FXUS62 KRAH 241901


AFDRAH





AREA FORECAST DISCUSSION


NATIONAL WEATHER SERVICE RALEIGH NC


300 PM EDT SAT APR 24 2010





.SYNOPSIS...


A STORM SYSTEM OVER THE CENTRAL STATES AND LOWER MISSISSIPPI VALLEY 


WILL MOVE NORTHEAST TOWARD THE GREAT LAKES THIS WEEKEND. DEEP 


SOUTHWEST FLOW DEVELOPING OVER THE SOUTHEAST AND MIDATLANTIC REGION 


WILL BRING IN INCREASINGLY MOIST AND UNSTABLE AIR... KEEPING THE 


WEATHER UNSETTLED THROUGH SUNDAY NIGHT. A COLD FRONT WILL SWEEP 


THROUGH THE AREA MONDAY... USHERING IN COOLER AND DRIER AIR.





$$





.NEAR TERM /THROUGH SUNDAY NIGHT/...


AS OF 245 PM SATURDAY...





REST OF THIS AFTERNOON: THE EARLIER LIGHT RAIN ACROSS THE SOUTHERN 


TIER... ON THE NORTHERN PERIPHERY OF AN APPARENT MCV (PER REGIONAL 


RADAR LOOPS) AND SPAWNED BY MS/AL CONVECTION LAST 


EVENING-OVERNIGHT... HAS MOVED EAST. 





SUBSIDENCE BEHIND THE DEPARTING MCV TO THE SOUTH AND OTHERWISE 


INITIALLY WEAK LARGER SCALE FORCING FOR ASCENT EAST OF THE MOUNTAINS 


SHOULD KEEP ANY PRECIPITATION RELATIVELY ISOLATED THROUGH MOST OF 


THE AFTERNOON... DESPITE THE PRESENCE OF A SURFACE FRONT THAT 


BISECTED CENTRAL NC FROM WNW TO ESE AT 18Z. THE EXCEPTION WILL BE 


OVER THE SOUTHERN AND WESTERN PIEDMONT AND WESTERN SANDHILLS BY LATE 


THIS AFTERNOON AND ESPECIALLY THIS EVENING... WHEN THE LEADING 


ELEVATED CONVECTIVE BAND FROM NORTHERN KY TO NORTHEASTERN GA -- 


DRIVEN BY A ZONE OF MID LEVEL FGEN/WAA AND BENEATH THE EXIT REGION 


OF THE STJ ANALYZED THIS MORNING ALONG THE GULF COAST -- SPREADS 


EAST OF THE APPALACHIANS.  





TONIGHT: CONVECTIVE COVERAGE AND INTENSITY SHOULD THEN INCREASE 


DURING THE OVERNIGHT... WITH THE ARRIVAL OF A 40-50 KT LLJ 


DOWNSTREAM OF AN UPPER IMPULSE CENTERED NEAR DEL RIO TX AT 18Z AND 


BENEATH CONTINUED UPPER DIVERGENCE IN THE AFOREMENTIONED STJ EXIT 


REGION. LOW LEVEL THETA-E ADVECTION IN A BREEZY SOUTHWEST LOW LEVEL 


FLOW SHOULD PARTIALLY OFFSET OTHERWISE MARGINAL... NEARLY MOIST 


ADIABATIC DEEP LAYER LAPSE RATES.. AND CONTRIBUTE TO UP TO SEVERAL 


HUNDRED J/KG MLCAPE AND 500-1000 J/KG OF MUCAPE BETWEEN 06-12Z. 


FORECAST SOUNDINGS SUGGEST CONVECTION SHOULD BE SLIGHTLY ELEVATED 


WITH JUST ENOUGH NEAR SURFACE-PARCEL CIN... HOWEVER... WHICH WOULD 


TEND TO LIMIT MOST OF THE SEVERE THREAT. NONETHELESS... THE ARRIVAL 


OF THE LLJ AMIDST STRONG MID-UPPER WIND FIELDS WILL CREATE FAVORABLY 


LONG AND SLIGHTLY CURVED HODOGRAPHS TO SUPPORT A CONDITIONAL TORNADO 


AND DMGG WIND THREAT WITH ANY SUSTAINED UPDRAFTS ROOTED IN THE 


SURFACE LAYER. THOUGH AGAIN... AT THIS TIME IT APPEARS INFLOW 


PARCELS MAY INDEED REMAIN SLIGHTLY ELEVATED AND MITIGATE THAT 


THREAT. TEMPERATURES QUITE MILD GIVEN THE BREEZY SOUTHWEST WIND... 


WITH GENERALLY LOWER TO MIDDLE 60S EXPECTED.  





