Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 210006 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 806 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 /UNTIL 6 AM WEDNESDAY MORNING/... As of 710 PM Tuesday...Cooler surface air has knocked instability values for surface parcels down to zero with the exception of the I-95 corridor where SBCAPE is still near 1000 J/kg and new storms have lit up near and just northeast of Florence recently. As colder air aloft works in from the west, a few new cells could still develop from Dillon and Lumberton to Elizabethtown as the last of the elevated instability aloft over the frontal surface is expended. Rain chances are still anticipated to ramp down from south to north over the next few hours. Freezing levels are plunging with the incoming cold air aloft, and we`ve observed almost any echo over 60 dBZ is correlated with small hail at the ground. Emergency Management in Bladen County reported small hail in multiple locations from Elizabethtown to White Lake within the past 30 minutes. Discussion from 550 PM follows... Severe thunderstorms earlier this afternoon dropped hail at least one inch in diameter near Trio, SC, but have weakened. The convective cap has since broken and more widespread thunderstorms have since developed east of I-95 to the coast. One strong storm dropped a little pea sized hail here at the NWS office in Wilmington, and hail will remain a possibility for the next few hours as steep mid-level lapse rates will promote large parcel acceleration aloft. Visible satellite and radar shows the surface cold front moving southward through Hartsville, Marion, Whiteville, to just north Wilmington. The HRRR is doing an excellent job currently and is our model of choice for the next 6 hours with convective development and movement. Convection will remain largely east of I-95, shifting almost exclusively into SE North Carolina in the next couple of hours, then ending by late this evening as colder and more stable air wraps in behind developing low pressure exiting the coast. Some light showers should redevelop late tonight across the northern sections of the Pee Dee into SE North Carolina associated with a strong shortwave wrapping around deepening upper level low pressure to our north. One more change made to the forecast concerns sea fog that has developed over the past few hours and is reducing visibility at the beaches according to multiple beach cams across the Cape Fear area. High dewpoint boundary layer air chilled by its passage across the cold nearshore waters is responsible. Once the cold front moves through the fog should quickly dissipate. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... As of 340 PM Tuesday...NNW to NW flow through most of the column Wednesday night ushering in cooler and drier air. The flow will still be rather vort-laden, but most of the maxima will be sheared out and to our south. So while a few of these impulses may bring batches of mid level cloud the area will remain rain- free. Lows in the mid 30s will support some frost especially where winds grow light enough and guidance is trending colder away from the ocean and much of the area may experience a light freeze, at least according to the colder MET MOS. It bears pointing out at this time that there is a good 6 degree separation between these values and the warmer MAV numbers. Cold air advection continues Thursday and Thursday night albeit weakening especially late in the period. Thursday night may be a better candidate for a light freeze especially over northern zones and our normal chilly spots as surface-based decoupling appears more likely. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 340 PM Tuesday...this forecast period continues to show a cool down as an upper level trough will be remain along the east coast. In the large scale trough a shortwave is seen dropping southward on the west side. This will bring in a colder shot of air and a back door cold front. The 12 UTC GFS and ECMWF are not in good agreement with the GFS being much faster than the ECMWF. So uncertainty is high on timing of this front. Will favor the faster GFS and its ensemble and introduce a chance of showers late Saturday into Sunday night as the frontal boundary shifts southward. Temperatures will be below normal for the period with a frost/freeze possible Friday night. Otherwise lows in the 40s and highs in the mid to upper 50s to lower 60s. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 00Z...Surface front was located just south of a KFLO- KILM line, with low center southwest of KFLO. Numerous weakening showers were along and north of this boundary, and will continue through about 03Z. The front will sag further south and make it to the vicinity of KMYR before the low moves offshore and winds shift to the W and NW. Expect MVFR ceilings overnight, with some potential for IFR. Westerly winds will become gusty Wednesday morning and continue through the day as low pressure deepens off the Mid-Atlantic coast. Extended outlook...VFR. MVFR/IFR/Rain Sunday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 710 PM Tuesday...Quick update to remove the tornado watch headline from the forecast. Severe thunderstorm potential has really diminished in the past 60-90 minutes, and the remaining showers on radar should gradually diminishing from south to north over the next few hours. Discussion from 550 PM follows... Forecast has been updated for sea fog that has developed over the past few hours as high dewpoint air south of a cold front has been cooled by contact with the cold sea surface. This fog should be with us south of Cape Fear for another few hours before increasing northwesterly winds bring drier and colder air southward, dissipating the fog. Showers and thunderstorms developing across the area should clear the SC coastal waters by 8 PM, but may linger for another few hours across the SE North Carolina/Cape Fear waters as surface low pressure develops overhead. All convective activity should be out of the area by midnight, but light showers may redevelop later tonight, brought southward by cold winds draining offshore from northern North Carolina and Virginia where snow may actually be falling late tonight. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 340 PM Tuesday...As is usually the case in a strong cold advection regime accompanied by strong dynamics aloft conditions will be hostile over the marine environment early in the period. Advisory-worthy winds will be bringing steep, short period waves that will also satisfy the (6ft) criteria. Relaxation of wind and seas will be quite gradual on Thursday as cold advection continues but weakens as does the strength of the upper impulses moving overhead. Current 5PM ending time of the advisory appears on track enough this far out int time to preclude any changes. Northwest flow lasts into Thursday night with the abating trend ongoing. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 340 PM Monday...high pressure will ridge down the coast with a surge of cooler air on Sunday. The high pressure will extend down over the local waters Friday through Saturday before a cold front approaches from the north. Northwest flow of 10 to 15 knots will continue through Friday before veering to the south and west on Saturday and Sunday. Winds will increase on Sunday with a backdoor front and seas are expected to increase to 4 to 7 feet by Sunday late. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 6 PM EDT Thursday for AMZ250-252- 254-256. && $$ SYNOPSIS...DRH NEAR TERM...TRA SHORT TERM...MBB LONG TERM...DRH AVIATION...CRM is the U.S. government's official web portal to all federal, state and local government web resources and services.