Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211332 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 932 AM EDT Sat Apr 21 2018 .SYNOPSIS... Canadian high pressure will build into the Carolinas through the weekend, bringing dry weather with chilly temperatures. Slow-moving low pressure will cross the Southeastern U.S. Monday through Wednesday, bringing widespread rainfall with continued below-normal temperatures. Another system may affect the Carolinas Thursday into Friday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 930 AM Saturday...Another day of clear skies, low-level easterly winds and very dry air aloft with a strong subsidence inversion. Temperatures should run several degrees warmer than yesterday due to a gradual moderation of the airmass. Air temperatures out at the buoys are indication of this. I`ve tweaked forecast highs upwards slight, with temperatures expected to range from the lower 70s inland to the upper 60s at the coastal cities. The beaches themselves may get stuck in the lower 60s with the cool onshore wind. Discussion from 300 AM follows... Surface high over the Ohio Valley this morning will drift southeast today, ending up just north of the Outer Banks late in the day. The high will be reinforced by Canadian high late tonight into early Sun. Northerly flow continues through the period, but does become a little more onshore in the afternoon. Low level moisture return will be limited, even with developing onshore flow. Pattern aloft also works against any significant moisture return with weak shortwave ridge keeping flow above 10k ft from the northwest. Precipitable water under half an inch through the period shows just how dry this air mass is. Mid- level ridge does start to weaken/flatten later tonight with flow aloft becoming westerly. This might lead to an increase in upper level moisture and a bit of high cloud above 20k ft overnight. However, precip chances remain zero through the period. Highs should end up a little warmer than yesterday, although the slightly cooler start this morning will keep the region below climo. Coastal areas will struggle to hit 70, especially with onshore flow starting to materialize. Outside of the coastal influence highs should be in the lower 70s. Weak east to northeast flow overnight along with air mass modification will keep lows slightly warmer than the last few nights, but temps still end up well below climo.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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As of 400 AM Saturday...The beginning of this period, Sunday, will be the last dry day and glimpses of the sun for the next few days. Expect deteriorating conditions starting Sun night and progressively worse through early Tuesday. POPs will commence Sun night with pcpn developing and spreading from southwest to northeast. Looking at basically overrunning stratiform light rains Sun night that will progress to light to moderate rains Mon through early Tue. Have included isolated or slight chance for thunder from Mon into Tue. This in response to the sfc low trying to re-organize literally overhead by Tue, farther away from the closed mid-level low that is progged to be over TN. Will have plenty of sources of moisture with Gulf of Mexico and Atlantic tapped. The FA could see 1.5 to 2.5 inches of rainfall over a time period running from Sun night through Tue. This beneficial rain over a 2 day period is what farmers need for their crops. The mid-level closed low is taking it`s sweet ole time moving across the Southeast States and by Tue night it`s progged to only have pushed to the Ohio River Valley but is weakening as it becomes an open s/w trough. Rainfall totals will depend on the future movement of this mid-level low and could end up higher if this upper low either slows down even further or moves toward the Southeast U.S. Coast.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM Friday...Cutoff low will continue to move east along the Gulf Coast states Mon into Tues spreading clouds and rain across the area from south to north. Increasing moist on shore flow will push pcp water values up to near 1.5 inches late Mon into Tues. The center of the low should reach the SC coast Tues night and then track up along the Carolina Coast lifting off to the northeast late Wed. The best moisture and lift should come together to produce the greatest QPF Mon night through Tues with fairly widespread amounts between a half inch and an inch with locally higher amounts. Some dry air should wrap in with westerly flow on the back end of the system on Wed, but lingering upper level energy could keep some lingering clouds and showers around. By Thurs, another cutoff low will track across the Appalachian Mtns, with increased potential for clouds and pcp late Thurs into Fri. Overall a damp week ahead with a good amount of clouds and pcp through the week. Temps running on the cooler side on Mon will return toward normal Tues into Wed. Overall temps will remain near or just below climo through much of the week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 12Z...Another nice aviation day in store with high pressure in control. Light gradient today will allow an onshore wind by midday. Light winds tonight with some fog possible after 08Z., best chance CRE. Extended outlook...VFR. Mon periods of MVFR/RA. Tue periods of IFR/RA becoming MVFR. Wed VFR. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 930 AM Saturday...Current wind speeds are about 5 knots higher than forecast, however this could be a low-level nocturnal jet that will dissipate shortly. All model guidance is indicating 12-15 knot easterly winds today. A check of latest buoy observations shows 2-3 feet with only a slight uptick expected during the afternoon. Today`s seabreeze should be weak as the preexisting onshore flow should prevent a significant temperature variation from developing along the coastline. Discussion from 300 AM follows... Surface high over the Ohio Valley will gradually move southeast today. The high will end up centered just north of the Outer Banks later today. Slight increase in the pressure gradient later today into tonight results in a slight increase in east- northeast flow this afternoon but speeds are not expected to exceed 15 kt. Winds will become more easterly later today and overnight. Seas will run 2 to 3 ft though the period. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 400 AM Saturday...Deteriorating conditions both winds and seas, will steadily get worse during this period and climax late Mon night through Early Tue. The sfc pg will begin tightening at the start of this period and persist through Tue. Onshore winds will dominate the local waters with SCA conditions by Mon morning. Will see a steady increase in winds with sustained speeds peaking in the 25 to 30 kt range late Mon into Tue with Gale force gusts of 35 to possibly 40 kt. Will have to contemplate the possibility of raising Gales during the next 1 to 2 full forecast packages if this trend continues. Due to increasing onshore winds throughout this period and peaking early Tue, significant seas will likely reach double digits across the outer waters, 10 to 20 nm out and especially off Cape Fear and Romain respectively. Wind driven waves at 5 to 7 second periods will dominate the local waters and will likely transform into a pseudo swell at 6 to 9 second periods late Mon into Tue. Pcpn from late Sun night through Mon into Tue will produce lowered vsby to 1 to 3 nm and lower from moderate to heavy rains or from an isolated tstorm. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Low pressure system will move east across the Gulf Coast States to the coast of SC by Tues night and then will track NE parallel to the Carolina coast. A strong onshore flow will persist Mon into Tues in a tightened gradient flow between this low pressure system and high pressure moving slowly off the Northeast coast. Winds will diminish as they back from E-SE to N-NE Tues night as the center of the low tracks northeast becoming elongated just off the Carolina coast. Eventually an off shore W-SW flow will develop late Wed as the low exits off to the northeast. Overall, expect this onshore push of easterly winds up to 25 to 30 kts to push seas up through Mon into Tues, from near 6 ft Mon morning up to possibly 10 to 12 ft by Tues morning and then subsiding slowly as winds back around further becoming offshore Wed. Expect SCA conditions through much of the period.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...III NEAR TERM...TRA/III SHORT TERM...DCH LONG TERM...RGZ AVIATION...III

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