Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 232224 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 624 PM EDT Tue May 23 2017 .SYNOPSIS... Waves of low pressure will continue to move along stalled cold front producing a good chance of showers and thunderstorms through mid week. Another cold front trailing from a deep low pressure system over the Ohio Valley on Thursday will cross the area, bringing the final round of showers to the area. High pressure will build in late Thursday into Friday maintaining quieter weather for much of the weekend. Low pressure may affect the area early next week producing more unsettled weather. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 630 PM Tuesday...Only minor changes to the forecast with this early evening update: Forecast PoPs are solidly 100 percent now through about 11 PM area-wide, with gradual drying then expected from west to east as a dry slot over central Georgia spreads up into our area. In terms of heavy rainfall and potential flooding, I`m concerned with the next batch of heavy precipitation spreading northward through southern South Carolina now. The latest HRRR/RAP model runs may be too far west with this next wave of rain, so I`m increased forecast rainfall totals east of I-95 by an additional half inch tonight, mainly before midnight. Although my forecast new rainfall totals from 6 PM until 6 AM are 0.50 to 1.00 inches, there will undoubtedly be spots that pick up 2-3 inches with flash flooding becoming a possibility due to increasingly saturated ground and elevated retention ponds and small streams. Discussion from 300 PM follows... Convective coverage has solidly increased over the last few hours ahead of a wave of low pressure. This wave will be moving NE along a stalled font with its main impacts being felt across our area during the eve hours with widespread showers and thunderstorms expected. The heavy rain potential will continue, thus a Flash Flood Watch remains in effect. Precipitable water values are at record levels for this time of year, 2 inches. Thus, training thunderstorms will have the potential to bring excessive rainfall. We are forecasting 1 to 3 inches of additional rainfall through Wed with amounts locally in excess of 4 inches. This may lead to significant ponding in many low- lying an poor drainage areas and even the risk for flash flooding, although the flash flood risk should be more localized. Urban areas will be the most susceptible to flooding. Low level jetting increases this eve and SPC has the area in a slight risk for severe weather. There is a non zero risk for damaging wind gusts in a wet microburst or even a brief tornado. The limiting factor for severe weather will be marginal lapse rates/ marginal instability as cloud cover has been extensive today. Once this wave moves by, there should be an overnight lull which should persist into Wed morning. Then another low pressure wave later Wed and Wed eve should bring an increase in showers and thunderstorms. Expect extensive clouds to dominate the period with low stratus overnight and Wed morning.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Deep moisture associated with cold front now progged to get shunted offshore more quickly than previously thought early Wednesday night and this period should mark the end of appreciable rainfall. Light shower activity will persist but in a more spotty fashion thereafter as increasingly strong PVA and height falls impinge from the west. In fact, the coverage and intensity should pick up midday Thursday as the fairly impressive 32 s-1 vort and -21C trough axis swings through at 500mb. In fact this energy swings through so quickly that the low level CAA shuts off Thursday night but not before dropping enough to support some lows in the upper 50s with low 60s along beaches. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...Plenty of dry air will move in with deep westerly flow on the back end of exiting low pressure system on Fri. Pcp water values drop down to .75 inches or below early Fri but do creep back up over an inch by late Friday. Overall expect a sunny dry day on Friday with temps reaching into the mid 80s. High pressure ridge to the south will reach up into the Carolinas maintaining pleasant weather through much of the weekend. A shortwave rides across the top of the ridge over the weekend mainly remaining north of the forecast area. This could produce some clouds or a spotty shower late Sat into Sat night, mainly over NC. The GFS builds the ridge a little farther north and therefore holds any weather farther to the north with a deep warm southerly flow and sunnier weather overall all weekend. A deeper mid to upper trough digs down late in the weekend and could produce an increase of clouds and showers Sun through Tues timeframe. Will have to see how the models evolve. For now, will keep chc of shwrs north of area through Sat night but will include Pops for Sun through Tues. The building ridge and westerly downslope flow through the mid levels will produce above normal temps through much of the period with temps reaching above 90 in spots especially over the weekend. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 18Z Tuesday...Much of the TAF period will be dominated by convection with MVFR and IFR ceilings and visibility. One wave will bring widespread convection into the later eve hours. Then there should be a decrease in the number of thunderstorms, but ceilings should remain near or within the IFR category if not lower overnight. The coverage of showers and thunderstorms will again increase on Wed, most likely after 18z. As low level jetting increases this eve, the risk for wind shear will increase. At this time, have included wind shear at KFLO. Extended Outlook...Reduced flight categories will be possible in periodic showers and thunderstorms into Thursday. && .MARINE...
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NEAR TERM /THROUGH WEDNESDAY/... As of 600 PM Tuesday...No significant changes have been made to the forecast with this early evening update. Increasing south- southwesterly winds are still expected this evening as a wave of low pressure moves northeastward along the stalled front inland. Another wave of heavy rainfall and thunderstorms between Charleston and Savannah and moving our way will make conditions uncomfortable to dangerous across the coastal waters tonight. Discussion from 300 PM follows... A Small Craft Advisory is in effect for all waters through the period and beyond. Wind speeds will be up to 20 to 25 kt with gusts up to 30 kt. The highest wind speeds during this period will be tonight. However, although wind speeds will slacken during the first half of Wed, they are expected to increase to similar levels during Wed afternoon and eve. The wind direction will be SW through the period. Seas will build to 5 to 7 ft tonight, then perhaps subside a foot or so before building to similar levels during the later stages of Wed afternoon. Bouts of showers and thunderstorms with heavy rain will drop visibility to a mile or less. The most widespread coverage during this forecast period will be tonight. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Solid small craft advisory conditions Wednesday night in not only a moderately pinched gradient but also an environment characterized by increased wind fields aloft leading to vertical momentum transfer. So now peak wind gusts may attain 35kt but at this time they do not appear to be near frequent enough to warrant Gale Warning. Frontal passage comes early Thursday leading to a veering to the west and a gradual decrease in sustained wind speeds. The upper trough meanwhile may persist the gustiness factor into the early afternoon. Winds may tick up a category in speed in the CAA Thursday night, likely continuing the Advisory. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...A stronger off shore westerly flow on Friday will diminish and back around to the W-SW through the day as low pressure system exits farther off to the east and high pressure builds up from the south. Seas of 3 to 5 ft will diminish to 2 to 4 ft through Friday and down below 3 ft by Fri night in weakening offshore flow. High pressure south of the area waters will shift east through the weekend into early next week producing a persistent SW return flow. Initially winds will only be 10 kts or so but low pressure moving by to the north Sat night into Sun and an approaching cold front late in the weekend into early next week may produce an increase in SW winds. Seas less than 3 ft Saturday in lighter winds will rise up to 3 to 5 ft in increasing SW winds Sat night into Sun.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Flash Flood Watch through Wednesday evening for SCZ017-023-024- 032-033-039-053>056. Beach Hazards Statement through Wednesday evening for SCZ054- 056. NC...Flash Flood Watch through Wednesday evening for NCZ087-096-099- 105>110. Beach Hazards Statement through Wednesday evening for NCZ106- 108. MARINE...Small Craft Advisory until 8 AM EDT Thursday for AMZ250-252- 254-256.
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&& $$ SYNOPSIS...MBB NEAR TERM...RJD/TRA SHORT TERM...MBB LONG TERM...RGZ AVIATION...RJD

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