780  
FXUS61 KLWX 240247  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
1047 PM EDT MON OCT 23 2017  
   
SYNOPSIS
 
 
A COLD FRONT WILL MOVE ACROSS THE AREA LATE TONIGHT AND PUSH  
EAST OF THE CHESAPEAKE BAY TUESDAY MORNING. HIGH PRESSURE WILL  
GRADUALLY BUILD ACROSS THE REGION DURING THE SECOND HALF OF THE  
WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
FRONTAL BOUNDARY RESIDES FROM OHIO THROUGH KHTS TO WESTERN SOUTH  
CAROLINA AT THIS TIME. A SOLID LINE OF SHOWERS RESIDES EAST OF  
THERE...ACROSS THE POTOMAC HIGHLANDS THROUGH CENTRAL VIRGINIA  
AND INTO NORTH CAROLINA...IN A ZONE OF 50+ KT EFFECTIVE SHEAR.  
INSTABILITY, ON THE OTHER HAND, REMAINS QUITE A CHALLENGE. THERE  
IS ALMOST NONE (23 J/KG MUCAPE OR 1 J/KG MLCAPE) FROM THE 00Z  
IAD RAOB WITH A CAPPING INVERSION AT 800 MB. WINDS HAVE NOT  
BEEN MIXING DOWN AT ALL. EVEN WHERE INSTABILITY, AND CONVECTIVE  
DEVELOPMENT, IS BETTER...MIXING HAS BEEN PROBLEMATIC.  
 
GUIDANCE SUGGESTING THAT THERE WILL BE ANOTHER SURGE IN THE LOW  
LEVEL JET BETWEEN 11 PM AND 2 AM. THIS IS COINCIDENT WITH THE  
ENHANCED RADAR ECHOES ENTERING VIRGINIA. THEREFORE, THE THREAT  
FOR ISOLATED THUNDER HAS NOT ENDED. THE BIG QUESTION IS WHETHER  
ANYTHING WILL MIX TO THE SURFACE. WOULD NOT BANK ON IT, BUT AT  
THE SOME TIME CANNOT COMPLETELY RULE IT OUT EITHER.  
 
THE SHEAR AXIS HAS PASSED EAST OF NELSON COUNTY, SO THE TORNADO  
WATCH HAS BEEN DROPPED. IN ADDITION, HAVE MADE ADJUSTMENTS TO  
THE WIND ADVISORY. STILL BELIEVE THAT THE RIDGES VULNERABLE TO  
THE LOW LEVEL JET BUMPING INTO IT. BUT, GIVEN THE POOR MIXING,  
HAVE REMOVED THE I-95 CORRIDOR. FURTHER, SINCE THE JET WILL BE  
EAST OF THE BLUE RIDGE, HAVE CANCELLED THE ADVISORY FOR POINTS  
WEST.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
CDFNT WILL PUSH EAST OF THE BAY BY 12Z WITH SHOWERS ENDING.  
STILL MILD UNDER WESTERLY FLOW. UPPER TROUGH AXIS CROSSES THE  
AREA WED (GFS) OR WED NIGHT (ECMWF) WITH TEMPS STAYING IN THE  
60S DURING THE DAY AND 40S AT NIGHT. ANY PRECIP WOULD BE  
CONFINED TO THE UPSLOPE AREAS.  
 

 
   
LONG TERM /THURSDAY THROUGH MONDAY/
 
 
TROUGHING WILL REMAIN ENTRENCHED OVER THE EASTERN CONUS THROUGH THE  
PERIOD AS RIDGING PERSISTS OUT WEST AND OVER THE NORTH ATLANTIC.  
THIS WILL LEAD TO NEAR NORMAL TEMPERATURES LATE THIS WEEK INTO THE  
WEEKEND. A SPOKE OF ENERGY WILL ROTATE AROUND AN UPPER LOW STATIONED  
JUST SOUTHWEST OF JAMES BAY LIKELY BRINGING ANOTHER PERIOD OF  
UNSETTLED WEATHER AT SOME POINT NEXT WEEKEND, BUT TIMING/PLACEMENT  
DETAILS REMAIN FUZZY THIS FAR OUT.  
 

