Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220048 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 848 PM EDT Fri Apr 21 2017 .SYNOPSIS... A pre-frontal surface trough will linger over western NC tonight. Meanwhile, a cold front will approach from the north tonight, then sag into NC Saturday. The front will stall over far southern NC late Saturday into Sunday, as a slow-moving area of low pressure tracks along the front through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 355 PM Friday... The latest observational data indicated a pre-frontal surface trough over the western Piedmont extending NE into southern VA. Scattered thunderstorms were already underway along this trough and back over the higher terrain of the Appalachians. It still appears that the Triad region extending ENE through the northern Piedmont into the northern Coastal Plain will continue to be the areas affected by these showers and thunderstorms this afternoon. MLCapes were rather modest, with near 1000 J/KG noted over the northern Piedmont. This is where this instability was aiding the storm development along the trough. Hi-res models, in particular the HRRR, performance thus far has been good with the general locations of this convection. We will continue to use that guidance as a starting point with the forecast of convection this afternoon into the early evening, gradually transitioning to a blend with the operational GFS/EC and the ensembles. It appears that at least scattered thunderstorms can be expected, mainly over the Piedmont into the northern Coastal Plain this afternoon. This activity should begin to weaken as it shifts ESE into the Triangle area around rush hour. POP may end up being rather minimal in the east and south where the convective parameters were not as favorable, even with the sea breeze boundary. Additional shower and thunderstorm clusters are expected to develop back northward toward the air mass that has not been convectively overturned into the NW zones late afternoon and early evening, while the convection in the east should die off with sunset. Locally 1 inch of rain may occur in 30 to 45 minutes with the storms in the NW Piedmont through the afternoon/evening. In addition, one or two of the storms may approach severe wind criteria before sunset before weakening somewhat this evening. Lows tonight will be very warm for late April with mid 60s expected (+12 to +15 above normal). Just a slight chance or low chance of showers will be continued well after midnight in the NW. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 355 PM Friday... The focus for showers and thunderstorms is expected to remain over the western and northern zones of the Piedmont, as far south as Albemarle to Raleigh to Rocky Mount - mainly Saturday afternoon into the evening. This is where the low level boundaries should aid in focusing the convective development. A blend of the Hi-res models along with the GFS/EC were used in trying to place the main synoptic cold front that is forecast to dive into the northern Piedmont Saturday afternoon. Convection and associated outflows tonight will greatly aid in convective initiation Saturday. The latest Hi-Res HRRR suggests this may occur by early afternoon in a SW-NE corridor from west-central NC to just north of the Triangle area. The main push of much cooler and damp NE flow should hold off until late afternoon and evening, which will eventually stabilize the boundary layer and spread a low deck of clouds with it. Therefore, the temperatures should show a very large range from upper 50s NE into the mid 80s south during the late afternoon. A few marginally severe storms may occur especially along the leading temperature/cloud gradients. Showers and a few thunderstorms (elevated north of the cold front) are expected for much of the Piedmont, Sandhills, and Coastal Plain Saturday night. Widespread activity is expected in the west into the central portions of NC, with more scattered activity down east. The cold front should backdoor much of central NC, except the far SE zones by 12z/Sunday. This will eliminate much of the severe threat, but elevated storms will likely produce locally 1 to 2 inches of rain in the western and central Piedmont by 12z/Sunday. Since it has been dry recently, flash flooding is not likely through 12z/Sunday unless 1.5+ inch/hour rates and/or 3+ inches in 3 hours materialize. Lows will cool into the 50s, except 60s south Saturday night with POP nearly 100 all zones. && .LONG TERM /SUNDAY THROUGH SATURDAY/... As of 255 PM EDT Friday... An amplifying upper level low digging SE from the Rockies into the Lower Midwest this afternoon will track eastward through the TN valley on Saturday, progress ESE/SE toward the Southeast coast on Sun/Mon, then shift offshore the GA/SC coast on Tue. Shortwave ridging /WSW flow aloft/ is expected in the wake of the upper wave on Wed/Thu. Even though the upper wave has moved ashore and been sampled by the RAOB network, confidence in forecast specifics (precip amounts, severe weather potential, temperatures) remains below average due to the potential interaction between the aforementioned upper low and northern stream shortwave energy progressing east across the Great Lakes into New England, with additional uncertainty assoc/w the effects of upstream convection (heavy precipitation /latent heat release/) progged over portions of the Carolinas/Southeast late this weekend. Broadly speaking, expect mostly cloudy skies, cooler temperatures, and increasing chances for convection over the weekend, particularly Sunday/Sunday night. The best potential for surface based convection will be on Sat, though coverage is difficult to ascertain at this time. Elevated convection is more likely on Sunday, though some potential for surface based convection may exist in the far S/SE. Chances for precipitation will diminish from west-east and skies will clear by Tue/Tue evening as the upper level wave progresses offshore. Expect dry conditions and a warming trend Wed-Sat as an upper level ridge builds over the Southeast CONUS. The next best chance for precipitation may not materialize until early next week. -Vincent && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... As of 840 PM Friday... 24 Hour TAF Period: Several rounds of isolated to scattered showers and thunderstorms are expected over the next 24 hours across central NC in advance of a cold front. Convection this afternoon/evening has generally remain isolated to widely scattered and is expected to generally remain so into the overnight hours. However, KGSO/KINT stand to see the best chance of seeing some showers and storms for the remainder of the evening into early Saturday morning as another round of showers and storms is expected to clip the NW Piedmont of central NC. Brief IFR/MVFR conditions will be possible with any convection this evening along with perhaps a wind gust or two to around 25 to 30 kts. Otherwise, VFR conditions are generally expected tonight. However, there is a small chance we could see some sub-VFR cigs at KGSO/KINT/KRDU around daybreak Saturday. A cold front will approach the region from the north-northeast on Saturday, possibly move south-southwestward across KRWI and KRDU near the end of the TAF period. Near and behind the front, expect we will see some showers and storms, along with accompanying sub-VFR conditions and possible strong wind gusts. Thus, have included a prob30 group for all the northern TAF sites for the last 4 hours or so of the TAF period. Behind the front, expect cigs will quickly fall to low end MVFR or IFR, with winds out of the north to northeast. Outlook: The cold front should stall over the region through Sunday night, though likely just to the south of the central NC TAF sites. This will allow for several waves of low pressure to track along the front and bring numerous showers and possibly some thunderstorms. Periods of showers and storms with MVFR to IFR CIGS and IFR VSBYS will occur Sat PM through Monday night, possibly lingering into Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Badgett LONG TERM...Vincent AVIATION...BSD/Badgett is the U.S. government's official web portal to all federal, state and local government web resources and services.