709  
FXUS61 KAKQ 271331  
AFDAKQ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE WAKEFIELD VA  
931 AM EDT THU APR 27 2017  
   
SYNOPSIS
 
 
A COLD FRONT APPROACHES THE MID ATLANTIC REGION TODAY, STALLING  
NEAR THE MOUNTAINS TONIGHT. HIGH PRESSURE PREVAILS OFF THE  
SOUTHEAST COAST THE REST OF FRIDAY THROUGH THE WEEKEND. THE NEXT  
COLD FRONT PUSHES ACROSS THE REGION EARLY NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
UPDATE...BASED ON WEBCAMS AND OBSERVATION TRENDS, ANY FOG ON THE  
MD LOWER EASTERN SHORE HAS LIFTED INTO LOW STRATUS AND WILL  
CONTINUE TO LIFT AND SCOUR OUT OVER THE NEXT HOUR OR SO AS  
SOUTH WINDS INCREASE. MEANWHILE, STRATOCUMULUS IS MOVING  
OFFSHORE AS OF 900 AM WITH HIGH CIRRUS PUSHING IN FROM THE WEST.  
ADDITIONAL MID TO HIGH LEVEL CLOUDS EXPECTED TO PUSH INTO THE  
EASTERN PIEDMONT THIS AFTERNOON AS A COLD FRONT APPROACHES THE  
OHIO VALLEY. THIS MAY HAMPER FULL WARMING POTENTIAL IN THESE  
AREAS AND ADJUSTED HIGH TEMPS DOWN A DEGREE OR TWO AS A RESULT.  
ALSO ADJUSTED ATLANTIC BEACHES DOWN 5-10 DEGREES FOR HIGHS WITH  
TEMPS STARTING OUT IN THE UPPER 50S THIS MORNING AND AN ONSHORE  
WIND COMPONENT OVER COLDER WATERS. OTHERWISE, TODAY WILL BE WARM  
WITH FAIR WEATHER CUMULUS DEVELOPMENT BY THIS AFTERNOON.  
 
PREVIOUS DISCUSSION...  
LATEST GOES WATER VAPOR IMAGERY DEPICTS A BROAD/ANOMALOUS UPPER  
TROUGH ENCOMPASSING MUCH OF THE WESTERN/CENTRAL CONUS, WITH AN  
UPPER LEVEL RIDGE OVER THE EAST. AT THE SURFACE, WEAK AREA OF  
LOW PRESSURE IS LOCATED OFFSHORE THE NORTHEAST COAST WITH HIGH  
PRESSURE WELL OFFSHORE EXTENDING WESTWARD OVER THE SOUTHEAST. A  
COLD FRONT ASSOCIATED WITH THE UPPER TROUGH IS LOCATED ALONG THE  
MISSISSIPPI RIVER VALLEY. A DENSE FOG ADVISORY REMAINS IN  
EFFECT FOR THE LOWER MARYLAND EASTERN SHORE, WITH AN AREA OF  
DENSE FOG VISIBLE IN THE OBS AND ON SATELLITE. OTHERWISE, ONLY  
SOME PATCHY FOG INLAND AS LIGHT SOUTHERLY FLOW AND RELATIVELY  
DRY LOW LEVELS HAVE KEPT WIDESPREAD FOG AT BAY.  
 
FOG EXPECTED TO ERODE/LIFT SHORTLY AFTER DAYBREAK IN RESPONSE TO  
QUICKLY WARMING TEMPERATURES. THE UPPER LEVEL RIDGE AXIS SLIDES  
OFFSHORE LATE MORNING AS THE CENTRAL US TROUGH DE-AMPLIFIES AND  
LIFTS OVER THE OHIO VALLEY AND INTO THE GREAT LAKES REGION. AN  
ASSOCIATED COLD FRONT WILL REACH THE CENTRAL APPALACHIANS LATE  
TODAY. INCREASING RETURN FLOW AHEAD OF THE FRONT (SOUTHWEST  
GUSTS OF 20-25 MPH) AND 850MB TEMPERATURES AROUND +14 TO +16C  
(+1 STANDARD DEVIATION) RESULTS IN A WARM DAY, WITH TEMPERATURES  
GENERALLY 10+ DEGREES WARMER THAN YESTERDAY. HIGHS GENERALLY IN  
THE MID 80'S. COOLER ALONG THE COAST. INCREASING MID TO UPPER  
LEVEL CLOUDS LATE TODAY MAY KEEP SOME OF THE FAR WESTERN  
PIEDMONT IN THE LOW TO MID 80'S. OTHERWISE, OUTSIDE OF SOME HIGH  
CLOUDS SPREADING OVER THE REGION TODAY FROM A DECAYING LINE OF  
SHOWERS, A MOSTLY SUNNY SKY IS EXPECTED.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/
 