SUNDAY: GIVEN THE AFOREMENTIONED FORCING AND DESTABILIZATION... A 


BAND OR BANDS OF SHOWERS AND THUNDERSTORMS -- PERHAPS IN THE FORM OF 


SYNOPTIC SCALE QLCS -- SHOULD BE ONGOING AND SPREADING EAST ACROSS 


CENTRAL NC EARLY SUNDAY. THE CONVECTION SHOULD BECOME INCREASINGLY 


NEAR SURFACE-BASED WITH EARLY DAY DIABATIC HEATING AND CONTINUED LOW 


LEVEL THETA-E ADVECTION AS IT PROGRESSES EASTWARD WITH THE LLJ 


THROUGH THE I-95 CORRIDOR/COASTAL PLAIN THROUGH MIDDAY. ACCORDINGLY 


EXPECT THE SEVERE THREAT (PRIMARILY DMGG WIND AND TORNADO THREAT) TO 


INCREASE AFTER SUNRISE... THOUGH IT WILL LIKELY BE LIMITED 


TEMPORALLY IN CENTRAL NC BY THE MIDDAY DEPARTURE INTO 


EAST-NEIGHBORING WFO CWA/S. DEPENDING ON THE EXACT TIMING OF THE 


LINE AND ATTENDANT SURFACE COLD POOL... SOME PRE-COLD POOL DISCRETE 


(HIGHER PROBABILITY OF SEVERE) DEVELOPMENT IS ALSO POSSIBLE. 





THEREAFTER... CLEARING IN THE WAKE OF THE EARLIER LOW OVERCAST AND 


CONVECTION -- COURTESY OF THE ARRIVAL OF A MID LEVEL DRY SLOT FROM 


HE SW -- WILL DEEPEN THE MIXED LAYER. THE DEEPENING MIXED LAYER WILL 


ALLOW THE HIGHER MOMENTUM ALOFT... ON THE WESTERN PERIPHERY OF THE 


PRIMARY LLJ AXIS... TO MIX TO THE SURFACE AND PRODUCE WINDY 


CONDITIONS (SW @20 MPH WITH GUSTS 30-40 MPH) THROUGH THE AFTERNOON. 


THE APPROACH OF A SURFACE TROUGH/DRYLINE INTO THE NC PIEDMONT DURING 


THE AFTERNOON... IN CONJUNCTION WITH CONTINUED LARGER SCALE FORCING 


AHEAD OF THE TROUGH AXIS ALOFT AND EMBEDDED IMPULSES STILL TO THE 


WEST... SHOULD THEN TRIGGER ADDITIONAL SCATTERED SHOWERS AND 


THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS. CONTINUED 


STRONG... MAINLY UNIDIRECTIONAL WINDS... AND POTENTIAL INSTABILITY 


(*TRUE CONVECTIVE INSTABILITY) OWING TO DRY AIR (FROM THE MID LEVEL 


DRY SLOT) ABOVE A STILL RELATIVELY MOIST IN THE LOWEST 1.5 TO 3 


KM... SUGGEST A THREAT OF DMGG WINDS AND LARGE HAIL. WARM... WITH 


AFTERNOON TEMPERATURES GENERALLY 80 TO 85 DEGREES. 





SUNDAY NIGHT: DESPITE NOCTURNAL STABILIZATION... THE 


STILL-TO-THE-WEST TROUGH AXIS ALOFT... CONTINUED RELATIVELY STEEP 


TEMPERATURE AND THETA-E LAPSE RATES... AND MODEST LOW-MID LEVEL 


MOISTURE WARRANT A SLIGHT CHANCE POP OVERNIGHT. STILL MILD AND 


BREEZY... WITH LOWS AGAIN GENERALLY INT HE LOWER TO MIDDLE 60S. 





&&





.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/....





AS OF 125 PM SATURDAY...





MONDAY THROUGH TUESDAY NIGHT:





MODELS IN GOOD AGREEMENT WITH A CLOSED LOW OR SHORT WAVE OVER OHIO 


MONDAY MORNING WITH A SECONDARY SYSTEM OVER THE UPPER MIDWEST 


DROPPING SOUTHEAST. THE FORMER LOW CAUSES THE SURFACE TROUGH OVER 


NORTH CAROLINA TO SHARPEN DURING THE DAY MONDAY AND SLOW TO WHERE 


THE TROUGH HAS NOT YET EXITED THE EASTERN PIEDMONT BY SUNSET MONDAY. 


BY EARLY TUESDAY THE UPPER MIDWEST LOW HAS REACHED THE MOUNTAINS 


WITH ANOTHER SURFACE TROUGH POISED TO DROP SOUTH OUT OF VIRGINIA 


TUESDAY MORNING. 





IN GENERAL THIS WILL ALL BOIL DOWN TO SMALL RAIN CHANCES WITH THE 


SURFACE TROUGHS BUT MOSTLY LIMITED COVERAGE AND RAINFALL AMOUNTS. 


THE EXCEPTION MAY BE IN THE EAST TUESDAY AFTERNOON AND EVENING WHEN 


A RELATIVELY VIGOROUS MID LEVEL TROUGH SWEEPS THROUGH... BUT WITH 


LIMITED INSTABILITY AND MOISTURE. THERE WILL BE A SMALL CHANCE FOR 


THUNDERSTORMS DURING THE ABOVE MENTIONED PERIOD... BUT COVERAGE 


FORECAST TO BE QUITE SPARSE. SMALLEST RAIN CHANCES MONDAY NIGHT 


BETWEEN THE TWO SURFACE TROUGHS. 





