Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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665 FXUS62 KRAH 181819 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 219 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/... As of 1135 AM Sunday... Cold air advection was evident in 12Z upr air data at 850-925 mb, behind a surface cold front that was analyzed at 15Z extending from a ~1008 mb frontal wave several hundred miles se of KHSE, wwd across swrn SC and n-cntl GA. Following weak, 1018 mb high pressure over nrn-cntl VA this morning will build swd into NC today. A multi-layered band of post-frontal, mostly scattered stratocumulus and altocumulus, will continue to pivot swwd across the srn and wrn half of the RAH forecast area during the next several hours, with following drier air and clear skies arriving from the ne. With resultant mostly sunny conditions, dry adiabatic mixing through around 900 mb favors high temperatures ranging from upr 50s ne to lwr-mid 60s sw. A low to mid level warm air advection regime, and contribution to forcing for ascent, will develop on the wrn periphery of the aforementioned ridge as it drifts toward the srn middle Atlantic coast tonight. Initially clear skies will consequently become cloudy or mostly so from west to east, from a developing multi-layered cloud deck through particularly the lowest 10 thousand ft, overnight. Temperatures will accordingly 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. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 345 AM Sunday... High pressure transitions off the Mid Atlantic Coast before sunrise Monday, as a Mid to upper-level low ejects east across the Great Plains states. Southerly to Southeasterly flow across the SE CONUS is enhanced between these two systems, lifting a warm front north into the Carolinas Monday. The result will be lowering overcast on Mon, with an increasing probability of rain from SW to NE with time along with subsequent likely to categorical probability of rain/showers Mon night, with nrn (climatologically-favored) counties likely to remain in a cooler and more stable wedge air mass, while srn ones experience milder and slightly unstable conditions, with an associated slight chance of thunder Mon night. Elevated thunder will be possible as far north as roughly the HWY 64 corridor. && .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...JJM/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.