781  
FXUS61 KLWX 301358  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
958 AM EDT SUN APR 30 2017  
   
SYNOPSIS
 
 
A FRONT WHICH IS DRAPED ACROSS THE AREA WILL LIFT NORTH AS A  
WARM FRONT LATER TODAY. A STRONGER COLD FRONT MOVE EAST OF THE  
MISSISSIPPI RIVER TONIGHT AND APPROACH THE APPALACHIANS BY  
MONDAY MORNING. THIS FRONT WILL CROSS THE REGION MONDAY EVENING.  
HIGH PRESSURE WILL BRING COOLER AND DRIER WEATHER DURING THE  
MIDDLE OF THE WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AT 9 AM SURFACE FRONT IN FORM OF WIND SHIFT IS LOCATED FROM NEAR  
FRANKLIN WV TO WARRENTON TO CHESAPEAKE BEACH. LOW CLOUDS ARE  
FARTHER NORTH THAN THAT LINE. WHILE IT APPEARS THE SOUTHERN EDGE  
IS TRYING TO SCATTER INTO CUMULUS, AM A LITTLE CONCERNED EROSION  
MAY BE ON THE SLOW SIDE SINCE WINDS NORTH OF THE BOUNDARY ARE  
VERIFYING WITH A MORE NORTHEASTERLY COMPONENT THAN ORIGINALLY  
PROGGED. WHILE THIS COULD HAVE SOME EFFECT ON THE TEMPERATURE  
GRADIENT, THE ALREADY-WARM START MEANS PORTIONS OF THE BALTIMORE  
AREA ARE ALREADY NEARING THEIR HIGHS DESPITE THE CLOUDS.  
TEMPERATURES ARE ON THEIR WAY TO THE 80S SOUTH OF THE BOUNDARY.  
 
THERE IS STILL A BIT OF UNCERTAINTY IN THE DETAILS OF HOW  
CONVECTION WILL TRANSPIRE TODAY. IN THE BIGGER PICTURE, THOUGH,  
IT WILL BE SAFE TO SAY THAT NORTH OF THE BOUNDARY SURFACE-BASED  
INSTABILITY WILL BE NIL. TO THE SOUTH, SBCAPE WILL BE IN THE  
NEIGHBORHOOD OF 1500-2500 J/KG WITH MORE THAN ADEQUATE DEEP  
SHEAR (30-35 KT BULK 0-6KM LAYER). THE STRUGGLE ONCE AGAIN IS  
FINDING THE TRIGGER. BELIEVE THAT TERRAIN AND FRONTAL  
CONVERGENCE WILL BE THAT MECHANISM, SUGGESTING THAT THE POTOMAC  
HIGHLANDS WILL BE THE FAVORED LOCATION. 12Z RNK SOUNDING HAS  
VERY DRY MID-LEVEL AIR WHICH IS EXPECTED TO ADVECT NORTHWARD,  
AND ALL REGIONAL SOUNDINGS SHOW MULTIPLE STABLE LAYERS. THUS AM  
CONTINUING THE PREVIOUS THINKING THAT COVERAGE WILL BE SCATTERED  
AT BEST. IF A STRONGER UPDRAFT CAN DEVELOP, GUSTY WINDS WILL BE  
A THREAT.  
 

 
   
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
 
 
INSTABILITY QUICKLY DISSIPATES WITH THE LOSS OF DIURNAL HEATING,  
AND HAVE REMOVED POPS FOR THE NIGHTTIME HOURS. AREA WILL BE  
NORTH OF THE WARM FRONT, IN AN AIR MASS WITH 60S DEWPOINTS, SO  
PATCHY FOG DEVELOPMENT WILL ONCE AGAIN BE A CONCERN. OTHERWISE,  
IT SHOULD BE A QUIET NIGHT. LOWS WON'T BE FAR REMOVED FROM  
DEWPOINTS.  
 
ON MONDAY, A WELL DEFINED COLD FRONT WILL BE APPROACHING THE  
AREA. THERE ARE STILL SOME TIMING DIFFERENCES AMONGST GUIDANCE.  
THIS BIGGER DISPARITY, THOUGH, IS WHETHER THUNDERSTORMS WILL  
DEVELOP ALONG THE FRONT OR ALONG A PRE-FRONTAL TROUGH. THE GFS  
IS THE QUICKEST SOLUTION, KEYING ON PRE-FRONTAL CONVECTION IN A  
DIURNALLY FAVORED TIMESLOT. IF THIS HAPPENS, THEN STRONG TO  
SEVERE THUNDERSTORMS WILL BE POSSIBLE. OTHER SOLUTIONS SUGGEST  
THUNDERSTORMS WILL BE NEARER THE FRONT, AND TIMED MORE IN THE  
EVENING. THE CHALLENGE WILL BE HOW MUCH INSTABILITY WILL  
GENERATED; MORE THAN AMPLE SHEAR IS PRESENT. POPS WILL BE LIKELY  
TO CATEGORICAL NONETHELESS, WITH EMPHASIS ON THE LATER AFTERNOON  
AND EVENING HOURS.  
 
