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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