 
SHOWERS AND THUNDERSTORMS PROGGED TO DEVELOP ALONG THE COLD  
FRONT THIS AFTERNOON FROM THE OHIO VALLEY TO THE SOUTHEAST. HI-  
RES GUIDANCE PUSHES A WEAKENED VERSION OF THE CONVECTIVE LINE  
INTO THE PIEDMONT EARLY THIS EVENING AS THE UPPER LEVEL FORCING  
BECOMES DISPLACED FROM THE DEEPEST GULF MOISTURE. SHORT TERM  
GUIDANCE INDICATING BETTER MOISTURE RETURN COMPARED TO 24 HOURS  
AGO THANKS TO A DEVELOPING 30-40 KT LOW LEVEL JET. GOOD MOISTURE  
FLUX ADVECTS ANOMALOUS PRECIPITABLE WATER VALUES INTO THE  
REGION AHEAD OF THE LINE/PRE-FRONTAL SURFACE TROUGH. THERMAL  
SOUNDINGS INDICATE ELEVATED INSTABILITY AS HEIGHT FALLS AND COLD  
AIR ADVECTION ALOFT STEEPEN MID LEVEL LAPSE RATES. SHOWALTERS  
RANGE FROM -1 TO -2. DEEP LAYER SHEAR PROGGED AROUND 30-40 KNOTS  
DUE TO INCREASING WINDS ALOFT. HOWEVER, GIVEN THE LACK OF  
OVERALL FORCING AND THE CONVECTIVE LINE OUTRACING THE FRONT,  
HAVE KEPT POPS IN THE CHANCE CATEGORY TONIGHT. MAIN THREAT FROM  
THUNDERSTORMS WILL BE LOCALLY HEAVY RAINFALL. MILD TONIGHT, WITH  
LOWS GENERALLY IN THE MID TO UPPER 60'S.  
 
WEAK SURFACE TROUGH/CONVERGENCE BOUNDARY STALLS NEAR THE COAST  
FRIDAY MORNING AS THE DEEPEST MOISTURE PUSHES OFFSHORE. EVEN  
THOUGH THE BEST MOISTURE PUSHES OFFSHORE, ENOUGH MOISTURE AND  
INSTABILITY NEAR THE COAST WILL KEEP MENTION OF ISOLATED TO  
SCATTERED SHOWERS AND THUNDERSTORMS IN THE FORECAST THROUGH  
EARLY-MID AFTERNOON. MEANWHILE, THE SUBTROPICAL RIDGE AMPLIFIES  
OFF THE SOUTHEAST COAST FRIDAY. EARLY MORNING CLOUDS AND  
CONVECTION WILL TEMPER TEMPERATURES FROM REACHING THEIR FULL  
POTENTIAL FRIDAY AFTERNOON. HIGHS SIMILAR TO TODAY, GENERALLY IN  
THE MID (POSSIBLY UPPER) 80'S. COOLER NEAR THE COAST.  
 
HEIGHTS CONTINUE TO BUILD INTO SUNDAY AS 850MB TEMPS WARM TO +16  
TO +18C (+2 STANDARD DEVIATIONS). THE RESULT WILL BE THE WARMEST  
DAY OF THE SEASON WITH WIDESPREAD READINGS IN THE LOW 90'S.  
DEWPOINTS IN THE 60'S WILL PUSH HEAT INDEX VALUES INTO THE MID  
90'S INLAND. A BACKDOOR FRONT PROGGED TO DROP INTO THE NORTHERN  
MID-ATLANTIC REGION LATE SATURDAY, BUT MODELS INDICATE LARGE  
SPATIAL AND TIMING DIFFERENCES. WHILE THE MODELS INDICATE A  
GREAT DEAL OF INSTABILITY, SOUNDINGS INDICATE A CAP JUST ABOVE  
850MB. MOISTURE IS ALSO LIMITED WITH PRECIPITABLE WATER VALUES  
AT OR BELOW 1.25 INCHES. WILL MAINTAIN SLIGHT CHANCE POPS ACROSS  
THE NORTH NEAR THE DROPPING FRONT, BUT BELIEVE SEA-BREEZE  
BOUNDARIES WILL STRUGGLE TO OVERCOME THE LACK OF MOISTURE AND  
WARM TEMPERATURES ALOFT.  
 

