Insomnia woke me around 4 AM, but I drifted back to sleep. A nearby lightning strike woke me around 5 AM. I’m trying to get back to sleep. It is a couple of hours before breakfast in the first (and mesoscale discussion) of the day have already been issued.
The NAM and GFS models are still calling for a big event today:
The current tornado probability [for the day as a whole] looks like this:
Severe wind probabilities for the day are as follows (per the 4 AM models):
And severe hail looks like this, per the same forecast for the day:
Current weather looks like this:
And the tornado parameters at the moment are well below any kind of threat threshold:
I will be watching these carefully as the day unfolds.
15:10 – Arrived at the Naperville emergency operation center (DOC). Started up the weather computers and radios, in preparation for arrivals about their staff later in the afternoon. Traded in my XL size polo shirt for a new uniform shirt in a medium. (Doing a happy dance on the inside!)
15:35CDT – An axis of steep lapse rates is oozing east from Iowa.
1730 CDT – Looks like a tornado watch is imminent, per mesoscale discussion MD1020.
While the situation could change from the forecast above, I heave a sigh of relief that the primary area of a risk is to the south of the Chicago metro area. Had this been forecast to occur 25 miles further north, the situation could have been very dangerous for the western suburbsand Chicago proper. Once again, we dodge the bullet, it seems.
1834 CDT – A severe thunderstorm warning goes up near Amboy, Illinois. Even at this point, Al Fisher and I spot a strong couple of forming on the base philosophy velocity plot.”Why aren’t they issuing a tornado warning on this,” we ask one another.
A few minutes later, that warning is issued. NWS policy states that once a storm is tornado-warned, it retains that warning until the storm falls apart. This is how the NWS errs on the side of caution.
The good news is that they are able to issue this with a high degree of confidence, as a number of spotters and chasers (the little red dots in the picture below) are already on the storm, As this radar scope pro composite reflectivity/base velocity product shows:
(Photo courtesy of Ethan Mulnix)
Chasers like Adam Lucio captured photos and video of other storms (at Marseilles, Illinois and further east). I will add links to those photos as I get a bit more time or the weekend.
(NWS has a preliminary page for this event up already.)