Area Forecast Discussion
Issued by NWS Wilmington, NC

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642 FXUS62 KILM 120527 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1220 AM EST Tue Dec 12 2017 .SYNOPSIS... The week looks dry although there is some risk for rainfall on Friday. Sunshine will bring a modest temperature rise and we will be close to normal by Tuesday. A strong cold front will move across the area late Tuesday with Arctic air returning Tuesday night through Wednesday night. Temperatures will moderate late week. A cold front may bring a brief cool down to start the weekend followed by a return to seasonable temperatures early next week. && .NEAR TERM /THROUGH TUESDAY/... As of 900 PM Monday...With the sfc based inversion having developed after sunset, winds have decoupled. This has resulted in temps nose-diving rather quickly even where winds have not decoupled entirely. The best rad cooling conditions and the stronger sfc based inversion will occur across the Northeast portions of the ILM CWA. With the sfc pg progged to tighten-some tonight and a low level southwesterly 35+ MPH jet at 950mb, SW winds will become active across the entire FA, wiping out much of the sfc based inversion. As a result, temps will bottom out this evening, close to their respective dewpoints, but then hold steady initially, then look for a slow increasing trend for temps. Lows tonight will likely occur late this evening or just after the midnight hour. Previous......................................................... As of 300 PM Monday...A cool but beautiful afternoon ongoing across the Carolinas as broad high pressure centered across the Gulf Coast expands into the region. This is accompanied by very dry air noted on WV imagery, and cloudless sky conditions are present across the entirety of the Southeast. Well upstream into the western Great Lakes, a surface low pressure beneath a strong shortwave is producing clouds in that region, with the accompanying cold front draping into the MO VLY. This front will cross the area on Tuesday, but before this occurs increasing WAA around the southern high pressure will create relatively warm temperatures for the next 24 hours. This is due to warm advection on increasing SW flow within the warm sector ahead of the aforementioned front. Moisture will slowly increase within the column, but latest RAP soundings show PWATs only to around 0.5 inches tonight, so the area will remain mostly cloud free. The exception may be well NW where a few mid/high clouds may advect in from the NW. Temperatures will drop quickly in the dry column after dark, but then will begin to level off as S/SW LLJ increases to 25- 35 kts. This will keep mins from bottoming out as radiational cooling gets inhibited, and mins are forecast to be 40-42 at the coast, 36-39 inland. SW winds increase Tuesday ahead of the front, and may gust above 25mph during the aftn/eve. THe strong cold front will cross the region precip-free thanks to the dry column, but mid-level cloudiness will increase during the aftn with FROPA occurring from NW to SE during the evening. Strong CAA follows this front and 850mb temps plummet from +1C to +3C early Tuesday, to -4C to -7C by the end of the period. This will be accompanied by gusty NW winds, and a very chilly night is forecast just beyond this period as temps begin to crash Tuesday evening from aftn highs very near 60 degrees. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...An arctic blast will bring the coldest day of this season so far. Temps will drop into the mid 20s most places Tues night in a rush of cold and dry air with Wed afternoon highs only making it into the 40s under bright sunshine. The brisk NW winds will make it feel even colder with apparent temps down in the teens right around daybreak Wed and feeling like the 30s most of the day. A very dry air mass will remain in place through Wed with dewpoint temps down in the teens and pcp water values a quarter of an inch or less. By Wed night, another shortwave will ride through the base of the long wave trough in place over the eastern CONUS. The associated sfc low will move by to our north, but may see some passing clouds overnight Wed into Thurs morning. The winds will back slightly but not expecting much of moisture return. Pcp water values will not even reach a half inch with moisture profiles showing potential for some mid level clouds as shortwave passes through overnight Wed into early Thurs morning. Temps overnight Wed may be a bit tricky as warmer air just above the surface may mix down if winds spike up at all overnight. Basically expect atmosphere to decouple allowing temps to drop out down to the upper 20s to around 30 most places, a few degrees warmer than previous night. Overall, a very cold and dry period from Tues night through Wed night. