Area Forecast Discussion
Issued by NWS Wilmington, NC

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016 FXUS62 KILM 192341 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 741 PM EDT Thu Apr 19 2018 .SYNOPSIS... A dry cold front will move off the coast this evening. Chilly temperatures are expected tonight through Sunday as Canadian high pressure builds into the Eastern U.S. Low pressure will move slowly across the area Monday through Wednesday next week, bringing rain back to the Carolinas. && .NEAR TERM /THROUGH FRIDAY/... As of 300 PM Thursday...A pair of shortwaves moving across the Northeastern U.S. coast has induced surface low pressure to develop southeast of Cape Cod. A cold front extending south from this low is moving through the Carolinas now, and should sweep off our portion of the coast between 5-8 PM. Strong westerly winds in advance of this front have gusted as high as 39 mph in Wilmington, 38 mph in Florence, and 37 mph in Marion, SC. As the front moves through this evening, winds will shift to the north with much drier and cooler air punching southward. High pressure over Iowa will only slowly move eastward tonight and Friday. Cold advection should drop 850 mb temps down to +4C tonight, and +2 to +3C Friday afternoon. At the surface we`re expecting lows tonight to range from 39-44, near a MOS consensus. For users of the new "National Blend of Models" MOS, it performed very poorly with nighttime lows (too warm) during the last cold blast we had back on April 8th, so I`ve ignored its output which has lows 42-46. Also during the last cold blast, the GFS MOS ran much warmer than other guidance with highs and did not verify well, so I`ve ignored its output for Friday. Following the cooler NAM and ECMWF guidance for tomorrow`s highs yields lower 60s in the Cape Fear area and the Grand Strand beaches, mid 60s across Whiteville, Lumberton and Marion, and upper 60s for Florence and Darlington. Temperatures this month so far have run 1.5 to 2.5 degrees colder than normal. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Weakly amplified mid-level pattern will transition from 5h troughing at the start of the period to weak shortwave ridging Sat and Sat night. Meanwhile, surface high over the Great Lakes at the start of the period will drift southeast Fri night and Sat, ending up over the Outer Banks Sat night. Northerly flow will be maintained through the period, keeping temperatures below to well below climo. On Sat most areas will end up with highs below 70, after starting out with lows in the upper 30s to lower 40s on the back on good radiational cooling. Sat night lows will be similar to Fri night although slight increase in boundary layer winds might help keep temps a bit warmer. Clouds let alone rainfall seem like a stretch. Precipitable water remains under half an inch through the period with forecast soundings suggesting the bulk of any cloud cover will be above 25k ft late Sat and Sat night. Forecast soundings continue to show a nice subsidence inversion in place through the period, preventing upward motion. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 300 PM Thursday...Very large high, more typical of the cool season, to be moving off the coast on Sunday. Meanwhile a cutoff upper low (also normally a cool season feature) to be crossing the Gulf States, leading to cyclogenesis. As often the case with a cutoff, the timing is often uncertain and too fast in guidance. Much of the cloudiness and rain expected to overspread the area Sunday night into Monday may now be about 12 hours slower. Another change from this time yesterday is that guidance is now suppressing the highest rainfall amounts to our south. Given the strength of the high to our north this seems plausible. Even so, the system will be slow moving and keep rain in the forecast through at least Wednesday. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 00Z...A dry cold front has pushed through all terminals as of 00Z. Most mid level clouds associated with the front have also moved offshore. Expect mostly clear skies/VFR overnight with northwest winds becoming north. Friday north to northeast winds expected under mostly clear skies. Winds will become east in the afternoon at KCRE/KMYR. Extended outlook...VFR. Periods of MVFR/RA Monday/Tuesday. && .MARINE... NEAR TERM /THROUGH FRIDAY/... As of 300 PM Thursday...A dry cold front extending from New Bern to Elizabethtown, Lumberton, and Bennettsville, SC will move off the coast between 5-8 PM, accompanied by a shift from westerly to northerly winds. Wind gusts around 25 knots all afternoon will continue behind the front, and should even increase late this evening to around 30 knots as colder air punches south across the Carolinas. High pressure across the Midwest will slowly build eastward Friday, with our winds weakening and veering northeasterly. The strong west and southwest winds of the past 24 hours have built an impressive wave set, particularly across the open waters of Long Bay and along Frying Pan Shoals where the CORMP Harbor buoy and the NDBC Frying Pan Shoals buoy have been reporting 7 foot seas all day. Dominant wave periods of 6-7 seconds should allow a great deal of this wave energy to make into shallower water nearshore, and I`ll continue the Small Craft Advisory through the night and into Thursday morning. SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Surface high northwest of the area Fri night will gradually drift southeast Sat. The high ends up centered over the Outer Banks Sat night. Flow will remain northerly Fri night into Sat before slowly veering to east-northeast late Sat. Gradient remains fairly static through the period with speeds mostly in the 10 to 15 kt range. Seas will be in the 2 to 3 ft range through the period. LONG TERM /SUNDAY THROUGH TUESDAY/... As of 300 PM Thursday...Onshore flow on Sunday the result of a very large area of high pressure moving eastward but remaining centered well north of the area. At the same time low pressure will be developing over the Gulf States. This setup will increasingly squeeze the gradient to where wind and seas both reach advisory levels. Both entities will be very slow moving, keeping advisory flags flying for the remainder of the period. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 9 AM EDT Friday for AMZ250-252-254- 256. && $$ SYNOPSIS...TRA NEAR TERM...TRA SHORT TERM...MBB LONG TERM...III AVIATION...MRR

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