Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201715 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 115 PM EDT Tue Mar 20 2018 .SYNOPSIS... Hazardous thunderstorms are possible this afternoon and tonight as a storm system approaches the region. Colder air will spill into the Carolinas Wednesday and especially Wednesday night, with frost and freeze conditions for portions of the area early Thursday and early Friday. High pressure will maintain cool daytime weather this weekend, with rain spreading in from the west Saturday night and Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 114 PM Tuesday...Tornado Watch 18 in effect for Georgetown and Williamsburg counties, and adjacent 0-20 NM waters from Murrells Inlet to South Santee River. No portions of NC are presently in a watch, but could be later today. No changes to a potentially volatile and dangerous weather afternoon/evening. No significant changes were made but fine tuning can be assured progressing through afternoon and evening. As of 10 AM Tuesday...Substantial cloud breaks allowing March sunshine to commence boosting surface based CAPEs. This, as a cold pool aloft approaches late today, and sharpens lapse rates. Along and south of an E-W surface boundary over the area, low level shear will exist of a magnitude potentially capable of inducing low-level rotation in convection initiated by, or upon encountering this boundary. The SPC has designated a 30% chance of winds higher than 50 kt along and near the Carolinas coast, a 30% chance of hail 1 inch in diameter or higher, and 5% risk of a tornado, mainly between mid-afternoon through evening. It is not clear if the dryish mid-levels will hinder storms or simply enhance downdrafts due to evaporative cooling, my hunch is steepening lapse rates, will draw convection into bursting the cap. Adjustments were needed to reduce POP values in the early going, and substantially reduce cloud cover. No plans to mess with Max-T at this time, as advertised temps well into the 70s is looking on target, considering the wind flow and visible data this morning. The front can be seen well in visible slipping S and SE over central NC. This boundary will impinge our northern tier of SE NC in the middle afternoon, and will stall across our forecast area. As of 3 AM Tuesday...Warm front pushes north of the area this morning with low level jet of 45 to 55 kt helping spread warm, moist air over the region. Highs today will climb into the mid to upper 70s with potential for low 80s with any peaks of sun. Dewpoints will rise into the low to mid 60s today. Aloft the progressive mid-level pattern becomes more amplified as a shortwave moves into the TN Valley and acquires a negative tilt. Lapse rates steepen from late morning into early afternoon, when CAPE values are forecast to be around 2k J/kg. Low pressure moving into the area this afternoon, along the front, will be gaining strength as it slowly moves east. Low level convergence along the cold front and dynamics associated with the developing low should be enough to generate widespread deep convection. There remains potential for strong to severe storms this afternoon, possibly lingering into the first part of the evening, and SPC continues to carry an enhanced risk for the coastal areas and a marginal for areas just inland from the coast. Second round of convection pushes offshore this evening, ending any severe threat and commencing a period of cold advection. Temps drop below climo by the end of the period with lows in the upper 30s to lower 40s possible. Although precip chances rapidly decrease this evening and overnight, moisture from 2-4k ft will help low clouds linger through the end of the period. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 430 AM Tuesday...The cold core upper closed low, extending across the FA at it`s furthest southward extent on Wed, will produce variably cloudy skies across the area especially during the heating of the day on Wed. At this point, looking at cold and patchy to occasional liquid rain with the possibility of graupel or pea size hail from the embedded stronger showers. Temps Wed into Wed night will run a conservative 10 to 15 degrees below normal. And there will be the increased potential for min temps Thu morning dropping into the 30-35 degree range and the same holds true for Friday morning. Have been favoring the cooler NAM MOS Guidance of late which has been consistent between model run times. The HWO references the possibility of freezing and/or frost issues come Thu and Fri mornings. The upper low is progged to pull away Thursday, in it`s wake the FA will remain under control of a decent amplified longwave upper trof with NW flow thru the atm column. The upper trof axis will remain primarily east of the FA this period. Sfc winds will remain active thruout this period due to a decent sfc pg across the FA due to deepening low pressure moving into the Canadian Maritimes and a nearly 1030mb high situated along the Gulf Coast States. