370
FXUS62 KRAH 021720
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
120 PM EDT SUN AUG 2 2026
WHAT HAS CHANGED
* UPDATED THE AVIATION DISCUSSION TO REFLECT THE 18Z TAFS.
KEY MESSAGES
AS OF 210 AM SATURDAY...
1) SCATTERED TO LOCALLY NUMEROUS SHOWERS AND STORMS ARE
EXPECTED THIS AFTERNOON INTO THE EARLY OVERNIGHT HOURS AND MAY
BRING A RISK LOCALIZED URBAN AND SMALL STREAM FLOODING AS WELL
AS STRONG WINDS GUSTS.
2) SHOWERS AND STORMS CAPABLE OF PRODUCING VERY HEAVY RAIN WILL
SHIFT EAST MONDAY AND TUESDAY, WITH MAINLY AFTERNOON AND
EVENING SHOWERS AND STORMS THROUGH THE REMAINDER OF THE WEEK.
DISCUSSION
AS OF 210 AM SATURDAY...
KEY MESSAGE 1... SCATTERED TO LOCALLY NUMEROUS SHOWERS AND
STORMS ARE EXPECTED THIS AFTERNOON INTO THE EARLY OVERNIGHT
HOURS AND MAY BRING A RISK LOCALIZED URBAN AND SMALL STREAM
FLOODING AS WELL AS STRONG WINDS GUSTS.
SOUTHWESTERLY FLOW ALOFT, AND DEEP MOISTURE CHARACTERIZED BY PW
VALUES OF 2-2.5 INCHES AND 125-150% OF NORMAL, CURRENTLY
LOCATED OVER THE WESTERN/CENTRAL NC PIEDMONT AS WELL AS NEAR THE
SC/GA COAST WILL CONTINUE BE DIRECTED ACROSS THE CAROLINAS AND
SOUTHERN MIDDLE ATLANTIC AHEAD OF A MID AND UPPER-LEVEL TROUGH
THAT WILL PIVOT INTO THE OH AND LOWER MS VALLEYS TODAY AND THEN
WEAKEN WHILE DRIFTING INTO THE TN VALLEY AND SOUTHERN
APPALACHIANS THROUGH EARLY MON. SEVERAL MCVS WILL PROBABLY BE
EMBEDDED WITHIN THAT SWLY FLOW REGIME ACROSS THE SOUTH ATLANTIC
STATES AND MAY LOCALLY FOCUS ASCENT ALONG THEIR TRACK.
AT THE SURFACE, MOIST, SLY/SELY FLOW WILL CONTINUE ACROSS THE
CAROLINAS, IN A MOIST/WARM SECTOR DOWNSTREAM OF A ~1003 MB LOW
THAT WILL DRIFT ACROSS THE OH VALLEY. A DIFFERENTIAL HEATING
ZONE IS LIKELY TO DEVELOP OVER THE PIEDMONT LATER THIS AFTERNOON
AS LOW OVERCAST ERODES FROM EAST TO WEST AND PROVIDE A SURFACE
FORCING MECHANISM FOR LOCALLY NUMEROUS SHOWERS/STORMS.
LARGE SCALE AND PERSISTENT FORCING MECHANISMS, SUCH AS THE
ELONGATED RRQ OF THE UPPER JET STREAK FROM THE LOWER MS VALLEY
INTO THE NORTHEAST AND SOUTHERN CANADA, WILL LIKELY REMAIN JUST
WEST OF THE FORECAST AREA AMIDST NEAR NEUTRAL MID-LVL HEIGHT
TENDENCIES. HOWEVER, A DEEPLY MOIST, UNINHIBITED, AND
CONDITIONALLY UNSTABLE PROFILES --WEAKLY TO MODERATELY SO-- WILL
OTHERWISE FAVOR THE DEVELOPMENT OF SCATTERED TO LOCALLY
NUMEROUS CELLS AMID 25-30 KTS OF SWLY FLOW. A (MARGINAL) RISK OF
WATER-LOADED, DAMAGING DOWNBURSTS REMAINS POSSIBLE BUT HIGHLY
CONDITIONAL AS THE THERMODYNAMIC ENVIRONMENT WILL ONLY PROMOTE
MINIMAL DIABATIC ENHANCEMENT TO THE DOWNDRAFTS AND ASSOCIATED
SURFACE WIND GUSTS; STORM ORGANIZATION MAY BE REQUIRED TO
PRODUCE SEVERE MAGNITUDE WIND GUSTS. ALTHOUGH HEAVY DOWNPOURS
WILL ALSO RESULT, RELATIVELY FAST CELL MOTIONS TO THE NORTHEAST
WILL COUNTER SOME TENDENCY FOR BACK-BUILDING AND CONSEQUENTLY
LIMIT THE OVERALL RISK OF FLOODING. HOWEVER, GIVEN THE POTENTIAL
FOR A FAVORABLE ALIGNMENT OF THE DIFFERENTIAL HEATING BOUNDARY,
AND SUBSEQUENT OUTFLOW REINFORCEMENT, TO THE MEAN-WIND IN THE
850-300MB LAYER, REPEATED CELLS TRAINING OVER THE SAME AREA MAY
BE POSSIBLE TO PRODUCE LOCALLY GREATER RAINFALL AMOUNTS OF 2-4+
INCHES.
KEY MESSAGE 2... SHOWERS AND STORMS CAPABLE OF PRODUCING VERY
HEAVY RAIN WILL SHIFT EAST MONDAY AND TUESDAY, WITH MAINLY
AFTERNOON AND EVENING SHOWERS AND STORMS THROUGH THE REMAINDER
OF THE WEEK.
