Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 222324 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 724 PM EDT Mon May 22 2017 .SYNOPSIS... Waves of low pressure will develop along stalled cold front producing increased chance of showers and thunderstorms through mid week. A cold front trailing from a deep low pressure system over the Ohio Valley on Thursday will push through bringing the final round of storms to the area. High pressure will build in on Friday maintaining quieter weather for much of the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 545 PM Monday...This early evening forecast update increased forecast PoPs to 100 percent for almost the entire forecast area tonight with the expectation of a widespread 0.50 to 1.00 inches of rain with embedded 4 inch amounts. If rainfall amounts over the past two weeks weren`t so low, I would probably have issued a flash flood watch given the potential for such heavy rainfall this evening in a short period of time. Severe weather potential is low given fairly low CAPE values and a saturated airmass. The HRRR model is performing best with the convective outflow boundary massing along a line from Florence through Dillon, Whiteville, and just north of Wilmington. Two week rainfall totals and percentages of normal (from this morning) over the past two weeks: Wilmington, NC 0.01"...<1 percent of normal Lumberton, NC 0.22"...16 percent of normal North Myrtle Beach, SC 0.42"...29 percent of normal Florence, SC 1.05"...76 percent of normal Discussion from 300 PM follows... Waves of low pressure will move along a stalled frontal boundary which appears to be running from SW to NE west of local forecast area. A deep W to SW flow of warm and moist air with dewpoint temps near 70 degrees will persist ahead of this front. The moisture profiles show RH greater than 80 percent from near the sfc up through the mid to upper levels. Pcp water values remain above 1.75 inches increasing up near 2 inches for most of tonight. With deep moisture present, just need a forcing mechanism to help to produce showers and thunderstorms over the area. Shortwave energy rotating around a deepening mid to upper trough digging down from the Upper Great Lakes combined with increased jet dynamics will produce periods of showers and thunderstorms through the period focused along and ahead of this boundary. Overall expect plenty of clouds but enough instability to initiate showers and storms especially along the stalled front, sea breeze front or any other localized boundaries. The HRRR depicted the sea breeze development and other shwrs/tstms inland this afternoon and shows more widespread activity developing along waves of low pressure along front just along the west to northwest periphery of our local forecast area closer to the vicinity of I-95 corridor later this aftn into early this evening and shifting eastward toward the coast overnight. SPC shows marginal risk for severe storms over western zones and farther west and south with main threat of damaging wind gusts. WPC has issued a MPD for localized pcp amounts greater than 3 inches focused along the stalled front nosing into our inland SC zones, mainly into Darlington, Marlboro, Florence area. Not much will change for Tuesday as the front remains wavering over the area as shortwave energy moves around deepening upper trough right across our area. The models show a MCS type feature with the strongest storms and heaviest rain exiting the area off to the northeast by noon on Tues, but clouds and shwrs should persist through Tues aftn. A very warm and moist airmass along with clouds and pcp will keep temps well above normal overnight, remaining around 70 degrees most places. High temps tomorrow will only gain about 10 degrees making it to around 80 degrees. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Front remains stalled in the area Tue night, moving a little closer to the coast by Wed morning. Although moisture will be on the high side there will be a lack of upward motion. In fact there may be a lull as the passage of a surface wave Tue evening and its associated shortwave will lead to a period of subsidence Tue night. Forecast soundings depict this rather well showing a mid level subsidence inversion developing and precipitable water values dropping close by as much as 0.50 inch overnight. Mid level trough axis remains well west of the area Wed which will keep the front lingering in the region. Passage of the surface wave Tue night may briefly push the front south of the area early Wed but it is quick to return north as a warm front around midday Wed. Better rainfall chances develop later Wed and Wed night as potent shortwave dropping into the 5h trough early Wed helps kick the mid level pattern in motion. The 5h trough rotates east-northeast Wed into Wed night, driving a stronger cold front into the region Wed night. Increasing southwest flow ahead of the front, as well as strengthening low level jet, increases