FROST ADVISORY OUT AGAIN Wednesday Night—BRIEF SURGE IN TEMPS DUE THURSDAY–TEMPS HEADED 12° HIGHER—BUT WITH COOLING SHORELINE LAKE BREEZES.

Chicagoans shivered through the 2nd chilliest night of April overnight with a 31-deg low at O’Hare (34 Midway)–but inland readings as low as 24 at Richmond in McHenry County Wed morning and 25-deg lows at McHenry, Sugar Grove and Pell Lake, WI and widespread mid to upper 20s away from the city and in northwest Indiana.

Another Frosty Night Overnight Wednesday

Limited cloud cover and light winds favor another night of freezing temps many area promoting frost development tonight—thus A FROST ADVISORY is out across the Greater Chicago area in all but lakeside areas of Cook County.

Thursday afternoon temperature outlook—mildest weather in a week across the Chicago metro for areas away from Lake Michigan  

Thursday sees a 12-degree temp rebound and the first 60+ degree highs here since last Friday. But its a temporary reprieve and the day as a whole will post another temp deficit given its chilly morning start.

4PM TEMPERATURE SNAPSHOT—mid 60s likely for inland locations: 

How much warmer than the same period Wednesday afternoon :

Thursday Night-Friday Morning Rain

NORTHEASTBOUND TEXAS DISTURBANCE TO SWIPE PARTS OF THE CHICAGO AREA WITH SOME THURSDAY NIGHT/FRIDAY MORNING RAIN—MODELING CONTINUES TO PREDICT COLD UPPER LOW PRESSURE SPINNING UP OVER MID-US THIS WEEKEND PRODUCING TEMP-SUPPRESSING CLOUD COVER AND INSTABILITY SHOWERS–SOME MIXED SMALL HAILSTONES AGAIN SUNDAY/MONDAY

While showers are likely at some point many of the coming seven days, the total amount of rain is likely to be 0.50” or less for most of the area—heaviest totals likely in sections of Indiana, Michigan and Ohio.

PARTS OF THE AREA TO BE SWIPED WITH SOME SHOWERS LATE THU NIGHT INTO FRIDAY–BUT DEVELOPMENT OF A COLD UPPER LOW ACROSS THE MIDWEST THIS WEEKEND INTO NEXT WEEK IS THE BIGGER WEATHER STORY

More clouds sweep in later Thursday and Friday as a disturbance lifts out of Texas, swiping parts of the area–particularly southern sections of the metro area— with some rain later Thu night into Friday morning. The east winds on its north side will keep breezes off the lake and limit Friday warming as a result

Powerful 165 jet stream levels winds have swept off the Gulf of Alaska into British Columbia in Canada and will now dive south into the Plains, spinning up an upper air low pressure which bodes poorly for any warming this weekend into early next week.

While weekend temps this Saturday and Sunday will be a modest 7-deg milder than last week–with its March-like daytime 40s—the developing cold pool and upper low promise a good deal of cloudiness and the same sort of unstable atmosphere that promoted lots of clouds and scattered instability showers last weekend. And also like last weekend, sub-freezing cloud level temps by Sunday and Monday suggest small hailstones may make it down to the ground with some of the showers then.

TEMPS TO REMAIN BELOW NORMAL IN THE COMING 2 WEEKS

Temps are to post a modest rebound into the 60s later next week. But readings are still to come in 1 to 5-deg below normal as models now suggest another push of cooler air by the weekend to follow next week may restrain warming.

Chicago Warm Spells in the Month of May

DESPITE THE CURRENT CHILL—CHICAGO WEATHER HISTORY TELLS WARM SPELLS INCREASE IN MAY

A review of Chicago’s May temps over the past 81 years (May begins in just 4 days—next Monday) highlight increased chances for warm spells. Mays are rarely uniformly warm. But May temps since 1942—when Midway Airport became the city’s official observation site; O’Hare became official in 1980—all but guarantee one or more 80-degree highs before the month is out. In fact, 99% of Mays since 1942 have recorded an 80-degree or warmer temp; 85 deg highs have occurred at some point in 90% of Mays and even 90-degree readings can be part of Chicago’s weather scene having occurred in the city 40 of the past 81 Mays.

Warmth may not be continuous–but climatology is clear—warmer weather becomes more frequent. What’s more, we pick up another 70 minutes of daylight by May’s close–added to the 4 hours and 41 minutes of daylight we’ve added since our shortest day back on Dec 21.

VIEW SLIDESHOW of the Current Weather Developments:

  • FROST & FREEZE WARNINGS are in effect Wednesday and early Thursday over a wide swath of the Midwest.
  • This plot of temps mid-Wed afternoon shows 60s to Chicago’s west—warmth which will temporarily boost Chicago temps Thursday.
  • Here’s how temps through mid Wed afternoon have increased compared to 24 hours ago.
  • The highlighted area is an area in which UPPER WINDS are strong. Morning upper air observations showed a 165 mph jet stream wind max sweeping toward the British Columbia, Canada coast. It’s those winds which are going to dive into the nation’s mid-section spinning up a slow moving upper air low pressure–a harbinger of more clouds and showers this weekend into the opening days next week
  • Surface winds Wednesday are shown blowing off Lake Michigan–a flow which reinforced Wed’s chilly daytime temps.
  • Watch the wind max sweeping into western North America from the Gulf of Alaska. The winds are blowing within the orange and red shaded area coming across the British Columbia and Washington State region.
  • THIS FORECAST 34,000 FT. FLOW PATTERN shows those strong upper winds proceeding into the northern Rockies Thursday….
  • then into Wyoming and Colorado Friday morning initiated UPPER LOW PRESSURE FORMATION which is to dominate Chicago’s weather over the weekend and into the opening days of next week.
  • HERE’S AN ANALYSIS of UPPER AIR CONDITIONS at 7am CDT Wed morning from Environment Canada.
  • If you look at the stippled area coming into the British Columbia coast Wed morning, you see a 143 kt. wind max (the equivalent of 165 mph) at the 34,000 ft. level.
  • WATCH THIS SEQUENCE OF FORECAST UPPER AIR PANELS which lay out the development of a slow-moving COLD POOL/UPPER AIR LOW PRESSURE ALOFT. This panel is for 7am CDT Friday
  • 7am CDT Saturday morning forecast
  • 7pm Saturday evening UPPER AIR FORECAST
  • 1pm CDT Sunday UPPER AIR FORECAST
  • Upper lows are home to a good deal of cloudiness and to instability showers, some of which could be mixed with some small hail Sunday and Monday. Check out this series of cloud cover forecasts–this one from 7am CDT SAT
  • 1pm CDT Sat
  • 7pm CDT Sat
  • 1am CDT Mon
  • 7am CDT Mon
  • 1pm CDT Mon
  • 7pm CDT Mon
  • 1am CDT Tue
  • 7am CDT Tue
  • PREDICTED TEMP TREND Days 1 to 5 per the National Weather Service’s GFS ensemble model
  • DAY 6 to 10 TEMP TREND FORECAST
  • PROBABILITY OF PRECIP Saturday
  • PRECIP PROBS Sat night
  • PRECIP PROBS Sunday
  • PRECIP PROBS Sunday night
  • PRECIP PROBS Monday