Monitoring possible significant winter storm;

FAR AND AWAY—The weather system of greatest potential concern is a potential winter storm, still indicated as likely to sweep into the Midwest early next week—its precipitation reaching Chicago in the Monday night, Tuesday and Tuesday night time frame.  The storm has been establishing near record low barometric pressure readings in sections of southwest Alaska and the northern Gulf of Alaska—where it produced a central barometric pressure of 942 mb (27.81″).  With a 165 mph jet stream involved in its development overhead and surface winds gusting past 60 mph on sections of the southwest Alaska coastline, it’s a formidable system.  

Models are still taking it south across the U.S. Rockies and positioning over eastern Colorado, northeast New Mexico, and the Texas and Oklahoma panhandle by the close of this weekend.  From there, the storm—with a huge precip shield and strong winds that will build into Chicago by Tuesday—is to lift northeastward. Early model guidance, with a projected storm track suggesting a potentially significant band of snow could set up in areas close to Chicago if not involving Chicago, make this a storm potential to monitor.

IT IS FAR TOO EARLY FOR ANY STORM-RELATED WATCHES, WARNINGS OR ADVISORIES—AND WELL AHEAD OF THE PRODUCTION OF RELIABLE SNOW ESTIMATES.  All are days away if they become necessary at all.  But the consistency of model forecasts in producing what could be the most significant system of a winter season which has completely lacked storms of this intensity suggests we have some potentially challenging winter weather coming into parts of the Midwest next week.

Potential for significant winter storm remains elevated

The potential continues—At this distance in time from this system’s projected arrival, refinements/changes in the forecast scenario are still quite possible

Model forecasts—including ensemble versions of the various models, which involve running scores of forecasts generated by feeding several interpretations of observations that are used to describe the initial state of the atmosphere—continue to indicate a winter storm potential early next week for the central U.S.

HERE ARE FORECAST PANELS from three ensemble models–the National Weather Service’s “GEFS”, Environment Canada’s CMC ensemble and the European Centre’s EPS ensemble. Ensemble projections cut down on run to run forecast swings and offer an average of the range in each model’s collection of forecasts and for that reason help reconcile huge run to run forecast varitations.

What’s being depicted is a storm system which warrants monitoring and may well be the most prolific precip producer of the 2023-24 winter season to date.

NOTE:–and this is important: IT’S STILL FAR TOO EARLY for reliable snowfall projections to be issued. Models generate snow forecasts, but at this early hour, much refinement is necessary and specific forecasts won’t be available for days.

What is clear, from the forecast guidance we’re receiving at this point, is that weather issues may threaten a broad region of the CENTRAL U.S. next week–and, in Chicago, the period from Monday night through Tuesday and well into Tuesday night is the focus of our attention at the moment. This window may shift as newer data arrives in coming days.

This system is MANY DAYS AWAY and this introduces uncertainty on the exact placement of its most potent weather features. Studies and experience indicate SNOWFALL ACCUMULATION FORECAST issued at this distance in time are UNRELIABLE. What can be done is a general indication of the large area within which future forecasts may require watches or warnings–and for which future forecasts are likely to focus when reliable accumulation projections become available.

INTERESTING NOT ON THIS 6 PM MONDAY UPPER AIR FCST off the NWS GEFS model. Evident here is what’s referred to as the Uccellini-Kocin coupled jet streak feature. This is where wind maxima in 2 different jet streams are positioned to produce MAXIMUM LIFT of incoming moist air. This sort of feature supports storm development. But given the distance this is predicted to occur in the future, modifications of this forecast can occur. So, while impressive now–future projections will have to be monitored to see if the reasoning on the jet stream’s projected structure remains intact.

Lack of seasonal snowfall to date

Check out the plot of seasonal snow tallies since the late 1950s as measured at Chicago O’Hare.

How much less snow has occurred across the Lower 48 compared to the most recent 15-year average?

Seasonal snow departures from 15 year mean:

MEASURABLE ICE AND SNOW PROBABILITY from the NWS Weather Prediction Center for the 24 hour period from 6am CST Monday to 6am CST Tuesday.

‘Crazy warm’ this past December

IT WAS CRAZY WARM HERE IN CHICAGO DURING DECEMBER, 2023 WHERE WE RECORDED ONLY TWO OF THE 31 DAYS WITH A “BELOW NORMAL” TEMP–BUT WE WEREN’T ALONE IN THE LOWER 48 WITH THE “WARMTH

Chicago concluded December, 2023 with an average of 39-degrees—an eye-catching 8.5-degrees above normal.

However, WE WERE NOT ALONE IN THE LOWER 48 WITH OUR DECEMBER, 2023 “WARMTH” reports NWS climatologist and climate analytical guru Dr. Brian Brettschneider who points out SUB-32-degree temps across the Lower 48 were reported, according to an analysis of PRISM temp data, over just 20 to 23% of the country—”….a full 10% lower than any other year,” reports Brettschneider.

Percent of Contiguous U.S. with a December temp of 32°F or less:

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