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 PM Sunday...Although I would not discount a few flurries as potent shortwave swings through the back end of the upper trough early in the period, the moisture will be very limited. Therefore will not include any pcp in forecast early Thurs morning as upper trough swings off the coast. CAA continues through Thurs into Friday in strong NW flow as high pressure builds in from the north. The 850 temps drop down around -4c and do not return above 0c until Sat. Temps will drop into the 30s most places with some frost or freeze potential in spots again early Fri morning. Temps both Thurs and Fri may not reach above 60. Low pressure system will brush the Carolinas Fri night into Sat as it moves toward the Mid Atlantic coast. This will produce increase in clouds and greater chc of rain across the area late Fri into early Sat. The latest model runs show a possible wedge type scenario setting up for the weekend with clouds and periods of rain possible. Overall, the weather may turn out to be cooler and more unsettled than originally forecast. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... As of 18Z...A cold front has moved southeast and extends from near KLBT to northwest of KILM. Currently MVFR except for mid- level cigs at KCRE/KMYR. Thunderstorms expected to develop south of the cold front within the next few hours in the warm air initially near KCRE/KMYR, and then towards KILM/KFLO as the afternoon progresses. Confidence of thunderstorms is highest at the coastal terminals, lowest at KFLO. Showers/MVFR cigs expected in the cooler air near KLBT. Tempo MVFR likely in thunderstorms with brief IFR in heavy rainfall. IFR expected at KLBT later this afternoon and KILM by evening, but could occur earlier based on current trends. Convection should weaken to showers by 00Z. MVFR cigs expected this evening and overnight, with best confidence of IFR cigs KLBT/KILM. Cigs improve early Wednesday except at KLBT. Extended outlook...VFR. MVFR/IFR/Rain Sunday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 10 AM Tuesday...No significant changes, seas and winds will rise through the day, SCA begins at 5 PM. The Gulf Stream and very outer waters are already experiencing gusts AOA 25 kt. As of 3 AM Tuesday...Southerly flow will develop and then increase today as low pressure develops to the west. Gradient will supports southwest winds of 15 to 20 kt into this afternoon. Further strengthening of the low will push speeds close to 25 kt with gusts in excess of 30 kt. Increasing southerly flow will build seas across the waters today and tonight. 6 ft will be possible in some areas as early as mid to late afternoon and have decided to raise a Small Craft Advisory for all zones starting at 5 PM and lasting well beyond the end of the period. There is potential for 10 ft seas in isolated spots open to extended southerly fetch late tonight. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 430 AM Tuesday...Not one of your better 2 day fcst for spending time on the open Atlantic waters. A decent sfc pg will basically keep a hold of the local waters thruout this 2 day period. This a result of the upper low and associated sfc low pulls away to the NE while a nearly 1030mb high moves along the Gulf coast states. This will result in a west but mainly NW flow across the local waters with speeds of 15 to 25 kt with gusts to 30 kt. With mainly an offshore NW trajectory, the local waters will see a decent range of significant seas with 1 to 4 ft within 10 nm of the coast and 4 to 7 ft at 10 to 20 nm off the coast. Dominating periods will run 4 to 6 seconds. Will need to monitor for Gales and won`t take much for them to occur. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Monday...Cold and dry high pressure will extend down over the local waters Friday through Saturday. Strong off shore flow up to 15 to 20 kts early Thurs will weaken and become more northerly through the period down to 10 kt or less by Sat. This will allow seas to subside from close to 3 to 5 ft early Thursday down less than 3 ft by Fri aftn into Sat. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory from 5 PM this afternoon to 6 PM EDT Thursday for AMZ250-252-254-256. && $$ SYNOPSIS...MJC NEAR TERM...III/MJC SHORT TERM...DCH LONG TERM...RGZ AVIATION...MRR is the U.S. government's official web portal to all federal, state and local government web resources and services.