909
FXUS62 KRAH 191751
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
151 PM EDT FRI OCT 19 2018
SYNOPSIS
HIGH PRESSURE WILL EXTEND OVER CENTRAL NORTH CAROLINA TODAY, THEN
MOVE OFF THE MID ATLANTIC COAST TONIGHT. A COLD FRONT WILL CROSS THE
AREA LATE SATURDAY. MUCH COOLER AND DRIER AIR WILL ARRIVE FOR SUNDAY
AND MONDAY.
NEAR TERM /THROUGH TONIGHT/
AS OF 1030 AM FRIDAY...
FORECAST IS IN GOOD SHAPE. ISOLATED FOG PATCHES NEAR BODIES OF WATER
HAVE VANISHED WITH HEATING, AND PLENTIFUL SUNSHINE IS EXPECTED FOR
MUCH OF THE DAY, ALTHOUGH CLOUDS WILL BEGIN TO INCREASE THIS
AFTERNOON. ISOLATED SPRINKLES NOW LOCATED JUST OFF THE GA AND S SC
COAST IS ASSOCIATED WITH A DEVELOPING BUT WEAK INVERTED TROUGH, AND
AS THIS RIDES NE JUST OFF THE S NC COAST LATE TODAY, A FEW SPRINKLES
MAY WORK INTO OUR FAR SE, BUT OTHERWISE A DRY FORECAST WILL BE
MAINTAINED. SHEARED VORTICITY STREAMING OUT AHEAD OF THE BROAD MID
LEVEL TROUGH CROSSING THE MIDWEST/GREAT LAKES APPEARS UNLIKELY TO
GATHER ENOUGH MOISTURE FOR ANY PRECIP OVER CENTRAL NC UNTIL AFTER
MIDNIGHT AT THE EARLIEST, SO HAVE BACKED OFF/SLOWED THE
EVENING/NIGHT POPS. UNDER MOSTLY SUNNY SKIES (BECOMING PARTLY SUNNY
FAR SE), AND WITH THICKNESSES THIS MORNING SUGGESTING TEMPS AROUND A
CATEGORY WARMER THAN YESTERDAY, EXPECT HIGHS IN THE MID 60S TO LOWER
70S. -GIH
EARLIER DISCUSSION FROM 330 AM: A BROAD UPPER LEVEL HIGH CENTERED
OVER THE EASTERN GULF EARLY THIS MORNING IS SUPPORTING A SFC RIDGE
OVER CENTRAL NC. THE BROAD HIGH ALOFT WILL DRIFT SWD TODAY AND
TONIGHT AS A SERIES OF S/W DIVE SEWD FROM THE UPPER MIDWEST INTO THE
GREAT LAKES AND BEGIN THE PROCESS OF DIGGING A L/W TROUGH OVER THE
EASTERN THIRD OF THE U.S. THE SWD DRIFT OF THE UPPER HIGH WILL CAUSE
THE SFC RIDGE OVERHEAD TO MOVE EAST, RESULTING IN A RETURN SLY FLOW
OVER THE FORECAST AREA TODAY AND TONIGHT. UNDER SUNNY SKIES,
TEMPERATURES WILL REBOUND QUICKLY, WARMING FROM THE 40S (WITH A FEW
30S AT THE NORMALLY COLDER SPOTS) EARLY THIS MORNING INTO THE UPPER
50S-LOWER 60S BY NOON, AND SOLIDLY IN THE 60S TO AROUND 70 BY MID
AFTERNOON.
THE S/WS CROSSING THE GREAT LAKES WILL PROPEL A SFC COLD FRONT
TOWARD CENTRAL NC TONIGHT. SOUTHWESTERLY FLOW AHEAD OF THE FRONT
WILL ADVECT A MARGINALLY MOIST AIR MASS INTO CENTRAL NC, LEADING TO
INCREASING/THICKENING MID/HIGH LEVEL CLOUDINESS. A NARROW ZONE OF
ISENTROPIC LIFT IN THE 290-300K LAYER MAY SUPPORT A FEW SPRINKLES OR
PATCHY LIGHT RAIN EARLY THIS EVENING OVER THE SOUTHERN COASTAL
PLAIN, AND THEN SHIFT AND FOCUS MORE OVER THE NORTHERN PIEDMONT
CLOSER TO MIDNIGHT. APPEARS THAT THE ATMOSPHERE WILL BE MOIST ENOUGH
AND MID-UPPER LEVEL LIFT STRONG ENOUGH TO PERMIT SPOTTY LIGHT RAIN
TO OCCUR ALONG AND NORTH OF THE I-40/85 CORRIDOR OVERNIGHT. THE MILD
SLY FLOW AND INCREASING CLOUDINESS WILL RESULT IN MILDER
TEMPERATURES COMPARED TO THIS MORNING. IN FACT, SOME, IF NOT MOST,
PLACES WILL LIKELY SEE THEIR OVERNIGHT LOW TEMPERATURES OCCURRING
AROUND MIDNIGHT WITH TEMPERATURES EITHER HOLDING STEADY OR SLOWLY
RISING OVERNIGHT. MIN TEMPS GENERALLY IN THE MID-UPPER 50S.
SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/
AS OF 330 AM FRIDAY...
THE SFC COLD FRONT WILL BE POISED IMMEDIATELY TO OUR NORTH-NORTHWEST
SATURDAY MORNING, AND PROJECTED TO GLIDE SEWD ACROSS THE REGION
DURING THE LATE MORNING THROUGH THE AFTERNOON HOURS. A PRONOUNCED
WLY FLOW IN THEW 850-700MB LAYER MAY RESULT IN THE PRECIP BECOMING
PATCHY AND RELATIVELY LIGHT. STILL PLAN TO ADVERTISE HIGH CHANCE-
LIKELY POPS FOR SATURDAY, THOUGH DO NOT EXPECT THE RAIN TO PERSIST
ANY ONE LOCATION FOR MORE THAN A COUPLE OF HOURS AND TOTAL AMOUNTS
GENERALLY LESS THAN A QUARTER OF AN INCH. THE SOUTHWEST FLOW AHEAD
OF THE FRONT WILL ADVECT A WARMER AIR MASS INTO THE REGION,
ESPECIALLY THE SOUTHERN COUNTIES WHERE THE SHOWERS/PATCHY RAIN MAY
NOT BE AS PROMINENT AS COMPARED ACROSS THE NORTH. HIGHS SATURDAY
SHOULD VARY FROM THE UPPER 60S NORTH TO THE LOW-MID 70S SOUTH.
LOW LEVEL FLOW WILL VEER TO A NWLY DIRECTION BEHIND THE FRONT,
INITIATING A TREND TOWARD DRIER AND MORE STABLE CONDITIONS. EXPECT
CLEARING SKIES TO COMMENCE IN THE NW PIEDMONT BY MID AFTERNOON, WITH
THE CLEARING TREND PROGRESSING SEWD INTO THE CENTRAL-SOUTHERN
COASTAL PLAIN AROUND SUNSET-EARLY EVENING. THE PASSAGE OF THE 850MB
TROUGH DURING THE EVENING WILL COMMENCE THE TRUE COLD AIR ADVECTION.
THE PASSAGE OF THE 850MB TROUGH WILL BE NOTED BY THE NW SFC WINDS
BECOMING BLUSTERY WITH GUSTS 18-23KTS PROBABLE DURING THE LATE
EVENING AND THROUGH THE OVERNIGHT HOURS. MIN TEMPS BY EARLY SUNDAY
SHOULD RANGE FROM THE LOWER 40S/NEAR 40 NW TO THE MID-UPPER 40S EAST
AND SOUTH.
LONG TERM /SUNDAY THROUGH THURSDAY/
AS OF 150 PM FRIDAY...
SUNDAY AND SUNDAY NIGHT: THE CLEAR, COOL AND BREEZY CONDITIONS WILL
CONTINUE THROUGH SUNDAY AS NC REMAINS SANDWICHED BETWEEN THE FRONT
OFFSHORE AND THE SURFACE HIGH OVER THE MIDWEST. THE RESULTANT
PRESSURE GRADIENT WILL BE RESPONSIBLE FOR THE WINDY CONDITIONS,
WHILE SUBSIDENCE IN NW FLOW WILL YIELD THE CLEAR SKIES. DESPITE THE
CLEAR SKIES, STRONG COLD ADVECTION WILL RESULT IN HIGHS TOPPING OUT
IN THE MID 50S NW TO AROUND 60 DEGREES SE, WITH THE WIND MAKING THE
TEMPERATURE FEEL A FEW DEGREES LOWER. AS THE SURFACE HIGH BUILDS
EASTWARD INTO AND OVER THE CAROLINAS SUNDAY NIGHT, THE PRESSURE
GRADIENT WILL RELAX, RESULTING IN ABATING WINDS, CLEAR SKIES AND
EXCELLENT RADIATIONAL COOLING CONDITIONS. LOWS SUNDAY NIGHT WILL BE
THE COOLEST OF THE SEASON, MID 30 NW TO UPPER 30S SE.
