Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200741 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 340 AM EDT MON OCT 20 2014 .SYNOPSIS....HIGH PRESSURE CENTERED OVER NC THIS MORNING WILL MOVE OFFSHORE TODAY. A LEAD SHORTWAVE TROUGH ALOFT WILL CROSS OUR REGION TONIGHT...FOLLOWED BY A STRONGER ONE - AND PRECEDING SURFACE COLD FRONT - THAT WILL SETTLE ACROSS THE MIDDLE ATLANTIC STATES LATE TUE AND TUE NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM MONDAY... A DEAMPLIFYING SOUTHERN STREAM MID-UPPER DISTURBANCE OVER WESTERN TN...AND PRECEDING AREA OF CIRRUS AT 07Z...WILL CONTINUE ENE ACROSS NC/VA THROUGH NOON. SURFACE HIGH PRESSURE CENTERED DIRECTLY OVER CENTRAL NC THIS MORNING WILL MOVE OFFSHORE TODAY...AS A STRONGER NORTHERN STREAM SHORTWAVE TROUGH AND ASSOCIATED AREA OF MAXIMUM HEIGHT FALLS ALOFT (~60 M/12 HR) AMPLIFY ACROSS THE UPPER MIDWEST AND LOWER OH VALLEY. CIRRUS ASSOCIATED WITH THE NORTHERN STREAM WAVE WILL FOLLOW QUICKLY ON THE DEPARTING HEELS OF THE ONES FROM SOUTHERN STREAM...WHILE THE LOW LEVEL RETURN FLOW ALSO PROMOTES THE ONSHORE DEVELOPMENT/ADVECTION OF AN AREA OF STRATOCUMULUS MAINLY OVER THE COASTAL PLAIN AND EASTERN PIEDMONT/SANDHILLS. TEMPERATURES WILL ALSO MODERATE IN RETURN/WARMING SW FLOW...INTO THE UPPER 60S TO LOWER 70S. TONIGHT: THE SHORTWAVE TROUGH FORECAST TO AMPLIFY FROM THE UPPER MIDWEST THIS MORNING TO THE LEE OF THE CENTRAL APPALACHIANS OVERNIGHT...WILL CAUSE A MID LEVEL CLOUD BAND AND ASSOCIATED VIRGA OR ISOLATED SPRINKLES TO MOVE EAST ACROSS CENTRAL NC BETWEEN 06-12Z. A DRY SUB-CLOUD LAYER/BELOW 10 THOUSAND FT SHOULD PRECLUDE THE OCCURRENCE OF ANY MEASURABLE PRECIPITATION. NOT AS COOL...WITH LOWS IN THE UPPER 40S TO LOWER 50S. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 340 AM MONDAY... ANOTHER STRONG NORTHERN STREAM SHORTWAVE TROUGH...ONE LOCATED OVER ONTARIO THIS MORNING...WILL AMPLIFY SHARPLY SSE ACROSS THE OH VALLEY TUE AND CENTRAL APPALACHIANS TUE NIGHT...CULMINATING IN THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC REGION BY EARLY WED. A SURFACE COLD FRONT PRECEDING THE AMPLIFYING SHORTWAVE TROUGH WILL CROSS CENTRAL NC TUE AFTERNOON...BUT NOT BEFORE TEMPERATURES CLIMB INTO THE LOWER TO MIDDLE 70S. THOUGH MOISTURE AND INSTABILITY IS FORECAST TO REMAIN WEAK OVERALL...THE FORMER CONFINED TO A THIN LAYER BETWEEN 850-750 MB AND THE LATTER AOB 200 J/KG PER BUFR SOUNDINGS...LOW LEVEL CONVERGENCE ALONG THE FRONT AMIDST THE RENEWED HEIGHT FALLS ALOFT MAY SUPPORT A BAND OF WIDELY SCATTERED SHOWERS MAINLY ACROSS THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN...WHERE VERY WEAK INSTABILITY AND DEEPER LIFT SHOULD BE RELATIVELY MAXIMIZED IN CLOSEST PROXIMITY TO THE AMPLIFYING SHORTWAVE TROUGH AND ASSOCIATED COLD POOL ALOFT. ANY SCATTERED SHOWERS SHOULD MOVE EAST AND/OR DISSIPATE WITH THE ONSET OF NOCTURNAL COOLING AND THE PASSAGE OF THE COLD FRONT BY EVENING...BUT WITH A LATE NIGHT RENEWED CHANCE (20-30 PERCENT) OF SHOWERS AGAIN OVER THE NORTHEAST PORTION OF THE CWFA...AS THE STRONGEST HEIGHT FALLS/COOLING TEMPERATURES ALOFT...AND MID-UPPER LEVEL DIVERGENCE AND DEFORMATION OVERSPREAD NE NC AND SE VA. DRY ELSEWHERE...BUT WITH PARTLY TO MOSTLY CLOUDY CONDITIONS OWING TO THE STEEP LAPSE RATES AND CYCLONIC FLOW ALOFT. LOWS MOSTLY 45 TO 50 DEGREES. