Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 090745 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 245 AM EST Sat Dec 9 2017 .SYNOPSIS...
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A cold rain will end today with bright sunshine returning Sunday and Monday and dry weather expected for all of next week. Sunshine will bring a modest temperature rise, but still just below normal, even on the warmest day of next week, Tuesday. Another strong cold front will move across the area Tuesday night with Arctic air returning Wednesday. Temperatures will gradually moderate late next week with another cold front possibly moving across the area with the start of next weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM Saturday...Satellite imagery shows deepest moisture being shunted offshore by the approaching upper trough. Radar returns should fill back in along the coast though as this system induces a flat wave of low pressure along the offshore frontal boundary, passing by at around 10Z. Thereafter rainfall trends should reverse and start to wane from west to east. Light rain or drizzle may persist into the afternoon especially along the coast as the main trough axis doesn`t swing through until the evening. Overnight cold and dry advection will both strengthen as the system accelerates off to the NE while deepening. Temperatures will be stuck in the 40s all day but readily drop below freezing away from the beaches tonight in the CAA regime.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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As of 300 AM Saturday...850 mb temps will be warming through the period, from -4 to -7C at the start of the period to +7 to +9C Mon night. Precipitable water values will generally range from a quarter to around a third of an inch and we are expecting sunshine in a deep westerly flow. This sunshine will serve not only to begin to dry us out, but also to moderate the very cold airmass. Highs on Sun will still be well below normal, mainly mid 40s. Highs on Mon will still be below normal, but 10 degrees warmer than on Sun. Light to calm wind will allow for radiational cooling which will drop temps into the mid and upper 20s Sun night with lower 30s at the immediate coast. Low-level SW flow and a slightly tighter pressure gradient Mon night should keep lows from falling below the mid and upper 30s with lower 40s at the coast.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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As of 300 PM Friday...Period will be dominated by 5h longwave troughing and temperatures below to well below normal. Precip chances will be limited by a pattern where deep west to northwest flow is dominant. Only chances will be with one of several stronger shortwaves dropping into the trough and helping to reinforce the cold air. Looks like there will be three waves with potential to produce at least limited rainfall. The first arrives late Tue, the second late Thu, and the final one arrives Fri night. Forecast soundings keep precipitable water values below half an inch through the period with numbers dropping as low as a tenth of an inch on Wed. Measurable precip seems highly unlikely given the depth and abundance of dry air, but a brief period of increased cloud cover is likely. Temperatures will be below climo to start the period, although only just and will be trending up from Mon into Tue. However, the first shortwave will sweep a strong cold front across the region. The front will be followed by another shot of Arctic air and temperatures will tumble. Highs during the middle of next week will be in the 40s with lows in the 20s. Low level return flow is quick to develop on Thu and temperatures will moderate a little for the end of the period. Temperatures will still end up below climo to end the period, but only by a few degrees.
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&& .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 06Z...IFR cigs through most of the TAF period as very cold air at the surface is overrun by warmer air aloft. Visibility restrictions in rain will tend to be MVFR but could occasionally dip lower. NE winds will back in direction as the period wears on due to flat low pressure moving up along the offshore frontal boundary. Improving conditions slated to begin right at the end of the TAF forecast, especially at non-coastal terminals. Extended Outlook...VFR developing Sat evening and persisting through Wed. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 300 AM Saturday...Small Craft Advisory is in effect as the offshore frontal boundary will host a flat wave of low pressure before daybreak. Behind this feature however there is some uncertainty regarding how quickly wind and seas abate. The advisory currently runs through the entire period but guidance now suggesting that conditions may fall short of criteria as early as this afternoon/evening. Have opted to leave as-is however in light of underestimation by previous model runs of the wind speeds currently observed. The SSTs are warmer than the airmass and so vertical convection likely being underplayed by guidance. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...Winds will be diminishing during this period and we should be able to drop the Small Craft Advisory and replace it with a Small Craft Should Exercise Caution headline by/during Sun morning. Wind speeds will lower from 15 to 25 kt near the start of the period to 10 to 15 kt by Sun afternoon. Wind speeds will then remain in this range until Mon night when they will increase to around 20 kt. The direction will back from NW Sun to W Sun night and Mon and then WSW Mon night. Seas will be subsiding from 4 and 5 ft Sun morning to 3 and 4 ft Sun afternoon. Seas of 2 to 3 ft Sun night and Mon will build to 4 and 5 ft Mon night. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Winds will become southwest and increase Tue as a strong cold front approaches from the west. Wind speeds may require a Small Craft Exercise Caution headline by midday Tue, but it seems quite likely that seas will reach 6 ft before winds hit 25 kt. Confidence in a Small Craft Advisory headline is on the high side. Strong offshore flow develops in the wake of the front as cold advection kicks in. Offshore flow of 20 to 25 kt is possible while the offshore component works to drop seas. Offshore flow continues through Wednesday with speeds gradually decreasing as strong cold advection shuts off.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Sunday for AMZ250-252-254-256.
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&& $$ NEAR TERM...MBB SHORT TERM...RJD LONG TERM...III AVIATION...MBB

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