302  
FXUS61 KAKQ 212015  
AFDAKQ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE WAKEFIELD VA  
415 PM EDT FRI JUL 21 2017  
   
SYNOPSIS
 
 
HOT AND HUMID CONDITIONS WILL CONTINUE OVER THE REGION THROUGH  
SUNDAY. A WEAKENING COLD FRONT WILL GRADUALLY PUSH ACROSS THE  
AREA LATE SUNDAY THROUGH MONDAY, WITH TEMPERATURES COOLING DOWN  
TO NEAR NORMAL LEVELS MONDAY THROUGH THURSDAY.  
 

 
   
NEAR TERM /THROUGH SATURDAY/
 
 
WEAK SFC/LEE TROUGH IN PLACE ACROSS THE LOCAL AREA THIS AFTN,  
WITH WNW FLOW PREVAILING ALOFT AROUND THE BASE OF AN UPPER  
LEVEL TROUGH CENTERED OVER EASTERN CANADA. HOT/HUMID AIRMASS IN  
PLACE, PARTICULARLY HUMID OVER THE E AND SE ZONES WITH DEW PTS  
STILL RANGING FROM 75 TO 80 F, WITH SOMEWHAT LOWER (THOUGH STILL  
ELEVATED) DEW PTS OVER CENTRAL AND S CENTRAL VA (MAINLY FROM  
THE MID/UPPER 60S TO AROUND 70 F). HEAT ADVISORY REMAINS IN  
EFFECT THROUGH 8 PM FOR MOST OF THE AREA (THOUGH AREAS THAT  
RECEIVE RAIN WILL RAPIDLY COOL).  
 
THE WNW FLOW PATTERN APPEARS TO BE ALLOWING THE ONGOING  
CONVECTION/MCS ALONG THE MTNS TO HOLD TOGETHER AS IT APPROACHES  
THE NW FLANK OF THE CWA. HAVE RAMPED POPS UP TO LIKELY THROUGH  
6PM FOR THE NW, AND HIGH CHANCE 30-50% FOR MUCH OF THE NORTHERN  
1/2 OF THE CWA THROUGH MIDNIGHT, LINGERING INTO SAT MORNING FOR NE  
ZONES.  
 
VERY WARM/HUMID TONIGHT WITH LOWS MAINLY 75 TO 80 F. NOT AS HOT  
MOST AREAS FOR SAT, DUE TO POTENTIAL FOR MORE CLOUDS AND AS  
CORE OF 850 MB HEAT SHIFTS A BIT S. HOWEVER, WITH SLIGHTLY  
HIGHER DEW PTS THAN FRI EXPECT MOST OF THE AREA TO REACH HEAT  
ADVISORY CRITERIA SAT AFTN EVEN WITH HIGHS ON AVG ONLY IN THE  
MID 90S. AS AIRMASS DESTABILIZES MORE BY SAT AFTN/EARLY  
EVENING, AND AS HEIGHTS ALOFT DROP, CONVECTION DEVELOPING FROM  
THE NW WILL BE MORE LIKELY TO HOLD TOGETHER FOR AT LEAST 30-50%  
POPS ACROSS MOST AREAS (20% NE NC) FROM LATE SAT AFTN THROUGH  
SAT NIGHT. DEEP LAYER SHEAR WILL BE HIGHER AS THE UPPER TROUGH  
SHARPENS A BIT AND H5 TO H7 FLOW INCREASES. MOST OF THE CWA IS  
IN A MARGINAL RISK FOR SEVERE WX, WITH A SLIGHT RISK FOR THE  
FAR N/NE. WIND WILL BE THE PRIMARY THREAT WITH LARGE HAIL ALSO  
POSSIBLE.  
 

 
   
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
 
 
LOWS MAINLY IN THE MID TO UPPER 70S SAT NIGHT, AND CONTINUED  
HOT AND HUMID WITH ADDITIONAL HEAT HEADLINES LIKELY NEEDED FOR  
SOME OF THE REGION ON SUN. HIGHS MAINLY IN THE MID TO UPPER 90S  
SUNDAY. SLIGHT RISK IN PLACE FOR MOST OF THE CWA, BUT MORE  
UNCERTAINTY EXISTS DEPENDING ON HOW LONG CONVECTIVE DEBRIS FROM  
SAT NIGHT HANGS AROUND AND POTENTIALLY KEEPS MORE CLOUDS AROUND.  
COLD FRONT SLATED TO PASS THROUGH WHILE WEAKENING LATE SUN NIGHT  
THROUGH MON. WILL MAINTAIN CHC POPS ALL ZONES SUN NIGHT, AND  
FAVOR HIGHEST POPS MON ACROSS THES WITH 20% POPS FOR THE N.  
SLIGHTLY LESS HUMID MONDAY, ESPECIALLY N. HIGHS MON 90 TO 95 F.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
 
