356
FXUS62 KRAH 041133
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
733 AM EDT SAT JUL 4 2009
SYNOPSIS
WEAK HIGH PRESSURE WILL LINGER OVER THE CAROLINAS TODAY. A LOW
PRESSURE SYSTEM WILL APPROACH FROM THE WEST TONIGHT AND CROSS THE
REGION SUNDAY AND SUNDAY NIGHT.
NEAR TERM /THROUGH TONIGHT/
AS OF 245 AM SATURDAY...
TODAY: ANOTHER DRY/CAPPED AND ATYPICALLY COMFORTABLE JULY DAY WITH
DEWPOINTS AGAIN IN THE 50S EXPECTED. SKIES WILL START THE DAY
MOSTLY SUNNY (A LITTLE CIRRUS)... THOUGH INCREASING MID AND HIGH
CLOUDINESS IN WNW FLOW ALOFT MAY FILTER THE SUNSHINE A BIT BY LATE
AFTERNOON. PROJECTED LOW LEVEL THICKNESSES AROUND 1410 +/- 5
METERS SUGGEST HIGH TEMPERATURES 3-5 DEGREES WARMER THAN THOSE OF
FRIDAY... RANGING FROM 86 DEGREES OR SO AT INT TO LOWER 90S AT MEB
AND FAY.
TONIGHT: A DEVELOPING WARM FRONTAL ZONE TO OUR WEST AND
SOUTHWEST... AHEAD OF A STORM SYSTEM OVER THE CENTRAL PLAINS THIS
MORNING... WILL APPROACH THE REGION OVERNIGHT. WHILE CLOUDS SHOULD
CONTINUE TO THICKEN AND LOWER IN RESPONSE TO A STRENGTHENING MID
LEVEL WAA REGIME (PARTICULARLY ACROSS THE NORTHERN PIEDMONT)... ANY
PRECIPITATION SHOULD HOLD OFF UNTIL CLOSE TO OR AFTER DAYBREAK
OWING TO A CONTINUED DRY LOW LEVEL AIRMASS. EVEN THEN... WILL
MENTION A SLIGHT CHANCE OF A SHOWER ONLY IN THE NORTHERN AND
WESTERN PIEDMONT... IN CLOSER PROXIMITY TO THE PRECIPITATION
SHIELD EXPECTED TO SPREAD FROM THE UPPER MIDWEST THIS MORNING INTO
THE VIRGINIAS OVERNIGHT. THE INCREASING CLOUD COVER AND RESULTANT
L/W RADIATION SUGGEST OVERNIGHT LOWS A COUPLE OF DEGREES ABOVE
CONSENSUS MOS... GENERALLY UPPER 60S TO AROUND 70 DEGREES. -MWS
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
AS OF 345 AM SATURDAY...
FOR SUNDAY AND SUNDAY NIGHT: AN H85 WARM FRONT AND ASSOCIATED STRONG
LLJ (ON THE ORDER OF 25-40 KTS AT H85)... AND RESULTANT STRONG LOW
LEVEL WARM MOIST ADVECTION WILL CONTRIBUTE TO BROAD LARGE SCALE
ASCENT ACROSS CENTRAL NC THROUGH SUNDAY EVENING. THE ASCENT SHOULD
BE AUGMENTED BY THE DIVERGENT RIGHT ENTRANCE REGION OF A 80-100 KT
UPPER LEVEL JET. THESE FORCING FEATURES... IN CONJUNCTION WITH AN
INCREASE IN PRECIPITABLE WATER VALUES TO BETWEEN 1.75 AND 2.25
INCHES... SUGGEST SHOWERS AND PERHAPS THUNDERSTORMS WILL BE LIKELY.
THE NWP MODELS INDICATE THE PRIMARY SURFACE FRONTAL ZONE MAY BE
SUPPRESSED OVER EXTREME SOUTHERN NC OWING TO WIDESPREAD CLOUD COVER
WITHIN THE PRIMARY LOW-MID LEVEL FRONTAL CLOUD BAND OVER VA AND MOST
OF NC. THE WIDESPREAD CLOUD COVER SHOULD SERVE TO MAINTAIN
RELATIVELY WEAK LOW TO MID LEVEL LAPSE RATES THAT MAY LIMIT THE
COVERAGE AND STRENGTH OF ANY THUNDERSTORMS. HOWEVER... THE NWP
MODELS DO INDICATE THAT SOME DEGREE OF MID LEVEL DRYING MAY TAKE
PLACE ABOVE THE INCREASINGLY MOIST AND SATURATED H85 LLJ... WHICH
MAY CONTRIBUTE TO POTENTIAL/CONVECTIVE INSTABILITY AND RESULTANT
CAPE THAT THE MODELS CURRENTLY FAIL TO DEPICT. A CONDITIONAL SEVERE
WEATHER THREAT EXISTS IF ANY SUSTAINED UPDRAFTS INDEED FORM... GIVEN
THE STRENGTH AND VEERING OF THE LOW TO MID LEVEL WIND FIELDS WITHIN
THE STRONG LOW-MID LEVEL WAA REGIME. DMGG WINDS AND TORNADOES WOULD
BE A THREAT FOR ANY STORMS THAT CAN ROOT INTO THE BL. GIVEN THE
EXPECTED CLOUD COVER AND PRECIPITATION... HAVE LOWERED TEMPERATURES
TO REFLECT HIGHS IN THE 76 TO 85 DEGREE RANGE FROM NW TO SE... AND
THESE MAY STILL BE OPTIMISTIC BY A CATEGORY OR EVEN TWO...
