008  
FXUS61 KLWX 180029  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
829 PM EDT SUN OCT 17 2021  
   
SYNOPSIS
 
 
HIGH PRESSURE IS EXPECTED TO SLOWLY BUILD EASTWARD TO OUR SOUTH  
THROUGH THE MIDDLE OF THE WEEK. A COLD FRONT WILL LIKELY CROSS  
THE REGION LATE IN THE WEEK.  
 

 
   
NEAR TERM /THROUGH MONDAY/
 
 
A POTENT UPPER-LEVEL JETMAX WILL PASS THROUGH THE AREA THIS  
EVENING WHILE HIGH PRESSURE REMAINS OFF TO THE SOUTHWEST. COLD  
ADVECTION AND FORCING FROM THE DISTURBANCE MAY BRING A FEW  
SPRINKLES ACROSS NORTHERN/WESTERN MD INTO THE ALLEGHENY AND  
POTOMAC HIGHLANDS AS WELL AS THE EXTREME NORTHERN SHENANDOAH  
VALLEY. HOWEVER, MOST PLACES WILL BE DRY SINCE MOISTURE IS  
LIMITED.  
 
THE DISTURBANCE WILL MOVE OFF TO THE EAST OVERNIGHT AND HIGH  
PRESSURE WILL CENTER ITSELF OVER THE TENNESSEE VALLEY. GUSTY  
NORTHWEST WINDS WILL CONTINUE ALONG THE RIDGE TOPS, BUT THERE  
SHOULD BE ENOUGH RADIATION FOR A NOCTURNAL INVERSION TO SET IN  
OVER MANY OF THE VALLEYS. THIS WILL CAUSE LIGHT WINDS OVERNIGHT,  
AND RADIATIONAL COOLING WILL TAKE PLACE. MIN TEMPS WILL RANGE  
FROM THE MID TO UPPER 30S IN THE COLDER VALLEYS, TO THE 40S  
ACROSS MOST OTHER LOCATIONS, TO NEAR 50 IN DOWNTOWN WASHINGTON  
AND BALTIMORE. SOME FROST IS POSSIBLE IN THE COLDER VALLEYS WEST  
OF THE BLUE RIDGE MOUNTAINS, BUT CONFIDENCE FOR ANY HEADLINE IS  
TOO LOW AT THIS TIME DUE SINCE THE HIGH IS CENTERED OFF TO THE  
SOUTHWEST AND A GRADIENT WILL REMAIN IN PLACE.  
 
HIGH PRESSURE WILL REMAIN OVER THE TENNESSEE VALLEY FOR MONDAY,  
AND MORE GUSTY NORTHWEST WINDS ARE EXPECTED, ESPECIALLY IN THE  
LATE MORNING AND AFTERNOON AS THE MIXING LAYER INCREASES.  
TEMPERATURES ARE EXPECTED TO BE NEAR NORMAL THROUGH MONDAY WITH  
HIGHS GENERALLY IN THE 60S AND LOWS IN THE 40S (COOLER OVER THE  
HIGHER ELEVATIONS WHERE SUB-FREEZING WIND CHILLS ARE LIKELY).  
 

 
   
SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/
 
 
THE TROUGH WILL BEGIN TO SLOWLY LIFT AWAY FROM THE AREA AS HIGH  
PRESSURE SETTLES NEARBY TO OUR SOUTH BY TUESDAY. THIS SHOULD  
CAUSE THE BREEZY CONDITIONS TO RELENT. SHELTERED HIGH ELEVATION  
VALLEYS MAY EXPERIENCE FROST MONDAY NIGHT AS A RESULT, WITH ONE  
OF THE COOLEST NIGHTS OF THE SEASON EXPECTED THUS FAR AREAWIDE.  
 
A WARMING TREND WILL COMMENCE TUESDAY AS COLD AIR ADVECTION  
CEASES. THIS WILL LIKELY RESULT IN HIGH TEMPERATURES PUSHING  
INTO THE LOWER 70S ACROSS MUCH OF THE REGION.  
 
DRY WEATHER IS EXPECTED THROUGH AT LEAST TUESDAY NIGHT WITH HIGH  
PRESSURE IN CONTROL.  
 

