Significant Rain and Snow Forecast for Northern Illinois on Wednesday and Thursday; Track Uncertain

We Might Get it All: Significant Rain, Freezing Rain, Significant Snow

UPDATE …

Winter Storm Watch Late Wednesday Night to Early Thursday Evening

Significant rainfall and snowfall is forecast for Arlington Heights and surrounding communities Wednesday February 16, 2022 and Thursday, respectively with the hourly forecast indicating …

0.80 inches of rain from noon Wednesday until 3 AM Thursday,

0.01 inches of freezing rain from 3 AM to 4 AM Thursday, and

5.20 inches of snow from 3 AM to 9 PM Thursday.

First here is a detailed look at Tuesday’s setup. A Surface Ridge will move east today allowing for gradually increasing southeasterly winds Tuesday. Winds will start out almost calm but will peak with gusts to about 40 MPH tonight, when a very strong low level and associated Warm Air Advection will develop in response to strong height from Manitoba south across the central U.S.

The NWS Office Chicago office still anticipates rising temperatures tonight, which should aid in lessening the boundary layer stability somewhat, and allow for at least a little bit of the stronger momentum air associated with vigorous low level jet to transport to the surface in wind gusts tonight. By mid- to late-evening, expecting at least occasional gusts over 30 mph, probably strongest in the Chicago area aided a bit by milder temps in the urban corridor.

Early morning temps as high as 45°F at midnight should set the stage for highs at 50°F or in the 50s across the County Warning Area. Rain timing looks a bit later than earlier runs and have nudged Probability of Precipitation slower accordingly. The later arriving rain and temps on the warmer end of the guidance spectrum should allow for strong wind gusts in the 30 MPH range to continue Wednesday. Confidence a little low on magnitude of gusts due to expected cloud cover, but 30 to 40 mph gusts seems attainable if temps warm into the 50s as forecast.

RAINFALL

According to the NWS Chicago, there is a heavy rainfall and flood threat Wednesday night. The heavy rainfall threat Wednesday night into Thursday morning exists far southeast in the County Warning Area. Guidance is still in good agreement in PWATs (precipitable water or “rain”) over an inch (nearly 300% of normal) pooling ahead of the slow moving cold front. The extreme moisture for this time of year combined with strong and deep forcing associated with coupled upper level jet structure and strong low level jet replenishing moisture all suggests an anomalous heavy rainfall event.

There is still a bit of uncertainty regarding where the axis of heaviest rain will set up. In addition to the expected heavy rainfall, frozen ground, expected snow melt, clogged drainage due to snow and ice, and river ice all will contribute to an elevated flood risk if forecasted rainfall materializes as expected.

Map shows snow cover and GFS data. Tap an area to get forecast model inches of snow depth (new snow) for specific areas. The 8:00 a.m. Tuesday look at the GFS showed 10″ accumulation for Arlington Heights for the upcoming storm Wednesday and Thursday.

WINTER STORM THREAT

A Winter Storm Watch has not been activated by the NWS Chicago because there is still rather large variance among the guidance members in the outcome for Thursday with respect to magnitude and placement of heavier snowfall amounts.

The GFS (United States) model for the track is considerably further north compared to the ECMWF (European) model.

Concerns and Confidence:

A period of freezing rain and some sleet near and north of I-80 after the rain later Wednesday night: Confidence is high in occurrence but lower confidence in exact amounts. Latest trends suggest less than 1/10″ ice accumulation though would still anticipate slick road travel impacts.

Accumulating snow and wind late Wednesday night and Thursday, but primarily on Thursday: High confidence in a swath of several inches of snow occurring within the CWA, but low confidence in top end amounts and exactly where the swath of heavier totals will occur. High confidence in at least 30-35 mph wind gusts with the wintry precipitation on Thursday, but lower confidence in top end gust magnitude, which will be dictated by exact strength and track of the surface low to our south.