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...The East Coast longwave trough will reload late this week as another strong shortwave moves through the Carolinas on Friday. This upper system should induce low pressure to develop at the surface over North Carolina during the day Friday. Moisture is going to be tough to find given deep layer winds have so much offshore component, virtually eliminating Gulf of Atlantic inflow. In fact the only moisture I can find arrives in the 850-700 mb layer from the northwest -- most likely Pacific moisture that came onshore in British Columbia several days earlier. Dynamics are going to be so strong that I still think there will be some light measurable rainfall around, and I`m including a 30 percent chance of showers in the forecast for Friday. Dry weather will develop for Saturday and Sunday as a weak upper level ridge pokes north from the Caribbean and surface high pressure moves eastward along the Gulf Coast. Model depictions of another shortwave trough arriving on the East Coast Monday vary quite a bit from model to model, reducing confidence about what impacts we may see. PoPs of 30 percent have been introduced into the forecast for Monday along with some increased cloud cover. Temperatures will be on a roller coaster ride through the weekend, likely coolest on Saturday as the upper trough moves overhead and offshore. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 06Z...Though VFR expected through the period still not the smoothest of sailing for aviation concerns. Winds are very light/less than 5-7kt across the area as high pressure sinks into the Gulf. An approaching front and disturbance aloft will really tighten the gradient as the night wears on, increasing wind speed through the column. As the stalwart surface-based inversion holds strong this will mean a wind shear layer develops atop the inversion. By mid morning the inversion quickly mixes out for a windy afternoon in the prefrontal flow regime. FROPA will then bring a sharp change in direction by early afternoon. Wind may stay gusty through the evening albeit with a gradual decreasing trend. Extended Outlook...VFR.
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&& .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 915 PM Monday...Light and variable winds early this evening, will become southwest thruout at 10 to 15 kt by midnight as the sfc pg begins to tighten. In addition, a low level SW 30+ knot jet, will eventually partially mix down to the ocean sfc late tonight into daylight Tue. Latest SSTS are not quite cold enough yet for a deep sfc based marine layer to prevent that mixing to the ocean sfc. With that said, winds will reach SCA thresholds late in the pre-dawn Tue hours and continuing thru daylight Tue. With the CFP slated for Tue aftn, SCA threshold westerly winds will veer to the NW and become gusty at times. The increasing NW winds will be the result of a continued tightened sfc pg and CAA occurring across relatively mild SSTs. Previous...................................................... As of 300 PM Monday...Light S/SW winds across the waters are occurring in response to broad high pressure ridging eastward from the Gulf Coast. These winds will generally become all SW and increase steadily tonight and on Tuesday in the warm sector ahead of a strong cold front. The current wind speeds of 5-10 kts will become 20-25 kts this evening and on Tuesday, becoming NW at these same speeds behind the FROPA Tuesday evening. These winds will push seas quickly up from their current amplitudes of 2-3 ft to 4-6 ft by Tuesday morning, and the ongoing SCA remains in place. Have started the hazard a bit earlier than inherited to capture the 20-25 kt winds just before seas climb towards 6 ft, and the SCA goes into effect at 6am Tuesday. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...A rush of cold arctic air will keep marine layer well mixed in gusty NW winds up to 20 to 25 kts Tues night. A Small Craft Advisory will remain in effect through early Wed in this surge, but winds will back and diminish through the day on Wed allowing seas to subside. Overall expect seas up to 4 to 6 ft Tues night dropping down to 2 to 3 ft by Wed night. The off shore flow will keep highest seas in the outer waters. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...An active and windy weather pattern will continue into Thursday and Friday. Another Canadian cold front will slide across the area on Friday. Low pressure is expected to develop along the front, helping produce a surge of offshore winds Friday night. The latest GFS model is actually showing gale-force winds Friday afternoon and night, but other model guidance is not that strong, instead keeping winds strong but below 30 knots. Our forecast will go with this weaker wind forecast for now, implying a period of Small Craft Advisory conditions (W winds 20-25 kt) Friday into Friday night. Winds and seas should improve on Saturday as Canadian high pressure builds in from the west. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory from 6 AM Tuesday to 7 AM EST Wednesday for AMZ250-252-254-256. && $$ SYNOPSIS...JDW NEAR TERM...DCH/JDW SHORT TERM...RGZ LONG TERM...TRA AVIATION...MBB

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