE  
CHESAPEAKE BAY. AT THIS TIME, THERE IS A MARGINAL RISK OF SEVERE  
THUNDERSTORMS ACROSS LOWER SOUTHERN MARYLAND AND SOUTH INTO THE  
TIDEWATER OF VIRGINIA WEDNESDAY AFTERNOON AND EVENING. HIGH  
TEMPERATURES, ALONG AND NORTH OF THE FRONT, WILL BE COOLER WITH  
HIGHS IN THE LOWER TO MIDDLE 80S. HUMIDITY WILL BE LOWER AS WELL  
WITH HIGH PRESSURE TO THE NORTHWEST BUILDING SOUTHWARD AND  
USHERING IN LOWER DEWPOINT TEMPERATURES. THROUGHOUT THE  
OVERNIGHT OF WEDNESDAY, THE FRONT SHOULD MOVE FAR ENOUGH  
SOUTHEAST TO ALLOW FOR CONDITIONS TO DRY OUT WITH THE BUILDING  
HIGH PRESSURE.  
 
HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE REGION THURSDAY AND  
THURSDAY NIGHT. SOME UPPER LEVEL ENERGY WILL TRY TO SCOOT OVER THE  
RIDGE OF HIGH PRESSURE BUT SHOULD BE UNSUCCESSFUL OF PRODUCING ANY  
PRECIPITATION THURSDAY INTO THURSDAY NIGHT.  
 

 
   
LONG TERM /FRIDAY THROUGH MONDAY/
 
 
THE WEEKEND FORECAST STILL LOOKS QUIET AS HIGH PRESSURE PASSES  
NORTH OF THE FORECAST AREA. ONE MINOR CHANGE IS THAT GUIDANCE  
SUGGESTING THERE MAY BE A FEW TERRAIN CIRCULATIONS, FOR A STRAY  
SHOWER OR THUNDERSTORM, COINCIDENT WITH DAYTIME HEATING IN THE  
MOUNTAINS. OTHERWISE, SUNSHINE SHOULD BE PLENTIFUL AND  
TEMPERATURES SHOULD BE SLIGHTLY BELOW NORMAL...WITH DEWPOINTS IN  
THE 50S.  
 

 
   
AVIATION /14Z TUESDAY THROUGH SATURDAY/
 
 
VFR CONDITIONS EXPECTED AT ALL TERMINALS THROUGH THURSDAY NIGHT.  
THE BIGGEST CONCERN IS THE COLD FRONT ENTERING THE OHIO VALLEY.  
WHILE THE STRONGEST ACTIVITY IS EXPECTED TO BE TO OUR NORTH  
SHOWERS AND THUNDERSTORMS COULD REDUCE VISIBILITIES TO IFR IN  
HEAVY RAINFALL LATE THIS AFTERNOON AND EVENING.  
 
VFR CONDITIONS ANTICIPATED FRI-SAT UNDER HIGH PRESSURE.  
 

 
   
MARINE
 
 
WE ARE SEEING GUSTS INTO THE UPPER TEENS ON THE WIDER PART OF  
THE BAY. SCA IN EFFECT THERE. SMALL CRAFT ADVISORIES ARE ALSO  
IN EFFECT FROM NOON TODAY THROUGH 11 PM TONIGHT. NO MARINE  
HAZARDS EXPECTED WEDNESDAY THROUGH THURSDAY NIGHT.  
NORTH/NORTHWEST WINDS WILL BE IN THE 5-10 KT RANGE FRIDAY-  
SATURDAY UNDER HIGH PRESSURE.  
 

 
   
TIDES/COASTAL FLOODING
 
 
NORTHWEST WINDS WILL ARRIVE WEDNESDAY MORNING. WE SHALL SEE IF  
THAT WILL BE SOON ENOUGH TO PRECLUDE ANOTHER BORDERLINE  
SITUATION AT ANNAPOLIS/DC EARLY WEDNESDAY.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR  
ANZ530>543.  
 

 
 

 
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