Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 290156 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 956 PM EDT Fri Apr 28 2017 .SYNOPSIS... High pressure will extend across the area from offshore through Sunday. Expect warm temperatures and isolated sea breeze showers or storms, mainly Sunday. The next cold front will bring a chance of showers and thunderstorms late Monday into early Tuesday. High pressure will follow for the mid-week period. Low pressure system may impact the region during Thursday with a soaking rain. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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As of 1000 PM Friday...It`s been fascinating watching the low clouds along the coast on 11-3.9 micron satellite imagery this evening. Low clouds from Myrtle Beach northward appear to eroding along the south edge, but clouds in the Georgetown vicinity are holding together a little better. Not even the HRRR model is good enough to forecast the movement of such a small mesoscale phenomenon, so I`ve attempted to manually extrapolate the cloud movement northward in the forecast grids over the next 4-6 hours as they spread inland but spare the immediate Cape Fear coastline. No significant changes to forecast low temperatures. Discussion from 630 PM follows... An unbelievably humid airmass for this early in the year covers the Carolinas. Dewpoints in the mid 70s are practically unheard of in April, and even with nearshore ocean water temperatures near record warm territory these dewpoints have generated areas of sea stratus and even sea fog earlier along the GA and SC coast. Inland cumulus should die away fairly quickly this evening with the loss of daytime heating. It`s a little more uncertain how clouds will respond near the coast: very humid air streaming onshore will experience frictional/speed convergence which could maintain a very low stratocumulus deck affecting Georgetown, Myrtle Beach, and Wilmington through the evening hours. Precipitation appears unlikely overnight as the depth of our moisture is very limited and will be capped off by warm and very dry air aloft. Lows tonight will run at least 15 degrees above normal for the date with 69-74 expected, coolest inland. Climate note: Wilmington`s low temperature so far today has been 74 degrees. Assuming we don`t drop below 74 between now and midnight standard time (1 AM daylight time) this will establish a new all-time record warm low temperature for the month of April in Wilmington. Records extend back to the year 1874.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY NIGHT/... Saturday and Sunday: The synoptic pattern will be dominated by deep layered subtropical ridging with the region positioned just to the west of the 850-500 hPa anticyclone. Modified forecast soundings for both Saturday and Sunday show pronounced capping with only the far interior west of I-95 becoming uncapped for about 1-2 hours with the sea breeze. Given lower tropospheric moisture looks pretty meager outside of the boundary layer, prefer to go with a dry forecast for both days. Temperatures will remain above normal with highs ranging form the lower 90s well inland to around 80 at the beaches. Lows Sunday morning will range from the upper 60s inland to the lower 70s at the beaches. Monday: A cold front will approach from the west Monday as high pressure shifts farther offshore and a powerful storm system moves into the upper Mississippi Valley. Moisture return ahead of the front looks solid with taps noted from off the Gulf of Mexico and Atlantic. Although the upper low and the core of the strongest forcing looks to pass well to the north, there will be enough to support a broad swath of showers/tstms across the frontal zone. Pops will be increased to 70% for most zones Monday night as the front sweeps offshore. Highs will warm into the lower-mid 80s away from the beaches Monday afternoon with lows Tuesday morning ranging from the upper 50s well inland to the mid 60s at the beaches. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Surface and mid level ridge will weaken and drift east Mon, allowing a cold front to approach from the W. Low pressure and associated strong dynamics and upper level support will be well dislocated from the Carolinas as a cold front moves across the area Mon night. This suggests convection weakening as it moves into the eastern Carolinas. Current timing brings the likelihood for showers and thunderstorms later Mon and Mon night. As the front moves off the coast Tue morning, high pressure along the Gulf Coast will slide east and then offshore to our S during Wed. This should bring a dry period. Deep low pressure will move out of the mid south and Gulf coast states Wed, lifting slowly to the NE. Its associated cold front will move into the Southeast states Thu-Thu night, bringing the risk for robust thunderstorms. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 00Z Saturday...Low confidence forecast with cloud heights along the coast over the next several hours as we transition from day to night. Very rich low level moisture streaming onshore has supported MVFR/IFR ceilings along the coast of the Carolinas this afternoon. While the moisture will remain overnight, the loss of daytime heating could cause an erosion of this cloud cover -- but to what degree is unknown. The last few visible satellite images show fairly solid low cloud cover extending from Charleston and Georgetown which should move northward along the coast now through 06Z. Forecasts are for IFR ceilings to perhaps improve to MVFR temporarily in the MYR/CRE area after 02Z, but confidence in low. At least scattered low clouds below 1000 feet AGL will persist all night even if ceilings do not develop. Models even suggest after 06Z enough moisture will push inland that FLO and LBT could see some scattered low clouds develop. VFR conditions should develop after daybreak. Extended outlook...Periods of IFR/MVFR conditions are possible in showers and thunderstorms late Monday into early Tuesday. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 1000 PM Friday...The seabreeze has died away leaving winds mainly in the 10-13 knot range which should persist overnight. No significant changes are needed to the forecast. Discussion from 630 PM follows... South winds across the coastal waters have been strongest nearshore for the afternoon with the seabreeze. Farther offshore winds are barely 10 knots at the Frying Pan Shoals buoy and the Edisto buoy east of Charleston. Once the seabreeze dies away expect a very warm and humid onshore flow to continue overnight. Although we don`t expect true sea fog to develop, periods of low stratus clouds and hazy visibilities in the 2-4 mile range are possible. SHORT TERM /SATURDAY THROUGH MONDAY/... As of 300 PM Friday...Southerly wind regime will persist through Monday as the region remains along the western flanks of Atlantic high pressure centered well offshore. Speeds will generally remain 10-15 kt through the period, except Sunday Night into Monday where speeds increase to 15-20 kt and 20-25 kt Monday night as low-level jetting and a tightening pressure gradient settle in ahead of a cold front. Seas will slowly build over the weekend, peaking 5-7 ft by Monday night ahead of the cold front. A Small Craft Advisory could be needed as early as Monday morning. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...In the wake of the cold frontal passage early Tuesday, offshore winds will slowly diminish. The offshore trajectories will knock seas down and should drop below Small Craft Advisory levels by Tuesday afternoon. There are no concerns for Wednesday into Thursday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...Coastal Flood Advisory until 2 AM EDT Saturday for NCZ107. MARINE...None.
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&& $$ SYNOPSIS...99/CHS NEAR TERM...TRA SHORT TERM...99/CHS LONG TERM...99/CHS AVIATION...TRA

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