Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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162 FXUS62 KRAH 182000 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 400 PM EDT Sat May 18 2024 .SYNOPSIS... The region will remain in a warm, humid, and unsettled weather pattern through tomorrow. Cool high pressure will build in from the north tomorrow afternoon through Monday, then shift off the Mid Atlantic coast late Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 355 PM Saturday... Water vapor imagery depicts a shortwave over western TN and northern MS and mid/upper ridging over the western Atlantic, with central NC under the influence of southwesterly flow in between these two features. This is helping bring deep Gulf moisture into the area with PW values ranging from 1.2 to 1.7 inches, highest SE. Scattered showers and storms have begun popping up in the moist and unstable airmass, particularly in two lines. One line stretches across the southern Piedmont, Sandhills and central Coastal Plain and may be associated with a remnant outflow boundary from the convection that largely passed to our south earlier today. The other line is focused along a W-E oriented boundary that is currently analyzed from near the Triad to the Triangle to the northern Coastal Plain, and there is quite a temperature gradient along it as it is still 82F at KRDU but only 64F at KTDF and 64 at KIXA. This line of storms will gradually fill in and slowly move south the rest of this afternoon and evening as the front sinks south. Timing looks to be around 21z to 00z for the Triad and Triangle regions, and 00z to 04z for the Sandhills and central/southern Coastal Plain. Went with categorical POPs with this line, and the rain could be heavy at times with 1-2 inch per hour rates possible. 12z HREF PMM totals depict potential for totals of 1.5 to 2 inches in localized spots. There were localized spots in the NE Piedmont that received 2+ inches of rain in the last 24 hours, particularly around northern Durham/Orange and southern Granville counties. However, these totals were isolated enough and the high totals today are expected to be isolated enough to prevent widespread flash flooding. Even still, the showers and storms are slow moving and isolated flash flooding is certainly possible, especially in urban areas. The WPC has all of central NC in a marginal (level 1 of 5) risk for excessive rain. The line will clear our CWA by around 06z, but isolated light showers can`t be ruled out overnight as the shortwave approaches from the west. As for the severe threat, SPC also has all of central NC in a marginal risk for severe storms, with a primary threat of damaging winds. Not expecting a tornado threat given the very weak 0-1 km shear of around 5 kts or less. The 0-6 km shear is better but still marginal for severe weather, around 30-35 kts. Instability is limited somewhat by the widespread cloud cover in place across the area, but SPC mesoanalysis and latest RAP forecasts still depict as much as 1000-1500 J/kg of MLCAPE from now until sunset. The greatest instability will be across our south, while our far northern counties to the north of the boundary (especially from Person County east to Halifax County) will be mostly stable and not expecting a severe threat there. Lows tonight will be mild (upper-50s to mid-60s) thanks to the widespread low cloud cover. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 220 PM Saturday... By Sunday morning, surface low pressure should be off the NC/SC coast with a positively tilted upper trough axis extending across the Delmarva Peninsula through North Carolina into northern Georgia. Both the surface low and the upper trough will move east through the daytime, with the trough axis near the Atlantic coastline by the evening. High-resolution and synoptic models have continued the trend from the last couple days of showing drier conditions overall. It now appears that locations north of US-64 should be dry through the day, with a slight chance of showers to the south of that and a chance of thunderstorms along the southernmost border. Any precipitation should come to an end by the evening, with dry conditions overnight. The upper trough will help to keep conditions mostly cloudy through the morning, then at least some partial clearing will occur during the afternoon. Northeasterly flow should occur through the day, becoming lighter overnight, but the cold advection on the backside of the surface low should make Sunday the coolest day out of the next seven. Some locations across the northeast should remain in the upper 60s, but otherwise highs will be in the lower 70s. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 134 PM Saturday... Monday through Wednesday: Aloft, the trough should be offshore, with the sub-tropical ridge building from the southern plains to the Northeast US early Mon. While the trough should linger off the mid- Atlantic coast through Wed night, the ridge will shift slightly sewd, extending from the lower MS Valley to the mid-Atlantic by 12Z Wed. The ridge axis will generally remain over the area through at least Wed night, albeit continuing to drift sewd. At the surface, the ridge will remain in place through Mon night, while the low sits/drifts eastward offshore. The surface high will settle south over the mid-Atlantic coast through Tue before drifting eastward over the Atlantic, but continuing to ridge westward toward/into the area, on Wed. A warm front may lift northward through the area Wed as the high moves away, with a lee trough strengthening over the area Wed night. While Mon should be largely dry, there is still the possibility for a brief period of lingering light rain early. Otherwise, the forecast through Wed night is currently dry. As for temperatures, there some continued uncertainty in highs on Mon, but for now expect low/mid 70s east to upper 70s west. Lows should generally be in the low to mid 50s Mon night. Expect temperatures to moderate through mid-week. Thursday onward: A northern stream low will track enewd through the western Great Lakes and into Ontario Canada Wed/Thu. The ridge will be suppressed sewd Thu/Fri as a s/w tracks from the mid-MS Valley, enewd into the northern mid-Atlantic/Northeast US. This wave may briefly amplify the larger scale trough over the Northeast and mid- Atlantic Thu night/Fri. There is the potential for showers/storms across the area with this disturbance Thu/Thu night. Meanwhile, another s/w will move through the southern/central Plains Thu, through the mid-MS Valley Thu night/Fri, then enewd through the Appalachians Fri/Fri night. There are still some timing/location difference between the medium-range model solutions, so those details remain unclear. However, there will be another chance for showers/storms with this system if/when it track through the mid- Atlantic/Carolinas Fri/Sat. Expect continued near to above normal temperatures through Sat. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 200 PM Saturday... Mostly VFR conditions are now being observed across central NC, but several sites are still reporting MVFR ceilings. The region is mostly precipitation free, but a few showers and storms are beginning to pop up in the south around FAY and across the north. The northern line will strengthen and become the main focus for poor aviation conditions from later this afternoon into this evening as it sinks south through the area. Heavy rain, gusty winds, MVFR ceilings and IFR visibilities will be possible with these storms. Behind the line, a few showers may linger into the overnight hours especially across the east. Ceilings will also drop to IFR everywhere, with periods of LIFR ceilings not out of the question. Ceilings will slowly improve to MVFR by late morning and early afternoon tomorrow. Winds will shift from SW to NE this afternoon and evening, remaining NE around 5-10 kts from the overnight hours into the day tomorrow. Outlook: Some moisture will linger during the day Sunday with at least MVFR cigs possible Sunday night. A return to dry weather and VFR is more plausible from Monday onward. The next cold front will bring a chance of showers and storms on Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield/Leins NEAR TERM...Danco SHORT TERM...Green LONG TERM...KC AVIATION...Danco/Leins