124
FXUS62 KRAH 180703
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
202 AM EST MON NOV 18 2024
SYNOPSIS
OFFSHORE HIGH PRESSURE WILL EXTEND ACROSS THE SOUTH ATLANTIC STATES
AHEAD OF A STRONG COLD FRONT THAT WILL MOVE THROUGH THE REGION
WEDNESDAY NIGHT.
NEAR TERM /TONIGHT/
AS OF 955 PM SUNDAY...
A SUB-TROPICAL HIGH AT THE SURFACE AND ALOFT WILL CONTINUE TO EXTEND
ACROSS THE SOUTHEAST TONIGHT. ASSOCIATED CALM, TO OCCASIONAL, LIGHT,
SWLY STIRRING WITH THE CENTER OF THE SURFACE HIGH OFF THE SC COAST,
WILL FAVOR STRONG RADIATIONAL COOLING AMID PASSING CIRRUS. WITH
ANOTHER DAY OF MODIFICATION OF THE ASSOCIATED AIRMASS, OVERNIGHT-MON
MORNING TEMPERATURES WILL BE LESS CHILLY/FROSTY THAN SUN MORNING --
BY 4-8 F ON AVERAGE-- AND MOSTLY IN THE UPR 30S TO MID 40S. LOW-
LEVEL MOISTURE HAS LIKELY NOT INCREASED OR DEEPENED SUFFICIENTLY, AS
INDICATED BY NEARLY STEADY, OBSERVED MEAN MIXING RATIOS AT GSO AND
MHX FOR THE PAST COUPLE OF DAYS, TO ALLOW FOR ANYTHING MORE THAN
PATCHY MIST/FOG DEVELOPMENT AT THE USUAL AWOS SITES AND RWI.
SHORT TERM /MONDAY AND MONDAY NIGHT/
AS OF 135 PM SUNDAY...
ALOFT, THE SUB-TROPICAL RIDGE WILL BUILD TO THE WEST MON, THEN SHIFT
EWD INTO THE AREA MON NIGHT. AT THE SURFACE, HIGH PRESSURE WILL SIT
JUST OFF THE SOUTHEAST US COAST THROUGH MON NIGHT, WITH GENERALLY
WEAK HIGH PRESSURE OVER CENTRAL NC IN THE WAKE OF A WEAK TROUGH
EXITING TO THE EAST EARLY MON. WINDS SHOULD INITIALLY BE WLY TO NWLY
AT 3-5 KTS DURING THE DAY, THEN BECOME MORE WSWLY/SWLY BEFORE GOING
CALM OVERNIGHT. THE WEATHER SHOULD REMAIN DRY THROUGH MON NIGHT. AS
FOR TEMPERATURES, HIGHS SHOULD RANGE FROM UPPER 60S TO LOW 70S. AS
FOR LOWS SUN NIGHT, LOW-LEVEL THICKNESSES ARE AGAIN FORECAST TO BE
IN THE 1360-1375 METER RANGE BY 12Z TUE, WITH CLOUD COVER INCREASING
FROM THE WNW AFTER MIDNIGHT. GIVE THE GENERALLY CALM WINDS EXPECTED,
LOWS MAY BE SIMILAR TO PERHAPS A CATEGORY HIGHER THAN TONIGHT,
MAINLY IN THE MID 40S.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
AS OF 202 AM MONDAY...
* STRONG COLD FRONTAL PASSAGE WED NIGHT, WITH A CONDITIONAL ISOLATED
SEVERE THREAT
* MUCH COLDER THU INTO SAT, WITH WSW TO WNW WINDS BRISK AT TIMES OF
25-35 MPH
WE CONTINUE TO TRACK A STRONG COLD FRONTAL PASSAGE SET TO MOVE
THROUGH WED NIGHT. MUCH OF THE GUIDANCE REMAINS IN GOOD AGREEMENT
THAT THE FRONT MOVES THROUGH BETWEEN 6 PM AND 1 AM. A VIGOROUS MID-
LEVEL SHORTWAVE TROUGH OVER THE UPPER MS VALLEY AND GREAT LAKES IS
FORECAST TO TRACK INTO THE OH VALLEY AND MID-ATLANTIC BY EARLY THU.
MOST GUIDANCE SUGGESTS SOME LIGHT RAIN MAY PERSIST INTO LATE MORNING
ALONG/EAST OF US-1 TIED TO WEAK ISENTROPIC ASCENT IN THE 700-500 MB
LAYER. THIS IS THEN FORECAST TO MOVE OUT BY MIDDAY, OWING TO ONE
LAST MILD DAY IN THE UPPER 60S TO LOW 70S.
