Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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132 FXUS62 KRAH 231021 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 521 AM EST Mon Jan 23 2017 .SYNOPSIS... A potent low pressure system over the southern Appalachians will track east-northeast through the Carolinas today, then track off the Mid-Atlantic coast on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 335 AM Monday... Through daybreak: In advance of the vertically stack cyclone over Northern GA, low-topped convection within the mid-level dry slot will pivot northward across the area as the occluded front along the NC/SC state line lifts north into Central and Eastern NC through daybreak. Elevated instability of 500 to 1000 J/Kg of MUCAPE will develop briefly across the area between 06 to 12z as tongue of 850- 700mb moist warm air advection lifts north into the area, and further aided by the proximity of the cold temperatures aloft and relatively steep mid-level lapse rates of 7.5-8.0 C/km. This may lead to a slight uptick in coverage and intensity, with some isolated elevated thunder possible across the NC Piedmont. Latest Rap tries to develop some very weak sfc base buoyancy ~100 J/Kg across the far southeastern zones over the next couple of hours, coincident with the lower 60s Td air. This will be the one area we will have to monitor for some weak rotation and possibly a weak isolated tornado. Today: Upper low will track eastward across southern NC through 00z, and off the NC coast tonight. In the wake of the occluded front lifting north into Virginia, we could see some breaks develop in the low clouds across the central and eastern zones during the mid to late morning hours, before the approach of the cold core aloft(-22 to -24C)and steep lapse rates aloft(7-7.5C/km) will support the re- development of scattered showers across the area, with best coverage and best chance for thunder across the far SE where stronger diurnal heating is expected. Given cold temps aloft, could see some small hail with any decent updraft. Highs ranging from mid 50s NW to lower 60s east. Tonight: Drier air filtering into the area with the departure of the system should lead to SW to NE clearing late tonight into Tuesday morning. Lows in the lower 40s NW to mid 40s elsewhere. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY/... As of 400 AM Monday... In the wake of the vertically stacked low progressing offshore the Mid-Atlantic coast, a shortwave ridge aloft will build eastward over the Carolinas and Mid-Atlantic Tue afternoon/evening, progressing offshore by Wed morning as an upper level trough (moving ashore the Pacific coast today/tonight) digs/expands across the Intermountain west/Rockies and shortwave energy rounding the base of the trough (in vicinity of the 4-corners region) ejects northeastward through the Central Plains into the Upper Great Lakes, establishing southwest flow aloft downstream along the Gulf/Southeast Coast and Eastern Seaboard. A cold front assoc/w a sfc cyclone attendant the aforementioned shortwave energy ejecting NE into the Upper Great Lakes will slowly approach the Appalachians from the west Wed aft/eve. Expect dry conditions through this period, with a breezy NW wind gusting 20-30 mph on Tue and a breezy SW wind gusting 20-30 mph on Wed. Highs near 60F on Tue will fall into the upper 30s to lower 40s Tue night, then rebound into the upper 60s on Wed. -Vincent && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 400 AM Monday... Wed Night-Thu: The aforementioned cold front is expected to slowly track east across the Carolinas/Mid-Atlantic Wed night/Thu morning. With the parent shortwave/sfc cyclone tracking rapidly NE away from the front at this latitude, the NAM suggests the front will progress through central NC with little more than a few sprinkles. However, both the GFS/ECMWF suggest a SW-NE oriented swath of light rain may develop along/behind the pre-frontal trough in association with low- mid level frontogenesis. At this time will indicate a 30% chance of rain across central NC Thu morning through early afternoon. Fri-Sun: The latest long range guidance suggests Fri and the upcoming weekend will be dry albeit a little chilly with highs generally in the mid/upper 40s, lows in the upper 20s to lower 30s, and a brisk W to WNW breeze during the aft hours each day. -Vincent && .AVIATION /06Z MONDAY THROUGH FRIDAY/... As of 118 AM Monday... 24-Hour TAF period: Low-topped convection, mainly in the form of showers, will lift north across the area through 12 to 14z. Could see some isolated elevated thunder across the far NW Piedmont over the next couple of hours, while isolated surface based thunder is possible at KFAY. Ceilings are expected to remain IFR/LIFR through 12 to 15z. Easterly winds of 10 to 12kts will become southwesterly around daybreak as the occluded boundary to our south lifts north of the area. Conditions should improve to MVFR/VFR between 15 to 18z. However, as the upper low moves across the area, we could see another round of scattered low-topped convection. Cannot rule out some isolated elevated thunder at KFAY this afternoon, in closer proximity to the upper low. MVFR ceilings will linger into the evening before drier air begins to filter into the area from the southwest between 06 to 12z, bringing a return to VFR by Tuesday morning. Looking ahead: Ridging aloft and at the surface will produced VFR conditions Tuesday and Wednesday. A cold front will cross the region late Wednesday night/early Thursday, bringing with a chance of showers and sub-VFR ceilings to the area. VFR conditions should return late Thursday afternoon/evening. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...CBL SHORT TERM...Vincent LONG TERM...Vincent AVIATION...CBL

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