Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 222038 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 338 PM EST Mon Jan 22 2018 .SYNOPSIS... A cold front will bring showers and a few thunderstorms tonight into tomorrow along with some gusty winds. Dry and seasonable weather is expected all week. A warmup Saturday will be followed by rain and thunderstorms Sunday as well as a return of seasonable weather on Monday. && .NEAR TERM /THROUGH TUESDAY/... As of 300 PM Monday...Several concerns this period make for a challenging near term forecast, with rain, thunderstorms, sea fog, and strong winds all likely during the next 24 hours. batch of rain associated with a coastal trough is lifting NE across Cape Fear this evening, and will continue to push NE while weakening during the next few hours. Although the NAM and latest HRRR have modeled this the best today, the rain has been surprisingly heavy when compared to forecast soundings. Even the more robust NAM has moisture confined to a shallow layer between 900 and 800mb, but there is just enough instability within that layer to produce efficient rain processes. Fortunately, showers are exiting quickly to the NE so an end to the rain is expected by sunset. The showers near the coast combined with the widespread cloud cover have kept temps below guidance today for a change, with highs inland peaking the low to mid 60s, mid to upr 50s at the coast. After the rain exits, a lull will occur as the area becomes increasingly entrenched into the warm sector ahead of an approaching cold front. Increasingly southerly winds will have the two pronged effect of keeping temps from falling much overnight, while also advecting more moisture into the near-surface layer. Forecast mins reflect a very warm night, with lows about 2 degrees either side of 60, above typical highs for late January. Forecast profiles show full saturation developing near the surface, supportive of fog, however the winds ramp up quickly, rising to 25kts or more at the top of the nocturnal PBL even by midnight, so a stratus layer is more likely and have shown a rapid increase in cloud cover tonight. The front will approach from the west, and a pre-frontal line of convection is likely to push across the CWA late tonight and into the first part of Tuesday. Guidance is in pretty good agreement with a slower progression of this feature, and the best chance for tstms will be beginning after midnight west of I-95, to clearing the coast late Tuesday morning. It is a tricky setup however, as several of the reliable high-res models suggest a convective "split" across the CWA as the best dynamics lift NE while convection across the GOM and off FL "steal" the moisture to the south. Even so, the local area should see a line of showers with embedded tstms thanks to SREF MLCape of 200-300 J/kg combined with very strong shear as the LLJ rises to 50 kts and SHERB approaching 1.0. SPC has kept the area in just a GNRL risk, but an isolated wind gust is not out of the question, especially near Cape Fear Tuesday morning as surface instability tries to re-develop. Convection will exit late Tuesday morning, but the very strong wind fields remain. As the column dries and sunshine develops, wind gusts from the West may reach 30-35 mph, slightly higher possible if the maximum available mixing (40+ kts on forecast soundings) occurs. Additionally, the true cold advection lags considerably into Tuesday aftn so highs will reach over 70 in many places, with slightly earlier CAA west, and more cloud cover east, keeping those areas in the upper 60s. The exception may be where sea fog develops and advects onshore along the Grand Strand. The setup is not ideal for sea fog, but with continued cold ocean waters and strong S/SW winds driving dewpoints to near 60, have added patchy sea fog for the Grand Strand into Brunswick County. If this becomes more widespread, highs would be severely limited despite the warm airmass. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 3 PM Monday...Surface high building in from the west and subtle 5h troughing over the much of the CONUS will be the story during the period. Weak cold advection Tue night will come to an end before daybreak. Cooler air mass and light winds combined with clear skies will allow for some radiational cooling, although conditions will not be ideal. Lows will end up near to slightly above climo. High pressure continues to drift east Wed and Wed night, ending up over the TN valley as the period ends. Shortwave quickly moving from the Upper Mississippi Valley to the Mid-Atlantic Wed will drag a cold front across the area late Wed. The front passes dry but will bring a reinforcing shot of cooler and drier air to the region. Clear skies in the morning will give way to increasing high clouds as the shortwave passes to the north. Cloud is not likely to be thick enough to block out the sun but it will limit heating a bit. Highs Wed will be near to slightly above climo. Reinforcing shot of cold air moves in Wed night with temps dropping to or just below freezing. Mixed boundary layer should prevent most areas from experiencing any significant radiational cooling. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...Thursday into Friday will bring a transition to seasonable weather as high pressure goes from our west to our northeast. Onshore flow Saturday will import Atlantic moisture into the area and clouds should increase. A warmer afternoon is also expected though ocean moderation may extend pretty far inland. Winds go south on Sunday ahead of a strong upper wave and surface cold front. Showers and thunderstorms appear likely including some areas of moderate to heavy rainfall. Back to sunny and seasonable on Monday. && .AVIATION /18Z MONDAY THROUGH FRIDAY/... As of 18Z...Challenging set of TAFs with a lot going on. A cold front approaches from the west tonight. Ahead of the front, rising dewpoints and a south southwest will give us favorable conditions for sea fog/stratus at the Myrtles. Just ahead of the front look for increasing winds and convection. The NAM is more pessimistic and I have leaned on it, although my confidence is not high. Most of the convection will be confined to the coast after daybreak. Look for quite strong southwest winds at the end of the forecast period. Extended Outlook...Becoming VFR Tuesday evening, through the end of the forecast period. && .MARINE...
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NEAR TERM MARINE/THROUGH TUESDAY/... As of 300 PM Monday...High pressure exiting to the east will give way to a cold front approaching from the west. This will drive a strengthening warm sector across the waters, so winds will veer to the South tonight, and then Southwest on Tuesday, with speeds increasing steadily to 20-25 kts. The current SCA will remain unchanged and goes into effect at 6am and persists through Tuesday evening. This hazard is for both the winds, and seas being pushed up to 4-6 ft late tonight and much of Tuesday, after being just 1-3 ft most of today. A line of convection is expect to move across the waters early on Tuesday as well. This will bring the potential for briefly heavy rainfall and cloud to sea lightning, as well as locally higher seas and stronger wind gusts. Additionally, although the setup is not ideal for sea fog, increasingly S/SW winds will advect high dewpoint air across the still cold shelf waters. SREF probabilities are relatively high, 30- 40%, for low visibility late tonight through much of Tuesday, so have added patchy sea fog into the Wx grids. Best chance of this will be across the SC waters and south of Brunswick County, where visibility below 1NM is possible. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 3 PM Monday...High pressure will build in from the west through the period. Winds will slowly veer from west to northwest Tue night but a lack of cold advection keeps wind speeds mainly on the low end of the 15 to 20 kt range. Gradient further weakens on Wed with northwest flow dropping to 10 kt or less. Dry cold front moves across the area late Wed with some modest cold advection developing Wed night. Winds increase to 15 to 20 kt overnight, becoming northerly late in the period. Offshore flow through the period will keep seas under headline criteria but seas as high as 4 or 5 ft will be possible Tue night. By Wed morning seas seas will be 2 to 3 ft and will remain 2 to 3 ft through the end of the period. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...High pressure initially to our west on Thursday bringing northerly flow. The high shifts offshore and becomes centered further to the north on Friday. Northerly winds will start diminishing and veering. Expect easterly winds by Friday and SE on Saturday. Swell energy will increase as a long onshore fetch develops but any increase in wind wave should be minimal.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory from 6 AM to 6 PM EST Tuesday for AMZ250- 252-254-256. && $$ SYNOPSIS...MBB NEAR TERM...JDW SHORT TERM...III LONG TERM...MBB AVIATION...DL

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