textproduct: Wilmington

WHAT HAS CHANGED

Issued cold weather advisory in northwest CWA for Friday morning.

Snowfall amounts slightly increased for weekend system.

KEY MESSAGES

1) Cold weather advisory in effect for Friday morning.

2) A significant winter storm this weekend will bring heavy accumulations of snowfall, with impacts to travel expected to continue through Monday.

3) Cold temperatures are expected through the weekend and especially early next week.

DISCUSSION

KEY MESSAGE 1) Cold weather advisory in effect for Friday morning.

Apparent temperature below -10 Friday morning in northwest 1/4 of CWA. While temperatures remain fairly steady, wind will decrease in the afternoon, pushing apparent temperatures above advisory criteria of -10. Across the region, falling temperatures Friday morning with little if any recovery occurring in the early afternoon.

KEY MESSAGE 2) A significant winter storm this weekend will bring heavy accumulations of snowfall, with impacts to travel expected to continue through Monday.

Although there is still uncertainty regarding some of the specifics, all signs continue to point to a significant winter storm affecting the region this weekend, with impacts continuing into early next week.

What is most clear is that an extended period of wintry precipitation will occur from Saturday afternoon through early Monday morning. The heaviest precipitation is expected to occur Saturday night through mid-day Sunday. Snowfall forecast amounts have increased slightly during this forecast cycle from the previous forecast overnight, and the official ILN forecast reflects this with about a 1" increase across the forecast area. Heavy snow of this magnitude will create significant travel problems, particularly Sunday into Monday, and the very cold temperatures will exacerbate impacts as snow will be difficult to clear.

Two sources of uncertainty:

1) Some models suggest the initial wave on Saturday afternoon will be somewhat light, perhaps with a lull before snow becomes heavier to the north of the surface low track overnight into Sunday morning. If this occurs, it could reduce the final snow amounts by an inch or two.

2) The bigger issue is the potential for warm air aloft cutting down on snow ratios, or even mixing some sleet/FZRA into the area. This is not an uncommon scenario for the middle Ohio Valley, and there has been a trend toward some mixed precip getting into the southern ILN CWA Sunday morning on some of the model guidance. Forecast soundings suggest that the deep saturated layer will, in large part, be quite a bit warmer than the DGZ. Even if no mixed precipitation occurs, profiles like this will not support efficient snowfall production. If mixed precipitation does occur, then overall snowfall totals will be lower. The nature of the snow may change through the event, with fluffier / higher ratio snow Saturday into Saturday night, then slightly heavier snow (or possibly mixed precip) Sunday morning, then back to fluffier / higher ratio snow later Sunday into Monday morning as the precipitation gradually tapers off.

Regardless of the details mentioned above, there will still be a lengthy period of snowfall, which should easily meet warning level impacts for most if not all of the ILN CWA. It is fair to note that there are indications some locations in the ILN area could receive as much as a foot of snow. While events of that magnitude are rare, snowfall totals that high are absolutely in the realm of possibility with this storm.

KEY MESSAGE 3) Cold temperatures are expected through the weekend and especially early next week.

Frigid temperatures will combine with winds of around 10kts to create dangerous wind chills through Tuesday. This will be a lengthy period of time in which temperatures will remain below freezing, and wind chills (particularly in the morning hours) will be well below zero. With an expected snow pack and clearing skies, min temps on Tuesday morning are now expected to be the coldest, with much if not all of the forecast area going below zero in terms of raw temperature. Wind chills Tuesday morning may be as low as -10F to -20F.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

VFR conditions will continue through the TAF period. Steady winds from the west to southwest will become northwesterly late tonight into Friday morning behind a dry arctic cold front. OUTLOOK...Snow with IFR or lower visibility likely Saturday afternoon through Sunday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Cold Weather Advisory from 6 AM to noon EST Friday for OHZ026-034- 035-042>044. Winter Storm Watch from Saturday morning through late Sunday night for OHZ026-034-035-042>046-051>056-060>065-070>074-077>082-088. KY...Winter Storm Watch from Saturday morning through late Sunday night for KYZ089>100. IN...Cold Weather Advisory from 6 AM to noon EST Friday for INZ050. Winter Storm Watch from Saturday morning through late Sunday night for INZ050-058-059-066-073>075-080.