Winter Storm tracks east – significant pattern change ahead

Much cloudier than normal in Chicago

61% of the days have been overcast (0% sunshine) since December 5th
The December – January period is the cloudiest time of the year (average 40% of possible sunshine each month), and this winter it’s been much cloudier than normal. The end of 2022 and the start of 2023 has seen an extended period of cloudiness in Chicago. Since Dec. 5th, 27 of the 44 days have had 0% sunshine. In the Dec. 6-17 period we saw sun on only one day. December had 17 days with 0% sunshine and overall only 30% of possible sunshine.

Thursday’s set-up (18,000-ft Steering-level wind flow)

• Ingredients in place for severe storms over Ohio  – later afternoon/evening hours
  
• Low pressure center aloft with associated short/wave (S/W) moving east – should be over Indiana during afternoon, producing lift/instability over Ohio during peak-heating hours
• 125 mph southwest jet streak ahead of (to the east of) the approaching low pressure will be over Ohio, enhancing additional upward-motion, lift and instability.
•  Afternoon temps at the surface Ohio-wide will be very mild for mid-January in the 50s to lower 60s
• Dew-points will be in the moist 50s.
• A surface low pressure system will be in place with SW winds gusting to 30 mph. 

Weather pattern Outlook
Upper-level 30,000-ft Jet stream flow and low-level/surface temp distribution

• Huge Ridging of high pressure over U.S./Canadian west coast – No “Atmospheric River.”
• Storm systems steered into Canada.
• Broad trough of low pressure over much of Canada into central U.S.
• Bitter Cold Arctic Air still holds over northernmost Canada.
• Primary Jet stream flow west-east well to the south of Chicago
• Main storm track to our south.
• Chicago positioned in southern portion of more “Seasonably Cool” air – closer to “normal”.
• Better Chances of Snow as opposed to rain.

Winter Storm Thursday – Friday

Low pressure will track east out of northern Illinois through southern Lower Michigan into New York Thursday – Friday laying out a band of heavy snow to the north of the low pressure. Severe storms may develop over Ohio later Thursday afternoon/evening. Widespread rains to the south of the low track.

Some heavy snow reports (inches) as of 6 PM Wednesday

23.0” Callaway, NE
22.0” Merna, NE
22.0” Anselmo, NE
19.0” Broken Bow, NE
17.0” Stapleton, NE
15.5” Oconto, NE
12.0” Burns, WY
11.0” Veteran, WY
12.5” Manila Village, CO
12.0” Elizabeth, CO

More than a dozen states under winter weather advisories

Latest weather hazards as of Wednesday evening

Thursday Precipitation

Thursday to begin quiet as Wednesday night rains exit the area—but new round of showers then potentially snow showers due as colder air hits.

Next weather system to bring potentially accumulating snow Sunday

The month of January has only seen 0.4” thus far but current modeling suggest a 70-80% chance of doubling that amount. Snowfall probability of seeing 1” or more of snow late Saturday night/Sunday shown in the map below.

Pattern change next week to bring the coldest weather in over a month.
FULL DAY TEMPERATURE DEPARTURES FROM NORMAL