Update #1, 11:20 AM...corrected cloud cover today to read "becoming mostly cloudy", not cloudy. FORECAST FOR DEKALB AND VICINITY, 6/18/13, 11:20 AM Today...becoming mostly cloudy with a chance of a light shower through mid-afternoon. Much cooler and less humid with a high of 74 degrees in DeKalb and our western campuses...and in the upper 60s eastern campuses. Northeast winds 10-20 MPH, with a few higher gusts. Tonight...clearing and cool. Low of 53 degrees. Northeast winds 5-10 MPH. Tomorrow...sunny and excellent. High of 78 degrees. East to southeast winds 10-20 MPH. Extended outlook...Thursday through Monday... Thursday...partly cloudy. Low in the upper 50s. High in the lower 80s. Friday...partly cloudy. Low around 60. High in the middle 80s. Saturday...partly cloudy, hot and more humid. Low in the upper 60s. High in the lower 90s. Sunday and Monday...variable cloudiness, hot and humid with a chance of a thunderstorm both days. Low in the upper 60s. High around 90. **************************************************************************** CLIMATE DATA: Yesterday's high, 87 degrees; last night's low, 56 degrees. The average high/low temperature is 82/61. We have had a trace of rainfall equivalent at the DeKalb campus over the last 24 hours ending at 7 AM this morning. Forecast was for 87/58 and a trace to .33" and 30% coverage of rain; this all verified. Sycamore got hit; we just got sprinkles in DeKalb. We have had 1.70" of rainfall equivalent this month. On average, we should see 4.18" of rainfall equivalent by June 30. We have had 21.14" of rainfall equivalent so far this year. By June 30, our average annual liquid total should be 17.27". **************************************************************************** SEVERE/HAZARDOUS WEATHER OUTLOOK: There is a chance of thunderstorms on Sunday and Monday across the area. Otherwise, summer heat and humidity...with heat indicies at or around 100 degrees...should begin on Saturday and could last for a considerable part of next week. Should that forecast verify, heat indicies around 100 degrees are in the extreme caution category, so drink plenty of fluids when working outside. ***************************************************************************** PRECIPITATION: Tuesday: a trace to .10", and 30% coverage, mainly at our Lorado Taft and DeKalb campuses. **************************************************************************** FORECAST DISCUSSION: The only change I made to the forecast was to bump the temperatures up a notch this weekend, and down a notch for today as we got a few degrees cooler last night, which will impact our temperatures today a bit. The cold front is obviously through the area with low humidity, but an upper level disturbance coming through late this morning and through mid-afternoon could provide enough lift for a few showers here and there. The best chance of showers and thunderstorms will remain south of the forecast area, in central Illinois where greater lift, moisture, heat and instability will be...but the disturbance is potent enough that it should bring clouds to much of the area this afternoon, and again, scattered showers along and west of a Freeport-DeKalb line. Once that passes, we clear out rapidly towards sunset, and experience a clear, cool night. That's followed by two nice days tomorrow and Thursday, with highs in the 70s again tomorrow, and in the lower 80s on Thursday. Southerly winds on Friday, however, will warm us up into the middle 80s, and you'll start to feel a little humidity. You'll feel a considerable amount of humidity and heat this weekend as it now appears that we'll see enough sunshine to hit the 90s both Saturday and Sunday. On the surface map at 11:30 AM...a low over far eastern Canada has a cold front trailing southwest to New York City, to Lincoln, IL, to Des Moines, IA to eastern South Dakota. Behind it, northeast winds are bringing in cooler and much drier air into the region. Ahead of and along the front, scattered showers and thunderstorms will once again occur this afternoon. Some will also occur north of the front in Illinois with an upper disturbance flying by in the jet stream aloft. A few storms could become severe in east central Illinois and central Indiana ahead of the cold front where instability and a little wind shear will be maximized. A weak stationary front from near Amarillo, TX to south of Dallas to eastern Tennessee will bring clouds, showers and thunderstorms along and near that frontal boundary. A few thunderstorms could produce damaging winds and hail. A low over western Montana had a warm front southeast into eastern Colorado, and a cold front southwest into northern California. With upslope flow and this warm front developing, lift will produce scattered thunderstorms just east of the Rockies from Montana to New Mexico, and some should produce damaging winds and some hail. An isolated tornado cannot be ruled out with any of those thunderstorms. High pressure dominated the Great Lakes and northern Plains...and also in the southwestern U.S., although monsoon thunderstorms will occur there later this afternoon. In the tropics...tropical depression #2 developed yesterday and is now producing some heavy rain over northeastern Guatemala. It should go back over the southwestern Gulf of Mexico briefly into the Bay of Campeche as a weak system, and then move over land again and dissipate in far southeastern Mexico. Our forecast problems...the system today...and then the heat this weekend and next week, and rain chances for next week. Today...about 15 minutes after I sent out the forecast, I had "buyers remorse" for buying into our chances for very light showers today. While the upper disturbance will be moving through this afternoon, the rain has dissipated off the radar. That will reform as the heating continues this afternoon, but almost all of it will be south of us. Furthermore, the sunshine we have now will continue to be coming through on and off through the afternoon, and I backed off on the cloudy wording based on the latest satellite trends since I put out the forecast. Even mostly cloudy may be going overboard here. But you get the picture: some sun, much cooler and less humid today vs. yesterday, with a low chance of very light rain. Look for highs in the lower to middle 70s here in DeKalb, and only in the upper 60s at our eastern campuses with a lake breeze. Tonight through Saturday...high pressure will move slowly across the northern Great Lakes and then move east of us on Thursday, switching winds from northeasterly to southerly on Thursday. So, tomorrow and Thursday will be nice, but the heat and humidity start to come back on Friday, and then with a vengeance this weekend. All indications are we'll see highs of 90 degrees on Saturday and Sunday, and it now appears Saturday could by dry with a good chunk of sun, so I went lower 90s for then. So, look for upper 70s tomorrow, warming into the 80s on Thursday and Friday, and then a hot and steamy weekend this weekend. Next week...a couple of weak cold fronts dance around our area on Sunday and Monday, but then dissipate before another one tries it's hand on Wednesday or so. But the overall message is that it may be hot and humid right through the middle of next week, with highs around 90 or warmer through the middle of next week, with high humidity. Summer is coming! So, look for below average temperatures through Thursday, then we go above average through the middle of next week, with little or no rain through Saturday, and then widely varying amounts through the middle of next week. Gilbert ******************************************************************************* Gilbert Sebenste ******** (My opinions only!) ****** Staff Meteorologist, Northern Illinois University **** E-mail: sebenste@weather.admin.niu.edu *** web: http://weather.admin.niu.edu ** Twitter: http://www.twitter.com/NIU_Weather ** Facebook: http://www.facebook.com/niu.weather * *******************************************************************************