WARMTH IN CHICAGO TO LINGER INTO SATURDAY NIGHT–A “REX” BLOCKING PATTERN ALOFT IS BEHIND THE WARMTH’S EXTENDED STAY–GOOD CHANCE OF A 4-DAY STRING OF 80s–THE FIRST SUCH STRING IN 7 MONTHS–BUT LAKE COOLING ON SHORELINE FRIDAY COLD FRONT WHICH BREAKS THE WARMTH HITS WITH T-STORM SAT NIGHT–WINDY, COOLER

So how is it this summer-like warmth is sticking around into the weekend? That a pretty healthy stay for such an unseasonably warm air mass. In fact, it appears 80-degree and warmer highs, such as those which have occurred Wednesday and today (Thursday), will be followed by 80s again Friday and Saturday. The one exception will be along Lake Michigan where cooler air will make it onto the shoreline Friday–though the cool air isn’t likely to penetrate very far far inland.

The development of SOUTHEAST WINDS means the flow will swipe the beaches and shoreline locations with cooler air off LAKE MICHIGAN Friday. Lake water temps currently average 46.5-degrees sets which means quite a spread in temps will develop across the Chicago area Friday afternoon from mid 60s on the immediate lakeshore and beaches to mid 80s inland.

Thursday’s “July-level” warmth sets scores of new records across the Midwest—including Chicago

Thursday high temperature departures from normal—some areas 30 or more degrees above normal 

Thursday’s “July-level” warmth sets scores of new records across the Midwest—including Chicago

Thursday’s record high temperatures—including Chicago’s 83 degrees eclipsing the old record of 82 set in 1941 and 1887 

‘REX BLOCK’ BEHIND CHICAGO WARMTH

One look at the current upper air pattern and you can see the REX BLOCK in place. There’s a BIG EXPANDED DOME OF UNSEASONABLY WARM AIR in place over the Midwest and Plains within a big upper air high pressure—yet a WET, STORMY low pressure sits to the south over the Gulf Coast producing areas of active t-storms and heavy rain. Together, they are producing the current REX BLOCK and, lucky for us here in Chicago and the Midwest, this has slowed the movement of the warm air from the air allowing us the first four day stretch of 80-deg temps to occur here since Sept. 15-18 last fall—nearly 7 months ago.

THE LONG STAY OF THIS EARLY SEASON WARM SPELL has to do with what meteorologists refer to as a ‘BLOCKING PATTERN” aloft. BLOCKING PATTERNS in the atmosphere slow the eastward progression of weather systems. If you’re lucky enough to get into warm weather when such a blocking pattern develops, you find the warmth stays put for awhile.

THE CURRENT BLOCKING PATTERN IS KNOWN AS A “REX BLOCK”. It’s also referred to as a “HIGH OVER LOW BLOCKING PATTERN”. The name “REX BLOCK” derives from the meteorologist who identified the upper air configuration which leads to this type of blocking pattern back in 1950. His name was Daniel Rex.

One look at the current upper air pattern and you can see the REX BLOCK in place. There’s a BIG EXPANDED DOME OF UNSEASONABLY WARM AIR in place over the Midwest and Plains within a big upper air high pressure—yet a WET, STORMY low pressure sits to the south over the Gulf Coast producing areas of active t-storms and heavy rain. Together, they are producing the current REX BLOCK and, lucky for us here in Chicago and the Midwest, this has slowed the movement of the warm air from the air allowing us the first four day stretch of 80-deg temps to occur here since Sept. 15-18 last fall—nearly 7 months ago.

VIEW SLIDE SHOW OF DEVELOPING PATTERN:

Early-Season Warmth Melts Away North Woods Snowcover

CHECK OUT THE SNOWMELT UNDERWAY IN THE EARLY SEASON WARMTH ON THIS HIGH RESOLUTION TRUE COLOR WEATHER WEDNESDAY SATELLITE ANIMATION OUT OF THE CIMSS at the University of Wisconsin-Madison

This was posted by CIMSS satellite researcher Scott Bachmeier. The resolution of our weather satellite imagery these days is stunning. You can can see ice covering North Woods lakes even as the surrounding snowpack decreases with the onset of the current warm-and quite dramatically!

NOTE: Snow can still occur across the North Woods–but the trend as warmer weather visits more frequently this time of year is clear.

FLORiDA DELUGE

HEAVY RAINS CLOSE AIRPORT–FT. LAUDERDALE/HOLLYWOOD AIRPORT REPORTS IT’S CLOSED THROUGH 7AM EDT FRIDAY TO PERMIT CREWS TO CLEAR DEBRIS

The National Weather Service Miami Office has storm survey crews out cataloguing the damage. The thundery downpours left lifelong residents in a state of disbelief. Dawn Gray, 49, who was mired in a four hour traffic jam near the Ft. Lauderdale/Hollywood Airport only to find her flight to Las Vegas cancelled, told the New York Times, “I’ve lived here my entire life. I’ve never seen anything like that happen before.”

If the 25.60″ tally near the airport verifies, it will have blown the previous 24 hour Ft. Lauderdale record for rainfall—14.59″ set April 25, 1979—away by more than 10″.

I’m posting a series of radar images with the graphic package below which shows the re-generating supercell thunderstorms regenerating over the same area to produce the biblical rainfall.

From 8 p.m. EDT Wednesday to 7 p.m. EDT Thursday:

The National Weather Service Miami Office has storm survey crews out cataloguing the damage. The thundery downpours left lifelong residents in a state of disbelief. Dawn Gray, 49, who was mired in a four hour traffic jam near the Ft. Lauderdale/Hollywood Airport only to find her flight to Las Vegas cancelled, told the New York Times, “I’ve lived here my entire life. I’ve never seen anything like that happen before.”

If the 25.60″ tally near the airport verifies, it will have blown the previous 24 hour Ft. Lauderdale record for rainfall—14.59″ set April 25, 1979—away by more than 10″.

I’m posting a series of radar images with the graphic package below which shows the re-generating supercell thunderstorms regenerating over the same area to produce the biblical rainfall.