02/24/07 FCST: NE/SD/MN/IA/WI/IL (WINTER PRECIP)

[Jim Hunt]

At my home in north central Indiana, we have an ice storm warning for a 1/4"+ 25MPH winds with 35MPH gusts. They are anticipating power outages to be common in this area of the state.

 

[Robert Dewey]

Don't know what happened to the 06Z and 12Z NAM... It's not even close to the ensembles -- GFS is much more consistent. I bet that big jog (+200 miles) to the NW is some sort of feedback issue. I'm dissapointed to see this given the NAM has the best resolution, and most of the WRF models are based off of it.

 

[Robert Dewey]

Latest 12Z models are showing warmer air over southern MI... FSL RUC indicating ZR through most of the event SE of BEH to LAN. With temps so close to 0C through the column, it really could go either way -- SN, IP, or ZR. However, with dynamic cooling, I'm thinking more along the lines of SN/IP or IP. Either way, it might not be enough to give us warning criteria as we could end up with 0.10-0.15 inches of ice, an inch of sleet, and a few inches of snow.

 

[Joel Wright]

Man, this is one hell of a storm!

We are facing some very big challenges with trying to forecast exactly what we're going to get in northern IL. One thing is for sure, a lot of something is going to come down over the next 36hrs, with a bullseye of over 2" QPF right over the area.

Most of the models show the warm layer just above the ground rappidly cooling off later tonight, but by that time we will be getting dry slotted. I'm not sure how well the models are going to handle the evaporative cooling by the tremendous lift this storm is generating. This is the main forecast problem.

Blizzard warnings are up to the county to my north, but I'm thinking my area will see more ice transitioning to rain than anything. If the evaporative cooling is strong enough though that would change everything. Literally.

 

[Robert Dewey]

Just went over some cross sections of the 18Z NAM over southern MI. There's a pretty solid warm layer (AOA 0C) centered at and below the 850MB level. There's also convective instability present within the strong lift, so I don't see why the convective stuff in IL/IN should have any problem advecting in. Heavy precipitation looks rather likely, and I expect storm total QPF's (through 12Z MON) to be around 1.00 inch across most areas of southern lower MI and northern IN.

Precipitation type is the biggest question. Cross sections and time heights show a sneaky warm layer at or just below 850MB. I've been watching this warm layer become more significant with each model run. However, if heavy convective precipitation occurs, this warm layer may collapse, leading to mainly SN. If it stays in tact or continues to trend warmer, then we'll be looking at primarily ZR.

The 12Z NAM on BUFKIT shows mainly ZR, and with T's below the >0C layer staying AOA -3C, I don't think it will have time to refreeze into IP -- especially since the >0C layer extends down to 1.5K FT. That's keeping in mind that the 18Z NAM is even warmer...

EDIT: WRF ARW based on the 18Z NAM is in, and it's even warmer than the operational NAM. It moves convective precipitation across northern IN and lower MI with isolated areas seeing in excess of 1.25 inches (probably where convection persists the longest). If this is accurate, I would expect a damaging ice storm SE of LAN to FNT. We'll see about that.