Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 290526 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 126 AM EDT Wed Mar 29 2017 .SYNOPSIS...
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A cold front which will drop south across the area by late tonight or early Wed. Relatively cooler and drier high pressure will build in from the north Wed into Thu night. Showers and thunderstorms are expected on Fri as warmer and more humid air returns ahead of an approaching cold front. The cold front will sweep eastward across the area and offshore late Fri night. Some of the thunderstorms may become strong to severe Fri. The weekend should be dry and warm on Sat with temps dropping back to near normal on Sun as high pressure builds in from the Great Lakes.
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&& .NEAR TERM /THROUGH TODAY/... As of 945 PM Tuesday...Sfc cold front will sink slowly across the area overnight. The convergence along this front is evident with Cu and SC strewn along it from west to east. A few of these Cu are building just enough to produce isolated showers. However, aloft, NVA ie. Subsidence, is now affecting the FA with the mid-level s/w trof having pushed off the DELMARVA Coast this evening. As a result, do not expect much vertical development with these showers. May continue the slight chance POP well into this evening as this boundary drops southward. Not much tweaking to tonights lows from the previous fcst update. However, am concerned for the possibility of fog eventhough models are not highlighting its potential. Will update to include patchy for now and could get worse with time depending how much drier air, ie. lower dewpoints, are able to advect into the FA overnight. Seen it many times after FROPA in the evening and winds go NW to N less than 5 kt. And with ground moisture avbl from rainfall having occurred earlier today and also late this aftn and evening. Previous..................................................... As of 3 PM Tuesday...A second shortwave is crossing the Carolinas this afternoon and with the early shortwave there has been a delay in additional convection developing. The GOES-16 1-minute imagery is showing cumulus developing west of Florence to Pembroke and isolated cumulus developing to the west. The 16 UTC HRRR is only showing isolated convection through sunset. So will keep a 20 to 30% chance of convection with the higher chances for the northern coastal areas. The frontal boundary will shift across the area after midnight and sweep to the south with high pressure building in the area into Wednesday. Lows tonight are expected to fall into the upper 50s and highs on Wednesday to around 80 except cooler at the beaches with a northeast flow. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...Mid level ridge axis over the southeast will be deamplifying and shifting east Wed night as surface high over southern Canada builds down the east coast. Cooler air associated with the Canadian high spreads over the region Wed night with lows dropping close to climo. Northeast winds will be in the 5 to 8 mph range which should prevent any radiational cooling. Low will be in the low to mid 50s across much of the area. Surface high shifts off the coast later Thu with weak return flow developing Thu night. Ridging aloft Wed night and Thu will keep the region dry through at least Thu evening. Forecast soundings show impressive subsidence from 850mb through 700mb into Thu night before approaching high amplitude southern stream system shunts the 5h ridge axis farther off the coast. Developing deep southwest flow Thu night increases moisture in the region, precipitable water values increase from around 0.80" Thu evening to 1.40" by the end of the period. Arrival of this deeper moisture along with an increase in mid level lapse rates should open the door for some convection late in the period. The unfavorable timing and lack of strong low level jetting does suggest coverage will be rather limited and do not plan on much in the way of changes to inherited Thu night precip chances. Temperatures Thu will be near to slightly below climo, upper 60s to lower 70s, with temps Thu night running above to well above climo and likely following an atypical curve with slight warming after midnight. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 AM Tuesday...Next in series of potent southern stream systems will impact the eastern Carolinas Fri and Fri night with a categorical risk for showers and thunderstorms developing. The combination of significant upper level support and strong and deep moisture return and lift provides at least the opportunity for a more widespread and significant rainfall event. There will be some risk for strong to severe thunderstorms during this time. 0-6 km effective bulk shear parameters are not particularly impressive. However, instability does grow with mixed layer CAPE values on the order of 500 to 1000 J/kg as the warm front should move to our N. Mid-level lapse rates are forecast to be rather modest. The potential is there for an active day/night leading into the weekend, although magnitude is certainly still a question mark. In the wake of this system, dry weather and near to above normal temps are expected for the weekend as mid-level ridging builds across the area and surface high pressure builds from the NW and N. Attention then will turn westward as next southern stream system along the Gulf Coast Sun night lifts to the NE and drags a warm front to the N. This will again bring deep moisture into the Carolinas, and with that, showers and thunderstorms early next week. Given timing differences between long range models and a general slower trend as compared to 24 hours ago, will cap POPs in the chance category until we can gain better resolution as to when the highest risk for showers and thunderstorms will occur. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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As of 0530Z...VFR conditions expected through the period. Some fog has developed to the north where there was more rainfall in the past 24 hours. However the lower dewpoints have begun to make progress from the northwest with LBT dropping six degrees in the past hour. Can`t rule out a brief period more along the coast but confidence is not sufficient to include in the forecast. Some scattered to broken ceilings of four thousand feet should develop late morning moreso across the northern areas as a push of cold air noses in from the northeast. Extended outlook...VFR conditions through Thursday. MVFR/IFR conditions likely in showers and strong to severe thunderstorms Fri/Fri night. VFR conditions Sat thru Sun.
