203  
FXUS61 KLWX 181900  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
300 PM EDT WED JUL 18 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE OVER THE GREAT LAKES WILL MOVE TO NEW ENGLAND BY  
FRIDAY. DEVELOPING LOW PRESSURE IN THE MIDWEST WILL APPROACH THE  
AREA THIS WEEKEND.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
HIGH PRESSURE OVER THE GREAT LAKES HAS PROVIDED THE AREA WITH A  
SEASONABLY COOL, DRY AIRMASS. DEWPOINTS ONCE AGAIN ARE IN THE  
LOWER-MID 50S. SCATTERED TO IN PLACES NUMEROUS DIURNAL CUMULUS  
HAVE DEVELOPED. ANTICIPATE THIS WILL DISSIPATE WITH SUNSET.  
THEREFORE IT WILL BE A CLEAR, COOL NIGHT. AM NOT TAKING LOWS  
DOWN TO DEWPOINT LEVELS. THEREFORE, EARLY MORNING FOG SHOULD BE  
LIMITED TO PERHAPS RIVER VALLEYS.  
 

 
   
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
 
 
THE RIDGE OF HIGH PRESSURE WILL REMAIN CENTERED NORTH OF THE  
AREA THURSDAY THROUGH FRIDAY...SLIDING SLOWLY TOWARD AND THEN  
OFF THE NEW ENGLAND COAST. THAT WILL AFFECT WIND DIRECTION, BUT  
LITTLE ELSE. THERE IS STILL THE POTENTIAL FOR A FEW DIURNAL  
CUMULUS TOMORROW, WITH A BETTER CHANCE FOR IT ON FRIDAY.  
 
BY FRIDAY AFTERNOON, AREA SHOULD BE EXPERIENCING WARM  
ADVECTION/ISENTROPIC LIFT. ANTICIPATE SOME MID DECK CLOUD AS  
WELL BY THEN. SHOWERS SHOULD HOLD OFF DURING THE DAY. WOULD NOT  
COMPLETELY RULE OUT A SHOWER AT NIGHT, ESPECIALLY FOR THE  
MOUNTAINS.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
ON SATURDAY, A STRONG NEGATIVELY TILTED UPPER LEVEL TROUGH WILL  
EXTEND FROM THE GREAT LAKES SOUTHWARD ACROSS THE OHIO AND TENNESSEE  
RIVER VALLEY'S AND EVEN DOWN INTO THE CAROLINAS. THIS TROUGH WILL  
INTERACT WITH A STALLED FRONTAL BOUNDARY OFF THE SOUTHEAST COAST,  
DEVELOPING A SURFACE LOW ALONG THE COAST. THE GFS AND EURO BOTH  
DEPICT THIS STORM MOVING ALONG THE EAST COAST SATURDAY THROUGH  
SUNDAY. BOTH MODELS TEND TO KEEP THIS SYSTEM FAR ENOUGH EAST TO  
AVOID ANY DIRECT IMPACTS. THESE TWO FEATURES WILL ACT TOGETHER TO  
PROVIDE PLENTY OF MOISTURE AND LIFT ACROSS THE AREA FOR A CHANCE AT  
SOME SHOWERS AND THUNDERSTORMS. THIS CHANCE APPEARS TO BE HIGHER  
LATER ON SATURDAY, AS A WARM FRONT LIFTS NORTHWARD ACROSS THE  
REGION. WITH UNSETTLED WEATHER EXPECTED MUCH OF THE DAY, EXPECTING  
TEMPS TO BE BELOW AVERAGE, WITH HIGHS IN THE UPPER 70S TO LOW 80S.  
THIS PATTERN WILL CONTINUE TO EVOLVE INTO SUNDAY, AS THE UPPER LEVEL  
TROUGH MOVES OVER THE AREA. EXPECTING MAX TEMPERATURES TO BE IN THE  
LOW TO MID 80S SUNDAY AFTERNOON, WITH AN EVEN HIGHER CHANCE FOR  
SHOWERS AND STORMS THROUGHOUT THE DAY.  
 
THE TROUGH WILL REMAIN OVER THE REGION ON MONDAY, BUT LOOKS TO BEGIN  
TO WEAKEN AND DRIFT SOUTH. GIVEN THE CONTINUED PRESENCE OF THIS  
UPPER LOW, AND A DEVELOPING SURFACE LOW OVER THE OHIO VALLEY, I  
EXPECT PRECIPITATION TO CONTINUE, BUT SHOULD BE A LITTLE LESS  
WIDESPREAD THAN ON SUNDAY. HIGH TEMPERATURES WILL BEGIN TO INCREASE  
THANKS TO A RETURN TO SOUTHERLY FLOW, WITH MAX TEMPS REACHING THE  
MID TO UPPER 80S.  
 
