Summer-level warmth to take hold in what promises to be the warmest weather to date in 2023

TEMPS TO FLIRT WITH/REACH 80 WEDNESDAY AND THURSDAY—TEMPERATURE DOWNTURN TO ARRIVE THIS WEEKEND

Temperatures this week are to average 14-degrees warmer than last week and an eye-catching 18-degrees above normal. Not since late last September—nearly 7 months ago—have back to back 80-degree temps occurred here. Yet that’s just what may occur this Wednesday and Thursday.
There are several keys to warming this time of year. For one, cloud cover must be limited. There will be some clouds to filter incoming sunlight Tuesday but those clouds back off allowing sunnier, limited cloud coverage Wednesday and Thursday. So we can check that box in terms of warm temps in the days ahead.
Second—and right up there in importance—is producing a strong enough westerly flow to hold the layer of colder, denser air which sits over the STILL COOL WATERS of Lake Michigan which currently average 43.6-degrees. We can check that box too, because a strengthening pressure gradient is to produce a well developing southwesterly wind flow which is to hold any chilly lake air at bay and even push warmth UP TO and OVER AREA beaches. It should get warm enough this week that some who love the beach may lay a towel out and soak up the mid week sunshine Wednesday and Thursday amid temps likely to approach 80-degrees.
A third component to warming has to do with moisture levels in the atmosphere. You want enough moisture limit nighttime cooling YET NOT DEVELOP a cloud cover. Dew points are the best measure of moisture in the air and they are to surge from today’s (Monday’s) 30s to the upper 40s and low 50s by Wednesday and Thursday. That’s HARDLY humid air—but there’s enough moisture to buoy nighttime temps and allow daytime sun to build on the warmer temperatures at the start of the day. Moisture also makes the air feel a bit warmer than would otherwise be the case.

THE WARM-UP HAS ALREADY BEGUN

There’s been a steady upward trend in high temperatures here in Chicago. Friday’s high only made it to 49-degrees. But Saturday warmed to 63 and Sunday made it to 68. We’re likely to see 71-degrees today (Monday) then head for 77 Tuesday, 80 Wednesday and 83 Thursday.
More clouds (though hardly a total overcast) are predicted Friday when temps will reach a STILL ABOVE NORMAL 77, with a 75 likely Saturday. Normal highs this time of year are in the mid and upper 50s—so we’re talking of a week (Tuesday through Saturday) with daytime highs anywhere from 16 to 25-degrees ABOVE NORMAL. Not bad at all!

COOL WEATHER ISN’T COMPLETELY BEHIND US YET

April is a finnicky month when it comes to temps—and we’ll see readings drop off the 50s this coming Monday and Tuesday. And, freezing temps aren’t yet behind us—a fact area gardeners may remember—especially in areas away from the city and Lake Michigan.
While the average last day with a 32-degrees or lower temp since 2000 has been on or about April 17th in the city, the average date for freezing temps (and lower) away from the city has come as late as May 2nd in Wanatah, IN; April 28 in Lowell, IN; April 26th in Rockford; April 23rd in DeKalb and April 21 in Kankakee. And frost can occur even with thermometer-level temperatures (taken approximately 5 ft above the ground) at or just above freezing. So the frost threat can occur even beyond these dates.

NORTHERN LIGHTS WERE OUT AGAIN ACROSS CANADA OVERNIGHT

Check out these satellite images from two of NOAA’s polar orbiters–the NOAA-20 and Suomi-NPP weather satellites. These images have been posted by the folks at CIMSS (the Cooperative Institute for Meteorological Studies) at the University of Wisconsin-Madison. (https://twitter.com/UWCIMSS).
The CIMSS post noted: Ribbon candy Aurora Borealis overnight via NOAA20 and Suomi-NPP. The waning gibbous moon (80%) illuminated cloud tops below for stunning nighttime scenes.

THE TERRIFIC “TORNADO TALK” WEBSITE: TWITTER.COM/TORNADO_TALK

“Tornado Talk” noted that yesterday (Sunday) marked the 70th anniversary of the first tornado detected “hook echo,” recognized as one of the most recognizable radar signatures of a tornadic thunderstorm. The radar image was captured quite by accident on April 9, 1953 just outside Champaign/Urbana by an Illinois state water survey engineer, Donald Staggs.

The first documented association of a HOOK ECHO with the presence of a tornado happened quite by accident and in an era before the national weather radar network operated today by the National Weather Service and in a number of locations by the Department of Defense. As a post on “hook echoes” by Wikipedia recounts:
“This event was unintentionally discovered by Illinois State Water Survey electrical engineer, Donald Staggs. Staggs was repairing and testing an experimental precipitation measurement radar unit when he noticed an unusual radar echo which was associated with a nearby thunderstorm. The unusual echo appeared to be an area of precipitation in the shape of the number six-hence the modern term ‘hook echo’. Staggs chose to record the echo for further analysis by meteorologists. Upon review of the unusual echo data, meteorologists F.A. Huff, H.W. Heiser, and S.G. Bigler determined that a destructive tornado had occurred in the geographical location which corresponded with the ‘six-shaped’ echo seen on radar.
“Prominent severe storm researcher Ted Fujita also documented hook echoes with various supercell thunderstorms which occurred on 9 April 1953—the same day as the Huff et al. discovery.[8] After detailed study of the evolution of hook echoes, Fujita hypothesized that certain strong thunderstorms may be capable of rotation.” READ THE FULL WIKIPEDIA POST ON ‘HOOK ECHOS’ here: https://en.wikipedia.org/wiki/Hook_echo”
Dr. Jim Angel, a personal friend to Tom and for many years our state climatologist in Illinois, posted a wonderful account of that first radar-detected HOOK ECHO on the Illinois State Climatologist website back in April, 2015—and noted the radar there was supposed to have been turned off for repairs—and further referenced a 1954 report out of the Illinois State Water Survey: “It may be possible to establish radar storm warning systems in tornado areas to reduce loss of lives.” The April 9, 1953, event, along with subsequent events, helped provide the push in the US for developing a nationwide network of weather radars.” READ Dr. ANGEL’S FULL ACCOUNT OF THE FIRST “HOOK ECHO” DETECTION AT THE ILLINOIS STATE WATER SURVEY OUTSIDE CHAMPAGN/URBANA: https://stateclimatologist.web.illinois.edu/…/on-this…/
Today, DOPPLER RADARS scan the airspace over the U.S. and have added the crucial capability of scanning the winds within t-storms—a life saving development which enables far more accurate detection and tracking of the winds within t-storms which serve as proxies for tornadoes.