Precipitation type trends for southern sections south of I-80 on Thursday: High confidence in freezing rain and at least some sleet in these areas, though low confidence in duration and timing of precipitation type changeover, including to snow. This will also be affected by the exact strength and track of the surface low pressure to our south.

Regarding the above items of Concerns and Confidence, unfortunately despite addition of better Radiosonde Observation (Upper-Air Observation or RAOB) sampling of the key primary short-wave, the model guidance stayed generally in their respective camps that had been established the past few/several cycles

GFS/GEFS/NAM stronger, deeper (track targeting Chicagoland),

ECMWF middle ground with track targeting Central Illinois (though with notable variance in ensemble members that is discussed below), and

Canadian and UKMET though Canadian ensemble/GEPS with a farther south track (but did show evidence of a shift).

The initial part of the forecast, transition from the warmth and rain to freezing rain and some sleet, is less affected by the lingering variance in the model camps, but the National Centers for Environmental Prediction (NCEP) guidance (especially GFS/GEFS) with its slightly more amplified ridging downstream of southern track short-wave does result in a bit slower precipitation-type (p-type)transition and warm nose aloft lingering longer while being undercut from shallow low level Arctic air as surface boundary sags south. NWS Chicago opted to maintain the consensus approach in the forecast and gridded database, for north to south p-type transition. Duration of freezing rain as primary p-type may be rather short, on the order of 2-3 hours with northward extent as sufficiently cold air aloft for snow catches up to the pace of boundary layer cooling.

Following Wednesday and Wednesday night’s much longer duration of well-above freezing temperatures and dew points, plus several hours of plain rain, and moderate precipitation intensity during freezing rain, suggests less efficient snowfall accretion rates. On the other hand, the rain may wash away road treatments, according to the NWS Chicago office. All in all, not looking at a significant icing threat here for north (or northwest) half of County Warning Area, but even absent the Thursday wildcard, the NWS Chicago office anticipates an advisory with a glaze to locally upwards of 1/10″ ice accumulation.

Now, what about the snow on Thursday? First, it is quite remarkable how consistent the GFS/GEFS has been in maintaining a stronger, more amplified solution with the synoptic system, demarcating the northwest side of the guidance envelope. The NAM has more or less been along the lines of most of the GFS suite members, though appeared to be a bit of a slow outlier at 00z (6:00 PM CT), albeit with a slight slowing trend noted overall.

The ECMWF continued, as noted above, to hold in its “middle ground” solution, while the other commonly cited operational models held farther south (with northward shifts since 24-hours ago). The differences appear to be tied to the handling of the currently impressive looking water vapor imagery with mid-level short-wave trough digging south-southeast across northern California. In short, the NCEP suite is insistent upon this wave emerging more negatively tilted out of the southern Plains and better coupling/phasing of northern stream and southern stream jet streaks. This causes the notably stronger surface low tracking north of the Ohio River. While it would be tempting to assume consistency = accuracy, the same could be said for consistently slightly weaker and farther south surface low on ECMWF.

So it looks as though a Chicagoland track or a Central Illinois track are both still in the running. Somebody’s going to get a lot of snow between Champaign, Illinois and Kenosha, Wisconsin. How’s that?

While the primary southern track wave will be headed into more confluent flow from encroaching northern stream wave and thus casting some doubt on the highly amplified GFS operational solutions, the general guidance shift has been toward that supporting a sub 1000 mb surface low tracking north of the Ohio River. According to the NWS Chicago, there is increasing support for members northwest of the mean and operational on both ECMWF and Canadian suites. Thus, all in all, we may be headed for a relative compromise type solution, though one with an impactful swath of snow in the County Wide Area.

