textproduct: NWS Wilmington

WHAT HAS CHANGED

Aviation discussion updated with 12Z TAF Issuance.

259am Update... Thunderstorms are possible on Sunday for inland locations and coastal locations on Sunday night. Severe weather chances increase on Monday as a strong cold front moves through the area. SPC has maintained a 30% chance of severe weather within 25 miles of a point for Monday afternoon. Strong winds on Monday may bring impacts outside of convection. The chance for freezing temperatures on Tuesday night into Wednesday morning has increased

KEY MESSAGES

1) A strong cold front will bring impacts due to strong winds and severe weather on Monday. A few storms are possible ahead of the front on Sunday and Sunday night as well.

2) Freezing temperatures are expected on Tuesday night following the cold front.

DISCUSSION

KEY MESSAGE 1... A strong cold front will bring impacts due to strong winds and severe weather on Monday. A few storms are possible ahead of the front on Sunday and Sunday night as well.

A warm front will lift north of the area on Sunday and Sunday night. Showers induced by isentropic lift during the afternoon will have limited instability, but shear will be increasing ahead of an approaching cold front. Severe weather chances are low and this conditional threat is more likely for areas west of I-95. Once the front moves well north of the area on Sunday night, elevated instability may produce some stronger storms near the coast as the low level jet amplifies.

Severe weather potential peaks on Monday as a deep midlevel trough will move eastward through the southern Appalachians. The attendant cold front will provide a focused area of forced ascent in a warm advective regime with strong winds throughout the column. Instability will be marginal (as is typical for early Spring severe weather events), but effective shear around 40-50 knots could produce scattered damaging wind gusts. The arrival of the cold front favors the early afternoon, during peak heating. Although cirrus will limit some warming, this would generate maximum instability; the ensemble mean has increased slide to around 600 J/kg. Winds below 700 mb will approach 60 knots and the top of the boundary layer could have winds as strong as 50 knots. This suggests that damaging winds could easily reach the surface in shallow convection.

With the latest suite of deterministic guidance, nearly all major global models have 50 knot wind gusts near the top of the boundary layer, so winds outside of convection could reach 45-50 mph. This could lead to downed trees and power outages before the cold front arrives. SPC maintains a 30% chance of severe weather for Monday and there was some discussion to include part of the area in a Marginal Risk for Sunday.

KEY MESSAGE 2... Freezing temperatures are expected on Tuesday night following the cold front.

Cold high pressure will build into the southern and southeastern US behind the cold front on Tuesday. As the center of high pressure settles overhead late Tuesday and Tuesday night, winds will become calm and dry air will allow temperatures to radiate well. Temperatures should reach the freezing mark for a large portion of the area and a Freeze Watch may be needed in the coming days.

LREF probabilities indicate that inland locations have a greater than 80% chance of falling below freezing for areas along and west of I-95. Chances decrease linearly toward the coast with a 30% chance just inland from the beaches (including Wilmington and west of US-17 in SC). Chances for a hard freeze are less than 15% for areas west of I-95, nearly 0% closer to the coast. It is important to note that these coarse global ensembles cannot capture small scale radiative characteristics, so probabilities will likely increase as mesoscale models come into range. Agricultural interests should continue to monitor the forecast.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Predominantly VFR through the 12Z TAF 24 hr issuance period. Fog chances early this morning are on the low side for the individual terminals, however patchy fog remains possible in a corridor running from Williamsburg/Georgetown Counties northeast to southern Bladen County. If this area expands, it may overlap the local terminal sites and will keep monitoring. Otherwise, looking at periodic thin cirrus moving overhead today with opaque cirrus and possibly altocu tonight, could even possibly observe stratocu from off the water affecting the coastal terminals. Sfc frontal boundary drops southward and backdoors the area from late this afternoon thru tonight, then stalls between Charleston and Savannah by daybreak Sun. This will have a bearing on the wind directions and are noted in the individual TAF sites. Overall, winds will veer from the W-NW 3 to 6 kt this morning to the ENE-E 4 to 8 kt later tonight. The coastal terminals will experience a sea breeze with SE winds aob 10 kt this afternoon.

Extended Forecast...Flight restrictions become more likely Sun due to increasing rain chances and associated cloud decks. These restrictions are expected to become worse Mon, as a strong cold front sweeps through the area, potentially bringing severe weather. VFR should return late Mon night, remaining that way through Wed.

MARINE

Through Tonight... Main story will be the light winds, generally AOB 10 kt thru the period, except possibly and briefly 10-15 kt after the CFP that drops southward later today thru tonight. Ie. backdooring the area waters before stalling between Charleston and Savannah by Sun morning. Looking at a veering wind trend during this period, starting out SSW-SW and ending up NE-ENE later tonight. Could see a sea breeze affecting the nearshore waters this aftn and early evening, ie. ESE-SE around 10 kt. Seas this period will be in a subsiding tendency with an E-SE 6 to 8 second period fresh/pseudo swell dominating. Sea breeze nearshore, within 5 nm of the coast, will result in choppy conditions on top of this swell.

Sunday through Wednesday Night... High pressure departs on Sunday while an area of strong low pressure will deepen over the central US into Sunday night. The pressure gradient will increase late in the day as the cold front and associated trough approach the Southern Appalachians.

Warm advective flow over the relatively cooler waters will lead to a gradual increase in winds on Sunday night. Gusts will reach 25-30 knots by sunrise Monday and seas in excess of 6 feet are likely to be occurring at that time. Increasing dew points in southeast and southerly flow may produce some patchy dense sea fog. The primary cold front will approach the area on Monday. SCA conditions are likely to be occurring for most of day on Monday and Monday night, some gusts to gale force are possible during this time. Probabilities support the chance for prolonged wind gusts in excess of 34 knots (greater than 2 hours) at around 20%-30%. Seas peak at 7-9 feet late Monday.

The pressure gradient remains compressed on Monday night as winds turn northerly. Cold advection behind the cold front should keep winds and seas elevated into early Tuesday. Transient high pressure will move overhead and just offshore on Tuesday evening. Northerly flow will become northeasterly and should maintain some breeziness into Wednesday.

ILM WATCHES/WARNINGS/ADVISORIES

NC...None. SC...None. MARINE...None.