Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191529 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1120 AM EDT Mon Mar 19 2018 .SYNOPSIS...
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Weak high pressure over the area will migrate offshore, allowing a warm front to lift north into the area by evening where it will stall tonight. There will be a series of low pressure systems developing along the front as it pushes slowly south of the Carolinas through early Wednesday.
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As of 1120 PM Monday... Cloudiness will continue to slowly thickine and lower in weak isentropic upglide. Rain has been very light, with radar echoes mostly not reaching the ground, hence will lower PoPs through the evening when the lift will intensify ahead of the surface low moving across the southern tier. Temps are close to forecast and no changes of significance are needed. Previous discussion: Surface high pressure will continue to migrate east and offshore this morning. A warm front south of the area will lift north into the area late this afternoon and evening, in advance of an area of low pressure tracking east and into the Tn Valley. Today: Initial surge of weak to modest low/mid-level warm moist air advection, fueled by weak shortwave impulses embedded in the westerly flow aloft, well downstream of the compact upper low/vigorous shortwave trough moving east through the central Plains and Mid MS Valley, will support patchy light rain across the area today. There could potentially be a mid day/afternoon lull in precip before the arrival of the stronger moisture advection and lift this evening and overnight, owing to the approach of the aforementioned shortwave trough and associated sfc low into the Tn Valley. Forecast highs will be highly dependent on just how much precip we see and if it will linger into the afternoon, especially across the far northern Piedmont where sufficient precip falling into the residual low-level dry air will help to lock in in-situ wedge conditions. Highs ranging from lower to mid 50s north to lower 60s south. Tonight: As the area of low pressure tracks east into the Tn Valley/southern Appalachians, sfc warm front will lift north into the area. Strong southerly/southwesterly warm moist air advection rooted in a 40-50 kt LLJ overspreading the area from the SW, will support widespread showers and possibly a few thunderstorms across the southern zones as MUCAPE of 250 to 750 J/KG develops across the the warm sector. While models currently show a lack of sfc based instability across the area, the impressive deep layer shear combined with enhanced low-level shear/helicity in the vicinity of the secondary low pressure development, will need to be closely watched for damaging wind and isolated tornado potential across the far southern/southeastern zones overnight. Overnight lows ranging from lower 40s north to mid 50s south.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 350 AM Monday... Tuesday: A brief lull in the precip is generally expected on Tuesday as the first in a series of disturbances shifts to the east of the area. However, skies will continue to remain mostly cloudy to overcast will low level moisture lingering. Highs on Tuesday are expected to range from the lower 40s north to the lower to mid 60s south. Very tricky forecast for Tuesday night through Wednesday as an upper trough digs down into the area spurring surface cyclogenesis along the NC/SC border. While this surface low will quickly move up the Carolina coast, the upper low will linger behind and bring cold air down from the north. This in turn with some leftover moisture could lead to some deformation banding behind the system which could result in a brief period of rain mixed with snow, or if precipitation rates are high enough, a quick burst of snow resulting in some spotty accumulations, particularly across the northern counties. There are several mitigating factors however, that could result in very little to no snow. These include warming temperatures with the heating of the day. Thickness values in the wintry mix to indeterminate areas of the nomogram for much of the event except the very tail end where thicknesses drop to levels suggestive of all snow for a couple of hours when moisture may or may not still be available. Finally, lift drops off considerably after the surface low pulls off to the northeast, making it very hard to produce the rates needed for accumulating snow. What we are expecting at this time is a period of a few hours of rain/snow mix during the Wednesday morning hours resulting in very little to no impacts. There could be some localized heavier snow showers if precipitation rates are high enough. These should be brief but could result in some minimal accumulations of less than a half of an inch if they persist long enough. By the time a changeover to all snow would occur Wednesday night, there will likely not be enough lift or moisture left to produce more than a period of flurries. Bottom line is a late March nuisance event will minimal impacts. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 350 AM Monday... With the storm system moving up the New England coast and away from the area, any remaining flurries will come to an end Thursday morning and clearing will ensue as well as a return to dry weather. Temperatures will struggle to get out of the 40s across the north with mid 50s in the south. Dry weather continues on Friday as high pressure remains in control and a warming trend begins as low to upper 50s are expected north to south. The next low pressure system will move out of the Great Plains and into the Ohio Valley Saturday. Models then split on whether or not the low takes a southward dive into NC but standing in its way will be a moderately strong Bermuda high which may help to keep it north of the area, similar to the EC solution. This will keep us in the warm sector for the duration of the weekend with highs in the low 50s to low 60s Saturday and upper 50s to upper 60s Sunday. Precipitation will be determined by the track of the low with the GFS offering a much wetter solution than the EC. This low and any associated frontal zone will try to clear the area by Monday morning but will be quickly followed by several more shortwave disturbances moving across the deep south and arriving by midweek next week. && .AVIATION /06Z MONDAY THROUGH SATURDAY/... As of 740 AM Monday... 24-Hour TAF Period: Weak upglide will result in very patchy light rain across the area, with the potential for MVFR ceilings at KINT and KGSO. Otherwise, ceilings at at KRDU, KRWI, and KFAY should remain low-end VFR with ceilings between 4 to 6 kft. Conditions are expected to deteriorate everywhere this evening and overnight as a much stronger surge of southwesterly low-level moist warm air advection and lift, attendant to a warm front lifting north into the area, will support IFR/LIFR conditions with widespread showers and possibly a few thunderstorms spreading east across the area between 03 to 12z Tuesday. Looking ahead: Lingering low cigs, are expected into Tuesday, with a mix of MVFR/IFR prevailing. The passage across the Carolinas of a series of low pressure systems will result in sub-VFR conditions and periods of rain, probably mixed with or briefly changing to snow at nrn TAF sites late Tue night or Wed, through Wednesday. Drying and a return to VFR conditions from west to east will occur as the trailing low lifts away from the middle Atlantic coast Wednesday night. -MWS && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...Ellis LONG TERM...Ellis AVIATION...CBL/MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.