000 FXUS62 KRAH 041716 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 117 PM 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 115 PM SATURDAY... SFC ANALYSIS THIS AFTERNOON SHOWED WEAK/BROAD HIGH PRESSURE CENTERED WEST OF THE MOUNTAINS ACROSS THE OH/TN VALLEY...WITH A RIDGE AXIS EXTENDING EAST INTO THE CAROLINAS. AN AREA OF LOW PRESSURE WAS LOCATED IN THE CENTRAL PLAINS...CENTERED OVER MO/IA...WITH A WARM FRONT EXTENDING EAST INTO IL. ALOFT...12Z RAOB ANALYSIS SHOWED H5 FLOW FROM THE WNW ACROSS NC/VA. AN H5 SHORTWAVE WAS LOCATED UPSTREAM OVER MO/IA. REST OF TODAY: WITH SUNNY SKIES...NEAR NORMAL HIGH TEMPS...AND BELOW NORMAL HUMIDITY...EXPECT AN ATYPICALLY COMFORTABLE INDEPENDENCE DAY WITH EXCELLENT CONDITIONS FOR OUTDOOR ACTIVITIES/FIREWORKS. TODAY'S 12Z GSO SOUNDING CAME IN WITH A PWAT OF ONLY 0.80"...ROUGHLY 50% OF NORMAL FOR JULY. ADDITIONALLY...SURFACE DEWPOINTS THIS MORNING WERE ALREADY IN THE MID/UPPER 50S...WELL BELOW TYPICAL MORNING DEWPOINTS FOR THIS TIME OF YEAR. IN ADDITION TO THE ABNORMALLY DRY COLUMN... FCST SOUNDINGS CONTINUE TO SHOW A PROMINENT MID-LEVEL INVERSION/CAP THROUGHOUT THE DAY. AS SUCH...EXPECT MOSTLY SUNNY SKIES THROUGH THIS AFTERNOON. BY SUNSET...MID/UPPER LEVEL MOISTURE ASSOC/W PRECIPITATION UPSTREAM OVER THE MS RIVER VALLEY WILL BEGIN TO CROSS THE MOUNTAINS AND MOVE INTO THE WESTERN PIEDMONT...AND MOSTLY CLEAR SKIES WILL EVENTUALLY GIVE WAY TO PARTLY TO MOSTLY CLOUDY SKIES IN THE WEST/NW PIEDMONT BY OR SHORTLY AFTER SUNSET. LOW LEVEL THICKNESSES ARE EXPECTED TO REACH ~1410M THIS AFTERNOON...ABOUT 10M WARMER THAN YESTERDAY AFTERNOON. AS A RESULT...EXPECT HIGHS A FEW DEGREES WARMER THAN YESTERDAY...RANGING FROM THE MID 80S IN THE NW PIEDMONT TO THE LOWER 90S IN THE SANDHILLS...OR 86-91F. TONIGHT: THE LOW PRESSURE SYSTEM CURRENTLY APPROACHING THE MS RIVER VALLEY IS EXPECTED TO MOVE SOUTHEAST INTO THE TN VALLEY BY 12Z SUN MORNING. ALTHOUGH CLOUD CLOVER ACROSS CENTRAL NC WILL CONTINUE TO THICKEN AND LOWER OVERNIGHT (PARTICULARLY ACROSS THE NORTHERN PIEDMONT) IN RESPONSE TO STRENGTHENING MID LEVEL WARM ADVECTION ASSOC/W THE APPROACHING LOW PRESSURE SYSTEM...ANY PRECIPITATION IS EXPECTED TO HOLD OFF UNTIL CLOSE TO OR AFTER DAYBREAK DUE TO A CONTINUED DRY LOW LEVEL AIRMASS. SO...W/REGARD TO POPS...WILL KEEP THE FCST DRY FOR MOST OF THE NIGHT...INTRODUCING A SLIGHT CHANCE (20%) OF A SHOWER OR LIGHT RAIN JUST PRIOR TO SUNRISE ALONG/NORTH OF THE I-85 CORRIDOR... CLOSER IN PROXIMITY TO THE PRECIPITATION SHIELD EXPECTED TO SPREAD FROM THE OH VALLEY THIS AFTERNOON INTO THE VIRGINIAS OVERNIGHT. DUE TO INCREASING CLOUD COVER AND RESULTANT L/W RADIATION...WILL FCST LOWS A FEW DEGREES ABOVE MOS GUIDANCE...RANGING FROM THE MID/UPPER 60S TO NEAR 70F. -VINCENT && .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 /18Z SATURDAY THROUGH WEDNESDAY/... AS OF 115 PM SATURDAY... VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD...ALTHOUGH CONDITIONS ARE EXPECTED TO BEGIN TO DETERIORATE BY OR SHORTLY AFTER 18Z SUN. CLEAR/SUNNY SKIES THIS AFT/EVE WILL EVENTUALLY GIVE WAY TO INCREASING MID/UPPER LEVEL CLOUD COVER TONIGHT IN ADVANCE OF A LOW PRESSURE SYSTEM MOVING SOUTHEAST INTO THE LOWER OH AND TN VALLEY. BY 12Z SUN...BROKEN/OVERCAST CEILINGS ARE EXPECTED ACROSS THE ENTIRE AREA...WITH CLOUD BASES IN THE 8-12 KFT RANGE. DUE TO AN INITIALLY DRY AIRMASS IN THE LOWEST 4-8 KFT...VFR CONDITIONS ARE EXPECTED TO PREDOMINATE THROUGH 18Z SUN IN MOST LOCATIONS...ALTHOUGH LOCALIZED MVFR CONDITIONS CANNOT BE ENTIRELY RULED OUT PRIOR TO 18Z. WIDESPREAD SHOWERS AND PERHAPS ISOLATED THUNDERSTORMS ARE EXPECTED BETWEEN 18Z SUN AND 12Z MON AS A WAVE OF LOW PRESSURE MOVES ALONG A DEVELOPING FRONTAL ZONE DIRECTLY OVER CENTRAL NC...AND IT IS THIS TIME FRAME WHERE MVFR/IFR CONDITIONS ARE EXPECTED TO PREDOMINATE. WITH A WAVE OF LOW PRESSURE MOVING OVER THE AREA...INITIALLY LIGHT SOUTHERLY WINDS TONIGHT ARE LIKELY TO BECOME QUITE VARIABLE ACROSS THE AREA ON SUNDAY. LOOKING AHEAD TO EARLY NEXT WEEK...THE LOW PRESSURE SYSTEM CROSSING THE AREA SUN SHOULD MOVE OFFSHORE AFTER SUNRISE MON...AND VFR CONDITIONS MAY RETURN EVERYWHERE BY 18Z MON AFTERNOON AS THE FRONTAL ZONE SHIFTS SOUTH OF THE AREA. HOWEVER...THERE IS STILL SOME UNCERTAINTY WITH THE FORECAST ON MON...AND IT IS POSSIBLE THAT ANOTHER WAVE OF LOW PRESSURE MAY DEVELOP ALONG THE STALLED FRONTAL ZONE OVER CENTRAL SC AND SOUTHEAST NC DURING THE DAY MON...PERHAPS PROLONGING ADVERSE CONDITIONS OVER PORTIONS OF THE AREA (KFAY/KRWI). OTHERWISE...VFR CONDITIONS ARE EXPECTED TO PREDOMINATE THROUGH MID WEEK AS WEAK HIGH PRESSURE BUILDS TOWARD THE AREA. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...VINCENT SHORT TERM...MWS LONG TERM...RLH AVIATION...VINCENT