Area Forecast Discussion
Issued by NWS Wilmington, NC

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435 FXUS62 KILM 130014 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 714 PM EST Tue Dec 12 2017 .SYNOPSIS...
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Arctic air will pour into the eastern Carolinas tonight into Wednesday morning. The cold won`t last long as temperatures will return to normal Thursday and Friday. Another cold front bring chilly temperatures Saturday, before seasonable weather returns on Sunday. Low pressure approaching from the Gulf Coast may bring rain to the area Monday.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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As of 715 PM Tuesday...Latest obs show that the cold front has now moved offshore. Winds have not yet picked up to expected levels, but looking at upstream obs expect that they will increase and become more gusty in the next couple of hours. Forecast good to go with no changes. Previous discussion from this afternoon follows: Strong cold front is progressing quickly this aftn, and is currently aligned just west of the coast. This front will race eastward, and although temps will drop only slowly at first, strong CAA is accompanying this front so temps will likely seem to fall off a precipice this evening, falling 10-15 degrees in just a few hours. This front will also be accompanied by post- frontal stratus at 3-5 kft, although some of this will dry up on the downslope flow east of the Appalachians. Additionally, gusty W/NW winds are likely, with gusts of 20-25 mph forecast through the evening and even several hours past dark. A weak inversion will try to setup tonight, but will be somewhat inhibited by strong winds of 30-40 kts continuing just off the surface, so winds will remain elevated through the night even as gusts ease. This strong CAA will cause mins tonight to be quite cold, mid 20s inland to near 30 at the coast, a drop off of 30 degrees from this aftn highs. These cold temps combined with the elevated winds will produce wind chills colder than we have seen in quite some time - upper teens in many spots late tonight into Wednesday morning. After a breezy and cold morning, winds will slowly ease as high pressure ridges into the area from the west, but a very cold day is forecast. Despite abundant sunshine and aftn development of warm advection, highs are forecast to be only in the low 40s across NC, mid 40s SC, which is a few degrees below even the coolest guidance. Despite easing from overnight, winds will remain at least somewhat elevated through the aftn, so this combined with the cold temps will produce wind chills in the 30s most of the aftn. Bundle up!
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Essentially a temperature forecast for the short term period as the shortwave laden northwest flow continues across the region at least initially. The strongest feature will move across the area late Wednesday night with a weaker system to follow late Thursday as the flow relaxes somewhat. The cold air advection isn`t nearly as strong Thursday as the system tonight and is reflected in the warming guidance and the official high temperature forecast for Thursday. Lows have been increased a bit for Thursday AM as well. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...Model consensus is still not great in the long term. It`s a common problem in the winter: shortwave energy splits as it exits the Rockies with part coming eastward and part dropping southwestward into Baja Mexico. Each model is slightly different with the specifics how this energy cuts off over Mexico late this week, and then how it rejoins the westerlies early next week. The part of the shortwave that does make it to the East Coast on Friday should induce a weak surface low to develop along a cold front across the Carolinas on Friday. With so much westerly wind throughout the atmospheric column there will be virtually no influx of moisture, and rain chances appear very small. I have bumped PoPs down to only 10 percent inland and 20 percent along the coast Friday afternoon/evening. Friday night and Saturday should see chilly temperatures with mainly clear skies in the Canadian airmass in place. Surface high pressure will move off the coast Saturday night, with a moderating return flow setting up Sunday. The difference in model handling of the Baja Mexico shortwave energy really becomes apparent Sunday through Tuesday. The ECMWF is easily the fastest model to kick the low back into the westerlies, and shows rain breaking out during the day Sunday in association with a developing surface wave of low pressure along the Gulf Coast. Other models are at least 12 hours slower. There are some GFS ensemble members that show an early start to precip Sunday, but I don`t show rain developing until Sunday evening to maintain consistency with surrounding NWS offices and the bulk of our deterministic model guidance. Even the slower 12Z GFS and Canadian runs still show rain becoming a good bet Sunday night into Monday, and PoPs have been increased to 40-50 percent for this period. Temperatures should remain well above freezing during this event with no P-type concerns. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 00Z...There is a weak inversion setting up, enough to keep winds fairly steady, so took the gusts out through the overnight hours. Wednesday, time height indicates dryness at all levels, with little to no clouds expected. West winds will become southwesterly late in the forecast period. Extended Outlook...VFR. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 715 PM Tuesday...Cold front has now passed east of the waters with latest obs showing NW winds of 20 to 25 kts and seas ranging from 2 to 3 ft near shore and around 6 ft further out. Small Craft Advisory remains in effect as before with no changes planned. Previous discussion follows: Small Craft Advisory in effect for all waters into Wednesday morning. A strong cold front is currently exiting the coast and will cross the waters within the next 2-3 hours. SW winds across the waters presently are reaching 15-25 kts, and driving seas to as high as 7 ft at Wilmington Harbor, and 8 ft at Frying Pan Shoals. As winds become NW post-FROPA this evening, they will remain elevated, and may actually increase to 20-30 kts for a time overnight before easing into Wednesday morning, and then falling below SCA thresholds Wednesday aftn while maintaining a W/NW direction. These strong winds will keep the dominant wave period very short, around 5 sec, but wave heights will begin to fall thanks to the offshore component of the wind limiting available fetch. Seas overnight will remain 4-7 ft, but will fall to 2-4 ft by the end of the period. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...A strong shortwave will move across the area overnight Wednesday increasing the winds markedly. The flow is from the southwest and in warm air advection fortunately. Wind speeds will almost certainly increase to small craft criteria and a gale warning cannot be ruled out. The flow weakens quickly Thursday with a westerly flow of 10-15 knots and even further by Friday morning to ten knots or less. Significant seas will ramp up quickly from an initial 2-3 feet to 5-7 feet and fall almost as quickly late Thursday into early Friday back to 2-3 feet. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...A cold front will move across the Carolinas early Friday. Low pressure is still expected to develop along this front, but model consensus is that it may be weaker than expected yesterday, or at least weaker than the GFS model had been showing. Breezy west winds developing behind the front Friday will continue through Saturday morning before diminishing as high pressure moves in from the west. The next low pressure system is now expected to move eastward and toward the Carolinas a little faster than we thought yesterday, perhaps reaching the area Sunday night with rain and strengthening southerly winds.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Wednesday for AMZ250-252- 254-256. && $$ SYNOPSIS...TRA NEAR TERM...REK/JDW SHORT TERM...SHK LONG TERM...TRA AVIATION...MRR MARINE...REK/TRA/JDW/SHK

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