Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 131756 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1256 PM EST Sat Jan 13 2018 .SYNOPSIS... Cold and dry air will move into the area today as high pressure slowly wedges down the coast. An area of low pressure will develop off the Carolina coast and may bring a period of wintry precipitation Tuesday night into Wednesday evening. Arctic air will reach the Carolinas Wednesday and Thursday with a slow moderation in temperature beginning Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 10 AM Saturday...Secondary cold front (where the cold air lies) is pushing across the forecast area this morning. Low cloud associated with the feature over the area will shift northeast, but moisture trapped under the inversion, based around 3k ft, will likely keep varying amounts of cloud cover across the area for much of the day. Strong cold advection will persist through the day, keeping temperatures below climo. Temperature trends today will be interesting with far western areas experience a typical diurnal curve while closer to the coast temps will trend down through the morning then hold steady and possibly rise a few degrees during early afternoon. Highs will range from mid 50s along the coast (having already occurred) to upper 40s well inland. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...Canadian high pressure will build SE into New England Sunday and then ridge down into the Carolinas through Monday. This occurs beneath persistent but broad cyclonic flow across the eastern CONUS, with two distinct shortwaves rotating overhead through the period. The first of these occurs early Sunday and will be accompanied by a cool surge of north winds in advance of the ridge of high pressure. The second rotates overhead Monday morning but is noted with little fanfare as ridging begins to develop in its wake in response to a much more pronounced trough digging into the Great Lakes late Monday. While the weather will be quiet into early next week, temperatures will return to well below climo norms beneath the longwave eastern CONUS trough. 850mb temps below 0C most of the period combined with the cool surface high pressure will keep highs only in the low to mid 40s both days, with mins Sunday night falling to just below 20. Slightly warmer Monday night with mins expected to be 2-3 degrees either side of 25. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM Friday...Cold weather will persist through the period with a risk for wintry precipitation Tue night into Wed eve. Low pressure is expected to develop off the Carolina coast, but where and when this area of low pressure initiates is still a big question. Should the low develop close enough to the coast, then there will be a risk for precipitation along portions of the more immediate coast later Mon and Tue and possibly into Tue night. There is some potential that any precipitation which does clip the coast in direct association with the developing coastal low and trough could be a wintry mix. Confidence is a little higher that a vigorous upper low and associated strong shortwave energy will move across the eastern Carolinas and provide ample lift in the wake of the surface low. The column should be sufficiently moist and cold enough to support frozen precipitation, at least for a portion of the time. Timing is not quite nailed down, but the GFS has trended further S with the upper low and slowed its timing and is now in better agreement with the Euro in showing the brunt of the upper level support pivoting across the FA Wed into Wed eve. We have included POPs for Tue eve and night through Wed afternoon/eve, first starting across our inland most zones and ending lastly across the Cape Fear area. Snow is favored, although precipitation should tend to at least mix with rain during the warmest part of Wed afternoon before any left over precipitation trends back to snow. For obvious reasons, including the time range we are dealing with and model inconsistencies, we can not accurately forecast accumulations at this time. However, there is a good chance that some accumulation will occur. Generally speaking, in these scenarios, we do not receive significant precipitation. However, should the coastal low develop closer to the coast, then more significant QPF is possible. We will continue to monitor and later forecasts should provide more refined details. Highs will be mainly in the 40s Tue. The peak of the cold air advection this period should keep highs closer to the upper 30s to around 40 Wed and Thu with some temp recovery likely on Fri. Lows will be in the 20s Mon night and some 20s to around 30 Tue night. Lows will drop to the teens for most of the area Wed night and it should be about as cold Thu night. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 18Z...MVFR decreasing rapidly as cigs lift with the approach of the clearing line moving NW-SE. Clouds should scatter all terminals by this evening. winds will continue NW-NNE through te end of the TAF period. A return of broken VFR cigs possible later this evening into early tomorrow morning. Extended Outlook...Slight chance MVFR coastal terminals Sun morn, otherwise VFR. MVFR/IFR/wintry precipitation Wed. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 10 AM Saturday...Small craft advisory remains valid with strong offshore flow due to cold advection. Winds will slowly veer to northwest with a slight reduction in speed today before shifting to northeast this evening overnight. Offshore flow may drop seas below 6 ft for a brief period later today but seas below 6 ft will be short lived as cool surge develops and northeast flow increases, ensuring seas build back over 6 ft this evening and overnight. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 AM Saturday...North to northeast winds will dominate the period as high pressure builds down the coast maintaining its ridge axis west of the waters. Sunday will begin with gusty north winds of 20-25 kts, pushing seas up to 4-6 ft through much of Sunday even as winds begin to ease. This has necessitated a temporal extension of the ongoing SCA through Sunday night. The high pressure ride will weaken Monday, so although winds maintain a northerly direction, speeds will fall to 10-15 kts, with seas following suit to 2-3 ft by Tuesday morning. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Low pressure is expected to develop off the Carolina coast, but where and when this area of low pressure initiates is still a big question. Low pressure should move well NE of the waters Wed night. The highest risk for Small Craft Advisory conditions is Wed night and Thu, but this may flex a little earlier and will be dependent on timing of east coast trough and surface low development. Winds from the NW or even WNW for a time Tue and Tue night with NNW or NW winds dominating Wed and Wed night. Wind speeds will be around 15 kt Mon morning, but should trend to under 10 kt Mon night and Tue before reversing higher later Tue night. Wind speeds Wed will likely increase to 15 to 20 kt later in the day before peaking Wed night into Thu morning. Seas will be 4 to 5 ft Mon morning. Seas will subside Mon afternoon and this trend will persist into Tue night. Seas are expected to build on Wed and may reach 4 to 7 ft Wed night. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until midnight EST Sunday night for AMZ250-252-254-256. && $$ NEAR TERM...III SHORT TERM...RGZ LONG TERM...RJD AVIATION...MRR

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