087  
FXUS61 KLWX 180747  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
347 AM EDT THU APR 18 2019  
   
SYNOPSIS
 
 
A STALLED FRONT OVER THE REGION EARLY THIS MORNING WILL LIFT  
NORTHWARD AS A WARM FRONT TODAY. STRONG LOW PRESSURE AND ITS  
ASSOCIATED COLD FRONT WILL IMPACT THE REGION FRIDAY AND FRIDAY  
NIGHT, WITH AN UPPER LEVEL LOW AFFECTING THE AREA THROUGH  
SUNDAY. HIGH PRESSURE WILL RETURN ON MONDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
EASTERLY FLOW AND LOW CLOUDS HAVE DEVELOPED ACROSS MUCH OF THE  
REGION THIS MORNING ON THE COOL SIDE OF THE BACKDOOR FRONTAL  
BOUNDARY THAT HAS STALLED OUT ACROSS CENTRAL VIRGINIA. WARM AIR  
ADVECTION AND A WEAK DISTURBANCE ALOFT HAS LED TO THE  
DEVELOPMENT OF A FEW SHOWERS AND EVEN AN ISOLATED THUNDERSTORM  
OR TWO ACROSS PORTIONS OF CENTRAL/WESTERN WV AND WESTERN PA.  
THESE WILL WEAKEN AND LARGELY DISSIPATE AS THEY MOVE EASTWARD  
TOWARDS THE REGION, BUT A FEW SHOWERS ARE POSSIBLE ACROSS  
EASTERN WV AND NORTHERN MD IN THE EARLY MORNING HOURS.  
 
AS AN INITIAL AREA OF LOW PRESSURE MOVES NORTHEASTWARD THROUGH  
THE GREAT LAKES AND INTO ONTARIO/QUEBEC TODAY AND A MORE POTENT  
LOW PRESSURE SYSTEM ORGANIZES IN THE SOUTH CENTRAL US, SOUTHERLY  
FLOW WILL INCREASE ACROSS THE REGION, AND THE STALLED BOUNDARY  
WILL LIFT NORTHWARD AS A WARM FRONT THIS MORNING. THIS WILL  
PLACE THE ENTIRE REGION IN THE WARM SECTOR BY THE AFTERNOON  
HOURS. AS THE FRONT LIFTS, AND IN COMBINATION WITH SOME WEAK  
UPPER LEVEL ENERGY, A FEW ISOLATED SHOWERS/SPRINKLES ARE AGAIN  
POSSIBLE, MAINLY ACROSS CENTRAL/WESTERN VA AND EASTERN WV.  
 
TEMPERATURES MAY INITIALLY TAKE SOME TIME TO RISE WITH THE LOW  
CLOUDS, BUT ONCE THEY BREAK, HIGHS ARE EXPECTED TO REACH THE  
UPPER 70S TO LOWER 80S.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/
 
 
A STRONG UPPER LEVEL TROUGH WILL THEN DIG SOUTHWARD OVER THE  
MISSISSIPPI VALLEY TONIGHT AS A SURFACE LOW EJECTS  
NORTHEASTWARD INTO THE OHIO VALLEY. DEEP SOUTH TO SOUTHWEST FLOW  
WILL BE IN PLACE OVER THE REGION WITH INCREASING WARMTH AND  
MOISTURE. SOME SHOWERS ARE POSSIBLE TOWARDS MORNING, BUT MOST  
LOCATIONS LIKELY REMAIN ON THE DRIER SIDE. LOWS WILL ONLY FALL  
INTO THE 60S.  
 