COOLER AND DRIER AIR WILL OVERSPREAD THE AREA MONDAY NIGHT  
(OVERNIGHT) INTO TUESDAY MORNING. WE WILL HAVE A GLANCING BLOW  
FROM THE UPPER TROUGH AXIS DURING THE DAY TUESDAY, WHICH WILL  
SUSTAIN GUSTY WINDS MUCH OF THE DAY. BUT SINCE THE AIR WILL BE  
DRIER AND FLOW WILL BE DOWNSLOPING, DON'T BELIEVE THAT CLOUDS  
WILL BE NUMEROUS. TEMPERATURES WILL BE CLOSER TO NORMAL DURING  
THE DAY, WITH NIGHTTIME LOW IN THE 40S AND 50S AGAIN.  
 

 
   
LONG TERM /WEDNESDAY THROUGH SATURDAY/
 
 
HIGH PRESSURE WILL BUILD INTO THE REGION WEDNESDAY. COOLER  
CONDITIONS EXPECTED MID-WEEK AS NORTHERLY WINDS USHER IN COOLER  
AND DRYER CONDITIONS. HIGH TEMPS IN THE U60S/L70S EXPECTED WED.  
A STORM SYSTEM WILL BE COMING TOGETHER ACROSS THE MISSISSIPPI  
VALLEY WED NIGHT. WARM AIR ADVECTION WILL BEGIN ACROSS THE  
REGION WED NIGHT-THURSDAY AND CLOUDS AND SHOWERS ARE EXPECTED.  
MORE SHOWERS ARE EXPECTED TO MOVE INTO THE REGION THU NIGHT-  
FRIDAY AS THE SYSTEM BECOMES MORE DYNAMIC. THE UPPER LEVEL LOW  
BECOMES A CLOSED LOW THU NIGHT AND SFC LOW PRESSURE WILL  
CONTINUE TO DEEPEN ACROSS THE OHIO VALLEY. THIS SYSTEM MAY BRING  
THUNDERSTORMS CAPABLE OF HEAVY RAIN AS THE WIND FIELD  
STRENGTHENS AND DEWPTS RISE RAPIDLY FRIDAY. TIMING IS UNCERTAIN  
AND IT IS UNKNOWN AT THIS TIME IF CONDITIONS WILL BE HAZARDOUS.  
LOW PRESSURE WILL LIKELY MOVE OVERHEAD FRI-NIGHT- SATURDAY.  
CLOUDS AND SHOWERS WILL LIKELY KEEP TEMPERATURES BELOW NORMAL  
MID-LATE WEEK.  
 

 
   
AVIATION /14Z SUNDAY THROUGH THURSDAY/
 
 
A BACKDOOR COLD FRONT HAS SLIPPED SOUTH OF THE METRO TERMINALS  
BUT NOT TO CHO, PROVIDING A COMPLICATED FLIGHT CATEGORY REGIME.  
MVFR SEEMS TO BE THE RULE ON THE NORTH SIDE OF THE BOUNDARY.  
HAVE RATHER LOW CONFIDENCE AT HOW QUICKLY THE RESTRICTIONS WILL  
ERODE, ESPECIALLY SINCE WINDS ARE VERIFYING FROM A MORE  
NORTHEASTERLY DIRECTION. HOWEVER, SATELLITE SHOWS THE SOUTHERN  
EDGE OF THE CLOUDS TRYING TO ERODE. EXPECT BWI/MTN TO BE  
AFFECTED THE LONGEST. SCATTERED THUNDERSTORMS SHOULD DEVELOP  
SOUTH OF THE FRONT, BUT DIRECT IMPACT AT AN AIRFIELD TOO LIMITED  
TO FORECAST AT THIS JUNCTURE...AM THINKING THE HIGHEST CHANCE  
WILL BE NEAR MRB.  
 
ANYTHING THAT DOES DEVELOP WILL DISSIPATE WITH SUNSET TONIGHT.  
THE AIR WILL BE HUMID ENOUGH FOR MORE PATCHY FOG DEVELOPMENT  
OVERNIGHT INTO EARLY MONDAY MORNING. WILL BE KEEPING FORECASTS  
AT MVFR. LOWER RESULTS CERTAINLY POSSIBLE.  
 
A WELL DEFINED COLD FRONT WILL APPROACH THE TERMINALS MONDAY,  
AND CROSS THE REGION LATE MONDAY INTO MONDAY NIGHT. NUMEROUS  
THUNDERSTORMS ANTICIPATED ALONG/AHEAD OF THE FRONT, WITH BRIEF  
AOB IFR ALONG WITH LOCALLY GUSTY WINDS.  
 
THE FRONT WILL CLEAR THE AREA LATE MONDAY NIGHT. VFR EXPECTED  
THROUGH WEDNESDAY. RAIN WILL SPREAD EAST WEDNESDAY NIGHT INTO  
THURSDAY.  
 

