773 FXUS62 KRAH 190037 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 837 PM EDT MON MAR 18 2013 .SYNOPSIS... CHILLY AND DAMP HIGH PRESSURE WILL RIDGE SOUTHWARD FROM NEW ENGLAND TODAY...IN ADVANCE OF AN OCCLUDED FRONT THAT WILL SWEEP EAST ACROSS OUR REGION TONIGHT. MILD HIGH PRESSURE WILL FOLLOW FOR TUESDAY. && .NEAR TERM /THROUGH TUESDAY NIGHT/... AS OF 3 PM MONDAY... THROUGH TONIGHT: WE CONTINUE TO REMAIN UNDER THE INFLUENCE OF A COLD AIR DAMMING WEDGE AIRMASS EARLY THIS AFTERNOON. THE LATEST 12KM NAM HAS BACKED OFF A BIT ON HOW FAST THE CAD BOUNDARY MAY BEGIN TO RETREAT INTO SOUTHEAST PORTIONS OF OUR AREA. THIS WILL OF COURSE HAVE IMPLICATIONS WRT IF A SEVERE THREAT IS ABLE TO DEVELOP. GIVEN THIS ALONG WITH THE LATEST HIRES MODELS SHOWING WHAT APPEARS TO BE THE MORE INTENSE CONVECTIVE BANDS TRACKING TO THE SOUTH OF THE AREA... WILL HIGHLIGHT JUST THE FAR SE IN THE HWO WITH THE POSSIBILITY OF A WEAK BRIEF TOR AND/OR DAMAGING WIND GUST IN THE 7 PM TO MIDNIGHT TIME FRAME. EXPECT THE POTENTIAL FOR PATCHY DRIZZLE WILL CONTINUE FOR THE REST OF TODAY ACROSS THE HEART OF THE DAMMING REGION (THE NORTHERN/NORTHWESTERN PIEDMONT). LATER THIS EVENING AS A DEAMPLIFYING S/W APPROACHES THE REGION ALONG WITH AN OCCLUDED FRONT... WITH PERHAPS A WEAK MESO LOW ALONG IT AS IT MOVES ACROSS OUR FAR SOUTHEAST (LOW CONFIDENCE IN SVR THREAT THOUGH)... WE SHOULD SEE A BAND OF ELEVATED SHOWERS/RAIN (WITH A FEW EMBEDDED THUNDERSTORMS POSSIBLE ACROSS THE SOUTHEAST) MOVING ACROSS THE AREA IN THE 00Z TO 06Z TIME FRAME. WE THINK THIS WOULD BE THE WHEN THE VERY SMALL CHANCE OF SEEING ANY SVR (AS MENTIONED ABOVE)... BUT AGAIN INSTABILITY IS EXPECTED TO BE THE LIMITING FACTOR... AS WE WILL SEE LOW LEVEL FLOW INCREASE AND GOOD DEEP LAYER SHEAR... ALONG WITH 0-1 KM HELICITY VALUES EXPECTED TO BE 150-300 M2/S2 RANGE ACROSS THE FAR SE. AFTER MIDNIGHT THIS BAND AND THE ASSOCIATED 850 JET SHOULD BE TO THE EAST OF THE AREA... WITH PERHAPS A PERIOD OF AREAS OF FOG POSSIBLE UNTIL THE MAIN FRONT ARRIVES CLOSER TO MORNING TUESDAY. WE MAY SEE VERY LITTLE PRECIP WITH THE ACTUAL FRONT AS IT MOVES THROUGH THE AREA... BUT WILL MAINTAIN A SLIGHT CHANCE TO LOW END CHANCES POPS AFTER MIDNIGHT UNTIL FROPA AROUND DAYBREAK TUESDAY. LOWS TUESDAY MORNING WILL BE TRICKY. FOR NOW WILL GO WITH AROUND 40 NW (WHERE TEMPS WILL MOVE VERY LITTLE THROUGH DAYBREAK TUESDAY OR SO UNTIL FROPA) TO THE UPPER 50S SE. TUESDAY AND TUESDAY NIGHT: THE SURFACE COLD FRONT SHOULD BE TO THE EAST OF THE AREA BY NO LATER THAN 13-14Z TUESDAY... WITH SUNNY SKIES RETURNING BY LATE MORNING. HOWEVER... WE WILL CONTINUE TO SEE S/W ENERGY ROTATING AROUND A TROUGH ALOFT CENTERED ACROSS THE GREAT LAKES AND NORTHEAST DURING THIS TIME FRAME. ONE