Area Forecast Discussion
Issued by NWS Wilmington, NC

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422 FXUS62 KILM 131733 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1225 PM EST Wed Dec 13 2017 .SYNOPSIS... Arctic air will pour into the eastern Carolinas this morning. The cold won`t last long as temperatures will return to normal Thursday and Friday. Another cold front will bring chilly temperatures Saturday, before seasonable weather returns on Sunday. Low pressure approaching from the Gulf Coast may bring rain to the area early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Wednesday...minor updates for temp/dewpoint trends and to add some higher wind gusts through early aftn. RAP and NAMBUFR soundings suggest 20-25 kts of potential mixing through the next few hours before easing quickly as high pressure builds in from the west. Otherwise a cold and dry day forecast. Previous discussion below: As of 300 AM Wednesday...Deep cold and dry air mass settling into the Carolinas this morning. GFS showing 850 temps bottoming out right around daybreak today at -8C. The stiff NW winds this morning will make it feel 5 to 10 degrees colder. The wind chill temps will not reach above freezing until early this afternoon and even then, the temps will only reach into the 40s as winds lighten up, under full sunshine. Overall a cold and very dry day ahead. Gusty NW winds will lighten up and back to the SW by late today. This will allow for a slight return in moisture, but only slight as dewpoint temps rise from the single digits and teens this afternoon to mid to the upper 20s overnight. The actual temps will drop close to freezing tonight in most places. The next shortwave will ride across the Carolinas tonight. This will produce some passing mid level clouds after midnight and will kick the winds up once again as winds above the surface, in the low levels of the atmosphere, reach up to 45 to 50 kts. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A strong shortwave will be exiting the area Thu morning. A strong wind field is expected to develop in association with this feature, with a jet maxima of 50-60 kt down to around 2 kft. This low-level jet will be lifting out Thu morning, keeping a deep and dry westerly flow in place. Sunshine should be plentiful and we should see a good temp recovery with highs in the mid and upper 50s, so a good 10 or more degrees warmer than on Wed. A cold front will reach the area late Thu night and Fri morning and should stall for a time near or just offshore. Weak waves of low pressure are expected to consolidate near the Outer Banks with low pressure strengthening as it moves to the NE Fri night. This will allow for increasing clouds and it should become mostly cloudy overnight Thu into Fri and then clearing Fri night. A strong and deep westerly flow dominates the column during this portion of the forecast and significant shortwave energy is not able to directly influence the eastern Carolinas until Fri night. Although the column does undergo some modest moistening as we move through Thu night and into Fri, dry air in the mid and lower levels of the column will be tough to erode in this type of flow. It looks like the showers that do develop will be mainly offshore. We will continue to monitor, but our latest forecast will be dry. Lows Thu night will be in the mid 30s to around 40, coolest well inland. Although the current set of grids do not explicitly indicate a non-diurnal temp curve due to timing differences by the models, it certainly is plausible to believe that lows may occur early in the night and then stabilize if not rise with the arrival of thick cloud cover. Highs on Fri will be similar to Thu. The influx of colder and drier air Fri night should help to knock minimums to freezing, a little lower inland and perhaps a degree or two above at the coast. && .LONG TERM /SATURDAY 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. 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 /18Z WEDNESDAY THROUGH MONDAY/...
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As of 17Z...VFR through 14/18Z. W winds becoming SW this afternoon. As a surface based inversion sets up this evening, winds just above the inversion will increase ahead of the next system. LLWS will be likely this evening and overnight KFLO/KLBT. Have indicated LLWS at the coastal terminals although criteria may not be met if surface wind speeds increase sufficiently. Generally sct mid/upper clouds this evening/overnight. LLWS ends as surface winds become W Thur morning with sct skies. Extended Outlook...VFR.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Wednesday...No significant changes with the morning update. COnditions have fallen below SCA thresholds, but are expected to rejuvenate tonight so the ongoing SCA hazard remains unchanged. Previous discussion below: As of 300 AM Wednesday...These Small Craft Advisory conditions will improve briefly through this aftn as winds lighten and back to the SW, but another disturbance will move across the waters after midnight tonight producing another rise in both winds and seas. Therefore, the Small Craft Advisory will remain in effect although there will be a lull this afternoon as winds back to the SW and diminish to 10 to 15 kt allowing seas to drop to 2 to 3 ft. The increase tonight should come near midnight with winds up to 15 to 25 kt and seas up to 5 to 7 ft. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A strong shortwave will be exiting the area Thu morning. A strong wind field is expected to develop in association with this feature, with a jet maxima of 50-60 kt down to around 2 kft. This low-level jet will be lifting out Thu morning. Another cold front will reach the waters Fri morning with one or more waves of low pressure migrating along the front. Low pressure is expected to consolidate near the Outer Banks of North Carolina during Fri and then strengthen as it moves NE Fri night. The strongest winds this period will occur Thu morning, up to 20 to 25 kt. A Small Craft Advisory has already been issued through noon Thu. The direction will be W. Seas will still be in the 4 to 7 ft range Thu morning. W winds will decrease to 10 to 15 kt during Thu afternoon as seas subside to 3 to 4 ft. NW winds Thu night will decrease to 10 kt or less and may become variable in direction due to the proximity of a front and weak low pressure late. Seas will subside to 2 to 3 ft. Winds will increase during Fri and may be near Small Craft Advisory levels Fri afternoon and eve. The direction will be veering from W to NW during this time. Seas will build, reaching 4 to 5 ft with at least some 6 ft seas possible across the outermost northern waters. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Breezy west winds 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. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Thursday for AMZ250-252- 254-256. && $$ NEAR TERM...JDW/RGZ SHORT TERM...RJD LONG TERM...TRA AVIATION...MRR

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