THE BASE OF THE POSITIVELY TILTED UPPER TROUGH WEST OF THE
APPALACHIANS WILL CONTINUE TO SINK SOUTH TOWARD THE SOUTHERN
APPALACHIANS ON MONDAY, MAINTAINING DEEP MOIST SOUTHWESTERLY
FLOW ACROSS THE REGION. PRECIPITABLE WATER WILL CONTINUE TO
EXCEED 2 INCHES AND BE AS HIGH AS 2.5-2.6 INCHES ACROSS THE
EASTERN HALF OF THE AREA. DESPITE WEAK LAPSE RATES ALOFT, DEW
POINTS IN THE MID-70S WILL STILL SUPPORT AT LEAST SOME
INSTABILITY, WITH GUIDANCE SUGGESTING 500 TO PERHAPS 1000 J/KG
MLCAPE BY MONDAY AFTERNOON. 500 MB FLOW ALSO INCREASES SLIGHTLY,
AND BULK SHEAR MAY BE AS MUCH AS 20- 25 KNOTS. WHILE THE
LARGER-SCALE FORCING IS NOT PARTICULARLY STRONG WITH THE SLOW-
MOVING UPPER LOW, MODELS SUGGEST THERE MAY BE AN UPTICK IN
PERTURBATIONS IN THE SOUTHWESTERLY FLOW TO HELP KICK OFF
SCATTERED TO NUMEROUS SHOWERS AND STORMS, ESPECIALLY ACROSS THE
EAST. THE MAIN THREAT FROM CONVECTION APPEARS TO BE THE
POTENTIAL TRAINING OF STORM CLUSTERS AND HEAVY RAINFALL GIVEN
THE ANOMALOUSLY MOIST AIR MASS AND NEARLY UNIDIRECTIONAL
TROPOSPHERIC FLOW. HI-RES GUIDANCE AND PROBABILITY-MATCHED MEAN
(PMM) PRECIPITATION FIELDS SUGGEST LOCALIZED AREAS OF 1-3 INCHES
WILL BE POSSIBLE, ALTHOUGH WE HAVE SEEN AS MUCH AS 4-6 INCHES
WITH SOME FOCUSED CELLS IN THE FOOTHILLS TODAY.
A SIMILAR PATTERN IS LIKELY TO REPEAT ACROSS MAINLY EASTERN
AREAS ON TUESDAY AND TO A LESSER EXTENT INTO WEDNESDAY AS THE
UPPER LOW LIFTS AND WEAKENS. MOIST FLOW AROUND THE BERMUDA HIGH
WILL CONTINUE THROUGH THE END OF THE WEEK, SO DIURNAL CONVECTION
WILL BE POSSIBLE EACH DAY.
AVIATION /17Z SUNDAY THROUGH FRIDAY/
AS OF 120 PM SUNDAY...
TAF PERIOD: WHILE INT/GSO WILL HAVE MVFR CEILINGS TO START THE 18Z
TAF PERIOD, CEILING HEIGHTS SHOULD NOT TAKE TOO LONG TO LIFT TO VFR
LEVELS, AND SEVERAL HOURS OF VFR CONDITIONS ARE EXPECTED AT ALL
TERMINALS. AFTER A LULL IN SHOWER COVERAGE THIS MORNING, EXPECT
SCATTERED SHOWERS TO DEVELOP AT ALL SITES, WITH TEMPO GROUPS
MAINTAINED FROM THE PREVIOUS FORECAST DURING THE TIME PERIOD WHEN
THUNDERSTORMS ARE MOST LIKELY (ALTHOUGH THUNDERSTORMS ARE POSSIBLE
AT ANY TIME DURING THE AFTERNOON). AS THE COVERAGE OF SHOWERS
DECREASES, WIDESPREAD CEILINGS WITH FLIGHT RESTRICTIONS ARE EXPECTED
TO DEVELOP AFTER DUSK. THE GREATEST UNCERTAINTY IS HOW FAR EAST IFR
CONDITIONS WILL EXTEND, AND HAVE INCLUDED FAY IN ONLY A TEMPO GROUP
FOR NOW WHILE ALL OTHER SITES HAVE IFR AS PREVAILING CONDITIONS.
HAVE NOT SEEN MANY GUSTS SO FAR TODAY, AND HAVE REMOVED GUSTS
BETWEEN THE LACK OF OBSERVATIONS AND THE WIDESPREAD CLOUD COVER THAT
IS EXPECTED. WHILE THERE WILL BE SOME SPEED VARIATION, THE WIND WILL
GENERALLY BE OUT OF THE SOUTH THIS AFTERNOON AND VEER TO THE
SOUTHWEST OVERNIGHT.
OUTLOOK: COVERAGE OF SHOWERS AND THUNDERSTORMS ON MONDAY SHOULD BE
SIMILAR TO TODAY, THEN EXPECT GREATER COVERAGE OF PRECIPITATION ON
TUESDAY AND WEDNESDAY. SHOWER/STORM COVERAGE SHOULD DECREASE AGAIN
ON THURSDAY AND FRIDAY TO MORE SUMMER-LIKE SCATTERED. FLIGHT
RESTRICTIONS WILL BE LIKELY EACH NIGHT, ESPECIALLY AT ANY TERMINAL
THAT RECEIVES MODERATE TO HEAVY RAINFALL THE PREVIOUS DAY.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...MWS/AS/BS
AVIATION...GREEN
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