deep moisture in the region. Pwats rise to near 2 inches Wed afternoon and evening and mid level lapse rates steepen. PVA ahead of advancing shortwave, strong divergence aloft, and the abundance of moisture coupled with low level dynamics should yield a healthy line of convection Wed afternoon and evening. Although severe parameters are not particularly high there will be at least some potential for severe weather given the strengthening low level jet and modest shear. Large dry slot sweeps in late Wed night as the trough axis moves east, ending any precip prior to daybreak Thu. Cold front likely to be moving into the region as the period ends so cooler and drier air will not arrive until after the end of the period. High temperatures will continue running below climo with lows above to well above climo due to clouds and moisture. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...Deep frontal moisture to be offshore by the start of the period. However the main trough axis and strongest shortwave will be crossing the area and this should manage to squeeze a few light and short-lived showers. Continued dry advection and the lifting of the trough Thursday night should keep us dry despite one last final and moderately strong vorticity center streaking by. Zonal flow will keep the weekend dry and fairly seasonable with only gradually increasing surface dewpoints. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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As of 00Z Tuesday...A cluster of heavy thunderstorms just west of Myrtle Beach is merging into a line of showers and embedded storms stretching across the Wilmington area. This will create a massive problem for aircraft operations in the ILM area for the next several hours with prevailing IFR visibilities continuing until this thunderstorm cluster pushes offshore. Elsewhere, mainly light rain falling from mid-level clouds aloft should prevail through the evening hours with temporary heavier convective showers potentially developing at times. Cloud ceilings should lower to the MVFR/IFR category late tonight as surface temperatures cool. Scattered showers may linger all night, with scattered thunderstorms redeveloping Tuesday during the heat of the day. Extended Outlook...Reduced flight categories will be possible in periodic showers and thunderstorms through Thursday. The strongest convective activity should occur Wednesday.
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&& .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 545 PM Monday...No thunderstorms have reached the coastal waters yet, but this will change over the next several hours as widespread storms inland advance east and offshore. Visibilities reduced below 2 miles in heavy rain with frequent lightning are expected. Prevailing southwesterly winds may turn northwesterly and gusty in and near storms. Discussion from 300 PM follows... South to southeast flow will increase from 10 to 15 kts up to 15 to 20 kts as gradient tightens between cold front to the west and high pressure to the east. This persistent southerly push will produce an increase in seas into early Tues morning from 2 to 4 ft this afternoon up to 3 to 5 ft heading into Tues. WNA model data shows a fairly sharp rise Tues with the greatest winds and seas occurring through the day on Tues. May see a period of SCEC conditions late Tuesday. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Front remains west of the waters through the period, maintaining southwest flow. Speeds start to increase later Wed and Wed night as the front moves to the coast and slowly strengthening low moving into the OH valley helps tighten the gradient. Southwest flow on the high end of the 15 to 20 kt range Tue night will increase to a solid 20 kt around midday Wed with 20 to 25 kt expected late Wed and Wed night, likely requiring SCA headlines for all waters. Seas will build due to prolonged and increasing southwest flow. Seas 4 to 5 ft at the start of the period will build to 4 to 6 ft during Wed, eventually reaching 7 ft Wed night. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...Small Craft Advisory will be in effect on Thursday just ahead of a cold front that will pinch the gradient. Within the agitated wind field of the pinched gradient a strong upper disturbance will traverse the area possibly to enhance wind gusts. In the wake of this boundary there will be west winds to round out the period of gradually diminishing speed. Wave heights will similarly abate somewhat slowly. && .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Beach Hazards Statement from 7 AM EDT Tuesday through Tuesday evening for SCZ054-056. NC...Beach Hazards Statement from 7 AM EDT Tuesday through Tuesday evening for NCZ106-108. MARINE...None.
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&& $$ SYNOPSIS...RGZ NEAR TERM...TRA/RGZ SHORT TERM...III LONG TERM...MBB AVIATION...TRA

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