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The chilliest spell of weather here in over five months moves into a 9th consecutive day Tuesday---but under cloudier skies than in recent days. Rainfall with the first of this week's two wet weather systems is predicted to begin from the day's rapidly lowering and thickening overcast by mid-morning and continues in waves through much of the afternoon. A suite of the 11 most recent computer projections places the day's potential rainfall from 0.10 inches to as much as 0.85---an amount which comes on top of the 1.22 inches recorded here in the past 8 days---a period which has averaged nearly 5 degrees below normal. Estimates based on temperatures since October's open suggest the cool spell has led to home furnace use nearly 60 percent more than the most recent 30 year average. 

Gusty west winds, likely to top 30 m.p.h. at times Tuesday night, deliver a reinforcing shot of chilly air. But, the far more significant cold surge---potentially the coolest in more than 5 months and likely to limit high temperatures to the 40s for the first time since last April---looms this weekend.
 
 
Wet storm system later this week could produce up to 3 times Tuesday's rainfall
 
A frontal wave expected to sweep the area as the cold air approaches is likely to produce a far wetter interlude than Tuesday's---doubling or tripling the amount of rain to fall today.
 

Thought you'd get a kick out of these shots of our visit Tuesday on board the Environmental Protection Agency's Lake Guardian research ship.  On board, scientists are keeping a close eye on the Great Lakes---monitoring everything from invasive species which are literally changing the food chain and character of these treasured bodies of water but also looking at toxins which flow into them. We went out onto Lake Michigan aboard the Lake Guardian and had a chance to see the equipment used in these Great Lakes studies up close. We report on our trip and introduce you to these scientists on Wednesday evening's (9/9/2009) WGN News at Nine!  Hope you have a chance to check our report out tonight at 9 P.M. and online!
 
Tom Skilling



 

Former Editor of the USA Today's weather page joins us on WGN Midday News Tuesday to talk about The AMS Weather Book

A terrific new book on the weather and climate has hit the nation's book stands and we plan to talk about it with its author and former editor of the USA Today's weather page Jack Williams on WGN Midday News Tuesday (July 28). The book has received rave reviews from meteorologists-----but it is written for anyone with an interest in weather and climate.



Its approach is unique among books on these subjects because it introduces its readers to the remarkable people who work in the fields of meteorology and climatology. The product of years of work by one of this country's leading science writers Jack Williams, the AMS Weather Book gives you a first hand look at the weather professionals who fly into hurricanes, the scientists who take arctic ice cores and in an attempt to better understand and predict global climate change, the storm chasers who penetrate hurricanes and are in regular pursuit of the nation's tornadoes to the forecasters who devote their work days to predict nature's next move. The book takes the reader into every corner of the meteorological and climatological profession introducing us to those whose life's work is dedicated to producing a better understanding of our weather and climate systems.

It's an outstanding book--beautifully illustrated and full of stunning photos of the weather at work--- and we hope you are able to join us around 12:45pm on WGN Midday News Tuesday, July 28 as we talk to Jack Williams about his own fascinating career and the widely touted USA Today weather page.

Tom Skilling

 
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AMS_weather_book.pdf

Far western sections of the greater Chicagoland area---an area which includes Rockford and possibly sections of Boone, McHenry, Ogle and Lee counties--are included in the Storm Prediction Center's latest severe weather outlook covering the period which runs through tonight. The latest run of our in-house 4 km. RPM (Rapid Precision Mesoscale) model brings clusters of thunderstorms into sections of northwest and north-central Illinois by 9:30 pm and suggests active thunderstorms could proceed eastward into northwest and western sections of the Chicago metro area toward midnight--proceeding in weakening fashion into Chicago late tonight.
It's one take on tonight's meteorological situation which we'll be monitoring and updating on our 5:30 pm and 9PM Monday evening programs and here on our WGN Weather Blog.

http://www.spc.noaa.gov/products/outlook/day1otlk.html

Tom Skilling

Friday night's outbreak of severe weather hit areas south and west of Chicago the hardest--but the Chicago area was swept by strong winds around midnight. The rapid development of a 45,000 ft. t-storm cell over central Cook County around midnight was accompanied by lightning and high winds.  Here's a rundown of some severe weather reports received by the National Weather Service during the night:

Peak area wind gusts:

65 mph Livingston

60 mph Winnebago

60 mph Rockford

44 mph  DuPage Airport

37 mph Peoria

38 mph O'Hare

36 mph Waukegan

33 mph Aurora

33mph Wheeling

 

Funnel cloud reports:

2W Rochelle

Woodstock

Rensselaer

 

Heavy rainfall:

2.25" Manhattan

1.95" 3S Earlville

1.87" Mendota

1.82" 4NNW Coal City

1.77" Peotone

1.73" ENE Peotone

1.69" 1N Mendota (fell in 90 mins)

1.28" Paw Paw

1.19" 5NW Polo

1.11" Momence

 

Wind damage reports:

5S Streator

Odell (Livingston Co)

 

 

 

 

 