 
   
LONG TERM /WEDNESDAY THROUGH SUNDAY/
 
 
HEIGHTS WILL RISE AS SURFACE RIDGING BUILDS ACROSS THE REGION INTO  
WEDNESDAY. THIS WILL PROMOTE DRY CONDITIONS WITH A CONTINUED WARMING  
TREND. BY THURSDAY EVENING, AN UPPER-LEVEL TROUGH AND SURFACE  
COLD FRONT WILL LIKELY MOVE THROUGH THE REGION. THIS MAY  
PROMOTE SHOWERS AND POSSIBLY THUNDERSTORMS ACROSS THE REGION.  
WITH A BROAD TROUGH REMAINING NEARBY INTO THE WEEKEND, SOME  
GUIDANCE HAS A REINFORCING FRONT MOVING INTO THE REGION FRIDAY  
OR SATURDAY. REGARDLESS, MORE SEASONABLE TEMPERATURES ARE  
EXPECTED TO END THE LONG TERM PERIOD AS CANADIAN HIGH PRESSURE  
BUILDS OVERHEAD.  
 
NO FROST OR FREEZE CONCERNS ARE ANTICIPATED AFTER TUESDAY  
MORNING UNTIL FRIDAY NIGHT. SOME UNCERTAINTY REMAINS WITH THE  
WINDS POSSIBLY REMAINING STRONG ENOUGH TO REDUCE THE FROST RISK  
ACROSS THE HIGHER TERRAIN, WITH LITTLE TO NO RISK TO THE EAST.  
THERE IS A BETTER CHANCE FOR A HARD FREEZE ACROSS THE HIGHER  
TERRAIN OF THE ALLEGHENY FRONT SATURDAY NIGHT WITH LOW  
TEMPERATURES NEAR OR JUST BELOW 32F, BUT CERTAINTY IS LOW THIS  
FAR OUT. THERE COULD ALSO BE PATCHY FROST AS FAR EAST AS THE  
I-81 CORRIDOR GIVEN CANADIAN HIGH PRESSURE BUILDING OVERHEAD,  
BUT AGAIN CONFIDENCE IS VERY LOW.  
 

 
   
AVIATION /01Z MONDAY THROUGH FRIDAY/
 
 
VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY NIGHT. THE MAIN  
CONCERN WILL BE GUSTS OF 20-25 KNOTS FROM THE NORTHWEST  
MONDAY FROM AROUND MID-MORNING THROUGH THE AFTERNOON. THE WIND  
WILL LIKELY RELAX MONDAY NIGHT AND TUESDAY.  
 
VFR CONDITIONS ARE EXPECTED WEDNESDAY. THERE MAY BE A PERIOD OF  
REDUCED VSBYS OR CIGS THURSDAY EVENING AS THE NEXT COLD FRONT  
POSSIBLY BRINGS SHOWERS AND A SHIFT/INCREASE IN WINDS.  
 

 
   
MARINE
 
 
GUSTY NORTHWEST WINDS WILL CONTINUE OVER THE OPEN WATERS THROUGH  
TONIGHT, WITH GUSTS AROUND 25 TO 30 KNOTS EXPECTED. THE SCA  
CONTINUES. HOWEVER, THE GALE WARNING WAS CANCELLED SINCE MOST  
GUIDANCE SHOWS AROUND 30 KNOTS IN THE MIXING LAYER INSTEAD OF 35  
KNOTS.  
 
THE WIND IS EXPECTED TO SUBSIDE (POSSIBLY QUICKLY) OVER THE  
NARROWER WATERWAYS THIS EVENING INTO THE OVERNIGHT, THEN  
INCREASE AGAIN WITH SOLID 20 TO 25 (POSSIBLY NEAR 30) KT GUSTS  
DURING THE DAYTIME MONDAY. WINDS SHOULD THEN GRADUALLY DIMINISH  
THROUGH TUESDAY, THOUGH SCAS WILL LIKELY NEED TO BE EXTENDED.  
 
SCA LEVEL WINDS MAY RETURN THURSDAY WITH A COLD FRONTAL PASSAGE  
AS WELL AS SHOWERS OR THUNDERSTORMS. SCA CONDITIONS COULD  
LINGER INTO FRIDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
PERSISTENT BRISK NORTHWESTERLY FLOW MAY LEAD TO NEAR BLOW OUT  
TIDES THROUGH MONDAY.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT MONDAY FOR ANZ531>534-537-  
539>543.  
SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ530-535-  
536-538.  
SMALL CRAFT ADVISORY FROM 10 AM TO 6 PM EDT MONDAY FOR ANZ530-  
535-536-538.  
 

 
 

 
SYNOPSIS...DHOF  
NEAR TERM...BJL/DHOF  
SHORT TERM...DHOF  
LONG TERM...CPB  
AVIATION...BJL/DHOF/CPB  
MARINE...BJL/DHOF/CPB  
TIDES/COASTAL FLOODING...DHOF  
 
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