 
   
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
 
 
TEMPERATURES ARE EXPECTED TO REMAIN WELL ABOVE NORMAL THROUGH  
SUN AS AN UPPER LEVEL RIDGE REMAINS ANCHORED JUST OFF THE EAST  
COAST. A BACKDOOR COLD FRONT COULD AFFECT NRN PORTIONS OF THE  
AREA SAT NIGHT THRU SUN MORNING WITH A SLGT CHC OF SHOWERS, THEN  
A SLOWLY APPROACHING COLD FRONT FROM THE WEST COULD PRODUCE  
ISOLATED OR WIDELY SCTD SHOWERS OR TSTMS SUN AFTN INTO SUN  
EVENING, ESPECIALLY WRN HALF OF THE REGION. LOWS SAT NIGHT IN  
THE MID 60S TO NEAR 70. HIGHS ON SUN IN THE UPPER 70S TO MID  
80S.  
 
THAT COLD FRONT WILL PUSH THRU THE MTS BY LATE MON, THEN CROSS  
THE AREA AND MOVE OFF THE COAST MON NIGHT INTO TUE MORNING. HAVE  
HIGH CHC TO LIKELY POPS FOR SHOWERS/TSTMS DURING THIS PERIOD.  
HIGHS ON MON IN THE UPPER 70S TO MID 80S. LOWS MON NIGHT MAINLY  
IN THE UPPER 50S TO MID 60S. WEAK HIGH PRESSURE WILL PROVIDE DRY  
WX FOR LATER TUE MORNING THRU AT LEAST MOST OF WED, AS IT  
SLIDES FROM THE GULF COAST STATES TO OFF THE SE COAST. HIGHS ON  
TUE IN THE 70S, AND MAINLY IN THE MID TO UPPER 70S ON WED.  
 

 
   
AVIATION /13Z THURSDAY THROUGH MONDAY/
 
 
OUTSIDE OF IFR CONDITIONS DUE TO FOG ACROSS THE MARYLAND LOWER  
EASTERN SHORE, WIDESPREAD VFR CONDITIONS OBSERVED EARLY THIS  
MORNING. LIGHT SOUTHERLY WINDS AND RELATIVELY DRY LOW LEVELS  
INDICATED IN SOUNDINGS WILL LIMIT OVERALL FOG DEVELOPMENT BUT  
SOME EARLY MORNING PATCHY FOG POSSIBLE NORTH AND EAST OF KRIC.  
IFR CONDITIONS PREVAIL THRU EARLY MORNING FOR KSBY, OTHERWISE  
SKC.  
 
COLD FRONT APPROACHES FROM THE WEST TODAY WITH INCREASING  
SOUTHWEST FLOW LATE MORNING THROUGH THE AFTERNOON. EXPECT GUSTS  
OF 20-25 KNOTS. SCATTERED AFTERNOON CU EXPECTED INLAND AROUND  
4-6KFT AGL. WEAKENING LINE OF CONVECTION EXPECTED TO PUSH ACROSS  
THE REGION THIS EVENING THROUGH LATE TONIGHT. LOWER  
CEILINGS/VISIBILITIES WILL BE TIED TO CONVECTION.  
 
OUTLOOK...NEXT FRONTAL BOUNDARY WILL PROVIDE A FOCUS FOR MORE  
SHOWER/TSTM DEVELOPMENT LATE SAT. CIGS/VSBYS LOWER IN ANY  
CONVECTIVE ACTIVITY.  
 

 
   
MARINE
 
 
A COLD FRONT APPROACHES THE WATERS TODAY RESULTING IN AN  
INCREASE OF SOUTH AND SOUTHWEST WINDS THROUGH TONIGHT. DEEP LOW  
PRESSURE OVER THE UPPER GREAT LAKES WILL MOVE NORTH INTO CANADA  
WHICH WILL RELAX THE PRESSURE GRADIENT BY FRIDAY.  
 
