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7/22
I'm glad to say yesterday's forecast was exactly right. There was good blue lift especially over refineries and other infrastructure, going to about 4500'.
Today
Synopsis: Pesky front just north of us Hot and humid southwest flow below front. .
Dupage TAF:
Forecast period: 1400 to 1700 UTC 22 July 2012
Forecast type: TEMPORARY: The following changes expected for less than half the time period
Weather: -RA (light rain)
Forecast period: 1700 to 2000 UTC 22 July 2012
Winds: from the SSW (210 degrees) at 12 MPH (10 knots; 5.2 m/s)
gusting to 17 MPH (15 knots; 7.8 m/s)
Visibility: 6 or more miles (10+ km)
Ceiling: 9000 feet AGL
Clouds: few clouds at 6000 feet AGL
overcast cloud deck at 9000 feet AGL
Weather: no significant weather forecast for this period
Satellite: Blob acoss Iowa, central illinois, appears headed this way.
Thermals: The NAM model says weaker, ony 400. The RAP model is much more enthusiastic. The difference seems to be placemennt of the front and degree of high clouds. NAM says more south/more, RAP says more north/less. Both models are much more enthusiastic than the TAF -- neither model shows the overcast cloud deck. The satellite does show overcast headed this way, but the models may think it dries up.
Forecast soundings. Are really interesting today. They show the signs of overcast -- red and blue lines are either close or actually touching. They also show slow heating. You only get to about 3100' at 18z, just from lack of heat (!) not because of an inversion. It keeps heating up, so thermals get to 7000' late in the day. But there is never a decent hockey-stick on the red line showing good heating below.
Forecast discussion: WOULD EXPECT DEBRIS CLOUDS TO RIDE SOUTHEAST INTO THE CWA WHICH WILL HELP KEEP TEMPERATURES IN CHECK NORTH OF I-80.... * DECAYING SHOWERS NEARING THE TERMINALS THIS MORNING THEN A SLIGHT CHANCE FOR TSRA THIS AFTERNOON AND TONIGHT. A WEAK FRONTAL BOUNDARY IS DRAPED FROM WEST TO EAST ACROSS SOUTHERN MN INTO CENTRAL WI THIS MORNING. WARM AIR OVERRIDING THIS WILL CONTINUE TO PROVIDE SOME SHOWERS INTO NORTHERN IL THROUGH MID TO LATE MORNING. THESE SHOULD FADE IN COVERAGE INTO EARLY AFTERNOON WITH FORCING FOR ASCENT EASING. WHILE THERE IS A SMALL CHANCE FOR CONVECTIVE REDEVELOPMENT THIS AFTERNOON DUE TO THE INFLUENCE OF THESE MORNING SHOWERS...THIS CHANCE REMAINS SMALL AT THIS TIME AND BELOW CONFIDENCE TO MENTION IN ANY OF THE TAFS AT PRESENT. BUT OVERALL MIXING WILL BE TEMPERED WITH THE DEBRIS CLOUDS BLOWING OVER FROM UPSTREAM CONVECTION.
The objective here is not just to look at the individual foreacasts, but to back up into a "story" for the day, to understand why things are happening. Then you have a better chance of adapting once you're in the air.
We start with prog charts. We need a general idea of highs, lows, fronts, and rain. Look at the "valid" top right to know when it's for. Click here for more times (adds)
Read the DuPage TAF to know what the weather service thinks is going to happen
Read the Joliet Forecast discussion to know why. Pay special attention to the aviation section.
Look at the satellite loop. I couldn't figure out how to include this automatically, so Click here
The forecast soundings are here (more options, airports, models etc. here. Look at the progression of the sounding through the day.
Now we're ready to look at the blipmaps. You can see all the blipmaps here. (You have to register but it's free). The links here should update automatically; hit "refresh" if not.
Start with thermal strength. thermal strength. 400 = soarable. 500 = great. 600 = superb. Look at the 21Z to see if the day is going to die. Look at patterns to figure out the underlying weather story. Compare the models. Often they differ a lot. Seeing where they differe helps you to know how uncertain the forecast is, and not to get hung up on small details.
NAM model
RAP (formerly RUC) model
The wind graph tells you more than just wind. It gives a picture of the weather story. The up/down motion is computed from where the wind is converging. It shows lake breeze, fronts, convergence lines, etc.
Next, the vital question...cu? The cumulus cloudbase for cu potential > 0 is a good overview for whether there will be cu. The NAM is usually optimistic (too wet) and the ruc is too pessimistic (too dry), so I look at them both
When that's not good enough, look at the separate cu potential and cloudbases. Cu potential is basically the thickness of the cu in thousands of feet. Too much is as bad as too little! When there is a threat of overdevelopment, the OD potential, cloudbase, and CAPE tell you how bad it is.
The surface dew point tells you about moisture in the air. This is usually the key to why NAM thinks there will be more clouds than RAP and explains variation in cloudbase height or presence/absence of clouds.
In the Fall or with no cu, the top of the boundary layer is key. It tells you how high thermals will go, MSL. Higher = stronger. 2000'=stay in bed. 3000'=desperation local soaring. 4000' = squeker cross country around the local area. 5000'+ get out to the airport.
The NAM total cloud cover and surface sun are very good at telling you if heating will be a problem, cirrus or other blowoff and locating fronts, od, and other parts of the "story." Be careful, even thin cirrus registers as cloud cover, so that's why you also look at surface sun. 7%-14% cloud cover in purple is a sign of a nice scattered cu field.
Finally, look at the forecast soundings. With the big picture in hand, we can look at fine details near the airport. Again, I don't know how to include this automatically. Click here for the sounding. (more options, airports, models etc. here. Look at the progression of the sounding through the day.
The same blipmap links for one and two days ahead. These change a lot as the time approaches!
Thermal strength
Top of lift
Wind
Up/Down
Cu cloudbase for cu pot>0
Cloud cover
Surface sun