EXPECTING BOUNDARY LAYER TO EXTEND ABOVE 7000 FEET AHEAD OF THE 


FIRST SURFACE TROUGH MONDAY... WITH 1000 TO 850 MILLIBAR THICKNESSES 


ABOVE 1390 METERS BEFORE DROPPING IN THE AFTERNOON. FORECASTING A 


GOOD SPREAD IN AFTERNOON HIGH TEMPERATURES... WITH MID 70S NORTHWEST 


AND NEAR 80 TO MID 80S HIGHWAY ONE AND EAST. MID LEVEL WINDS TO 


THIRTY KNOTS OR SO IN THIS LAYER WILL ALLOW FOR SOME GUSTS 


APPROACHING 30 MPH AT THE SURFACE FROM MID DAY INTO MID AFTERNOON. 


THICKNESSES DROP 20 METERS OR SO FROM THEIR MONDAY PEAK FOR TUESDAY 


AND CORRESPONDING TEMPERATURES WILL BE ABOUT TEN DEGREES COOLER 


TUESDAY AFTERNOON... AT 66 TO 73 DEGREES. OVERNIGHT LOW TEMPERATURES 


UPPER 40S TO MID 50S MONDAY NIGHT... COOLING TO MID TO UPPER 40S FOR 


TUESDAY NIGHT. 





&&





.LONG TERM/WEDNESDAY THROUGH SATURDAY/...


AS OF 125 PM SATURDAY...





WEDNESDAY THROUGH SATURDAY





LOW LEVEL THICKNESSES ON THE RISE DURING THIS PERIOD AS MID LEVEL 


RIDGING OVER THE MIDWEST WEDNESDAY MORNING REACHES THE MID ATLANTIC 


STATES SATURDAY MORNING. THIS PERIOD WILL BE DRY WITH RAIN CHANCES 


LESS THAN 10 PERCENT. 





AFTERNOON HIGH TEMPERATURES WEDNESDAY FROM THE MID 60S NORTHWEST TO 


MID 70S SOUTHEAST... THEN MID 70S THURSDAY... 80 TO 85 FRIDAY... AND 


MID 80S WITH A FEW UPPER 80S SATURDAY. OVERNIGHT LOW TEMPERATURES 


LOW TO MID 40S WEDNESDAY NIGHT... MID 50S THURSDAY NIGHT... AND 


UPPER 50S TO LOWER 60S SATURDAY NIGHT. 





&&





AVIATION /18Z SATURDAY THROUGH THURSDAY/...


AS OF 300 PM SATURDAY...





AHEAD OF A STRONG AND SLOW-MOVING STORM SYSTEM OVER THE SOUTHERN AND 


CENTRAL US... EXPECT INITIALLY VFR CONDITIONS AT PRESENT TO 


DETERIORATE TO MVFR AS THE CURRENT BAND OF SHOWERS AND ISOLATED 


THUNDERSTORMS ALONG THE SC/GA BORDER MOVES EASTWARD INTO CENTRAL NC 


BETWEEN 22-03Z. OTHER MORE ISOLATED SHOWERS... FORCED BY A LINGERING 


SURFACE FRONT OVER THE REGION... ARE POSSIBLE BEFORE THEN... BUT 


COVERAGE SHOULD BE LIMITED AND HAVE ACCORDINGLY OMITTED FROM THE 


TAFS. 





INCREASINGLY MOIST SOUTH SOUTHWESTERLY LOW LEVEL FLOW SHOULD 


INCREASE BOTH THE PROBABILITIES OF 500-1200 FT CEILINGS AND SHOWERS 


AND THUNDERSTORMS IN THE 06-12Z TIME FRAME. EXPECT LOW OVERCAST TO 


GRADUALLY LIFT THROUGH THE MVFR RANGE 13-17Z SUNDAY... AFTER WHICH 


TIME CONDITIONS SHOULD BECOME SCATTERED VFR. THE SCATTERING OF 


EARLIER OVERCAST SHOULD ALLOW THE ATMOSPHERE TO DESTABILIZE WITH 


AFTERNOON HEATING... AND THIS SHOULD LEAD TO SCATTERED AFTERNOON AND 


EVENING SHOWERS AND THUNDERSTORMS. SOUTHWESTERLY SURFACE WINDS WILL 


CONTINUE TO STRENGTHEN WITH TIME AND WILL BE QUITE STRONG BY MIDDAY 


SUNDAY (SW @20 MPH WITH GUSTS 30-40 MPH).  -MWS





LOOKING BEYOND SUNDAY...  ANOTHER ROUND OF MVFR SCATTERED SHOWERS 


IS EXPECTED MONDAY AFTERNOON AND EVENING WITH A COLD FRONT PASSAGE. 


THEN... ANY CIGS MONDAY NIGHT THROUGH WEDNESDAY ARE EXPECTED TO BE 


VFR WITH LITTLE RISK OF FOG. -GIH 





&&





.RAH WATCHES/WARNINGS/ADVISORIES...


NONE.





&&





$$





SYNOPSIS...RTE


NEAR TERM...MWS


SHORT TERM...


LONG TERM...


AVIATION...MWS/GIH