Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191051 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 651 AM EDT Tue Mar 19 2024 .SYNOPSIS... Canadian high pressure will build across the Southeast through midweek. A dry cold front will move though the Mid-Atlantic late Wednesday ahead of a low pressure system that will track through the Southeast and offshore into the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 400 AM Tuesday... ...A Freeze Warning is in effect for portions of the Southern Piedmont and Sandhills for sub-freezing temperatures this morning... A vigorous mid/upper trough will shift offshore by this morning with the secondary reinforcing surface cold front well offshore and the Canadian airmass sufficiently deposited over the Mid- Atlantic and a majority of the Southeast. Surface high pressure over the ArkLaTex Region will gradually elongate across the Gulf Coast states through the afternoon as a sub-1000mb low pressure slides from central Ontario into the Great Lakes Region by this evening. The result will back surface winds out of the southeast through the afternoon with a continued tight pressure gradient between the low to the north and the high to our south. Incredibly strong subsidence on the backside of the departing mid/upper trough on the order of 150-200m H5 height rises will result in mostly clear skies across the area today with only wisps of thin cirrus across northern NC into VA at the nose of a 100-120 kt northern stream upper jet. Surface stirring should continue for most locations across central NC given the pressure gradient across the area tonight and result in lows in the upper 30s. However pockets of light winds with periods of calm may allow temperatures to drop into the mid 30s. Enough stirring should take place to avoid optimal radiational cooling and prevent locations from reaching sub-freezing temperatures. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 400 AM Tuesday... The surface high draped out along the GOM states will continue to weaken as the strongly convergent mid-level flow becomes more zonal and the surface low over the Great Lakes continues its slow march into southern Quebec Wed afternoon. At the same time, Canadian high pressure over northern Saskatchewan/Alberta will be nosing down through the central Plains and Upper Midwest and help push a dry cold front through central NC late Wed into early Thurs. Moisture return ahead of the front will be lacking since the elongated area of high pressure to the south will prevent much appreciable moisture into the area. Temperatures will rise into upper 60s to low 70s within the southwesterly surface flow and rising 1000-850mb thicknesses. Surface winds will begin to increase during the early afternoon as the low- level inversion gets completely eroded and a deeply mixed boundary layer results in efficient momentum transfer up to 800 mb. This may result in sustained winds 10-20 mph with gusts up to 30 mph, greatest towards the NC/VA border. Winds will relax quickly after sunset as the boundary layer cools and a surface inversion sets up. Cooler air will filter in behind the cold front late Wed into early Thurs morning and lows will be dependent on the amount of CAA can occur at the surface before sunrise. Leaning on statistical guidance results in the lows in the upper 30s (N) to low/mid 40s (S). && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 330 AM Tuesday... Thursday and Thursday night: A strong, reinforcing high over SE Canada will build south down the mid-Atlantic Seaboard and into the Carolinas. Though clouds will increase Thursday night, it should remain dry with slightly below normal temps. Friday through Saturday night: A southern stream shortwave trough over the Southern US Plains Thursday morning is forecast to eject east through the Lower MS Valley and mid South Friday, across the southern Appalachians Friday night and then traverse the SE US on Saturday. The southern shortwave is expected to spur surface cyclogenesis over the northern Gulf Coast region Friday with less confidence in the exact track thereafter as it evolves eastward through the SE US Friday night and Saturday, before moving offshore Saturday night. This system is shaping up to produce a wet end to the week with rain chances increasing from the SW during the day on Friday, with the wettest period being Friday night, potentially lingering across eastern NC Saturday. Currently, expect rainfall amounts to range from 0.50-1.0" west of US 1 to 1-2" east of US 1. The residual continental airmass associated with a strong ~1030mb surface high preceding the arrival of the surface low into the region should greatly deter destabilization across the area. However, models do indicate the development of some weak instability late Friday night and into Saturday, mainly across SE portions of the forecast area. As far as temperatures, while it will depend on the track of the surface, the increasing likely development of an insitu CAD across the NC Piedmont will favor a sharp NW to SE temperature gradient across the area Friday. Highs potentially ranging from near 50 NW to lower/mid 60s SE. Highs Saturday could be similarly challenging with CAD likely to linger across the area and with secondary re- development of rain as the upper trough crosses the area. Highs in the upper 50s/near 60 north to lower/mid 60s elsewhere. Sunday through Monday: Canadian high pressure building into the area will bring cool below normal temps for early next week. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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As of 650 AM Tuesday... VFR conditions expected through the 24 hour TAF period. WNW surface winds 5 to 10 kts with gusts up to 15 kts will back to SW through the afternoon and strengthen to 10 to 15 kts with gusts 20 to 25 kts. As the winds relax later this evening and a surface inversion sets up, a strong LLJ will overspread all terminals through the night and weakening towards daybreak. Outlook: A storm system approaches the area Fri afternoon into Sat bringing widespread sub-VFR conditions within a CAD regime through Sat night.
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&& .FIRE WEATHER... As of 400 AM Tuesday... ...Increased Fire Danger from 11 AM through 8 PM today... Tuesday: Within the dry airmass deposited across central NC from the cold frontal passage last night, dew points will be in the teens to low 20s throughout the day. Surface winds will increase by this afternoon to 15 to 25 mph and combine with relative humidity values 20 to 30% and cause increased fire behavior today. Refer to your local burn- permitting authority on whether you may burn. If you do burn, exercise extreme caution. Wednesday: Ahead of a dry cold front, southwesterly winds have the potential to increase to 10 to 20 mph sustained with gusts up to 30 mph, especially across the Northern Piedmont and Northern Coastal Plain. These winds may overlap with dry antecedent conditions within the modifying continental airmass with relative humidity values dropping into the 20s to 30s. && .RAH WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 9 AM EDT this morning for NCZ073>076-083- 084. && $$ SYNOPSIS...Swiggett NEAR TERM...Swiggett SHORT TERM...Swiggett LONG TERM...CBL AVIATION...Swiggett FIRE WEATHER...Swiggett

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