ESPECIALLY OVER CENTRAL AND NORTHERN ZONES.
THE PASSAGE OF A TRAILING H85 COLD FRONT AND SOUTHWARD SETTLING JET
ALOFT SUGGEST PRECIPITATION SHOULD DIMINISH FROM NW TO SE SUNDAY
NIGHT. WILL ACCORDINGLY TAPER POPS INTO THE CHANCE RANGE... HIGHEST
SE... BY MONDAY MORNING. OVERNIGHT LOWS IN THE MIDDLE 60S TO LOWER
70S. WHILE THE NWP MODELS CONTINUE TO WAFFLE REGARDING QPF...
PARTICULARLY THE CONVECTIVE FEEDBACK AFFLICTED GFS... THE RELATIVELY
STEADFAST AND FAVORED ECMWF INDICATES STORM TOTAL PRECIPITATION
AMOUNTS COULD RANGE FROM ONE TO AS MUCH AS TWO INCHES ACROSS
PORTIONS OF CENTRAL NC.
MONDAY AND MONDAY NIGHT: THE UPPER JET AND LOW LEVEL FRONTAL ZONE
ARE EXPECTED TO STALL AND LURK JUST TO OUR SOUTH THIS PERIOD...
WHICH MAY SLOW THE CLEARING AND DRYING TREND OVER SOUTHERN NC. WILL
ACCORDINGLY MAINTAIN MORE CLOUD COVER AND A LOW CHANCE OF SHOWERS
AND ISOLATED THUNDERSTORMS OVER THE EXTREME SOUTHERN PORTIONS OF THE
FORECAST AREA THROUGH MONDAY EVENING... WITH A DRIER NORTHERLY FLOW
EXPECTED TO OTHERWISE ENVELOPE THE FORECAST AREA... AS WEAK HIGH
PRESSURE NOSES INTO THE REGION FROM THE NW. -MWS
LONG TERM /TUESDAY THROUGH FRIDAY/
AS OF 300 AM SATURDAY...
DRY AIR WILL AGAIN BE IN PLACE OVER CENTRAL NORTH CAROLINA TUESDAY
UNDER WEST TO WEST NORTHWEST FLOW ALOFT. BROAD MID LEVEL RIDGING
OVER THE MIDWEST CROSSES THE MISSISSIPPI RIVER WEDNESDAY NIGHT
ALLOWING DRY CONDITIONS TO PERSIST. NO MORE THAN ISOLATED AFTERNOON
THUNDERSTORMS POSSIBLE GIVEN THE DRYNESS AND LACK OF A SIGNIFICANT
TRIGGER OTHER THAN AFTERNOON HEATING. ANY MIDWEST MCS ACTIVITY IS
LIKELY TO BE STEERED NORTH OF OUR AREA UNTIL AT LEAST FRIDAY. RAIN
CHANCES FOR THE EXTENDED PERIOD ARE TOO LOW TO MENTION IN THE TEXT
PRODUCTS.
LOW LEVEL THICKNESS NEAR TO BELOW SEASONAL NORMALS INTO THURSDAY.
AFTERNOON HIGH TEMPERATURES 85 TO 92 EXCEPT 90 TO 95 POSSIBLE
FRIDAY. OVERNIGHT LOWS OF 65 TO 70.
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
AS OF 730 AM...
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.
HEAATING OF THE DAY WILL PRODUCE CUMULUS CLOUDS NEAR 7000 FEET BY
LATE MORNING. MOISTURE IN THE AIR COLUMN WILL BE ON THE INCREASE
TODAY AND EXPECT BROKEN CLOUDS NEAR 7000 AS SUNSET APPROACHES...
AND PERSISTING INTO THE NIGHT. LIGHT WINDS BECOMING WEST SOUTHWEST
LESS THAN 10 MPH DURING THE AFTERNOON.
MOISTURE WILL CONTINUE TO INCREASE LATE SATURDAY NIGHT INTO SUNDAY AS
A FRONT APPROACHES THE AREA. SHOWERS AND THUNDERSTORMS ACROSS
CENTRAL NORTH CAROLINA SUNDAY AFTERNOON INTO SUNDAY NIGHT. VFR
CONDITIONS ARE EXPECTED MONDAY THROUGH WEDNESDAY.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...
AVIATION...
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