Major Forecast Screw-Up

Twelve hours ago it looked like severe thunderstorms would develop, focusing along a cold front that would track across the area in the late afternoon to early evening hours.  Boy were we wrong.  In our defense, so was the National Weather Service.  However, that is no excuse.  Everybody just got duped.

The deciding factor in this forecast was the timing of the cold front.  We tried to pin it down for days, but that elusive rascal evaded all efforts at prognostication.  The cold front passed through the area early this afternoon, many hours before we thought it would arrive.  This more or less extinguished the chances of thunderstorm development during the afternoon and evening hours.

If the cold front had adhered to the later schedule, the setup would have been much different.  This would have given the sun a chance to raise temperatures higher.  It would also have allowed time for more moisture to flow into the area from the south.  Both of these things would pile more fuel on the fire, heightening the thunderstorm threat into the severe category.  This loaded-gun setup would have patiently waited for the cold front to arrive and initiate convection.  Instead, as we’ve discussed, the cold front rushed through the area and stalled out to the south of us, not even giving Mother Nature a chance to get the ammo out of the box.  So, that’s how our forecast managed to do a complete reversal in less than twelve hours.  Mea culpa, mea culpa.

Now, on to the next issue.  The beginnings of a Mesoscale Convective System (”MCS”, a large area of organized thunderstorms) is forming up over northwest Iowa.  Despite the rest of the forecast being ripped to shreds, we are all still confident that the conditions are right for this MCS to fully develop and propagate eastward.  Current estimates put arrival of the MCS in the late evening to overnight hours, possibly well after midnight.  While we are confident that this system will form, we’re not placing any bets yet on where exactly it will go.  There are basically three options:

• 1: The MCS will follow the cold front, staying on the warm side of the front and well to our south.
• 2: (caveat to the above)  The MCS will follow the cold front, stay on the warm side, but the cold front will retreat far enough north that we will be affected by the system.
• 3: The MCS will be strong enough and dew points behind the front will be high enough that the system will cross over the front, possibly tracking anywhere and maybe impacting Lake County.

To be completely honest, I have absolutely no idea which of the three options it will be.  Once we do get a feel for which way this thing will go, another update to the Severe Weather Outlook will be issued.  Of course there is the small and vaguely worrying chance that we could be wrong about the MCS forming.  It may fall apart before it gets here, or it may not form up at all.  However, current satellite imagery and radar indicate that the MCS is maturing over Iowa, so it’s a pretty safe bet that it will survive and track somewhere over Illinois.