Saturday, November 29, 2008

Winter Weather Advisories & Winter Storm Warning


Update (8:53pm): Walworth County to be upgraded to WINTER STORM WARNING.

Update (7:22pm): Milwaukee NWS is discussing the possibility of upgrading portions of southeastern Wisconsin to a Winter Storm Warning. I'll post as soon as I know.

Original Post: There are a few things that we look at for snowmakers around here. The track of the surface low pressure is the one that people are most familiar with. A surface low is pretty easy to find when it's a well developed system.

Another thing we look for is something called "phasing." That's when the lower levels of the atmosphere and the upper levels of the atmosphere work in tandem to create a stronger weather system. Tomorrow's system looks like it will phase pretty well. The included image is of water vapor imagery from this evening. Satellites don't just take pictures of clouds; they also can detect water vapor high in the atmosphere. The swirl located in Kansas is where the upper-level low pressure system is located (and is the cause of the snow in Iowa right now). To the south, a large plume of moisture is being pulled into the eastern U.S. That's also in the area where the surface low pressure is developing. All of those things will start to work together tonight, allowing for the evolution of a pretty decent winter storm.

That winter storm will move through the Ohio River Valley over the next 36 hours, bringing us our first widespread snow of the season. At this time, I-39 looks to be the general dividing line between the greater and lesser snow amounts. I have Rockford in the 1-3" range, although I believe we'll be closer to 3" than 1". Our far eastern communities (Walworth, McHenry, DeKalb Counties) are in the 3-6" range. I doubt there will be too many reports above 4" or 5" in those locations.

Obviously, this poses a significant travel problem, especially to those heading east. Planning for extra time and driving carefully and defensively will be important tomorrow.

With this being a fairly high-impact snowfall, I'll be checking the blog pretty frequently. If you have any questions, feel free to leave a comment! Also, if you have any snowfall reports, send them to us at weather@wrex.com.

5 comments:

Chad South Beloit said...

What type of snow are we looking at ? I'm a snow plow driver, so I'm also wondering if any of you have an idea about what time the snow should start to accumulate . Love the blog, it's the first site I hit when I get up in the mornings.

Take care and thanks for the wonderful job you all do. I really enjoy the occasional weather science posts.

Justin Gehrts said...

Thanks, Chad!

This looks to be a somewhat wet snow, especially until mid-afternoon. By that time, temperatures should start falling enough - along with some wind - to allow the snow to be a little fluffier. Blowing snow may be something to keep in mind later on Sunday.

As far as when we should start to see some accumulation... I would think by 6am we should see stuff sticking. I'm expecting the brunt of the snow to occur after noon, though.

Chad South Beloit said...

Awesome, that would work out great. Snow plowing can be hectic and the hours are long, but being able to prepare and get enough rest keeps ya going. Thanks for the quick response, keep up the great posts.

Take Care,

Chad

Anonymous said...

Snow amounts in Madison are forecasted 3-6" according weather.gov when I typed in Madison... 1-2" tomorrow and 2-4" tomorrow night... Isn't that enough to warrant a WWA?
And, It really irritates me that the Davenport Weather Service would issue a WWA for all counties except the 3 along Highway 20 in Iowa-- The Graphical Forecast and Forecast both advertise as much snow for Dubuque County as for Jo Daviess... Only because we have "all ready had a snow event thus far." I know it is not your fault, but we haven't really had much of a snow event, we had about .6" of an inch last weekend...
And I don't get why Madison doesn't have an advisory...

Oh, and the main reason I came... Why are they Winter Weather Advisories as opposed to Snow Advisories... Can we expect any mixed precip? I think either/or would be appropriate, I guess.

Do you think you might move that 3-6" band further west, or are you going to stand by that prediction?

Checking with the DVN CWA we've got about 4" of snow predicted for CR and IC, and about 3.2" for DBQ and points on west...

I know that is a lot of questions to answer, and a little bit of ventilation at the frustration of no advisory... But, oh well, the less snow the better! :)

Thanks.

Justin Gehrts said...

Haha, don't sweat it.

Snow advisories have now gone by the wayside; it was decided that there were just too many winter-type advisories to be useful anymore. You can learn more about what's been condensed on the main Weather page in the "13 Winter Authority" section. (yes, I'm shamelessly plugging)

There's the chance for a little bit of a wintry mix, but the window of opportunity for that appears to be pretty limited. The majority of precip should be in the form of snow.

I think Milwaukee NWS is using the same justification that the Quad Cities was using - since this is a fairly low-end event for Madison considering they've already experienced a similar snow already. While Winter Storm Warning criteria are somewhat rigid, Winter Wx Advisory criteria can be molded a little bit, based on what I've seen.