Copious moisture availability in the developing TROWAL (“tongue” of relatively warm/moist air aloft) and strong baroclinic zone favoring stout lower and mid-level f-gen (frontogenesis) circulation points toward potential/likelihood for a 6″+ swath of snow in the area, though it could be fairly narrow and thus tougher to pin down. The likelihood of mesoscale banding, favorable upper jet placement (right entrance and left exit), and steep lapse rates in the Dendritic Growth Zone (DGZ) all point toward heavy snowfall rates in reasonably strong synoptic system scenario. The NWS Chicago deterministic forecast is playing the more conservative route to give some deference to the lingering uncertainty. It actually ends up fairly close to the very consistent ECMWF (EPS) ensemble mean position of the snow swath. The NWS Chicago office is hoping to see better agreement in the guidance today (Tuesday, February 15, 2022), enough where watch issuance may be a more confident prospect to entertain.

Finally, the NWS Office indicated a few more items tied to the overall uncertainty:

1) the strong northerly wind likelihood in this set-up, and

2) the lingering mixed precip threat southern/southeastern sections.

These items will be directly influenced by exact track and strength of the surface low, which is not yet pinned down as NWS Chicago has extensively detailed above. However, setup of 1035 mb high to the northwest and 990-1000 mb low north of the Ohio River is classic for at least 30-35 mph northerly gusts (and associated blowing/drifting potential). Additionally, top end magnitude ranges from 30-35 mph to possibly 40-45+ mph. Freezing rain and sleet would hold on longer southeast in stronger surface low with farther north warm nose, but transition to snow quicker in the opposite case – sleet duration could be noteworthy in stronger surface low scenario.

Weather Radar shows

orRADARclear

Weather Radar in northeast Illinois was clear at 7:20 a.m.

 O’HARE FORECAST … 

Today: Partly sunny, with a high near 37. Southeast wind 5 to 10 mph increasing to 10 to 15 mph in the afternoon. Winds could gust as high as 25 mph.

Tonight: Mostly cloudy, with a temperature rising to around 45 by midnight. Breezy, with a south southwest wind 15 to 25 mph, with gusts as high as 40 mph.

Wednesday: Showers likely, mainly after 3pm. Cloudy, with a high near 51. Breezy, with a south southwest wind 20 to 25 mph, with gusts as high as 40 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday Night: Rain, possibly mixed with snow and sleet before 4am, then snow and sleet, possibly mixed with freezing rain between 4am and 5am, then snow after 5am. Low around 29. Blustery, with a south southwest wind 15 to 20 mph becoming north northeast after midnight. Winds could gust as high as 30 mph. Chance of precipitation is 90%. Little or no ice accumulation expected. New snow and sleet accumulation of less than a half inch possible.

Thursday: Snow. High near 30. Blustery, with a north wind 20 to 25 mph, with gusts as high as 35 mph. Chance of precipitation is 90%.

Thursday Night: A 30 percent chance of snow before midnight. Partly cloudy, with a low around 8. Blustery.

Friday: Mostly sunny, with a high near 24.

Friday Night: Partly cloudy, with a low around 18.

Saturday: Sunny, with a high near 29.

Saturday Night: Partly cloudy, with a low around 22.

Sunday: Sunny, with a high near 44.

Sunday Night: Partly cloudy, with a low around 35.

Washington’s Birthday: Partly sunny, with a high near 44.

 LAKE TEMPS … 

SOUTHERN LAKE MICHIGAN WATER TEMPERATURES
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
903 AM CST Mon Feb 14 2022

LAKE MICHIGAN WATER TEMPERATURES…

CHICAGO SHORE………33.

CHICAGO CRIB……….32.

MICHIGAN CITY……….33.

&&

M IS FOR MISSING DATA THAT IS NORMALLY AVAILABLE.

THE MICHIGAN CITY WATER TEMPERATURE SENSOR IS LOCATED AT A WATER
INTAKE ONE MILE OFFSHORE AND 60 FEET BELOW WATER SURFACE. IT IS READ
EVERY DAY OF THE YEAR.

february.chicagoweatherstation.com

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Ryan Hall, Y’all Forecast published Feb. 14, 2022 …

Big US outlook that includes very Dynamic Storm that will bring damaging winds, nocturnal tornadoes, rain, ice, and heavy snow, according to Ryan Hall. He thinks the NAM makes the most sense. YouTube Tips ⓘ