VERY ACTIVE WEATHER EXPECTED FOR FRIDAY AND FRIDAY NIGHT. THE  
UPPER TROUGH IS EXPECTED TO CLOSE OFF AND TRACK EASTWARD THROUGH  
TN/KY DURING THE DAY FRIDAY AND TOWARDS WV AND THE APPALACHIANS  
FRIDAY NIGHT, WITH ELONGATED SURFACE LOW PRESSURE MOVING  
THROUGH OH/KY/TN AND TOWARDS THE EASTERN GREAT LAKES. ALOFT,  
THE MID-ATLANTIC AND SOUTHEASTERN STATES WILL BE UNDER STRONG  
DIFFLUENT FLOW, WITH FORCING INCREASING THROUGH THE DAY AND  
ESPECIALLY IN THE EVENING AND OVERNIGHT AS THE CLOSED LOW  
APPROACHES. DEEP SOUTHERLY FLOW WILL BE IN PLACE WITH A  
CONNECTION TO THE TROPICS, AND PRECIPITABLE WATER VALUES IN  
EXCESS OF 1.5 INCHES. THIS WILL PROMOTE THE DEVELOPMENT OF  
SHOWERS/THUNDERSTORMS WITH THE POTENTIAL FOR HEAVY RAIN AND  
INCIDENTS OF FLOODING FRIDAY AND FRIDAY NIGHT. IN ADDITION, A  
STRONG LOW LEVEL WIND FIELD WILL AID IN THE DEVELOPMENT OF  
POTENTIALLY ORGANIZED CONVECTION, POSSIBLY SEVERE. THE LIMITING  
FACTOR WILL BE DEGREE OF STABILIZATION (500-900 J/KG SB/ML  
CAPE), BUT GIVEN STRONG WIND FIELD (850MB WINDS 50-60 KNOTS) AND  
STRONG FORCING, MUCH OF THE REGION REMAINS IN A SLIGHT RISK FOR  
SEVERE THUNDERSTORMS. HIGHS FRIDAY WILL BE IN THE LOW TO MID  
70S, WITH LOWS FRIDAY NIGHT IN THE 50S TO LOW 60S.  
 
THE MAIN FRONTAL PUSH WILL EXIT EASTWARD ON SATURDAY, HOWEVER  
THE FILLING SURFACE LOW AND CLOSED UPPER LOW WILL REMAIN NEAR  
OR WEST OF THE REGION ON SATURDAY. THIS WILL LEAD TO CONTINUED  
CHANCES OF RAIN SHOWERS, AND EVEN A FEW THUNDERSTORMS, WITH THE  
HIGHEST PROBABILITIES WEST OF THE BLUE RIDGE, CLOSER TO THE  
UPPER LOW. HIGHS SATURDAY IN THE 60S TO NEAR 70F. A FEW  
SNOWFLAKES MIXING IN WITH LINGERING RAIN SHOWERS ARE EVEN  
POSSIBLE IN THE MOUNTAINS SATURDAY NIGHT WITH THE UPPER LOW  
STILL OVERHEAD. LOWS SATURDAY NIGHT GENERALLY 40-50F.  
 

 
   
LONG TERM /SUNDAY THROUGH WEDNESDAY/
 
 
SHOWERS MAY LINGER SUNDAY INTO MONDAY AS AN UPPER LOW SLOWLY PIVOTS  
OVERHEAD. HIGH PRESSURE IS EXPECTED TO BUILD NEAR AND SOUTH OF THE  
REGION FROM THE OHIO VALLEY FOR EARLY NEXT WEEK. THIS SHOULD LEAD TO  
WARMING TEMPERATURES AND INCREASING HUMIDITY. MAINLY DRY WEATHER IS  
EXPECTED DURING THE FIRST HALF OF NEXT WEEK, THOUGH A COLD FRONT MAY  
APPROACH FROM THE NORTH ON WEDNESDAY.  
 

 
   
AVIATION /07Z THURSDAY THROUGH MONDAY/
 
 
MVFR STRATUS IS CURRENTLY IN PLACE AT IAD/BWI/MTN/DCA ON THE  
COOL SIDE OF THE BACKDOOR FRONTAL BOUNDARY. EXPECTING THIS TO  
SPREAD EVEN A BIT FURTHER WESTWARD TO MRB EARLY THIS MORNING. A  
PERIOD OF IFR IS ALSO LIKELY AT BWI/MTN, AND IS POSSIBLE AT THE  
OTHER SITES, ALTHOUGH LESS LIKELY. CHO SHOULD STAY RESTRICTION-  
FREE. VFR WILL RETURN BY THE EARLY AFTERNOON AT ALL TAF SITES  
UNDER INCREASING SOUTHERLY FLOW. ADDITIONAL LOW CEILINGS WILL  
LIKELY OVERSPREAD THE AREA LATER TONIGHT, WITH PERIODIC  
REDUCTIONS TO VISIBILITIES ALSO LIKELY FRIDAY AND FRIDAY NIGHT  
IN SHOWERS/THUNDERSTORMS. SOME THUNDERSTORMS MAY BECOME STRONG  
TO LOCALLY SEVERE. IN ADDITION PERIODIC GUSTY SOUTHERLY WINDS  
AND LOW LEVEL WIND SHEAR ARE LIKELY.  
 