SOUTHEAST TO SOUTH WINDS WERE GENERALLY 10 KNOTS OR LESS EARLY  
THIS MORNING. SEAS SUBSIDED OVERNIGHT BUT REMAIN 4 TO 5 FT NORTH  
OF PARRAMORE ISLAND. WHILE THERE MAY BE LULL IN 5 FOOT SEAS LATE  
THIS MORNING...THEY ARE EXPECTED TO BUILD ONCE AGAIN LATE TODAY  
AND INTO TONIGHT AS WINDS INCREASE.  
 
REPLACED SCA FOR HAZARDOUS SEAS WITH A SCA. THIS IS TO AVOID  
CONFUSION WITH WINDS INCREASING TODAY. THE SCA WAS ALSO EXPANDED  
TO ANZ654 (PARRAMORE ISLAND TO CAPE CHARLES) WHERE SCA  
CONDITIONS ARE EXPECTED TO DEVELOP BY THIS AFTERNOON. THERE IS  
INDICATION THE SCA MAY BE NEEDED FOR THE REST OF THE COASTAL  
ZONES FOR A SHORT PERIOD THIS EVENING BUT WILL LET THE DAY SHIFT  
ASSESS THE NEED. ELSEWHERE CONDITIONS ARE EXPECTED TO STAY BELOW  
SCA. ALTHOUGH WINDS OVER LAND ARE EXPECTED TO GUST OVER 20 KNOTS  
TODAY...THE COOL WATER WILL INHIBIT MIXING OVER THE MARINE AREA.  
 
THE COLD FRONT THAT APPROACHES THE WATERS TODAY WILL DISSIPATE  
OVER THE AREA FRIDAY MORNING. A DISORGANIZED PRESSURE PATTERN  
WILL PRODUCE LIGHT WINDS OVER THE WATERS FRIDAY. SEAS ARE  
FORECAST TO SUBSIDE TO BELOW 5 FEET BY MIDDAY FRIDAY. BENIGN  
CONDITIONS ARE INDICATED FOR THE MARINE AREA THROUGH THE  
WEEKEND. ANOTHER DEEP LOW PRESSURE SYSTEM WILL MOVE THROUGH THE  
UPPER MIDWEST EARLY NEXT WEEK. THIS ALONG WITH AN APPROACHING  
COLD FRONT WILL INCREASE THE PRESSURE GRADIENT LOCALLY AND  
ANOTHER SCA MAY BE NEEDED STARTING MONDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
THERE IS GRADUAL IMPROVEMENT IN WATER LEVELS THAT HAVE BEEN  
ELEVATED BY A NEW MOON AND LONG PERIOD SWELLS. SOME LOCATIONS  
WILL CONTINUE TO HAVE HIGH TIDES GET WITHIN A FEW TENTHS OF A  
FOOT OF MINOR FLOOD. AT THIS TIME...THE HIGH TIDE CYCLE EARLY  
FRIDAY MORNING AT BISHOPS HEAD MARYLAND TOUCHES MINOR FLOOD.  
 

 
   
CLIMATE
 
 
IT APPEARS LIKELY THAT RICHMOND AND NORFOLK WILL END THE MONTH  
WITH THE WARMEST APRIL ON RECORD. WARM TEMPERATURES DURING MOST  
OF THE MONTH COMBINED WITH AN UNSEASONABLY WARM PERIOD TO END  
APRIL ARE EXPECTED TO PUSH THE AVERAGE TEMPERATURE ABOVE THAT  
WHICH OCCURRED IN 1994. AT RICHMOND, THE PREVIOUS RECORD WAS  
63.2 AND AT NORFOLK IT WAS 64.7. BOTH WERE SET IN 1994. THIS  
MONTH'S TEMPERATURES COULD BE AROUND A DEGREE ABOVE THOSE  
VALUES.  
 

 
   
AKQ WATCHES/WARNINGS/ADVISORIES
 
 
MD...NONE.  
NC...NONE.  
VA...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EDT FRIDAY FOR ANZ650-652-654.  
 

 
 

 
SYNOPSIS...ALB/BMD  
NEAR TERM...BMD/SAM  
SHORT TERM...SAM  
LONG TERM...TMG  
AVIATION...SAM  
MARINE...LSA  
TIDES/COASTAL FLOODING...AKQ  
CLIMATE...AKQ  
 
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