AS THE FRONT APPROACHES FROM THE WEST WED EVENING, STRONG HEIGHT
FALLS AND DPVA WILL OVERSPREAD THE REGION. THERE STILL APPEARS TO BE
A SHORT WINDOW OF TIME WHEN SHEAR/INSTABILITY COULD OVERLAP AHEAD OF
THE FRONT TO FAVOR A CONDITIONAL SEVERE THREAT. WHAT REMAINS
CONDITIONAL IS THE AMOUNT OF INSTABILITY, AS WELL AS THE FACT THAT
THE DEEPER MOISTURE WILL SHIFT TOWARD THE COAST BY EVENING, LEAVING
A POTENTIAL LACK OF OVERLAP OF KINEMATICS AND THERMODYNAMICS. HIGH-
END AMOUNTS OF MLCAPE APPROACH ~ 500 J/KG, WITH LOW END AMOUNTS OF A
FEW HUNDRED J/KG. SHEAR IS NOT LACKING, WITH 50-60 KT IN THE 0-6 KM
LAYER, ~ 30 KT OF 0-3 KM, AND 20-25 KT OF 0-1 KM. IT WOULD APPEAR
MOST GUIDANCE SHOWS A POSSIBLE ISOLATED/BROKEN LINE OF SHOWERS
TRACKING EAST BETWEEN ABOUT 6 PM AND MIDNIGHT, THOUGH WHETHER ANY
STORMS COULD BECOME SURFACE BASED IS STILL UNCLEAR. A LOOK AT HIGH-
RES CAMS IN THE COMING DAYS WILL BE HELPFUL TO BETTER ASSESS THE
ENVIRONMENT.
IT STILL APPEARS MUCH COLDER THU INTO SAT AS THE VIGOROUS TROUGH
ROTATES CYCLONICALLY OVER THE MID-ATLANTIC AND NE US INTO SAT. HIGH
TEMPERATURES THU-SAT WILL BE SOME 15-20 DEGREES COLDER COMPARED TO
WED IN THE LOW TO MID/UPPER 50S, COOLEST ON FRI WITH STRONG CAA IN
PLACE. BRISK WSW TO WNW WINDS WILL BE IN PLACE AS WELL, GUSTING AT
TIMES TO BETWEEN 25 AND 35 MPH, HIGHEST ON FRI. GUIDANCE SHOWS THAT
RIDGING OR QUASI-ZONAL FLOW MAY BUILD IN SUN, WHICH SHOULD ALLOW A
SLIGHT MODERATION IN THE AIRMASS WITH MID 50S TO NEAR 60. LOWS FRI
AND SUN MORNING COULD APPROACH FROST/FREEZE POTENTIAL IN THE LOW TO
MID 30S, WITH PERHAPS THE BEST CHANCE SUN MORNING WITH HIGH PRESSURE
BUILDING IN WITH LIGHTER SFC WINDS.
AVIATION /06Z MONDAY THROUGH FRIDAY/
AS OF 1233 AM MONDAY...
GENERALLY VFR CONDITIONS UNDER HIGH PRESSURE WILL CONTINUE THROUGH
06Z/TUESDAY. THERE IS A CHANCE OF A PERIOD OF IFR FOG AT RWI, WITH
ONLY A FEW HOURS OF MVFR VSBYS POSSIBLE ELSEWHERE. ANY FOG THAT
DEVELOPS SHOULD MIX OUT BY MID MORNING, WITH ONLY HIGH CLOUDS IN
PLACE THROUGH THE END OF THE TAF PERIOD.
OUTLOOK: A STRONG COLD FRONT MOVING THROUGH THE REGION WILL BRING A
CHANCE OF SHOWERS AND ASSOCIATED SUB-VFR RESTRICTIONS TO THE AREA
LATE TUESDAY INTO WEDNESDAY. VFR CONDITIONS ARE EXPECTED TO RETURN
LATE WEDNESDAY AFTERNOON. A DEEPENING AREA OF LOW PRESSURE INVOF THE
GREAT LAKES WILL YIELD FREQUENT GUSTS OF 20 TO 30 KTS THURSDAY AND
AGAIN ON FRIDAY.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...KC
LONG TERM...KREN
AVIATION...BADGETT
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