Monday, December 28, 2015

Warning extended to 3pm

Our Winter Storm Warning has been extended to 3:00. So far the precip has tended to the heavy and frozen side, with many if not all locations reporting sleet, freezing rain or a mix. Accumulations are minor but meaningful, with many streets (even busy expressways) covered in a layer of ice/slush. Traffic is slow but volumes are light.

Thankfully the precip will trend toward all rain by late afternoon, with temps rising several degrees. But winds will pick up and that could result in power outages in places with ice accumulations.

Sunday, December 27, 2015

Winter Storm Warning

NWS has just upgraded the whole area (except for far southern areas) to a Winter Storm Warning. This is a marginal storm but it may present some problems tomorrow morning.

Overnight toward dawn an area of snow and freezing rain will spread north. Snow totals will be light (1-3") in a few affected areas, but there could be an accumulation of ice. And is VERY tough to forecast freezing rain. A difference of just 1-2 degrees at the surface could lead to all snow, all freezing rain, or a mix. I think warm lake waters and ground in the city will lead to minimal snow and ice accumulations in the city and most of Cook County. But areas west and north could see meaningful ice as well as some snow. Pre up should switch to rain tomorrow morning into the afternoon, and by the evening commute things look better. Very high winds (40-50 mph) could lead to lakeshore flooding, isolated power outages, and flight delays.

Temps will be seasonal this week -- mostly 20s and 30s, sliding about 10 degrees into the first genuinely wintry air by New Year's Day.

Tuesday, December 22, 2015

Solstice + severe threat

In a truly unusual twist, we're talking about the winter solstice and the threat of severe thunderstorms at the same time. 

We celebrated (or not) the winter solstice last night at 10:48pm local time. We've already had the earliest sunset (Dec. 8th), and even though the sunrise times lag for a little bit (adding three more minutes until Jan. 10th), we'll start to add to each day's length from here. 

Tomorrow we're likely to have our 10th day of 50+ temps in Chicago this December, which is stunning (although the record is 16). Tomorrow could see see highs of 60+ in many locations, nearly 30 degrees above normal and threatening the record high for the day. 

Along with tomorrow's mild temps will come a flood of moisture -- dew points will be in the 50s, so it really will feel like March or April -- and a cold front behind the warm-up will threaten to spawn some strong or even severe thunderstorms. The primary threat is well to our south, and the mid-South could even see a tornado outbreak. Areas here or nearby could still see damaging winds in legitimately severe storms. In any case, high winds are likely along with the rain, so airport delays are possible.

Behind the storms skies will clear and temps will fall but remain ~10 degrees above normal. Both Christmas Eve and Christmas Day look partly to mostly sunny with highs in the low/mid 40s. 

There are no major cold-air outbreaks on the horizon for now. A few long-range models are trying to pick up some cold in the first week of January, but that's too far away to have much reliability. In general, there are no pending signs of a major pattern shift. 









Tuesday, December 1, 2015

snow for morning commute, then mild

A quick burst of snow looks likely late tonight and into the morning commute tomorrow. Accumulations should be fairly minor, but given the timing, during the height of the morning rush, even an inch of snow could have a significant impact on travel times. 

Beyond that, a very mild December pattern is shaping up. Temps are likely to break 50 later this week and into the weekend. No major intrusions of cold air are on the horizon and the month may actually get milder as we go.