144  
FXUS61 KLWX 210228  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
928 PM EST WED FEB 20 2019  
   
SYNOPSIS
 
 
PRIMARY LOW PRESSURE OVER THE GREAT LAKES WILL TRACK INTO  
SOUTHERN CANADA TONIGHT WHILE SECONDARY LOW PRESSURE WILL MOVE  
UP THE ATLANTIC COAST. HIGH PRESSURE RETURNS BRIEFLY ON  
THURSDAY. A COLD FRONT WILL CROSS THE REGION THURSDAY EVENING  
AND STALL TO THE SOUTH ON FRIDAY. ANOTHER LARGE AND COMPLEX LOW  
PRESSURE SYSTEM WILL MOVE NORTHEAST ACROSS THE REGION SATURDAY  
INTO SUNDAY.  
 

 
   
NEAR TERM /THROUGH THURSDAY/
 
 
00Z SOUNDINGS FROM IAD, RNK, AND PBZ SHOW THE SHALLOW NATURE OF  
THE COLD AIR ACROSS THE REGION. HIGH ELEVATION LOCATIONS  
(WINTERGREEN, SPRUCE KNOB, ETC.) ARE NOW RISING INTO THE 40S AS  
THE STRONG SOUTHWEST FLOW ALOFT CHIPS AWAY AT THE SHALLOW COLD  
POOL. HOWEVER, SURFACE ANALYSIS SHOWS THE ENTRENCHED HIGH  
PRESSURE WEDGE EAST OF THE MOUNTAINS. COASTAL LOW PRESSURE IS  
TAKING SHAPE NEAR SOUTHEAST VIRGINIA THIS EVENING AND WILL LIFT  
NORTHEAST OVER NIGHT. IT WILL LIKELY TAKE UNTIL THIS LOW PASSES  
TO THE EAST AND A MORE WESTERLY GRADIENT DEVELOPS THAT  
TEMPERATURES WILL DEFINITIVELY BEGIN TO RISE. HAVE THUS EXTENDED  
ALL HEADLINES UNTIL 1 AM, WITH THE EXCEPTION OF GRANT AND  
PENDLETON COUNTIES, WHERE MOST TEMPERATURES APPEAR TO BE ABOVE  
FREEZING. FOR A GOO PART OF THE AREA NEAR AND SOUTH OF THE  
POTOMAC RIVER, ICING WILL LIKELY BE LIMITED TO ELEVATED SURFACES  
AT MOST AS TEMPERATURES ARE EITHER RIGHT AT OR JUST ABOVE  
FREEZING. SOME DEEPER COLD AIR RESIDES NORTH OF THE METROS,  
ESPECIALLY AT ELEVATION (REFERENCE IAD SOUNDING SHOWING  
TEMPERATURE DECREASE OFF THE SURFACE), SO ICE ACCRETION MAY BE  
MORE EFFICIENT IN THESE AREAS. HOWEVER, GIVEN SPOTTY NATURE OF  
REMAINING PRECIP, WOULD EXPECT MOST ICE TOTALS TO BE LESS THAN A  
QUARTER INCH.  
 
WHAT APPEARS TO BE THE LAST BATCH OF NOTABLE PRECIPITATION  
ASSOCIATED WITH A LOW LEVEL JET IS CURRENTLY CROSSING THE  
APPALACHIANS. THERE HAVE EVEN BEEN SOME LIGHTNING STRIKES  
ASSOCIATED WITH THIS ACTIVITY AND THUNDERSLEET IN ALLEGANY  
COUNTY. THESE SHOWERS SHOULD PUSH SOUTHEAST OF THE AREA BETWEEN  
MIDNIGHT AND 3 AM.  
 
LOW CLOUDS WILL LINGER INTO THE MORNING HOURS. THERE MAY EVEN BE  
SOME FOG OR MIST/DRIZZLE, BUT THERE MAY BE ENOUGH OF A WESTERLY  
FLOW TO PREVENT THAT. AFTER WESTERLY WINDS AND MIXING INCREASE  
BY MIDDAY THURSDAY, TEMPS SHOULD SURGE AS CLOUDS BREAK, WITH  
MANY AREAS LIKELY TO TOUCH 50. WILL HAVE TO WATCH OUT FOR  
POTENTIAL FOR THE LOW CLOUDS TO LINGER LONGER THAN EXPECTED, BUT  
OTHERWISE, THURSDAY SHOULD BE MUCH NICER THAN TODAY.  
 