 
   
AVIATION /03Z TUESDAY THROUGH SATURDAY/
 
 
SHALLOW LINE OF CONVECTION WILL MOVE ACROSS TERMINALS TONIGHT  
BETWEEN 03Z-09Z. AM KEEPING FLIGHT RESTRICTIONS AT MVFR AT THIS  
TIME. THERE MAY BE LOCAL IFR RESTRICTIONS, BUT CONFIDENCE LOW  
IN WHEN/WHERE. THUS FAR, WIND GUSTS HAVENT MADE IT TO THE GROUND  
EITHER, AND WILL BE REDUCING GUST FORECASTS TO 30-35 KT MAX.  
 
MAINLY VFR EXPECTED LATE IN THE WEEK WITH LIGHT FLOW.  
 

 
   
MARINE
 
 
WINDS ARE EXPECTED TO STRENGTHEN RAPIDLY TONIGHT IN RESPONSE TO  
STRENGTHENING LOW-LEVEL JET. MAIN CHANNEL OF THE BAY AND LOWER  
POTOMAC SHOULD EXPERIENCE GALE FORCE WINDS EASILY WHILE THE  
UPPER BAY AND UPPER POTOMAC THE WINDS WILL DEPEND MORE ON  
STRENGTH/INTENSITY OF CONVECTION. THINK THERE COULD BE A 3-HR  
PERIOD WHERE THEY ALSO EXPERIENCE BRIEF GALES, SO RAISED THE  
GALE WARNING EVERYWHERE. CONVECTIVE LINE MOVES EAST OF THE BAY  
BY 15Z TUE AT THE LATEST WITH WINDS DIMINISHING AND SHOWERS  
ENDING. SMWS MAY ALSO BE REQUIRED LATER TONIGHT.  
 
LIGHT FLOW WITH HIGH PRESSURE OVER THE WATERS THU-FRI.  
 

 
   
TIDES/COASTAL FLOODING
 
 
WATER LEVELS HAVE INCREASED WITH THE INCOMING TIDE UP THE  
CHESAPEAKE BAY. DEPARTURES HAVE RISEN TO AROUND 1 FT, WHICH  
WOULD BE PROBLEMATIC FOR BALTIMORE CITY/COUNTY. HAVE ADDED THEM  
TO THE ADVISORY FOR TONIGHT'S TIDE CYCLE. UNCERTAINTY AS TO HOW  
MUCH SURGE WILL REACH HAVRE DE GRACE REMAINS (ESTOFS OUTPUT  
OVERDONE) SO HAVE KEPT PEAK TIDE UNDER ADVISORY LEVELS. THE  
MARGIN OF ERROR STRADDLES THAT THRESHOLD.  
 
UPDATE, BASED ON CURRENT OBS, HAVE INCLUDED DC/ALEXANDRIA IN THE  
ADVISORY FOR TONIGHTS TIDE CYCLE.  
 
AN ADVISORY REMAINS IN EFFECT FOR ANNAPOLIS TOMORROW. WOULD NOT  
RULE OUT OTHER SITES AS WELL. (SNAP-EX SUGGESTS BALTIMORE SHOULD  
BE INCLUDED.) HOWEVER, THERE IS COPIOUS UNCERTAINTY AS WELL.  
HOPEFULLY WE WILL WORK SOME OF THOSE ISSUES OUT ONCE THE CURRENT  
TIDE CYCLE PASSES.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...COASTAL FLOOD ADVISORY UNTIL 2 AM EDT TUESDAY FOR DCZ001.  
MD...WIND ADVISORY UNTIL 6 AM EDT TUESDAY FOR MDZ004>006-503-505-  
507-508.  
COASTAL FLOOD ADVISORY UNTIL 2 AM EDT TUESDAY FOR MDZ011.  
COASTAL FLOOD ADVISORY UNTIL 1 PM EDT TUESDAY FOR MDZ014.  
VA...WIND ADVISORY UNTIL 6 AM EDT TUESDAY FOR VAZ037>040-050-051-  
501-502-505-507-508.  
COASTAL FLOOD ADVISORY UNTIL 2 AM EDT TUESDAY FOR VAZ054.  
WV...NONE.  
MARINE...GALE WARNING UNTIL 8 AM EDT TUESDAY FOR ANZ530>533-535>542.  
SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EDT TUESDAY FOR  
ANZ530>533-537>542.  
GALE WARNING UNTIL 3 PM EDT TUESDAY FOR ANZ534-543.  
 

 
 

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