MONDAY THROUGH THURSDAY: COOL, DRY WEATHER WILL CONTINUE THROUGH MID-
WEEK. ALTHOUGH THE SURFACE HIGH IS EXPECTED TO SHIFT OFFSHORE, IT
WILL CONTINUE TO RIDGE WESTWARD INTO THE CAROLINAS THROUGH MID-WEEK.
AN UPPER LEVEL SHORTWAVE TROUGH IS EXPECTED TO PASS OVER THE REGION
ON TUESDAY/TUESDAY NIGHT, BUT THE ONLY IMPACT EXPECTED IS SOME
INCREASED CLOUD COVERAGE. THE SURFACE REFLECTION OF THE TROUGH WILL
SWING THROUGH AS WELL, BRINGING A REINFORCING SHOT OF COLD AIR INTO
THE REGION WEDNESDAY NIGHT/THURSDAY. TEMPERATURES WILL MODERATE TO
NEAR NORMAL ON TUESDAY, WITH HIGHS IN THE MID 60S TO LOW 70S AND
LOWS TUESDAY NIGHT IN THE MID TO UPPER 40S. (FOR REFERENCE, NORMAL
HIGHS ARE IN THE UPPER 60S TO LOW 70S AND NORMAL LOWS ARE IN THE MID
TO UPPER 40S). TEMPERATURES WILL THEN DECREASE ONCE AGAIN WEDNESDAY
AND THURSDAY (BY APPROXIMATELY A CATEGORY/DAY) IN RESPONSE TO THE
REINFORCING SHOT OF COLD AIR.
AVIATION /18Z FRIDAY THROUGH WEDNESDAY/
AS OF 1245 PM FRIDAY...
HIGH CONFIDENCE IN VFR CONDITIONS HOLDING AT ALL SITES THROUGH AT
LEAST THIS EVENING, AS HIGH PRESSURE RIDGING AND DEEP DRY AIR
PERSISTS OVER THE REGION. AS THE SURFACE HIGH SHIFTS EAST AND OFF
THE MID ATLANTIC COAST LATE THIS AFTERNOON, LOW LEVEL FLOW WILL
REMAIN LIGHT BUT SWING AROUND TO SE AND S. THIS, AS WELL AS
INCREASING HIGH LEVEL MOISTURE AS AN UPPER TROUGH APPROACHES FROM
THE W, WILL CAUSE CLOUDS TO OVERSPREAD THE AREA FROM THE S AND W
OVERNIGHT. A PERIOD OF MVFR CIGS IS POSSIBLE AT FAY 08Z-13Z, AND A
PERIOD OF IFR/LIFR FOG IS POSSIBLE AT RWI 06Z-13Z. ELSEWHERE,
THOUGH, CIGS/VSBYS SHOULD REMAIN VFR THROUGH THE END OF THE TAF
VALID PERIOD. PATCHY SPRINKLES OR LIGHT RAIN ARE POSSIBLE LATE
TONIGHT INTO SAT, STARTING AT INT/GSO AFTER 09Z, AND AT RDU AFTER
12Z, AHEAD OF A COLD FRONT THAT WILL MOVE IN FROM THE NW. RAIN
CHANCES ARE MUCH SMALLER AT RWI/FAY.
LOOKING BEYOND 18Z SAT, THE COLD FRONT WILL SHIFT E OUT OF THE AREA
SAT AFTERNOON, WITH THE SHOWER RISK ENDING W TO E. VFR CONDITIONS
AND COOL HIGH PRESSURE WILL DOMINATE THROUGH WED, EXCEPT WE'LL SEE A
CHANCE FOR SUB-VFR CONDITIONS MON NIGHT/TUE AS AN UPPER DISTURBANCE
AND SECONDARY COLD FRONT CROSSES THE CAROLINAS. ALSO: AS THE COLD
FRONT CROSSES THE AREA LATE SAT, WE'LL SEE A SHIFT OF SURFACE WINDS
TO WNW WITH INCREASING SPEEDS TO 15-20 KTS AND GUSTS UP TO 20-25 KTS
POSSIBLE FROM LATE SAT AFTERNOON THROUGH EARLY SUN MORNING. -GIH
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...WSS
NEAR TERM...HARTFIELD/WSS
SHORT TERM...WSS
LONG TERM...KC
AVIATION...HARTFIELD
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