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&& .MARINE... NEAR TERM /THROUGH WEDNESDAY/... As of 945 PM Tuesday...Update concerned with pcpn eventually ending late this evening. And, re-adjusting the winds based on the slowly southward dropping sfc boundary that will result in winds becoming NW to N after its passage during this evening thru the pre-dawn Wed hours. The sfc pg is rather loose on either side of the sfc cold front, resulting with only 10 to 15 kt wind speeds being fcst. Significant seas will run 2 to 4 ft with 5 footers across the outer waters off Cape Romain and Cape Fear. The healthy SE ground swell at 10 to 11 second periods has peaked during today and should now exhibit a slow decaying trend. Will see wind driven waves become more dominant in the seas spectrum later Wed as NE winds increase due to sfc ridging down the east coast from Canada becoming more prominent. Previous.................................................... As of 3 PM Tuesday...SW winds around 15 knots with higher gust are seen at coastal CMAN stations...not receiving any offshore buoy data at this minute so have lower confidence of the current wind speeds at 10 to 20 miles off the coast. With cold front approaching expect to see winds increase to 15 to 20 knots with higher gust. Seas are expected to peak at 3 to 5 feet. Will continue to see longer period swells through this evening. With the cold frontal passage expected between 2 AM and 6 AM Wednesday, seas will slowly fall to the 3 to 4 feet range by the end of Wednesday. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...Northeast flow will continue Wed night and Thu as high pressure over southern Canada builds south. Gradient becomes pinched late Wed night as cold surge moves across the waters and northeast flow may briefly hit 20 kt. Northeast flow remains 15 to 20 kt Thu before starting to decrease and veer to east Thu evening and then southeast Thu night as the surface ridge axis moves offshore. Seas will range from 3 to 5 ft through Thu night with shorter wave periods expected given the strength of the northeast flow. Exercise caution headlines may be needed during the period, depending on the strength of the northeast surge late Wed night. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 AM Tuesday...A Small Craft Advisory is likely for all waters Fri and Fri night with conditions possibly lingering into Sat. Slow moving area of low pressure will be moving across the Ohio Valley Fri. Its accompanying warm front will move across the waters Fri. As low pressure moves offshore of the Mid-Atlantic states late Fri night and Sat morning, it will strengthen and drag a cold front across the waters. High pressure will slowly build across the area from the N and NW Sat night and Sun. SE winds Fri morning will become S and then SW Fri night. The wind direction will become westerly early Sat morning and then NW by Sat afternoon. N winds Sat night will become NE overnight Sat with NE winds persisting into Sun before veering to easterly during the afternoon. The strongest winds are expected Fri and Fri night, up to 20 to 25 kt. Seas late Fri and Fri night will build to 4 to 7 ft and around 8 ft at frying Pan Shoals. Seas during Sat will only slowly subside as backswell from departing storm system impacts the waters. Seas should drop below advisory levels by late Sat and to 2 to 4 ft on Sun. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...DCH/DRH SHORT TERM...III LONG TERM...RJD AVIATION...SHK MARINE...

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