 
   
MARINE
 
 
A BACKDOOR FRONT HAS SLIPPED TO AROUND CHESAPEAKE BEACH, AND  
FURTHER SOUTHWARD PROGRESSION MAY BE LIMITED BEFORE GRADUALLY  
RETURNING NORTHWARD. FLOW WILL BE NORTHEAST/EAST TO ITS NORTH,  
AND SOUTHEAST/SOUTH TO ITS SOUTH AND SHOULDN'T BE MUCH MORE  
THAN 10 KT SUSTAINED, SO SMALL CRAFT ADVISORIES ARE NOT  
ANTICIPATED. THIS FRONT WILL RETURN TO THE NORTH THIS EVENING.  
 
GRADIENT FLOW (SOUTHERLY) WILL INCREASE OVERNIGHT INTO MONDAY  
AHEAD OF A STRONGER COLD FRONT APPROACHING FROM THE WEST. A  
SMALL CRAFT ADVISORY GOES IN EFFECT AFTER MIDNIGHT TONIGHT FOR  
SOUTHERN WATERS, AND THEN FOR ALL WATERS ON MONDAY. THE FRONT  
ITSELF WILL IMPACT THE MARINE AREA MONDAY NIGHT, ALTHOUGH SOME  
THUNDERSTORMS MAY DEVELOP AHEAD OF THE FRONT MONDAY AFTERNOON.  
THESE THUNDERSTORMS MAY CONTAIN GUSTY WINDS.  
 
BEHIND THE FRONT FLOW TURNS WESTERLY. MIXED PROFILES APPEAR  
DEEP, AND EXPECT SMALL CRAFT CONDITIONS TO EXTEND INTO TUESDAY.  
 
A STORM SYSTEM MAY IMPACT THE WATERS LATE IN THE WORK WEEK.  
SHOWERS AND THUNDERSTORMS ARE POSSIBLE AS WELL AS GUSTY WINDS  
THAT MAY PRODUCE SCA CONDITIONS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
WATER LEVELS RUNNING VERY CLOSE TO ASTRONOMICAL NORMALS THIS  
MORNING. ANTICIPATE THAT WILL REMAIN THE CASE THROUGH THE NEXT  
TWO TIDE CYCLES. ESTOFS DOES SUGGEST THAT WATER LEVELS WILL RISE  
IN THE NORTHERN BAY, BUT BELIEVE THAT IS A RESULT OF A MODEL  
BIAS AND AM NEGLECTING THAT SOLUTION.  
 
AFTER THAT, UNCERTAINTY GROWS AS MODEL SOLUTIONS BECOME MORE  
DIVERGENT. AM PROVIDING A FORECAST OF WATER LEVELS BELOW CAUTION  
STAGE MONDAY. SOUTH FLOW COULD SUSTAIN AN INCREASE. SOME  
SOLUTIONS SUGGEST THESE ELEVATED LEVELS COULD LINGER INTO  
TUESDAY, AS WINDS WILL TURN GUSTY BUT WILL BE FROM THE  
WEST...AND THUS WON'T PROMPT A BLOWOUT.  
 
LOW PRESSURE WILL COME UP THE COAST THURSDAY, WHICH LIKELY WILL  
INCREASE WATER LEVELS FROM WHEREVER THEY STAND UP TO THAT  
POINT.  
 

 
   
CLIMATE
 
 
RECORD HIGHS WERE SET AT DCA AND IAD YESTERDAY, AND RECORD WARM  
LOWS WERE SET AT ALL THREE AIRPORTS (DCA, IAD, AND BWI). THE  
RECORD WARM LOW AT DCA WAS ALSO A RECORD FOR THE MONTH OF APRIL.  
 
RECORDS HIGHS ARE LESS LIKELY TODAY AS A BACKDOOR FRONT DROPS  
DOWN. HOWEVER, THE RECORD WARM LOWS ARE A POSSIBILITY. HERE ARE  
THE RECORD HIGHS/WARM LOWS FOR SUNDAY:  
 
WASHINGTON DC... HIGH 92 (IN 1942); WARM LOW 67 (IN 1983).  
BWI AIRPORT... HIGH 92 (IN 1910); WARM LOW 63 (IN 1983).  
DULLES AIRPORT.. HIGH 86 (IN 2007); WARM LOW 64 (IN 1983).  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EDT MONDAY FOR  
ANZ530>532-535-536-538>540-542.  
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EDT MONDAY  
FOR ANZ534-537-543.  
SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM EDT MONDAY FOR ANZ533-  
541.  
 

 
 

 
SYNOPSIS...HTS  
NEAR TERM...ADS/HTS  
SHORT TERM...HTS  
LONG TERM...HSK  
AVIATION...ADS/HTS  
MARINE...ADS/HSK/HTS  
TIDES/COASTAL FLOODING...HTS  
CLIMATE...HTS  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab VA Page
The Nexlab MD Page
The Nexlab WV Page Main Text Page