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FIRST–THE WEATHER HEADLINES

–Chicago logged its 11th consecutive BELOW NORMAL DAY today which drags August’s average temp to date to a fraction of a degree below normal. Yet August is, has opened, for all intents and purposes, practically “on the money” in terms of its average temp to date

–The month is running VERY DRY. My WGN meteorological colleague Mark Carroll has found this has been the driest opening 18 days of any August in Chicago since 1959. The paltry 0.44″ of rain on the books for the month to date is only 18% normal and nearly 2″ below normal

–Though there were few reports of Northern Lights last night, the potential for Northern Lights remains elevated. A barrage of charged particles from recent coronal mass ejections is headed for Earth’s upper atmosphere tonight and elevates the chance of auroral display south of their usual location, say NOAA space forecasters based in Colorado. Northern light may be seen as far south as Illinois and Iowa.

–Temps warm Friday and “SSW” winds may be strong enough to overcome lake cooling increasing to 11 to 22 mph. Friday’s predicted high of 87-deg in Chicago would be the warmest daytime high in 13 days.  Humidities will remain fairly low through Friday though cooling aloft may set the stage for an isolated afternoon shower or thunderstorm–but with only 10% coverage.

–The weekend continues to signal the best chance of clusters of showers and thunderstorms. Cooling aloft even as warmth and increasing humid conditions prevail here in the lower atmosphere sets the stage for convective showers & storms to develop. Rain chances are:  32% Friday night; 66% Saturday; 62% Sat night; 53% Sunday dropping off to 16% Sunday night and just 31% Monday.

–Averaged across 19 model forecasts, rainfall centered on Chicago comes in at 0.60″. But warm season rainfall doesn’t fall evenly—far from it. So, looking at the range of model rain tallies being predicted would suggest totals by the end of the weekend which could come in at anywhere from 0.40″ to as much as 1.25″. But A CAUTIONARY NOTE: At this time of year, forecasts best indicate trends rather than specific values. That’s why looking at a range in rainfall projection rather than a single figure is the best way to go.

—AN INTERESTING TREND as we look out over the coming 15 days. Temps, which have averaged below normal more than not in recent weeks, are indicated to trend modestly above normal. In fact, every day from next Thursday forward through the following week come in modestly ABOVE NORMAL. This suggests some warming is ahead. We know the hot weather isn’t over yet. History tells us 77% of years from this date forward have ended up producing at least one addition 90—-some far more than that. This is an interesting medium range trend to monitor.

HERE’S THE CHICAGO METRO FORECAST

TONIGHT: Partly cloudy, a little warmer than recent nights–but still comfortable. Low 67–but a few upper 50s well inland.

FRIDAY: Partly sunny, becoming breezy and a little warmer. Slight chance of an isolated shower but over perhaps 10 to 20% of the area max. High 87.

FRIDAY NIGHT: Mostly cloudy and warm. Several scattered showers and a few possible t-storms. Rain may fall over 20 to 30% of the area. Low 69.

SATURDAY through SUNDAY: Widespread cloudiness, warm with a moderate humidity increase. Scattered morning showers and possible isolated morning thunder become most numerous and increasingly thundery in the warmer hours of each day–particularly afternoons and evening. There will be rain-free interludes mixed in. High Saturday 83. Low Saturday night 65.  High Sunday 79.  Rain coverage: Near 70% of the area Saturday; 60% Saturday night and 50% of the area Sunday.

MONDAY: Mixed sun and clouds, warm, moderate humidities persist. Isolated mainly afternoon and evening thunderstorms can’t be ruled out–but impacting 20% of the area. High 80.

TUESDAY AND WEDNESDAY: A good deal of sunshine–just some mixed fair-weather clouds. Slight chance of an isolated shower or two mainly afternoon and principally away from the lake. Warm with only marginally elevated humidities (dew points upper 50s to mid 60s) and day to day easterly lake breezes on area beaches.  Highs both days 82–but mid to upper 70s lakeshore areas.

THURSDAY: Partly sunny, warm, moderate humidities. High 84.