SOME IMPROVEMENT LIKELY SATURDAY ALTHOUGH SCATTERED RAIN SHOWERS  
WILL STILL BE AROUND.  
 
BRIEF SUB-VFR POSSIBLE IN ANY SHOWER ACTIVITY OR LOWER CIGS SUN INTO  
MON IN GENERALLY W FLOW AS AN UPPER LOW MOVES OVERHEAD.  
 

 
   
MARINE
 
 
SUB-SCA CONDITIONS ARE CURRENTLY BEING OBSERVED THIS MORNING  
ACROSS ALL WATERS. A WARM FRONT WILL MOVE ACROSS THE AREA DURING  
THE FIRST HALF OF TODAY, WITH SOUTHERLY FLOW INCREASING BEHIND  
IT THIS AFTERNOON, THIS EVENING, AND TONIGHT. WILL LEAVE START  
TIME OF SCA AT NOON, HOWEVER, THERE MAY BE MIXING ISSUES  
INITIALLY, WITH THE HIGHER PROBABILITY OF SCA GUSTS LATE IN THE  
DAY AND EVENING. SCA WILL THEN LIKELY NEED TO BE EXTENDED  
THROUGH FRIDAY NIGHT, AND WITH STRONG LOW LEVEL FLOW AND  
PRESSURE GRADIENT AHEAD OF AN APPROACHING LOW AND COLD FRONT.  
GALES ARE POSSIBLE LATER FRIDAY INTO FRIDAY NIGHT. STRONGER  
GUSTS WILL MAY OCCUR WITH THUNDERSTORMS LATE FRIDAY INTO FRIDAY  
NIGHT, PERHAPS 50 KNOTS OR MORE AND SPECIAL MARINE WARNINGS MAY  
BE NECESSARY.  
 
LOW PRESSURE WILL CONTINUE TO RESIDE NEAR THE WATERS SATURDAY  
AND A SMALL CRAFT ADVISORY MAY STILL BE NEEDED FOR THE WATERS.  
 
SCA MAY LINGER INTO SUNDAY BEFORE GRADIENT RELAXES.  
 

 
   
HYDROLOGY
 
 
SOILS REMAIN MOIST ACROSS THE REGION WITH WATER LEVELS REMAINING  
AT OR ABOVE NORMAL. WITH STRONG SOUTHERLY FETCH BRINGING VERY  
HIGH PRECIPITABLE WATER VALUES (IN EXCESS OF 1.5 INCHES) AND  
STRONG DIFFLUENCE EXPECTED WITH A WARM ATMOSPHERE, HIGH  
INTENSITY RAINFALL IS EXPECTED LATE FRIDAY/FRIDAY NIGHT, WITH  
POTENTIAL PROLONGED MODERATE/HEAVY RAIN IF TRAINING OF RAIN  
BANDS OCCURS. THEREFORE, FLOODING, BOTH FLASH AND RIVER-TYPE, IS  
POSSIBLE FRIDAY INTO THE WEEKEND. FLOOD WATCHES AND/OR FLASH  
FLOOD WATCHES MAY BECOME NECESSARY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
SOUTHERLY FLOW WILL CAUSE TIDAL ANOMALIES TO INCREASE THROUGH THE  
END OF THE WEEK. THIS WILL LIKELY RESULT IN AT LEAST MINOR FLOODING  
AT MOST TIDE SITES, WITH NEAR MODERATE FLOODING NOT OUT OF THE  
QUESTION DEPENDING ON EXACT EVOLUTION OF APPROACHING LOW PRESSURE  
LATER THIS WEEK.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 6 AM EDT FRIDAY FOR  
ANZ530>543.  
 

 
 

 
SYNOPSIS...MM  
NEAR TERM...MM  
SHORT TERM...MM  
LONG TERM...DHOF  
AVIATION...MM/DHOF  
MARINE...MM/DHOF  
HYDROLOGY...MM/RCM  
TIDES/COASTAL FLOODING...DHOF  
 
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