Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 042037 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 335 PM EST Sun Dec 4 2016 .SYNOPSIS... Cold air damming surface high pressure will extend into the area from the north tonight as weak low pressure develops along the Gulf Coast. This weak low pressure will track NE along a coastal front tonight and offshore Monday. High pressure will build in briefly from the north Monday afternoon, then a second stronger low pressure system will cross the Gulf States and Carolinas Monday night through Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 335 PM Sunday... Headlines. Cold air damming over interior areas of NC leading to chilly rain. Rain to add up to 0.2 to 0.5 of an inch tonight before ending. Surface high pressure (of sufficient strength - greater than 1025 MB) and preferred location (extending from NY state south into the Carolina`s) to deliver a CAD event for our region, has evolved. The center of the high pressure was slowly shifting east and was located from eastern MD to western NC/SC. The CAA/DAA had essentially ended as the rain continued to saturate the near surface layer. The evaporative cooling process had already dropped temperatures into the upper 30s to 40 west. As of mid afternoon, there was still plenty of evaporative cooling to go as rain was slower to saturate the surface layer in the NE. Rain thus far has been 0.1 to 0.2 in the west, but only barely measurable in the NE. Rain will continue to overspread the region with high confidence through the afternoon, with temps steady in the west, and falling east. For tonight, the impressive plume of deep moisture and a general lift associated with the mid/upper jet and aided by the approaching wave will keep rain widespread through around midnight. Model consensus indicates a gradual shift of the rain out of the west between midnight and 300 am, then in the east between 300 am and 600 am. Only the SE will have lingering light rain chances around daybreak, with low clouds and some lingering fog and mist elsewhere. As for QPF, expect a general 0.10 to 0.25 in the NW ranging to 0.25 to 0.50 in the SE for storm totals (through tonight) - the next system will affect us with significant rain later Monday into Tuesday. See discussion below. The cold air damming will be locked in place tonight and the residual affects will linger through Monday morning. Lows tonight will hold where the evening temperatures land, mostly 38-43 NW to SE. Monday, areas of fog and low clouds will start Monday morning, before most guidance suggests scouring out of low clouds from the NNW Monday afternoon. This occurs only because of some weak downslope flow from the NNW develops from VA mountains into our Piedmont damming region (in the rear of the departing initial wave). Highs Monday will be dependent on the timing of the scouring out of the low clouds and the extent that the mid/upper level clouds linger as well. We will go a bit below statical guidance in the north- central and NE zone where the low clouds should linger longer with the residual CAD affects. Highs generally in the 50s, some lower 60s possible in the south. No POP during the day as central NC will be in between systems. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 325 PM Sunday... Headlines. CAD again expected Monday night and Tuesday with a chilly rain. QPF of 1 to 1.5 inches expected Monday night and Tuesday. Miller B type storm (parent low tracks west of our area - weakens - the secondary low becomes primary near the Carolina coast Tuesday, tracks away Tuesday night). Weak high pressure (less than 1025 mb) is forecast to move from the TN valley Monday to the mid-Atlantic Monday night setting the stage for the next significant system to approach our region from the western Gulf Coast Monday night. Yet another CAD event is expected even though the high pressure this time is weaker than the one today. It is still expected to be just strong enough (near 1025 mb) and in good position (PA to VA) Monday night to allow the deliverance of CAA/DAA into the Piedmont Damming Region, just before and early in the development of rain again Monday night. Dew points in the 30s will feed into the northern Piedmont providing a good start for evaporative cooling again once the rain arrives in earnest. Timing for now appears to be near or after midnight in the SW, spreading NE overnight to cover the area by 12z/Tuesday. Lows Monday night will likely be at 12z/TUE - and readings will likely fall further during the morning with the CAD. Lows 42-50 N to S with falling temps into the upper 30s and 40s all areas during the day Tuesday. Rain is expected much of the day Tuesday. Highs only in the 40s with 50s in the SE. The chance of the coastal front penetrating well inland into our region is very low given the expected Damming and Miller B type storm (and secondary development very near the coast Tuesday). This would keep the warm sector well to our SE. The storm system will lift NE and away Tuesday night with low overcast conditions expected and rapidly ending rain from south to north early in the evening. Temps should hold nearly steady in the 40s and lower 50s N to SE. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 335 AM Sunday... Wednesday and Thursday are expected to be dry and warmer with highs in the mid to upper 50s both days as the warm sector moves overhead in front of a longwave trough that will move across the plains and bring much colder temperatures to the area by Thursday night into Friday. The timing of this feature is quicker in the GFS solution and it is also drier as it moves through the area. The ECMWF solution lags the front and allows for significant development of the front with Gulf moisture. This scenario seems to be an outlier when compared to ensemble means and so the thinking at this time is for the drier/colder scenario seen in the GFS to prevail but I wouldn`t be surprised if the timing is a little fast, as can be the case with the GFS. Lows Thursday night in the mid 20s to low 30s with highs on Friday in the upper 30s to lower 40s. The cold drier airmass persists with the coldest lows of the period on Friday night with 20-25 degrees expected across the CWA. Only slight warming for Saturday with highs in the lower 40s. && .AVIATION /18Z Sunday through Thursday/... As of 130 PM Sunday... Confidence is high with lowering CIGS and VSBYS into the IFR/LIFR categories with rain and fog dominating through daybreak Mon. Winds will be light mainly from the NE at 10 kt or less. Some improvement will occur between 12z-15z monday as the CIGS lift as the system departs. A slow progression to MVFR TO VFR will occur before 18z most areas. Looking beyond 18z Monday, VFR conditions will dominate from around 18z Mon until around 06z Tue. Then another storm system will cause IFR conditions to return after 06z early Tue morning, lasting through much of Tue with steady widespread rain returning. Rain will end late Tue, although IFR clouds will hold into Tue night. Improvement to VFR is expected Wed and Thu. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Badgett LONG TERM...Ellis AVIATION...Badgett is the U.S. government's official web portal to all federal, state and local government web resources and services.