Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170712 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 212 AM EST Sun Dec 17 2017 .SYNOPSIS... High pressure will settle east across the southeastern US through the weekend. A series of upper level disturbances will move through the region through mid week. && .NEAR TERM /THROUGH TONIGHT/... As of 942 PM Saturday... Only a few thin cirrus were racing NE across NC this evening as ridging remains firmly in place. Based on satellite and the latest observational data it will be around daybreak before the mid level moisture is able to reach our SW Piedmont. The bulk of the night is expected to be mostly clear and cold. Temperatures at mid-evening were showing the typical wide range due to calm conditions. Readings around 900 PM ranged from the upper 20s to upper 30s. Expect lows solidly in the 20s in rural areas, ranging to near 30 in urban centers. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 355 PM Saturday... The open wave now lifting across the Big Bend area will get strongly- sheared/crushed in confluent and zonal flow, across the OH Valley and middle Atlantic states Sun and early Sun night, then offshore. Associated weak height falls aloft, on the order of 10-20 meters at 500 mb, for example, will glance cntl NC in the several hours centered around 00Z Mon. Preceding mid-high level moisture that will have begun to stream into at least w-cntl NC late tonight will thicken and lower throughout the day. Ceilings will consequently continue to lower, to between 5 and 10 thousand ft after 18Z Sun, with associated widespread virga owing to strong omega and saturation in a mid-level mixed phase layer. Some of this precipitation aloft may reach the ground in the form of patchy light rain or sprinkles by late Sun afternoon and Sun evening, particularly across the nrn and nwrn Piedmont, where the aforementioned height falls aloft, and lift and saturation, are expected to be maximized. Skies may partially clear Sun night, though the approach of a maritime warm front from the Deep South may result in the redevelopment of clouds over srn NC late, though this time lower level ones in a several thousand ft layer centered around 5-6 thousand, with an associated slight chance of warm rain process light rain there, as a strengthening and increasingly moist wswly llj jet isentropically-ascends the retreating sfc frontal zone. The periods of cloudiness will likely affect both high and low temperatures, most notably over the wrn and nrn piedmont during the day, and over the srn Piedmont and Sandhills overnight. Highs 49 to 58 from nnw to sse; and lows from the upr 30s north to lwr-middle 40 south. && .LONG TERM /TUESDAY THROUGH SATURDAY/...
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As of 212 AM Sunday... Below average confidence continues in this part of the forecast, but generally models are starting to trend toward one another, increasing confidence from previous days. The temperature forecast will be somewhat of a roller coaster, but mainly above to well above normal for mid-December. Best chances for rain will be Tuesday night through Wednesday and again Saturday and Sunday (next weekend). Through Wednesday: The upper level wave (the deamplifying low/trough) exiting the Southwest US on Tuesday will move eastward through the Midwest toward the Mid-Atlantic. Meanwhile, the flow over Central NC will be nearly zonal Tuesday and Tuesday night ahead of the approaching wave. The model differences with this wave as it moves into the region continue with the latest runs as the EC still holds onto a slightly stronger low/wave while the GFS continues to be more open/weaker. Regardless, both models indicate likely rainfall moving into the area from the west-southwest on Wednesday, lingering into Wednesday night. At the surface, a Piedmont trough sets up on Tuesday, keeping the better warm moist advection south of the area. South-southwesterly flow increases over the region Tuesday night into Wednesday as the surface low over the ARKLATEX moves eastward, impinging on the Carolinas and increasing the warm moist advection into Central NC. The placement of the surface low varies between the NAM, GFS and EC, thus so does the southward progression of the approaching cold front toward/into the area. The track of the low will also have an impact on the precipitation forecast as well, but chances increase farther south. Temps Tuesday/Tuesday night will be well above normal, highs in the mid 60s and lows in the low to mid 40s. Wednesday highs will depend on the location of the low and advancement of the front, generally in the mid 50s to low 60s. Wednesday Night through Saturday: In the wake of the upper wave and surface low, the upper level ridge will again extend northward into the Carolinas. A surface cold front will sink through the region, setting up a brief wedge Wednesday, which could stick around (primarily in the far NW) into Friday. The more interesting weather feature will be the upper level trough the digs southward through the Rockies and into Texas, swinging through the Midwest through Friday. A reflection of the upper level system will be extremely evident at the surface as a strong low develops over the Midwest/Plains on Thursday. The surface cold front associated with this low will strengthen as it progresses eastward with a strong Arctic high digging south out of Canada in it wake and increasing south-southwest flow ahead of it. As of the latest model runs, the front appears to get hung up over the Appalachians Friday night into Saturday, however the strong southwesterly flow into Central NC ahead of it will result in increasing chances for rain on Saturday. The coolest day of the period will be Thursday with the wedge/high lingering over the region. However, expect temperatures to moderate ahead of the next system to well above normal again by Friday and Saturday.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 1230 AM Sunday... Mid-level moisture plume associated with the de-amplifying southern stream shortwave that will track on the western and northern periphery of the mid/upper level ridge in place across the SE US will result in ceilings gradually lowering to the 4-5kft thousand foot range late this afternoon and evening. There could be fairly widespread virga that may reach the ground in the form of patchy light rain or sprinkles between 18Z Sun through 03Z Mon. It`s possible that ceilings could briefly lower to MVFR at KFAY between 06 to 12z. Outlook: Drier air will build into the area on Monday and Tuesday. There will then be a high chance of rain and sub-VFR conditions, heaviest and lowest at FAY, late Tue night through Wed night, with the passage of a low pressure system across the sern U.S. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ NEAR TERM...Badgett/MWS SHORT TERM...MWS LONG TERM...KC AVIATION...CBL/MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.