 
   
SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/
 
 
WEAK FRONT CROSSES THE REGION LATE THURSDAY AFTERNOON/EVENING,  
PERHAPS WITH SOME SHOWERS OR A LITTLE RAIN, ESPECIALLY IN  
CENTRAL VA. COOLER AIR WILL MOVE IN FOR FRIDAY BEHIND THIS  
FRONT, WITH TEMPS CLOSER TO SEASONABLE NORMS (40S). WITH THE  
FRONT STALLING JUST TO THE SOUTH, SOME RAIN MAY LINGER IN  
CENTRAL VA. COMPLEX LOW PRESSURE WILL THEN START TO ORGANIZE TO  
THE SOUTHWEST, SENDING WARM ADVECTION OUR WAY FRIDAY NIGHT. WILL  
NEED TO WATCH TEMPS CLOSELY FRIDAY NIGHT AS THE RAIN OVERSPREADS  
THE REGION AGAIN, AS NORTHERN AREAS COULD SLIP BELOW FREEZING  
OVERNIGHT AND RESULT IN SOME FREEZING RAIN. TEMPS WILL GENERALLY  
BE IN THE 30S FRIDAY NIGHT.  
 

 
   
LONG TERM /SATURDAY THROUGH WEDNESDAY/
 
 
A WARM FRONT WILL APPROACH THE REGION FROM THE SOUTH ON  
SATURDAY. OVERRUNNING PRECIPITATION AHEAD OF THE WARM FRONT IS  
FORECAST TO START AFFECTING OUR REGION AS EARLY AS FRIDAY  
EVENING.WINDS WILL BE MAINLY OUT OF THE SOUTH BEHIND THE WARM  
FRONT LEADING TO ADVECTION OF WARM AND MOIST AIR INTO OUR  
REGION. AS THE WARM FRONT SHIFTS NORTHWARD AND MOVES OUR OUR  
REGION, THE MODELS ARE TRYING TO TRANSFER ENERGY FROM THE  
SURFACE LOW TOO FORM A SECONDARY LOW ALONG THE WARM FRONT THAT  
SHIFTS EASTWARD TO THE EASTERN SEABOARD NEAR THE MID-ATLANTIC  
COAST. THIS WOULD LEAD TO INCREASED PRECIPITATION FOCUSED OVER  
OUR REGION. MODELS INDICATE THE POTENTIAL FOR OVER A INCH OF  
LIQUID DURING THE WARM FRONT TRANSITION NORTHWARD. THE WARM  
FRONT IS FORECAST TO SHIFT TO OUR NORTH AS THE COLD FRONT  
APPROACHES FROM THE WEST EARLY ON SUNDAY. THE COLD FRONT IS  
EXPECTED TO MOVE THROUGH OUR REGION SATURDAY AFTERNOON. WINDS  
WILL BECOME WESTERLY BEHIND THE FRONTAL PASSAGE. TEMPERATURES  
HAVE THE POTENTIAL TO REACH INTO THE 60S ON SUNDAY AHEAD OF THE  
FRONTAL PASSAGE.  
 
HIGH PRESSURE WILL BUILD INTO OUR REGION BEHIND THE COLD  
FRONTAL PASSAGE THROUGH MIDWAY NEXT WEEK. WINDS WILL START OUT  
OF THE WEST BUT AS THE HIGH MOVES OVER OUR REGION, WINDS WILL  
BECOME MORE NORTHERLY. TEMPERATURES WILL BE MILD TO SLIGHTLY  
BELOW AVERAGE THROUGH EARLY NEXT WEEK.  
 

 
   
AVIATION /02Z THURSDAY THROUGH MONDAY/
 
 
IFR TO LIFR CIGS AND VIS WITH LINGERING RAIN AND FREEZING RAIN  
THROUGH THE REMAINDER OF THE EVENING. PRECIP ENDS AROUND  
MIDNIGHT. STUBBORN LOW CLOUDS WILL LINGER THROUGH THE OVERNIGHT  
INTO THE EARLY MORNING HOURS ON THURSDAY. WITH THESE LOW  
CLOUDS, MVFR/IFR CIGS WILL REMAIN POSSIBLE THROUGH THE EARLY  
MORNING HOURS. VISIBILITY MAY REMAIN REDUCED AS WELL, DEPENDING  
ON HOW MUCH MIXING WESTERLY WINDS CAN ACCOMPLISH AFTER MIDNIGHT.  
 
THOSE LOW CLOUDS SHOULD GRADUALLY BREAK UP THROUGH THE LATE  
MORNING HOURS, GIVING WAY TO VFR CONDITIONS BY AFTERNOON. VFR  
CONDITIONS ARE EXPECTED THURSDAY AFTERNOON THROUGH THE DAY  
FRIDAY. RAIN WILL MOVE INTO OUR REGION WITH WINDS BECOMING  
SOUTHERLY ON SATURDAY. SUBVFR CONDITIONS ARE LIKELY.  
 
