Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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673 FXUS62 KRAH 170755 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 355 AM EDT Tue Sep 17 2024 .SYNOPSIS... An area of low pressure centered across far northeast South Carolina will drift west into upstate South Carolina tonight. The remnants of this system will linger and gradually dissipate across the mid- Atlantic through the end of the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 350 AM Tuesday... * Last large band/region of showers and storms spreading across the northern Coastal Plain and the northern Piedmont. * Flooding threat has abated and Flood Watch will be cancelled. The latest surface analysis shows the center of the surface low located just south of Charlotte, near Lancaster SC. A surface trough or occlusion extends east of the surface low with a narrow tongue of instability extending east to west, from near KWEN to near KGSB, just north of the boundary. In and north of this axis, the last band of showers and a few embedded thunderstorms are streaming west across the central and northern Coastal Plain and into the eastern portions of the Triangle. This band/region of showers and some thunderstorms will shift north during the morning, perhaps beginning to exit much of the Triangle area around the morning commute with generally dry weather to the south. By midday and continuing into the afternoon hours, most of the convection should be focused across the far northern Piedmont and VA border counties. The narrow region of instability will also transition north. With the wind field becoming less favorable into the afternoon, any lingering severe weather and tornado threat should transition north and fade away this morning. Will need to keep an eye on cells in Wayne, Wilson and Edgecombe counties this morning but the threat has decreased greatly. Additional rainfall amounts today will range around a half inch north of U.S. route 64, perhaps a little more near 0.75 inches across the northern Coastal Plain with rainfall amounts of a tenth or two south of U.S. 64. With the widespread precipitation amounts decreasing we plan on canceling the flood watch. Showers and a few storms across the north this afternoon will gradually diminish into the evening hours. A much less active radar is expected this evening and tonight although some spotty rain associated with the remnant low level circulation may spread a few showers across the far western Piedmont tonight. Gust northeast to easterly winds early this morning will decrease from south to north during the morning and especially this afternoon. A few gusts through around daybreak in the northern Piedmont and especially the Triad may range between 25 and 30 mph. Highs today will range from the lower 70s in the western Piedmont and VA border counties to the mid 70s to around 80 in the east. Lows tonight will range in the mid to upper 60s. -Blaes && .SHORT TERM /Wednesday/... As of 355 AM Tuesday... The surface and mid/upper low impacting the region over the past few days will weaken into Wednesday as it shifts north and east. Abundant moisture across the region will result in widespread low clouds and perhaps some fog on Wednesday morning. A few showers and perhaps a thunderstorm may develop during the afternoon with highs ranging from the upper 70s in the Triad to the lower 80s in the Coastal Plain. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... As of 345 AM Tuesday... Mid/upper troughing will extend down the Eastern Seaboard including into central NC from Wednesday night into Thursday. Meanwhile a surface low will linger off the northern Mid-Atlantic coast. This will bring one last day of upper forcing for ascent and above-normal PW values, so POPs on Thursday are generally in the 30-40% range, highest east and maximized during peak heating. There could be enough instability for a few storms. QPF amounts in the models are not impressive, so not concerned about an additional heavy rain threat, and looks fairly low impact overall. As a mid/upper ridge over the Plains begins to move east on Friday, it will begin to push the trough east and offshore. This will result in NW flow and much drier air moving into central NC, with PW values trending below normal. At the surface, high pressure will gradually nose down from SE Canada into the Mid-Atlantic from Friday into Monday. Overall this pattern supports limited rain chances at best, which is a significant change from last night when the models depicted the mid/upper low moving back south across the area. Now, they keep it and the associated surface low well to our east in the western Atlantic. Instability looks minimal to non-existent as well given the cool wedge of high pressure and NE flow near the surface. The best chance for clouds and isolated showers looks to be in the Coastal Plain closer to the low and where there will still be moist onshore flow in the low levels, but even there POPs are only slight. The GFS does try to bring a shortwave through the area on Sunday, so POPs are slight that day areawide. As for temperatures, highs should be within a few degrees of normal from Thursday through Saturday, in the upper-70s to lower-80s. Lows will gradually trend downward as the air mass turns drier, from mid- to-upper-60s on Wednesday night to upper-50s to lower-60s by Saturday night. On Sunday and Monday when the cool wedge of high pressure really takes hold, forecast highs are only in the 70s with lows in the mid-50s to lower-60s. If the raw GFS is to be believed, some places won`t even get above the 60s on these days, but would like to see more support from ensemble guidance before buying into this too much. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 230 AM EDT Tuesday... Widespread MVFR to IFR conditions primarily from low CIGS are noted across central NC early this morning. CIGS are expected to lower during the pre-dawn hours leading to IFR/LIFR conditions across much of the area through the mid morning hours. A broad area of light rain showers with a few embedded heavier showers extend from the central and northern Coastal Plain west across the northern Piedmont. This area of precipitation may also result in reduced VSBYs at times as the overall rain axis shifts north through the morning. An isolated thunderstorm is possible across the central Coastal Plain, near but mainly south of the KRWI terminal. Low CIGS are expected to persist for much of the day although cloud bases will lift during the late morning and early afternoon with MVFR CIG restrictions still commonplace during the afternoon. Some brief improvement with VFR CIGS are expected late in the afternoon across the Coastal Plain and Sandhills impacting the KRWI and KFAY terminals. There is a limited risk of additional showers and perhaps a storm this afternoon primarily near KINT/KGSO and KRDU. Another round of MVFR to IFR CIGS are expected to return tonight and continue into Wednesday morning. A low pressure area is expected to track northwest across northern SC through tonight. This will maintain a northeasterly surface wind with gusts of 15 to 25kts at times overnight, perhaps a little stronger in the Triad. Winds should begin to diminish from south to north later this morning and especially this afternoon. A prolonged period of LLWS should be relaxing early this morning. Recent data from the WRAL tall tower southeast of Raleigh shows wind speeds aloft at 2kft beginning to weaken. Will maintain a mention of LLWS in the TAFs through around 09Z with the greatest risk of LLWS condition in the Triad. Outlook: After another period of IFR/LIFR CIGS early Wednesday morning, an unsettled period will continue through Thursday with area of late night and early morning stratus and a risk of some afternoon showers and possibly a storm. Aviation conditions will generally improve on Friday and Saturday. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch until 8 AM EDT Tuesday for NCZ007>011-021>028- 038>043-073>078-083>086-088-089. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Blaes LONG TERM...Danco AVIATION...Blaes