 
COLD FRONT PROGGED TO PUSH OFFSHORE TUESDAY MORNING AS THE UPPER  
TROUGH SLIDES OVER THE NORTHEAST INTO THE CANADIAN MARITIMES.  
DEEPEST MOISTURE PUSHES OFFSHORE LATE MONDAY NIGHT, BUT WILL KEEP  
MENTION OF SLIGHT CHANCE TO CHANCE POPS NEAR THE COAST. SOUTHERN  
PORTION OF THE COLD FRONT EXPECTED TO STALL OVER THE CAROLINAS  
TUESDAY AS A BAGGY TROUGH LOCATES OVER THE SOUTHEAST. COMBINATION OF  
WEAK ENERGY IN THE UPPER FLOW AND A MOIST AIR MASS NEAR THE  
BOUNDARY, WILL KEEP MENTION OF SLIGHT CHANCE TO CHANCE POPS ACROSS  
THE FAR SOUTHEAST LOCAL AREA TUESDAY AFTERNOON. OTHERWISE, COOLER  
TUESDAY WITH A LIGHT NORTH TO NORTHEAST WIND. HIGHS GENERALLY IN THE  
UPPER 80'S TO AROUND 90 (NEAR SEASONABLE NORMS). HIGH PRESSURE AT  
THE SURFACE AND ALOFT SLIDES NORTH OF THE REGION TUESDAY NIGHT INTO  
WEDNESDAY AS ANOTHER TROUGH TRACKS ACROSS ONTARIO. MEANWHILE, A  
BROAD UPPER RIDGE OVER THE SOUTHERN PLAINS EXPANDS EASTWARD, BUT THE  
BAGGY TROUGH REMAINS OVER THE SOUTHEAST. BEST CHANCES FOR MEASURABLE  
PRECIP EXPECTED TO BE SOUTH OF THE REGION WEDNESDAY, BUT WILL CARRY  
SLIGHT CHANCE TO LOW END CHANCE POPS ACROSS THE SOUTHERN PORTIONS OF  
THE FORECAST AREA. HIGHS WEDNESDAY GENERALLY IN THE MID 80'S.  
ANOTHER TROUGH TRACKS INTO THE GREAT LAKES AND NORTHEAST WEDNESDAY  
NIGHT AND THURSDAY, PUSHING ANOTHER WEAKENING COLD FRONT INTO THE  
MID-ATLANTIC REGION THURSDAY AFTERNOON. WILL NEED TO WATCH FOR  
UPSTREAM CONVECTION WEDNESDAY NIGHT IN NORTHWEST FLOW ALOFT, SO HAVE  
ADDED CHANCE POPS FOR THE MARYLAND EASTERN SHORE. WITH THE BOUNDARY  
AND CYCLONIC FLOW OVER THE REGION THURSDAY, HAVE CHANCE POPS FOR  
DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS. HIGHS THURSDAY GENERALLY  
IN THE UPPER 80'S TO LOW 90'S. MEDIUM RANGE GUIDANCE DEPICTS  
ADDITIONAL ENERGY DIGGING DOWN THE BACKSIDE OF THE UPPER TROUGH  
FRIDAY, WITH A WAVE OF LOW PRESSURE PROGGED TO DEVELOP ALONG THE MID-  
ATLANTIC FRONT. TIMING AND SPATIAL DIFFERENCES AT THAT TIMEFRAME OF  
THE FORECAST CAUSE A GREAT DEAL OF UNCERTAINTY, SO HAVE ONLY  
MENTIONED 20-40% POPS AT THIS TIME. HIGHS BACK AROUND SEASONAL  
NORMS, IN THE UPPER 80'S TO LOW 90'S.  
 

 
   
AVIATION /20Z FRIDAY THROUGH WEDNESDAY/
 
 
MAINLY VFR CONDITIONS WILL PREVAIL AT THE TAF SITES THIS  
AFTERNOON...OVERNIGHT AND INTO SAT MORNING, AS SFC HIGH  
PRESSURE SITS WELL OFF THE SE COAST WITH A TROUGH TO THE LEE OF  
THE APPALACHIANS. SCATTERED CU AROUND 5-6KFT IS DEVELOPING  
ACROSS THE REGION IN ADDITION TO A FEW ISOLATED SHOWERS AS OF  
18Z. CONVECTION MOVING INTO WESTERN VA WILL LIKELY WEAKEN SOME  
AS IT CROSSES THE MOUNTAINS...HOWEVER...SOME SHOWER AND STORM  
ACTIVITY WILL MAKE IT INTO CENTRAL VA AND ACROSS THE EASTERN  
SHORE LATE THIS EVENING. HAVE VCSH AT RIC FROM 21Z-00Z,  
OTHERWISE MAINLY DRY MOST PLACES THIS EVENING WITH A 20-30% OF  
SHOWERS/TSTMS LATE THIS AFTN. EXPECT A LITTLE BETTER CHANCE  
OF STORMS LATE SAT ESPECIALLY FROM RIC NORTH INCLUDING THE MD  
EASTERN SHORE AS ANOTHER WAVE MOVE ACROSS IN THE NW FLOW ALOFT.  
 

