Friday, February 24, 2012

February 22-24 Snowfall Event Wrap-Up

Starting February 22, a strong 'Saskatchewan Screamer' system dropped from Canada and into the US. A Saskatchewan Screamer (SS) system is a storm system that forms in Saskatchewan, Canada, and quickly moves, or 'screams', through the US.

February 22, 2012 Surface Analysis at 03z
This is the surface analysis for 3z February 22, which is 9:00 PM CST February 21. We see the two parts of the storm- the Saskatchewan Screamer just northwest of North Dakota, and the storm system on the Oklahoma/Texas border. At this point, the storm is not of particular interest and not of particular strength.

February 22, 2012 Surface Analysis at 06z.

This is the surface analysis for midnight Feb. 22, CST. The Saskatchewan Screamer (which will now be referred to as System 1) is now racing into South Dakota with a central pressure of 998 millibars. At this point, it is of interest as the system is being strengthened by a jet stream that has winds at roughly 125 MPH. The jet stream of the 0z and 12z timeframes just before and after (respectively) of this surface analysis indicates that a strong trough had developed in the jet stream that had pushed it south. This trough in the jet stream tells me that its southward motion would continue, but the strength of the jet stream to the west would keep the southward movement also at an eastern movement, making for a southeast direction.

February 22, 2012 Surface Analysis at 12z
At 12z (6 AM CST), System 1 has now progressed into Iowa, keeping the main snows behind into the Dakotas. Central pressure indicates the system is at 999 millibars. Of more interest is System 2, now in Oklahoma. The central pressure is at 1005 millibars- not too strong. However, there is now a dry line in place that increases concern for severe thunderstorms. The presence of a warm front over what used to be a stationary front indicates that the warm air mass is now on the move and will now begin to displace other air masses, therefore instigating more thunderstorms along the front. Now, this would be a bigger concern if temperature differences were larger. Temperature readings (red numbers) north and south of the warm front are not too different from each other, thereby significantly lowering the severe weather threat.

After that, everything gets complicated as surface analysis maps do not clearly depict the system differences. However, it does come to point that the main snows begin to come back south towards the Lower Great Lakes.

February 23, 2012 Surface Analysis at 12z
A day later, the main system appears as a 989 millibar system. To watch now is the frontal system stretched from Kansas to West Virginia. Eventually, this cold front will turn into a warm front and move north as the 989mb system moves east into Missouri.

This warm front then becomes the focus for where snow will fall. Tight temperature gradients in the summer are typically the focus of thunderstorms. A temperature gradient is the difference of temperatures between points. This temperature gradient is also a good point for snowfall to occur in the winter. The gradient is also an area where snow banding sets up. This banding is typically where the heaviest of heavy snows fall.

In this situation, the temperature gradient (TG) appeared to set up in the northern half of Illinois. Yesterday afternoon, a line of precipitation moved north across northern Illinois. In areas of lighter precipitation, there was reported rain and a mix of precipitation. In the heaviest precipitation, very large snowflakes were reported to be falling. Accumulations of about an inch resulted.

In the aftermath of this band, it was mentioned by National Weather Service Chicago that this band of precipitation had indicated where the heaviest snow would fall overnight.
And that's where it became foggy.

The National Weather Service and RUC Short Range model were at odds. The RUC placed the heavier snows on the WI/IL border, while the NWS put Northeast Illinois in the heaviest snowfall. In the end, the RUC model won out.

Snowfall amounts were highest on the Wisconsin/Illinois border, where very isolated 8-10 inches were found. The National Weather Service became somewhat erratic in the first couple hours as the storm went on, with NWS Chicago suddenly lowering snowfall amounts and shifting the heaviest snowfall to right up against Lake Michigan.

The system then continued eastward with substantial strength. Again, the frontal positions were of issue, and snowfall amounts may have ended up slightly less than what is shown on here. The only reason that it is unsure is because the snow event is just ending.

If you have any reports, they would be appreciated below.
I am recovering from what may have turned out to be a brush with the flu and am feeling much better. Thanks to everyone who sent well wishes!



ERN WX said...

Hello Andrew. How muchsnow did you get?

Anonymous said...

SW Milwaukee 6.5" of wet snow, very picturesque!!

Anonymous said...

With some lake enhancement!!

Andrew said...

Eastern WX: A good 6 inches.

Anonymous: Thanks for the report!

ERN WX said...

Great, Andrew! Glad to know you got a good snow!!!