textproduct: Wilmington

WHAT HAS CHANGED

Slight increase to snow chances Sat/Sun.

KEY MESSAGES

1) Light precipitation and gusty winds expected Wednesday.

2) Very cold conditions expected Friday through early next week, with snow possible Saturday into Sunday.

DISCUSSION

KEY MESSAGE 1) Light precipitation and gusty winds expected Wednesday.

Surface high pressure currently over the region will move to the east tonight and into Wednesday. There will be a tightening pressure gradient on the back side of the surface high, as a weak area of low pressure also moves east through the lower peninsula of Michigan. In warm advection flow, wind gusts of 20-30 knots appear likely, with at least some chance of getting a few gusts to 35 knots, especially in the northern CWA.

While moisture will be lacking, forcing associated with a shortwave and right entrance region of a jet streak will eventually lead to boundary layer saturation and precipitation. While much of this will be in the form of snow, temperatures will probably be warm enough for rain to mix in across parts of the CWA, particularly the south and southeast. Overall precipitation amounts are fairly light across the suite of models, suggesting little if any snow accumulation will occur. The depth of the moisture is limited, and does not coincide with the DGZ.

Later Wednesday night, most of the forcing will be moving east, but low-level moisture and a mixed boundary layer may keep chances for light precipitation going for a while. This forecast will at least keep flurries in for part of the area through evening and into the overnight. There is definitely a chance that flurries or light snow showers could continue later in time than what is currently indicated in the forecast, possibly into Thursday morning. As a cold front moves into the area, there is also a chance for some additional gusty winds Wednesday night into Thursday morning.

KEY MESSAGE 2) Very cold conditions expected Friday through early next week, with snow possible Saturday into Sunday.

There is high confidence in another period of very cold temperatures from Friday through Monday of next week, although confidence is lower in the exact magnitude of the cold, and whether Cold Weather Advisory criteria will be met. Regardless of specific values, this will be another several-day period with temperatures well below normal, with low temperatures in the single digits, and highs that will remain well below freezing. From a synoptic standpoint, the coldest temperatures appear likely to be Friday night / Saturday morning. Temperatures could end up colder than currently forecast for later days, depending on snow cover after the Saturday night system.

The snow forecast with the Saturday night system remains low confidence for the ILN CWA, which will be on the northern end of the precipitation footprint associated with this system. With that said, confidence is fairly high that some snow will occur -- virtually all guidance brings accumulating snow to much (if not all) of the ILN CWA, and the cold temperatures mean that the p-type is settled. Looking at the array of GEFS members, it is interesting to note that the 12Z deterministic GFS is a massive outlier to the south and keeps much of the ILN CWA dry, while there is at least some snow on virtually every other member. Thus, the deterministic GFS does not seem like a reasonable solution at this time. With that said, the spread in ensemble guidance remains very high, reflecting the uncertainty in how far north the plume of moisture will be able to make it, and perhaps also dependent on the degree of amplification of the upper pattern over the Ohio Valley. Given that this snowfall is out on Day 5 into Day 6, forecast uncertainty is expected and normal. PoPs for snow have been increased through this time period, but still appears too early to discuss specific amounts based on the confidence level at this phase of the forecast process.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

VFR conditions are expected today, with some high clouds moving in later in the afternoon and evening. WSW winds will generally be around 10 knots, though up to 15 knots at times.

Overnight, LLWS will enter the forecast for all TAF sites. Conditions will remain VFR.

Tomorrow, winds out of the SSW will strengthen, with gusts of 20-25 knots likely, and possibly up to 30 knots. By mid to late morning, some light snow will be possible at all TAF sites, but coverage and magnitude of the snow is somewhat uncertain. This will be handled by a PROB30 for now, with MVFR conditions associated. It is also possible that instead of snow, some light rain could occur instead. Regardless, ceiling are expected to lower to MVFR by around 18Z.

OUTLOOK...MVFR to IFR conditions are expected Wednesday afternoon through Thursday morning. There is a chance of snow Saturday night and Sunday, and if snow occurs, IFR conditions would be likely.

ILN WATCHES/WARNINGS/ADVISORIES

OH...None. KY...None. IN...None.