Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 182008 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 408 PM EDT Sun Mar 18 2018 .SYNOPSIS... Weak high pressure will extend across the southern middle Atlantic states through tonight. A warm front will retreat north across the southeastern U.S. Monday, ahead of a series of low pressure systems that will track along the front, and across and offshore the Carolinas, Monday night through early Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 350 PM Sunday... WV satellite imagery indicates the ridging aloft that was over the MS Valley in 12Z RAOB data has expanded ewd to the Deep South and upr Midwest; and this ridge will continue to expand ewd across the sern U.S. tonight. While doing so, however, a srn stream perturbation, now evident in WV imagery invof the ArkLaTex, will deamplify while tracking across the TN Valley and srn Appalachians and consequently cause the preceding ridge to flatten with time. Associated mid to high level moistening will spread newd across cntl NC late tonight, along with weak forcing for ascent focused in the mid levels after 09Z. Additionally, a low to mid level warm air advection regime, and contribution to forcing for ascent, will develop on the wrn periphery of a weak ridge/antic-cyclone drifting to the srn middle Atlantic coast. Initially clear skies will consequently become cloudy or mostly so from west to east, from a developing multi- layered cloud deck overnight. A little light rain will also be possible over the far srn and wrn Piedmont toward daybreak, with otherwise dry conditions. Temperatures will likely reach lows earlier than is typical, then rise with the development and ewd expansion of the clouds - in the wrn Piedmont around or shortly before midnight, ranging to an hour or two before sunrise in the Coastal Plain. As such, low temperatures are expected to range from lwr-mid 30s in the nrn and cntl Coastal Plain to mid 40s over the srn and wrn Piedmont.
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As of 400 PM Sunday... A progressive trough aloft now over the cntl Rockies, one that will have become a compact closed mid-upr low as it migrates across the cntl Plains tonight, will deamplify as it tracks enewd across the lwr OH Valley and cntl Appalachians Mon-Mon night. This trough/low will support Miller "Type B" surface cyclogenesis, with a parent cyclone tracking from a position now over the Front Range of the cntl Rockies to the lwr OH/TN Valley by Mon eve, with subsequent energy transfer to a secondary wave forecast to track across cntl NC Mon night. The result will be a cloudy Monday, but not particularly wet owing to a lull between the weak srn stream forcing for ascent late tonight, and the later arrival of the forcing accompanying the deamplifying closed low Mon night. Rain will become widespread with the passage of the upper and lower waves Mon night, particularly along and north of the track of the surface wave - over the nrn Piedmont, where rainfall amounts as high as three quarters of an inch to one inch appear probable. Srn counties will meanwhile experience an increasingly convective character of the precipitation, not as uniform, and with a slight chance of thunder, where milder and slightly unstable conditions, particularly with respect to elevated parcels, are likely to materialize. Temperatures, hindered by the multi-layered overcast, will be cooler Mon, ranging from lwr 50s over the nw Piedmont to upr 50s-near 60s in the srn Coastal Plain, with lows Mon night ranging from mid 40s in the cool/stable wedge north of the low track, to low-mid 50s south.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 210 PM Sunday... Longer range forecast remains on track for a cold and unsettled Tuesday through Thursday with a warming trend toward the weekend. 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 mid 40s north to the lower to mid 60s south. Additional mid/upper level energy is expected to dive southeastward and into our area for Tuesday night into Wednesday. Models continuing to advertise the potential for some wintry precip late Tuesday night into Wednesday morning across the area, with the best chance of seeing some light accumulations of snowfall across the climatological favored northern Piedmont. The system will be similar to the last one, where the boundary layer will need to cooled by melting snow in order bring temps down to near freezing. Have kept temps ranging from the lower/mid 30s to lower 40s for the entire wintry event. Dry weather will return for late week with the mid upper level trough axis expected to shift to the east of the area. The next system is expected to approach the area next weekend, with increasing chances for showers. Temperatures will make a run toward seasonal normals by the weekend. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 215 PM Sunday... Under the influence of a ridge of high pressure over the srn middle Atlantic states, VFR conditions will persist through tonight. However, veering low/mid-level winds to a sly component, on the wrn periphery of the ridge, will favor the development and newd expansion of VFR (5-15 thousand ft) ceilings overnight-early Mon, with a subsequent lowering of ceilings to MVFR range and an increasing probability of rain, after 12Z. Outlook: 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. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BSD/Franklin AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.