The Chicago area remains at risk for severe weather Friday night-as we post this update at 3 pm Friday afternoon. NOAA's Storm Prediction Center (SPC) continues to outlook an area which includes sections of 7 states for possible severe weather--Chicago sits on the east side of that area (http://www.spc.noaa.gov/products/outlook/day1otlk.html). SPC has also just issued a tornado watch for eastern Iowa, northwest Illinois and southwest Wisconsin (http://www.spc.noaa.gov/products/watch/ww0617.html) until 5pm. Highly divergent winds over that area at jet stream level, daytime heating and an influx of energy-rich humid air form the basis of a significant severe weather risk even beyond 5pm in THAT region of the Midwest.  But, Chicago area residents must remain vigilant as well--especially Friday night.  The latest run of our in-house 4km RPM (Rapid Precision Mesoscale model) describes an atmosphere primed for potentially active thunderstorms across the Chicago area from roughly 8pm this evening far west and northwest sections to 2am in northwest Indiana. The city proper would seem at greatest potential risk somewhere in the 10pm to 1 am range. And, the model suggests at least some thunderstorms could continue develop across mainly southern sections beyond 2am.  Of course, computer representations of the atmosphere and the way the atmosphere ACTUALLY develops don't always dovetail.  But the fact that other models are and have been generating a similar set conditions in roughly the same time period makes the severe weather threat one which deserves to be watched.  
    Our RPM models---both 4km and 12 km versions--are run every 3 hours. The latest 4 km run available for this 3pm Friday posting is easily the most aggressive among the recent series of model runs in destabilizing an atmosphere Friday night predicted to be quite energetic. CAPE levels--an index of atmospheric energy levels--are predicted to surge during the 8pm to 2 am period to a worrisome 2500 to 3000 joules/kg in the most recent RPM run---1000 joules/kg is often cited as the level at which the severe weather risk becomes a concern. Several Weather Service models have been putting these values at or just above the 2000 joules/kg threshold in recent runs. At the same time, the RPM models suggest an even more unstable atmosphere than had been earlier predicted may develop with surface based lifted indicies--a reflection of how fast temperatures are to decline with altitude--- dropping to -6 to -8 during the 8pm to 2am.  Not all of you work with these indicies and may not know what to make of these numbers. But a -6 to -8 lifted index value is worrisome to meteorologists because it suggests a sharp drop in temperatures with height.  This means the increasingly humid air predicted to be entering the area overnight may well become quite buoyant because of faster than usual temperature declines with height and encouraged to ascend. These indicators plus the presence of 1.50" of evaporated water and shifting wind directions with height as well as the approach of a cold front along which low-level winds are to converge, all contribute to the view that Friday night's severe weather risk is elevated here and should be monitored.
   There are a couple of important wildcards in the Friday night weather---there almost always are in severe weather situations. Thunderstorms, currently making their southeastward trek from Minnesota, northeast Iowa and Wisconsin toward Illinois, are producing so-called "debris" cloudiness which moves with upper winds out ahead of the storms themselve. This debris cloudiness can affect the degree of warming. These storms are also producing outflows of cool air dragged to the surface by their rainfall. These factors can both act to stabilize the atmosphere and cut into its ability to support powerful thunderstorms. Our models don't always do a terrific job of handling these effects from thunderstorms--especially thunderstorms already underway as the forecast cycle begins. That's why these potentially mitigating factors are being monitored. But, The a consensus of model forecasts suggests these potentially stabilizing factors may well be overcome by the meteorological set-up expected to be in place Friday night. Thus, a  threat of severe weather can't be discounted over at least sections of the Chicago area--a threat even more acute in western Illinois.
If severe weather develops, we'll activate our wgntv.com "Severe Weather Blog"

http://weblogs.wgntv.com/chicago-weather/severe-weather/

to keep you posted on storm warnings and updates. And we'll have more on our WGN News programs at 5:30pm and 9 pm tonight---as well as here on our weather blog.

Tom Skilling

Several clusters of downpour-generating showers and few isolated thunderstorms are being tracked as we post this at 3:50pm Wednesday--one on the Kane/DuPage County line and still another producing lightning north of McHenry over Wisconsin's Walworth County. The most extensive collection of cells runs from southern Boone into DeKalb and LaSalle Counties.  All of these showers and thunderstorms been developing farther inland with time.  It's a trend being promoted by westward moving cool air off Lake Michigan which has tended to stabilize the air and limit rainfall in lakeside counties. As of this posting, the tallest and most prolific rain-generating cells are located about 75 miles west of Chicago from near Rochelle to near Compton in Ogle and Lee Counties. Lightning has really been quite limited and had been associated almost exclusively with the Walworth County storm until a series of cloud to ground strokes began in the Ogle/Lee county thunderstorms. Cooling temperatures as we approach and pass sunset will lead to a rapid demise of these cells--with the likelihood scattered thunderstorms will flare  again over sections of the Chicago metro area Thursday afternoon with daytime heating.
  
