Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 100153 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 850 PM EST Sat Dec 9 2023 .SYNOPSIS... High pressure will extend from near Bermuda to the South Atlantic states ahead of a powerful low pressure and frontal system that will move across the region Sunday and Sunday night. && .NEAR TERM /THROUGH TONIGHT/...
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As of 850 PM Saturday... WAA and isentropic lift atop the lingering CAD airmass and associated stratus cloud layer in place across western NC will result in occasional patchy light rain rain and sprinkles across the western Piedmont through the remainder of the evening and early overnight hours. Then during the predawn hours, strong moisture flux convergence coincident with the arrival of a 35 to 45 knot low-level jet will steer the lead band of heavier shower activity and possible embedded thunder east into the western Piedmont and Triad. Do not anticipate any severe threat during this time frame as instability appears to weak and elevated. Rainfall amounts of one-tenth to one- quarter of an inch will be possible through daybreak across the western counties. The far eastern/coastal plain counties could also see some isolated showers by the predawn morning hours as the nearby offshore shower activity moves onshore. Elsewhere it should remain mostly dry. However, there is the potential for fog, potentially dense, to spread north and inland from off the SE coast. Will need to monitor this hazard. Temperatures may cool another degree or two over the next few hours, followed by rising temperatures between 06 to 12z. Lows in the lower/mid 50 north to upper 50s/near 60 SE.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 350 PM Saturday... A high amplitude upper trough, extending south from a low over Hudson Bay to the Gulf Coast, will sharpen as it shifts eastward on Sun. A few embedded s/w disturbances moving through the parent trough will further impact the progression and orientation of the trough. A pair of disturbances, one over the Deep South and the other over the TN/OH Valley, will lift ENE in tandem through the Southeast and mid-Atlantic late Sun/Sun night. The disturbances could help the trough become quasi-negatively tilted over the region. At the surface, a strengthening cold front will approach the Appalachians on Sun, then move into and through central NC Sun eve/night. An area of low pressure may develop along the front as it moves into the Carolinas. Expect both the front and low to move out of the area early Mon morning. Confluent SSW flow off the Gulf ahead of the front and SSE return flow around the Bermuda high will result in anomalously high moisture advection into the area. PWATs should increase into the 1.4 to 1.6 inch range through Sun aft/eve. There will likely be multiple rounds of convection, one moving in from the west early Sun and the other late Sun aft/eve into Sun night. Rain should be exiting the area to the northeast by daybreak Mon. Severe Potential: One of the big questions will be how how far NW the warm front will retreat through the area, and whether or not the rain falling over the cooler air in the NW Piedmont will keep them locked into the stable side of the boundary. MUCAPE of generally 500- 800 J/Kg is expected across the area, highest across the south and east and peaking during the evening, although the forecast MLCAPE is slightly lower. The effective shear should be around 40 kts. There is at least a chance of thunder in the NW Piedmont on Sun, but the better chance for thunder and potentially strong to severe storms late Sun morn/early aft will be across the southern and eastern Piedmont. The second round of convection is a bit less certain wrt severe potential and overall character. While the convective parameters appear to maximize during the late aft/eve, it depends how much the earlier showers and storms work the environment over. If storms are able to tap into some higher instability late, then additional strong to severe storms may occur. In addition to the wind potential associated with the storms, wind gusts of 20 to 30 mph are possible. Also, hi-res model guidance suggest there may be a brief period of stronger wind gusts, 35 to 45 mph, mainly over the Sandhills and Coastal Plain as the surface low and rain lift NE out of the area Sun night. Precipitation: Confidence is increasing that rainfall totals could be in the 2-2.5 inch range by the end of the event, with anomalously high PWATs of 1.4 to 1.6 inches. While there is still a Marginal risk for isolated flash flooding, the system still appears fairly progressive and training of storms are not anticipated. Best chances for isolated flash flooding will generally be over the urban areas and areas of poor drainage. Lastly, have introduced a slight chance for a brief period of snow mixing in with the rain as the system lifts out Sun night. Confidence is relatively low, but the chance is there nonetheless. No impacts or accumulation expected. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 350 PM Saturday... Dry weather and mostly clear skies will prevail from Monday through Friday under the influence of surface high pressure and W/NW flow aloft. A strong pressure gradient between the deepening surface low over the New England coast and high pressure building in from the Deep South will result in strong NW winds continuing from Monday morning into early afternoon behind the cold frontal passage, gusting up to 20-25 mph. Thus much cooler temperatures are in store, with highs only in the mid-40s to lower-50s (5-10 degrees below normal). Winds will gradually relax in the afternoon and evening, becoming largely calm on Monday night as the surface high strengthens and becomes centered over the NC. This will allow for decent radiational cooling conditions. Lows will be mostly mid-to- upper-20s, but some isolated lower-20s will be possible in the coldest outlying areas. High temperatures will slowly moderate from slightly below normal on Tuesday to near or slightly above normal on Wednesday. As the surface high over the Carolinas on Tuesday gets absorbed by another cool ~1040 mb high building SE into the OH Valley and Mid-Atlantic, temperatures may drop a bit again on Thursday. The high will then weaken and lift north on Friday, helping temperatures climb back into the mid-to-upper-50s. Lows will be mid-20s to lower-30s each morning with continued good radiational cooling. Confidence in the sensible weather forecast decreases for Friday night and Saturday. Both the 12z GFS and 12z ECMWF depict a closed mid/upper low over the Southern Plains phasing with a northern stream shortwave energy diving down from the northwestern US. However, details including to what extent this influences the surface pattern are very uncertain. The GFS and a minority of GEFS develop a surface low that moves along the Southeast US coast on Friday night and Saturday, bringing some rain into central NC. However, the ECMWF has the phasing occurring much farther west, with surface cyclogenesis occurring over the Midwest instead. Given the wide range in deterministic and ensemble solutions, confidence is too low for anything beyond slight to low chance POPs (and increasing clouds) during this period. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 715 PM Saturday... Strengthening southerly flow through the lower atmosphere will rapidly bring in IFR/LIFR conditions as well as LLWS ahead of cold front, currently moving through OH, TN, and lower MS Valley. The cold front and a band of pre-frontal showers and storms are forecast to approach the Triad terminals around 10-12z Sun morning, RDU/FAY 15-18z and RWI around 18z. Periods of light to moderate rain will continue behind the first wave, with a second moderate to heavy area of rain/storms along the cold front expected to cross from the Triad terminals during the late afternoon through RWI around midnight. - Swiggett Beyond 00Z Monday: Strong and gusty nwly winds 20-25 kts will result behind the front Sunday night-Monday, including some locally enhanced ones between 30-40 kts at FAY immediately behind the front early Sunday night. Otherwise, VFR conditions are expected Monday through Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL/MWS NEAR TERM...CBL SHORT TERM...KC LONG TERM...Danco AVIATION...Swiggett/MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.