Image highlights the Excessive Heat Warning through Tuesday night for the Twin Cities in purple and Heat Advisory for southeast Minnesota and west central Wisconsin in light orange.
URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
324 PM CDT MON JUN 6 2011
...HOT AND HUMID CONDITIONS THROUGH TUESDAY...
.AN EXCESSIVE HEAT WARNING REMAINS IN EFFECT FOR HENNEPIN AND
RAMSEY COUNTIES UNTIL 7 AM ON WEDNESDAY.
A HEAT ADVISORY HAS BEEN ISSUED SURROUNDING THE EXCESSIVE HEAT
WARNING...AND EXTENDS TO THE SOUTHEAST ACROSS PORTIONS OF SOUTH
CENTRAL MINNESOTA...AS WELL AS PORTIONS OF WEST CENTRAL WISCONSIN
FROM NOON TO 8 PM TUESDAY. THIS INCLUDES ALBERT LEA...EAU
CLAIRE...AND THE REMAINDER OF THE TWIN CITIES METRO AREA.
HOT AND HUMID CONDITIONS WILL PREVAIL OVER THE AREA THIS
AFTERNOON AND CONTINUE THROUGH TUESDAY NIGHT. OVERNIGHT LOWS WILL
PROBABLY NOT DROP BELOW 75 DEGREES...AND THE HEAT WILL RETURN
TUESDAY AFTERNOON. HIGH TEMPERATURES BY TUESDAY AFTERNOON WILL
REACH THE MID TO UPPER 90S...WITH HEAT INDICES NEAR...OR
EXCEEDING 100 DEGREES FOR A FEW HOURS.
High temperatures were peaking in the 90s in southern Minnesota late this afternoon. Relative humidities ranged from 20 percent at Worthington to around 45 percent in St. Paul. The combination of the hot temperatures and the moderate relative humidities was producing Heat Index values that were very similar to the actual air temperature, which is taken in the shade.
The thermometer registered 99 degrees in Worthington at 4PM.
Heat Index values can be as much as 15 degrees warmer in the direct afternoon sun, without the impact of a cooling breeze.
Light winds overnight will allow for some warmth of the day to radiate back into the atmosphere in rural areas. The downtown Metro, with concrete and pavement, will prove the heat island concept and keep the temperatures from falling mcuh below 80 degrees in the wee morning hours.
Tuesday has the potential to bring even warmer temperatures as southwest winds kick in at speeds approaching 30 mph. Some bank thermometers may display triple digits, 100 degrees, late in the afternoon. A well timed cool front sweeps through Minnesota and Wisconsin on Wednesday. The timing of the front will impact the initiation of thunderstorms. There is a chance that showers could bypass parts of central Minnesota.
Graphical temperature forecast for high temperatures on Tuesday.
Wednesday brings the transition from heat to below normal temperatures for the end of the work week.
Here's a look at the forecast high temperatures for Thursday, some twenty to twenty-five degrees cooler in southern Minnesota the Tuesday.
Thunderstorms may form tonight through central and northern Minnesota, north of the bubble of hot air. Best chance for scattered thunderstorms appears to be from about Fargo to Hinckley.
Indications are that the temperatures will recover back to normal readings for the weekend.
Follow the recommendations of health officials to endure the next thirty-six hours of hot weather.
Cartographic correction: the purple polygons are not the Twin Cities, but the Twin Counties rather. Northern Dakota County is not shaded purple even though it's much more a part of the Twin Cities than NW Hennepin County, for example.