Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 182333 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 733 PM EDT Mon Mar 18 2024 .SYNOPSIS... Dry weather and below normal temperatures will continue through Tuesday night. Milder and continued dry through Thursday. Rain chances return Friday into Saturday as Gulf coast low pressure moves northeastward up the Southeast Atlantic coast. && .UPDATE...
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A mid-level shortwave trough is beginning to produce cloud cover across west-central NC/SC. Additionally, low-level frontogenesis is maximized ahead of what appears to be a surface trough or secondary cold front. Shortwave energy will catch the surface boundary tonight and these two will work to produce lowering cloud bases and a light shower or sprinkle. The latest update advertises a slight increase in PoPs where LCL-LFC RH will be nearly saturated: southern and eastern NC. Dry air beneath the LCL and a shallow warm cloud layer should keep the intensity at a sprinkle. Weaker echos on radar are unlikely to reach the ground all together. Forecast wind gusts have been increased with the latest update as well due to deep mixing behind the boundary. Dry adiabatic momentum transfer of 25-30 knots is possible before cooler air arrives and a surface inversion knocks surface winds back to around 10 knots. Observed dew points in western NC/SC are currently in the upper teens. While this exceptionally dry air pushes eastward tonight, the late night surface inversion will pause advection briefly. Therefore, I made an adjustment to daytime dew points and RH to more accurately reflect tomorrow`s mixing potential based on these initial observations. Tonight`s dew points seem OK, assuming dew point advection pauses briefly after 9Z. For this discussion: the routine aviation section has been updated for 00Z issuance and a Fire Weather section has been added to provide details on the Fire Danger Statement issued earlier.
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&& .NEAR TERM /THROUGH TUESDAY/... Latest surface analysis shows the old frontal boundary well offshore, while weak low pressure lingers across Appalachia and the Piedmont. The frontal passage from earlier this morning has allowed for very dry air to settle at the surface. Dewpoints this morning were in the mid 50s, and have now dropped into the upper 20s to lower 30s. Ironically enough, clouds aloft have filled in over the last couple of hours, as a potent shortwave aloft starts to drop into the area from the northwest. Said shortwave will quickly sweep through the area tonight. Cloud cover will continue to thicken aloft, despite the very dry air at the surface. There`s a subtle hint of moisture convergence north of Cape Fear after 10 PM, and the atmosphere will try to squeeze out whatever water it can. However, the saturation is very thin, lingering at around 700mb. Surface dewpoints continue to plummet into the lower 20s, so whatever falls out of the cloud may dry out before it hits the surface ("virga" being the technical term for that phenomena). Some folks may see a couple sprinkles at best before 2 AM tonight across the coastal regions of southeast NC. Elsewhere, lows tonight bottom out in the mid-to-upper 30s. The temperatures meet Frost Advisory criteria inland, but tonight looks looks much too dry and windy to actually issue one. Probabilistic guidance suggests a modest chance (30-50%) of temperatures actually near or even just below freezing across certain parts of Darlington and Marlboro Counties. I`m not so confident on that idea, given the elevated winds, and if anybody does hit the freezing mark, it probably would only be for an hour or so. Therefore, holding off on a Freeze Warning tonight. Plenty of sunshine on the way for Tuesday, but it`ll be on the chilly side, with high pressure from the Midwest having an influence. Highs only reach the mid-to-upper 50s in what looks to be the coolest day of the week. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Not much of note this period with the region under the influence of weak sfc high pressure, allowing for continued dry weather over the local area. Some moderation of temps noted as thicknesses increase...highs in the 60s/70s unlike the 50s forecasted for Tuesday. A weak front moving through Wednesday night will lead to slightly cooler temps Thursday than Wednesday, but still near normal. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Focus in the long term period will be on developing Gulf of Mexico sfc low pressure tracking northeastward. In general guidance seems a bit more progressive with this southern stream system now, however there remains large differences in timing. Enough confidence to retain likely PoPs for Friday and Friday night, with the rain moderate to heavy at times and a slight chance of thunder. A drying trend ensues over the weekend, but it remains unclear how long the rain will linger especially on Saturday should the mid-level trough slow down. Temps fairly close to normal for late March this period. && .AVIATION /23Z MONDAY THROUGH SATURDAY/...
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VFR. Gusts this evening behind a surface boundary could peak around 30-35 knots before cooler air initiates a surface inversion prior to morning flights. Upper trough may squeeze out a couple of sprinkles in NC, but no VIS/CIG issues expected. Clear tomorrow with winds gradually shifting from NW to SW during the afternoon. SW winds could be gusty prior to sunset. Extended Outlook... VFR expected through the rest of the period.
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&& .MARINE... Through Tuesday...Pressure gradient increases tonight with an upper level system moving through, bringing stiff northwesterly winds into the fold. These winds will initiate a Small Craft Advisory at 11 PM EDT tonight, going through noon EDT Tuesday. Wouldn`t be surprised to see a few gusts hit gale criteria tonight, particularly over the northeast SC coastal waters, but it`s not quite consistent enough to upgrade these to a Gale Warning at this time. These offshore winds cause wind waves to poke up at 3-4ft. After the upper level disturbance moves through, winds eventually decrease to 10-15kts from the southwest by Tuesday afternoon. Seas decrease to 1-2ft. Tuesday Night through Saturday...Couple more SCA headlines expected this period. First is Tuesday night as the pressure gradient increases in SW flow ahead of the next weak front. Somewhat improving conditions then for Wednesday and Thursday, before winds and seas ramp up Friday into Saturday in association with developing low pressure sliding up the SE coast. By early Saturday expect seas up to 8-9 ft and winds gusting to ~25 kt. && .FIRE WEATHER...
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A Fire Danger Statement has been issued for all of southeastern North Carolina. Minimum relative humidity tomorrow afternoon will fall to 15-25% across the area. Northwest and west winds will hover around 10-15 mph early in the day, but southwest winds will increase during the afternoon, becoming gusty later in the day. Gusts up to 25 mph are possible during the late afternoon and just prior to sunset. The combination of dry fuels, low relative humidity, and gusty winds will lead to increased fire danger on Tuesday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... NC...None. SC...None. MARINE...Small Craft Advisory from 11 PM this evening to noon EDT Tuesday for AMZ250-252-254-256. && $$ SYNOPSIS...ILM UPDATE...21 NEAR TERM...IGB SHORT TERM...MAS LONG TERM...MAS AVIATION...IGB MARINE...MAS/IGB FIRE WEATHER...ILM

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