 
   
MARINE
 
 
LATEST SURFACE ANALYSIS DEPICTS HIGH PRESSURE OVER THE  
WESTERN ATLANTIC WITH A TROUGH OF LOW PRESSURE OVER CENTRAL  
VIRGINIA. OBS INDICATE A LIGHT SOUTH TO SOUTHEAST WINDS AT OR BELOW  
10 KNOTS. WAVES ARE GENERALLY 1 FOOT AND SEAS 2 FEET. DIURNAL  
INCREASE IN THE LOW LEVEL WINDS EXPECTED AGAIN TONIGHT OVER THE LOW  
BAY AND SOUTHERN COASTAL WATERS. HI-RES GUIDANCE DEPICTS WINDS  
AROUND 15 KNOTS, WITH AN OCCASIONAL GUST OF 18 KNOTS, MAINLY  
CENTERED A FEW HOURS EITHER SIDE OF 11PM (03Z). CONDITIONS EXPECTED  
TO REMAIN SUB-SCA. WAVE KICK UP TO 2 FEET IN THE LOWER BAY AND SEAS  
2-3 FEET. STAGNANT SURFACE PATTERN PERSISTS THROUGH THE WEEKEND.  
WINDS GENERALLY SOUTHWEST AT OR BELOW 15 KNOTS, BUT NEAR SCA  
CONDITIONS POSSIBLE LATE EACH DAY INTO THE OVERNIGHT PERIOD. SEAS  
GENERALLY 2-3 FEET (UPWARDS OF 4 FEET OVERNIGHT) WITH WAVES OF 1-2  
FEET.  
 
A WEAKENING COLD FRONT APPROACHES THE REGION LATE MONDAY, DROPPING  
ACROSS THE REGION MONDAY NIGHT INTO TUESDAY MORNING. FLOW BACKS TO  
THE NORTHWEST TO NORTH TUESDAY AT OR BELOW 10-15 KNOTS. HIGH  
PRESSURE BUILDS ACROSS THE NORTHEAST INTO WEDNESDAY, RESULTING IN  
ONSHORE FLOW WEDNESDAY. ANOTHER WEAKENING COLD FRONT APPROACHES THE  
REGION WEDNESDAY NIGHT AND THURSDAY, STALLING OVER THE REGION INTO  
NEXT WEEKEND.  
 

 
   
CLIMATE
 
 
HEAT WAVE IS EXPECTED TO DEVELOP, MAINLY TODAY THROUGH SUNDAY.  
THE 2ND HALF OF JULY IS CLIMATOLOGICALLY THE HOTTEST FEW WEEKS  
OF THE YEAR, SO WE STILL MAY NOT SET ANY DAILY RECORDS AT OUR  
MAIN CLIMATE SITES. FOR REFERENCE, RECORD HIGHS TODAY THROUGH  
SUNDAY ARE LISTED BELOW:  
 
* DATE: FRI(7/21) SAT(7/22) SUN(7/23)  
 
* RIC: 104/1930 103/1952 103/1952  
* ORF: 101/1926 102/2011 103/2011  
* SBY: 106/1930 104/1930 103/2011  
* ECG: 102/1987 104/1952 104/1952  
 

 
   
AKQ WATCHES/WARNINGS/ADVISORIES
 
 
MD...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MDZ021>024.  
HEAT ADVISORY FROM 10 AM TO 8 PM EDT SATURDAY FOR MDZ021>024.  
NC...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NCZ012>017-  
030>032.  
HEAT ADVISORY FROM 10 AM TO 8 PM EDT SATURDAY FOR NCZ012>017-  
030>032.  
VA...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR VAZ048-061-062-  
064-067>069-075>090-092-093-095>100-509>525.  
HEAT ADVISORY FROM 10 AM TO 8 PM EDT SATURDAY FOR VAZ060>062-  
064>069-075>090-092-093-095>100-511>525.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...LKB  
NEAR TERM...LKB  
SHORT TERM...LKB/TMG  
LONG TERM...MAS  
AVIATION...TMG/JAO  
MARINE...MAM/SAM  
CLIMATE...  
 
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