Track these storms here through this University of Wisconsin-Madison satellite imagery:

http://www.ssec.wisc.edu/~tomw/wisgifloop.html

Several cold air funnels have been reported within showers and thunderstorms which have been forming northwest of Chicago in Wednesday afternoon's unstable atmosphere. Cold air funnels tend not to be damaging--often spinning beneath towering cumulus clouds without touching the ground.  Thunderstorms--some towering as high as 31,000 ft.--but topping out at 29,000 ft. as of this 2:45pm posting---have been developing and dissipating across sections McHenry County--some producing nickel size hail. Doppler radar indicates there has been slow southward development---even as remnant showers attempt to move southeast with with northwesterly upper steering winds. Thunderstorms weaken as they move into counties immediately adjacent to Lake Michigan as they encounter cooler air there. Weather Bug sensors are indicating temperatures are in the mid to upper 60s near the lake and in the vicinity of this afternoon's showers and thunderstorms--but in the low 80s at the warmer inland locations which haven't been subjected to cooling rainfall and storm outflows.  A funnel cloud was reported around 1:55 pm near Woodstock also in Mc Henry County--something which may happen from time to time with any of these thunderstorms. The situation doesn't support damaging or an organized outbreak of tornadoes.
   Temperatures are falling with height at a faster than normal pace which means the atmosphere is unstable.  The set-up is just the latest ramification of the cooler than normal air which northwest upper steering winds have continued to deliver and replenish so often this summer. Daytime heating encourages air near the surface of the earth to warm, rendering it buoyant. This heated air then ascends and cools prompting the thunderstorm development we've been observing much of the afternoon. It's a situation likely to spawn additional (though scattered) thunderstorms over at least sections of the Chicago area into evening.  The thunderstorm development is being further enhanced by the convergence of ground level winds along inland-moving easterly winds off Lake Michigan. The cooling these winds promote across the counties closest to the lake has been--and is likely to continue--inhibiting thunderstorm development by stabilizing the air. Only sprinkles or light showers--remanants of the west and north suburban thunderstorms---are able to make it into these lakeside counties.
    Indications are areas west and north of the Chicago--including DeKalb, Kane, McHenry, Boone, Ogle and Lee Counties will be affected from time to time by these thunderstorm clusters--any of which may spawn some cold air funnels and produce hail and some downpours.
    We'll have more on WGN News at 5:30 pm and 9PM tonight--and also a look at a surge of warmth Friday which appears poised to bring us July's warmest temperatures to date. That warmth may be followed by vigorous if not some possibly severe thunderstorms later Friday night into a portion of Saturday.

Tom Skilling

Given this summer's unusually cool weather---very much in evidence in the Chicago area this weekend---many have been asking "Where's this summer's warm/hot weather?" I thought you might find this 7-day animation of global temperatures produced each day by NOAA's Climate Diagnostics Center (CDC) of interest. When you stand back and look at the big picture, you can see the planet's pools of warmer than normal surface weather outnumber the cool pools. That probably will come as a surprise to many across the Midwest--especially with this weekend's cooler than normal temperatures. The presence of cool air over a good chunk of the nation's mid-section and the heat centered over the Western U.S. is very evident.  The green and yellow areas depicted on this animation are regions of above normal surface temperatures while the blue areas show where cooler than normal weather has been occurring.

http://www.cdc.noaa.gov/map/images/fnl/sfctmpmer_01a.fnl.anim.html

Hope you're having a good weekend!

 

Tom Skilling

Here are some unofficial Chicago area rainfall tallies from this morning's pre-dawn rains from our Weather Bug observation network:

O'Hare                       0.68"
Lake Geneva, WI        0.66
Valparaiso, IN            0.65"
Chicago (Robert S.
     Abbott School)     0.60"
Darien                      0.58"
Rockford                  0.55"
Highland, IN             0.54"
Wilmette                  0.54"
Wadsworth              0.52"
Trevor, WI                0.47"
Kenosha                 0.47"
Carpentersville         0.47"
Long Grove             0.46"
Park Ridge              0.45"
Itasca                     0.45"
Munster, IN            0.42"
Glenview                0.42"
Niles                      0.41"
Lombard                0.40"
Des Plaines           0.40"
River Grove             0.39
Lake Villa               0.39"
Alsip                     0.39"
Chesterton, IN       0.39"
Morton Grove         0.39"
Gary, IN                0.38"
Henry, IL               0.38"
Marseilles             0.37"
LaGrange              0.37"
Waukegan            0.37"
Janesville, WI        0.35"
Burr Ridge            0.35"
Oak Lawn             0.35"
Westchester         0.35"
Lombard               0.35"
Elgin                    0.33"
Mundelein            0.33"
Lansing                0.33"
Lombard               0.33"
Elmhurst               0.33"
Naperville              0.33"

May-level temperatures arrive as a pool of cool mid-summer Canadian air settles into the area late this week into the weekend. We'll have more on that predicted cooling on our WGN News programs at 5:30 and 9pm.  See you then!

Tom Skilling