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April-level warmth brings severe weather, but cooler pattern taking shape.

Thursday was the WARMEST DAY since the 59-degree reading 45 days ago on Christmas Day here in Chicago. The high hit 59° at O’Hare and touched 60° at Midway—and this warmth occurred amid wind gusts which topped 40 mph in parts of the area.

  • This marks the 18th consecutive day of ABOVE NORMAL TEMPS
  • This winter has seen a 5 to 1 ratio of warmer than normal versus colder than normal temps. That is to say—THIS HAS BEEN A COMPARATIVELY WARM WINTE  TO DATE OVERALL.
  • The 59-degree high is the warmest Feb. 8 reading here since a 60-degree high on this date.
  • Thursday’s high equals the normal high temp in Chicago in mid-April and comes 6 days ahead of the average first date for a 59-degree high which in the most recent 30-year period has been on or about Feb 15th.
  • This day’s average temp is to come in an eye-catching 24 degrees above normal and pushes the opening 8 days of February to a level more than 14 degrees above normal and 13 degrees warmer than the same period in February a year ago.

Thursday’s strong winds were the product of a vertical “stacking” of strong “SSW” winds through the atmosphere—and the gusty winds aren’t going away—this set-up continues Friday

Mild temps also continue, though some cooling is to occur this weekend. The warmth is to push this week’s average weekly Chicago temp to more than 20 degrees above normal.  By comparison, a modestly, but noticeably, colder weather regime takes hold this weekend and next week with the average weekly temp slipping nearly 15 degrees. That means instead of the mid-40 to upper 50-degree highs which have dominated this week, next week’s high temps will fall back to the mid-30s to low 40s.

April-level temps and a powerhouse jet stream ingredients for severe weather Thursday evening

We’re keeping an eye on a weather system lifting northeastward out of Texas and expected to clip sections of the Midwest with some potential snow or a wintry mix in the Monday/Monday night time frame. 

The set of ensemble models we track closely has the system in question tracking a bit farther south which would keep early week precipitation south of Chicago—affecting downstate sections of Indiana and Illinois.  But, we’ll keep an eye on that.

Also of interesting, Weather Service forecasters are cautioning another atmospheric river system may head toward the West Coast next week. That could mean more rain and heavy high elevation snows. That too will be interesting to monitor.

Long-range forecasters at the Weather Service’s Climate Prediction Center issued a forecast that the current El Niño is likely to come to an end in the April to June time frame

The pattern will be switching first to an ENSO NEUTRAL mode and then transitioning (given a 55% chance of occurring) to the LA NIÑA MODE in the June through August time frame. This is interesting because La Niñas can impact the Atlantic Basin hurricane season, enhancing storm formation.  It will be interesting to see how this development is assessed by tropical forecasters who will issue their outlook for the Atlantic Basin hurricane season later this spring.

La Niña refers to persistent colder-than-normal sea surface temperature anomalies across the central and eastern equatorial Pacific. La Niña typically brings cooler-than-average temperatures to the northern parts of the Midwest, while the southern regions may experience warmer and drier conditions.

During La Niña years, the upper Midwest and Great Lakes regions typically experience above-average snowfall, while the lower Midwest tends to have near-average snowfall. Negative effects commonly linked with La Niña include higher heating costs and increased snow removal efforts.

THE UPPER AIR FORECAST depicts steering winds aloft at roughly the 18,000 ft. level—what meteorologists refer to at the 500 millibar level—guiding weather movement. The building of warmth over Greenland next week is to buckle the jet stream and produce a wind flow from the northwest into the Midwest from Canada, reducing temps here in Chicago

At present, there are NO INDICATIONS the cooling will be as harsh as the arctic blast which swept into Chicago and the Midwest two weeks ago. But our current estimate, based on my in-house assessment of model forecasts, suggest next week could average close to 10-deg colder than the average temp this week. That will produce noticeable cooling. The 50-deg temps of coming days—possibly a near 60 in parts of the area Thursday—should fall back to the 30s next week.

You can see the predicted cooling indicated in the latest 6 to 10 and 8 to 14-day TEMP TREND FORECASTS out of the National Weather Service’s Climate Prediction Center.

While average temps will be cooler–though still above average in the 6 to 10-day period which occurs next week.

Temps are predicted to FALL BACK to near or below normal over a wide swath of the Lower 48 in the 8 to 14-day time range which reaches from Wednesday next week into the opening days of the following week.

The Arctic Oscillation (AO) involves a fluctuation in atmospheric pressure between the Arctic and the mid-latitudes of the North Pacific and North Atlantic. A strongly positive AO leads to a strong mid-latitude jet stream, directing storms northward and diminishing cold air incursions in the mid-latitudes. When the AO is strongly negative, a weaker jet dips farther south, allowing Arctic air to spill into the mid-latitudes.

Another key indicator is the predicted NORTH ATLANTIC OSCILLATION INDEX—which also goes “negative” and suggests a reversion to upper winds which sweep into the Midwest from Canada—also a COLD SIGNAL for the Midwest.

Predicted TEMP DEPARTURES over the coming 5 days (through Sunday morning) showing temps which average WELL ABOVE NORMAL:

This 5 to 10 day TEMP DEPARTURE FORECAST which runs from this Sunday through next Friday shows ABOVE NORMAL TEMPS–but the degree of warmth decreases from the preceding 5 days:

FINALLY, looking out 10 to 15 DAYS shows the region of ABOVE NORMAL TEMPS over the Midwest shrinks precipitously–underscoring the colder weather regime expected to take cold in the period from a week from this Friday into the following week.

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