SUCH S/W IS EXPECTED TO MOVE THROUGH THE AREA TUESDAY MORNING. DOWNSLOPE FLOW BEHIND THE FEATURE WILL ACTUALLY GIVE US A MUCH WARMER DAY TUESDAY... WITH TEMPS RANGING FROM MID 60S TO LOWER 70S. IN ADDITION... WE WILL SEE WESTERLY WINDS IN THE 15 TO 20 MPH RANGE... WITH GUSTS OF UP TO 25 TO 30 MPH DURING THE AFTERNOON. MID AND HIGH LEVEL CLOUD COVER IS EXPECTED TO INCREASE AGAIN ON TUESDAY NIGHT AS MORE S/W ENERGY IN THE CYCLONIC FLOW ALOFT ACROSS THE REGION APPROACHES THE AREA. THUS... HAVE RAISED LOW TEMPS A BIT FOR WEDNESDAY MORNING. EXPECT LOWS RANGING FROM THE LOWER TO MID 30S ACROSS THE NORTH TO UPPER 30S SOUTH. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 200 PM MONDAY... BLOCKED FLOW OVER THE NORTH ATLANTIC WILL LEAD TO A SLOW MOVING UPPER LOW OVER EASTERN CANADA AND BROAD TROFFING EXTENDING SOUTH INTO THE SOUTHEASTERN CONUS. LEE TROFFING DEVELOPING IN RESPONSE TO WEST TO NORTHWEST FLOW WILL BACK TO SOUTHWESTERLY AHEAD OF A LOW AMPLITUDE SHORTWAVE AND SECONDARY COLD FRONT EXPECTED TO CROSS THE AREA LATE WED/WED NIGHT. MOISTURE WILL BE LIMITED TO MID AND UPPER LEVELS WITH VERY DRY AIR IN THE LOW LEVELS...HENCE NOTHING IS EXPECTED TO REACH THE GROUND. WINDS WILL BE SOMEWHAT WEAKER THAN TUESDAYS GUSTINESS...WITH GUSTS TO PERHAPS 25 MPH DUE TO DEEP BOUNDARY LAYER MIXING. COLD AIR ADVECTION WILL BE TEMPERED A BIT BY LEE TROFFING...STILL LOOKING AT BELOW NORMAL AT 55-60 DEGREES. WEDNESDAY NIGHT AND THURSDAY... EXPECT REINFORCING SHOT OF MODEST COLD ADVECTION IN THE WAKE OF THE SECONDARY FRONT MENTIONED ABOVE. COOL NORTHWESTERLY WINDS AND CLEARING SKIES WILL CONTINUE THROUGH THURSDAY. NO CHANGE TO TRENDS ON TEMPS WED NIGHT AND THU...MOS GUIDANCE HAVE BOTTOMED OUT NEAR THE ONGOING FORECAST TEMPS...WITH MINS IN THE LOW AND MID 30S BOTH WED AND THU NIGHTS...WITH HIGHS ON THURSDAY TOPPING OUT IN THE 50 TO 55 RANGE. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 200 PM MONDAY... A PROLONGED COOL SPELL WILL CONTINUE INTO THE WEEKEND WITH BROAD TROUGHING OVER THE EASTERN CONUS AND A MEAN FRONTAL ZONE SUPPRESSED TOWARD THE GULF COAST. HIGH PRESSURE BUILDING SOUTH OUT OF THE GREAT LAKES REGION WILL SUPPRESS MOISTURE WITH DRY WEATHER FRIDAY... PERHAPS INTO SATURDAY. HIGHS BOTH DAYS WILL BE IN THE UPPER 40S TO MID 50S. SIGNIFICANT MODEL DIFFERENCES REAR THEIR HEAD CONCERNING DETAILS ON DEVELOPMENT OF A WAVE IN THE SOUTHERLY FRONTAL ZONE AND HOW QUICKLY MOISTURE ADVECTION SETS UP. GFS WOULD LIKE TO SET UP A MILLER B SCENARIO WITH COASTAL CYCLOGENESIS INITIATING ISENTROPIC LIFT AND SUBSEQUENT LIGHT PRECIP INTO THE AREA SATURDAY AFTERNOON...WITH THE MAIN COASTAL LOW NOT BECOMING DOMINANT UNTIL LATER SUNDAY. MEANWHILE...THE ECMWF SETS UP THE COASTAL CYCLOGENESIS