ON SUNDAY, RAIN WILL CLEAR THE AREA BY AFTERNOON, WITH SUB VFR  
CONDITIONS POSSIBLE DURING THE MORNING HOURS. CONDITIONS SHOULD  
IMPROVE TO VFR DURING THE AFTERNOON AS THE STORM DEPARTS. WINDS WILL  
PICK UP IN THE WAKE OF THE STORM SUNDAY AFTERNOON, WITH GUSTS IN  
EXCESS OF 30 KTS POSSIBLE.  
 

 
   
MARINE
 
 
WINDS ARE SUBSIDING OVER TANGIER SOUND, SO THE REMAINING SMALL  
CRAFT ADVISORY WILL BE ALLOWED TO EXPIRE. WINDS WILL REMAIN  
LIGHT THROUGH THURSDAY MORNING AS LOW PRESSURE LIFTS NORTH OF  
THE AREA. AS A WEAK FRONT CROSSES THE REGION LATER THURSDAY  
INTO THURSDAY EVENING, SCA MAY BE NEEDED ESPECIALLY OVER  
NORTHERN WATERS, LESS LIKELY TO THE SOUTH. LIGHT WINDS ARE  
LIKELY FRIDAY AND FRIDAY NIGHT AS HIGH PRESSURE SETTLES TO THE  
NORTH, FOLLOWED BY THE APPROACH OF THE NEXT SYSTEM FROM THE  
SOUTHWEST.  
 
ON SATURDAY, RAIN WILL MOVE THROUGH THE WATERS. WINDS ALOFT  
WILL HOVER NEAR THE 10 TO 15 KNOT RANGE. SMALL CRAFT LIKELY WONT  
BE NEEDED AT THIS TIME.  
 
SUNDAY, SHOWERS WILL MOVE THROUGH THE WATER SUNDAY AFTERNOON.  
WINDS ALOFT WILL BE STRONG ABOVE 35 KNOTS WITH THE POTENTIAL TO  
REACH UP TO 40 KNOTS. THIS INDICATES THAT AT LEAST A SMALL CRAFT  
ADVISORY WILL BE NEEDED WITH THE POTENTIAL FOR A GALE WARNING  
ON SUNDAY.  
 

 
   
HYDROLOGY
 
 
ULTIMATELY, OUR UPCOMING FLOOD POTENTIAL WILL BE DETERMINED  
AFTER WE SEE EXACTLY HOW MUCH SNOW FELL ON WEDNESDAY AND HOW  
MUCH LIQUID IS IN THAT SNOW. A GOOD MELT IS AHEAD FOR THURSDAY  
AND FRIDAY WITH TEMPERATURES ABOVE FREEZING AND A DECENT AMOUNT  
OF SUNSHINE. THAT WILL ELEVATE STREAMS AND KEEP THEM ELEVATED,  
AHEAD OF THE NEXT SYSTEM WHICH AFFECTS US OVER THE WEEKEND. THAT  
EVENT LOOKS LIKE ALL RAIN. CURRENT INDICATIONS ARE FOR BETWEEN  
0.5 INCH (LOW-END) AND 2.0 INCHES (HIGH-END) OF RAIN OVER THE  
WEEKEND, ON TOP OF REMAINING SNOWMELT. IF THERE'S STILL SNOW ON  
THE GROUND AND IF THE HIGHER RAINFALL AMOUNTS ARE REALIZED, THIS  
COMBINATION WOULD PRODUCE FLOODING BOTH ON SMALL AND LARGER  
STREAMS STARTING LATE SATURDAY THROUGH POSSIBLY EARLY NEXT WEEK.  
WE WILL CONTINUE TO MONITOR THE POTENTIAL IN THE COMING DAYS.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...WINTER WEATHER ADVISORY UNTIL 1 AM EST THURSDAY FOR DCZ001.  
MD...WINTER STORM WARNING UNTIL 1 AM EST THURSDAY FOR MDZ003>006-  
501>507.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST THURSDAY FOR MDZ011-013-  
014-016-508.  
VA...WINTER STORM WARNING UNTIL 1 AM EST THURSDAY FOR VAZ025>031-  
040-501-503>508.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST THURSDAY FOR VAZ036>039-  
050>056-502.  
WV...WINTER STORM WARNING UNTIL 1 AM EST THURSDAY FOR WVZ050>053-  
055-503-504.  
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ534-  
537-543.  
 

 
 

 
SYNOPSIS...RCM  
NEAR TERM...ADS/RCM  
SHORT TERM...RCM  
LONG TERM...JMG  
AVIATION...KJP/RCM/JMG  
MARINE...ADS/RCM/JMG  
HYDROLOGY...JE  
 
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