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AS OF 335 AM MONDAY... A STRONG SHORTWAVE DIVING THROUGH THE UPPER TROUGH OVER THE EASTERN US...AND CROSSING NC TUESDAY NIGHT...WILL CLOSE OFF INTO AN UPPER LOW OFF THE DELMARVA ON WEDNESDAY. BENEATH THE UPPER LOW...STEEP TROPOSPHERIC DEEP LAPSE RATES WILL SUPPORT SOME VERY WEAK INSTABILITY...BUT THE LACK OF ANY APPRECIABLE MOISTURE WILL KEEP MOST OF THE AREA FREE OF PRECIP. SLIGHTLY HIGHER DEWPOINTS AND MARGINALLY BETTER MOISTURE OVER THE NORTHERN COASTAL PLAIN SHOULD LEAD TO A MORE PRONOUNCED CUMULUS FIELD...WHERE AN ISOLATED SHOWER OR FEW SPRINKLES MAY BE POSSIBLE. HOWEVER...TO PROSPECTS ARE TOO LOW TO INCLUDE IN THE FORECAST FOR WEDNESDAY. HIGHS WILL BE NOTICEABLY COOLER WITH THICKNESSES DROPPING TO NEAR 1330M WEDNESDAY MORNING...WHICH SHOULD YIELD LOW TO MID 60S. SIMILAR THICKNESS VALUES THURSDAY MORNING SUGGEST LOWS WILL BE MOSTLY IN THE UPPER 30S TO MID 40S. THE LOW WILL THEN SLOWLY MEANDER NORTHEAST ALONG THE MID-ATLANTIC COAST THROUGH THE END OF THE WEEK...AS HIGH PRESSURE SETTLES AND LINGERS OVER THE OHIO/TENN VALLEYS. BETWEEN THESE FEATURES...DRY WEATHER IS EXPECTED THROUGH THE PERIOD WITH NORTHWEST FLOW REMAINING IN PLACE. THE GFS AND ECMWF HAVE BEEN INDICATING A SHORTWAVE WILL MOVE FROM THE NORTHERN PLAINS TOWARD THE SOUTHEAST US BY THE WEEKEND...THOUGH THERE HAS BEEN A LOT OF DISAGREEMENT REGARDING THE AMPLITUDE OF THE WAVE AND ITS FINAL DESTINATION. THE 00Z/20TH ECMWF...WHICH HAD BEEN SHOWING THE WAVE CUTTING OFF OVER THE DEEP SOUTH...NOW SHOWS A MORE PROGRESSIVE WAVE THAT SWINGS ALL THE WAY THROUGH THE REGION AND OFFSHORE BY SUNDAY...A SOLUTION THAT IS MORE LIKE PREVIOUS GFS RUNS. THE SENSIBLE IMPACTS OF THIS WAVE APPEAR TO BE MINIMAL AS THE AIRMASS OVER NC WILL BE QUITE DRY AND STABLE...WITH JUST A SLOW TREND IN TEMPS BACK TOWARD NORMAL THROUGH THE WEEKEND. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 220 AM MONDAY... CIRRUS AND CALM WILL PREVAIL THROUGH MID-MORNING...FOLLOWED BY A DEVELOPING SSW SURFACE WIND THAT WILL BECOME OCCASIONALLY GUSTY INTO THE MID-UPPER TEENS KTS MAINLY AT KINT/KGSO DURING THE MIDDAY-EARLY AFTERNOON HOURS. THE RETURN FLOW WILL ALSO RESULT IN THE ONSHORE DEVELOPMENT/ADVECTION OF AN AREA OF STRATOCUMULUS...THE WESTERN EDGE OF WHICH WILL PRODUCE SCATTERED TO BROKEN CLOUD BASES AROUND 3500- 4000 FT AT KFAY AND KRWI THIS AFTERNOON AND EVENING. OUTLOOK: THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC STATES...AND ASSOCIATED PASSAGE OF A SURFACE COLD FRONT LATE TUE... WILL RESULT IN A CHANCE OF SHOWERS TUE-WED...MAINLY FROM KRDU AND KRWI NORTHEAST TOWARD THE CHESAPEAKE BAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BLS AVIATION...MWS

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