SCENARIO DIFFERENTLY...WITH EARLIER PRECIP DUE TO AN INITIAL WEAK LOW OFF THE FL COAST ON FRIDAY. THERE IS LOW CONFIDENCE IN THE ONSET TIMING AND RATHER THAN WAVER TOWARDS ONE SOLUTION OR THE OTHER AT THIS POINT...WILL MAINTAIN THE ONGOING FORECAST TREND FOR CHANCES OF LIGHT RAIN MAINLY FROM THE PM ON SATURDAY THROUGH MONDAY MORNING WHEN THE PREDOMINATE EAST COAST LOW SHOULD BE PRODUCING ITS LAST VESTIGE OF WRAP AROUND PRECIP. TEMPS SATURDAY THROUGH MONDAY WILL BE IN THE UPPER 40S TO MID 50S AFTER MORNING LOWS MAINLY IN THE MID 30S. && .AVIATION /00Z TUESDAY THROUGH FRIDAY/... AS OF 800 PM MONDAY... A COLD AIR DAMMING WEDGE AIR MASS REMAINS FIRMLY IN PLACE ACROSS MUCH OF CENTRAL NC THIS EVENING...LEADING TO WIDESPREAD IFR/LIFR CONDITIONS. HOWEVER...THE EXCEPTION CONTINUES TO BE KFAY WHERE CONDITIONS HAVE TEMPORARILY IMPROVED AS THE WEDGE FRONT TRIES TO MOVE NORTHWARD. OTHERWISE...A BAND OF SHOWERS WILL MOVE ACROSS THE ENTIRE REGION...WITH ISOLATED THUNDERSTORMS POSSIBLE MAINLY ACROSS THE SOUTHERN HALF OF THE FORECAST AREA (KFAY). THE MAJORITY OF THE PRECIP WILL COME TO AN END FROM WEST TO EAST AFTER MIDNIGHT... ALTHOUGH DRIZZLE/MIST MAY PERSIST THROUGH THE MORNING HOURS. AS THE PRECIP MOVES OUT...THE COOL STABLE AIR MASS SHOULD BE REINFORCED... INCLUDING ACROSS THE KFAY REGION AND WIDESPREAD IFR/LIFR CONDITIONS ARE EXPECTED TO PERSIST UNTIL EARLY TUESDAY MORNING. THEN...A COLD FRONT WILL SWEEP ACROSS THE AREA NEAR DAYBREAK ON TUESDAY...WHICH WILL LEAD TO IMPROVING CONDITIONS. BEHIND THE DEPARTING FRONT...AM EXPECTING BREEZY WEST-NORTHWESTERLY WINDS ON TUESDAY...WITH GUSTS UP TO 25 KNOTS POSSIBLE. OUTLOOK: OVERALL VFR CONDITIONS ARE EXPECTED THROUGH THE REST OF THE WEEK...WITH BREEZY AFTERNOONS (ALTHOUGH NOT AS BREEZY AS TUESDAY). SEVERAL UPPER LEVEL DISTURBANCES/REINFORCING SHOTS OF COLD AIR MAY RESULT IN PERIODS OF INCREASED CLOUDINESS THROUGH THE PERIOD. ANOTHER MORE SIGNIFICANT SYSTEM MAY IMPACT THE REGION LATE IN THE WEEK...BUT THERE IS STILL A LOT OF UNCERTAINTY IN THE EVOLUTION OF THIS SYSTEM. && .FIRE WEATHER OUTLOOK FOR TUESDAY/... AS OF 300 PM MONDAY... INCREASED FIRE DANGER CONDITIONS ARE EXPECTED TUE AND POSSIBLY WED. WILL ISSUE AN INCREASED FIRE DANGER STATEMENT AFTER COORDINATION WITH NCFS. DEW POINTS FALLING OFF TOMORROW AFTERNOON WILL RESULT IN RH NEAR 25 PERCENT BY MID AFTERNOON. THIS COMBINED WITH GUSTS TO 25 MPH AS THE MIXED LAYER DEEPENS POST FROPA WILL RESULT INCREASED FIRE DANGER TUESDAY AFTERNOON AND EVENING. WINDS WILL BE DIMINISHED ON WEDNESDAY BUT IT WILL BE DRIER AND A STATEMENT MAY BE REQUIRED FOR WEDNESDAY AS WELL. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...BSD SHORT TERM..MLM LONG TERM...MLM AVIATION...KRR FIRE WEATHER...MLM