A COLD FRONT WILL BE APPROACHING FROM THE WEST ON TUESDAY, KEEPING  
FLOW OUT OF THE SOUTH THROUGHOUT THE DAY. THIS WILL CONTINUE TO PUMP  
MOISTURE INTO THE REGION. THUS, PRECIPITATION CHANCES WILL REMAIN  
INTO TUESDAY. MAX TEMPERATURES WILL BE SLIGHTLY WARMER THAN MONDAY.  
 

 
   
AVIATION /19Z WEDNESDAY THROUGH MONDAY/
 
 
VFR CONDITIONS WILL PREVAIL TODAY AND TONIGHT. THERE IS A SLIM  
CHANCE AT PATCHY RIVER VALLEY FOG, BUT DO NOT BELIEVE IT WILL  
IMPACT ANY TERMINAL. LIKE TODAY, A FEW DIURNAL CUMULUS SHOULD  
DEVELOP TOMORROW, WITH BASES 5000 FT.  
 
AREA WILL BEGIN EXPERIENCING RETURN FLOW FRIDAY. SHOWERS SHOULD  
HOLD OFF IN THE MOUNTAINS DURING THE AFTERNOON, BUT MAY SPREAD  
EAST TO CHO/MRB IN THE EVENING. INSTABILITY LOOKS MINIMAL, SO  
AM NOT FORECASTING THUNDER AT THIS TIME.  
 
UNSETTLED WEATHER RETURNS THIS WEEKEND AS AN UPPER LEVEL TROUGH  
NEARS FROM THE WEST AND A SURFACE WARM FRONT LIFTS NORTHWARD TOWARD  
THE TERMINALS SATURDAY NIGHT AND INTO SUNDAY. EXPECT INCREASING RAIN  
CHANCES DURING THIS TIME PERIOD WHICH WILL PROMOTE PERIODS OF SUB  
VFR CONDITIONS. THE UNSETTLED WEATHER WILL PERSIST INTO MONDAY AS  
THE UPPER LEVEL TROUGH BEGINS TO WEAKEN A BIT, BUT ENOUGH SUPPORT  
ALOFT WILL REMAIN TO PRODUCE DIURNALLY DRIVEN SHOWERS/STORMS. THE  
FLOW WILL REMAIN SOUTH SOUTHEAST THROUGH THE PERIOD AT 10 KNOTS OR  
LESS, OUTSIDE OF ANY CONVECTIVE ACTIVITY OF COURSE.  
 

 
   
MARINE
 
 
WINDS SHOULD BE 10 KT OR LESS ON THE WATERS THROUGH THE END OF  
THE WEEK. SCA CONDITIONS PLAUSIBLE THIS WEEKEND AND INTO MONDAY  
AS AN UPPER LEVEL TROUGH NEARS FROM THE WEST, DELIVERING  
SHOWERS AND THUNDERSTORMS ACROSS THE REGION, WITH THE AFTERNOON  
HOURS FAVORED WITH THE HIGHEST CHANCES FOR PRECIPITATION AND  
STRONGER SOUTHERLY BREEZES. ANY THUNDERSTORMS WILL BE CAPABLE OF  
PRODUCING LOCALLY GUSTY WINDS WHICH MAY REQUIRE THE NEED FOR  
SPECIAL MARINE WARNINGS SHOULD CONDITIONS WARRANT.  
 

 
   
TIDES/COASTAL FLOODING
 
 
WATER LEVELS NEAR TARGET ON THE POTOMAC AND MID BAY, BUT RUNNING  
SEVERAL TENTHS BELOW NORMAL ANNAPOLIS NORTH. BELIEVE THAT MORE  
WATER EVACUATED THE ESTUARY THAN MODELED, SO WATER FORECASTS  
HAVE GREATER THAN TYPICAL UNCERTAINTY FOR THE NEXT COUPLE OF  
DAYS. ANTICIPATE NO ISSUES THROUGH THE END OF THE WEEK, WITH  
CAUTION STAGE UNLIKELY UNTIL THIS WEEKEND.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...HTS  
NEAR TERM...HTS  
SHORT TERM...HTS  
LONG TERM...CJL  
AVIATION...HTS/CJL  
MARINE...HTS/CJL  
TIDES/COASTAL FLOODING...HTS  
 
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