Area Forecast Discussion
Issued by NWS Wilmington, NC

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046 FXUS62 KILM 221416 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1015 AM EDT Sat Jul 22 2017 .SYNOPSIS...
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Hot and humid conditions will peak today and tomorrow before beginning to moderate with more typical summertime heat expected next week. A cold front, approaching from the north, should push into the area mid week and then remain in close proximity through late week. The risk for thunderstorms with heavy rain will return next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 1015 AM Saturday...Primary forecast challenge today is related to heat and humidity, and subsequent high heat indices. 1200 UTC soundings support high temperatures from the lower to mid 90s at the coast to the upper 90s inland. In fact H85 temperatures from the morning RAOBs range from 19C at the coast to around 20C at KGSO. Combined with dewpoints in the mid 70s the heat index is expected to range from around 100 at the immediate coast to 105-109 inland areas. No changes made to the current Heat Advisory. Otherwise, subtropical ridging extends from the central plains and MS valley eastward across the Carolinas and into the western Atlantic. The mid- level ridging will supers any widespread convective development with the bulk of any severe weather to be found in the band of westerlies farther north. However, weak inland troughing could provide enough lift for a few storms to develop this afternoon and into the early evening. Thus the highest POPs (albeit on the low- side) will be found across the far inland areas. Anomalously higher than normal low temperatures are forecast again tonight with lows in the mid to upper 70s most areas.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...The Forecast Area will be in between two areas of high pressure. One area of hot high pressure will retrograde westward as the Bermuda High remains to our E. This will allow an upper trough to slowly dig across the eastern CONUS. At the surface, the Piedmont trough will remain prominent through Mon while a cold front slowly slips down the east coast, likely lying just to our N Tue morning. This scenario will allow for still humid, but slightly lower high temps, especially by Mon. Clouds will be more prevalent Mon as compared to Sun. The risk for thunderstorms will be increasing and should be highest Mon and Mon night as precipitable water values climb to near 2.25 inches. At this time, will show small POPs Sun with POPs trending higher and perhaps becoming numerous by Mon/Mon night. High moisture content should allow for very heavy rainfall amounts where thunderstorms are able to train. Temps on Sun will still be in the lower to mid 90s which will produce heat index values at or above 105 degrees across most areas and so a Heat Advisory may be required that day. On Mon, highs will be in the lower 90s. Heat index values on Mon are not expected to exceed 105 degrees, but may still top 100. Lows will be in the mid and upper 70s although if thunderstorms become widespread enough a cold pool may drop readings into the lower 70s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM Friday...A shortwave trough moving through New England on Monday night, and a large upper low developing across southern Quebec will help put a dent in the heat. Falling upper level heights associated with these systems will shift the core of the upper ridge (and its associated heat) farther west into Texas and New Mexico. Don`t expect a cleansing frontal passage by stretch, (06Z GFS ensemble 850 mb temps don`t fall below climatology next week) but at least we should lose the 100+ heat indices for a few days. Both the GFS and ECMWF show a cold front moving into northern North Carolina on Tuesday. The GFS then sinks the boundary a little farther south by Wednesday morning. There are enough GFS ensemble members showing the front making it into South Carolina that I`m leaning toward the GFS in this case. This front should enhance the coverage of t-storms Tuesday night and Wednesday, and I`ve placed my highest forecast PoPs (50-60 percent) of the extended period during this period. With a progressive upper level pattern to our north, surface high pressure will push off New England and out into the western Atlantic Thursday and Friday, probably with enough southerly wind developing over the Carolinas to lift the front or its remnants back to the north. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 12Z...Patchy IFR stratus and MVFR BR will burn off by 12z. VFR conditions are expected. However, there is potential for IFR stratus and some fog to redevelop late tonight. The seabreeze will again develop with SSW winds this afternoon and early eve gusting to around 20 kt at KCRE and KMYR. No organized thunderstorms during the period and a remote pop up shower or thunderstorm during the heating of the day is too low a probability for inclusion in the TAFs at this time. Extended Outlook...Possible IFR in patchy stratus/fog near sunrise Sun. Brief MVFR/IFR possible in showers and thunderstorms Sun night through Wed. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Saturday...Southwest flow around 10 knots currently prevails per local marine observations. The flow will increase as the pressure gradient tightens a notch between inland troughing and high pressure located far off the Southeast U.S. coast. Breezy southwest flow will persist into tonight, then diminish to 10-15 knots a few hours prior to day break. Choppy seas are expected as the southwest fetch increases across the waters. Seas of 3 to 5 ft appear reasonable given the strength of the fetch by this evening. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...Small Craft Should Exercise Caution headlines may be required for at least a portion of the time. A Piedmont trough on Sun will allow for a tightening pressure gradient across the waters. As upper trough slowly digs across the eastern CONUS, a cold front will slip progressively south, likely lying just N of the waters Tue morning. The approach of this front will keep the gradient rather tight as well. The wind direction will be SW through the period. Wind speeds will be as high as around 20 kt Sun afternoon and eve and again Mon afternoon. Seas will be 4 to 5 ft through the period. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Bermuda High Pressure well offshore will lose its influence on our weather by the middle of next week as low pressure in the Canadian maritime provinces pushes a cold front down the U.S. East Coast. This front is shown by the latest GFS and ECMWF models to make it down to near Hatteras on Tuesday. Models diverge slightly on Wednesday as the ECMWF keeps the front stalled to our north and the GFS brings it down to the Myrtle Beach vicinity Wednesday morning. Regardless of which solution is correct, the frisky southwest winds of the weekend should diminish by Tuesday within the weaker pressure gradient near the front. Unfortunately thunderstorm potential should also increase as the front approaches.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ017-023-024-032-033-039-053>056. NC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ087-096-099-105>110. MARINE...None. && $$ NEAR TERM...SRP SHORT TERM...RJD LONG TERM...TRA AVIATION...RJD

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