Saturday, December 19, 2009

Moderating Temps...Light Snow Sunday/Monday

After a cold first couple weeks of December, temps have warmed up into the mid 20's, and look to remain in the upper teens/mid 20's range for the next few days. A small, fast moving system, also called an "Alberta Clipper" looks to bring some light snow to the area on Sunday into Monday. I think that areas south and east of the Twin Cities (pretty much the southeastern corner of the state) will see the best chance at some minor accumulations, but really a trace to 2 inches seems likely for most of the area.

As mentioned before, temps look to stay somewhat seasonal for the next couple days, but the end of the week is looking quite interesting. For the past couple days, the models have been showing a large area of low pressure forming in the southern US, then moving NE towards the area. If this thing pans out the way it is being shown now, this would be a very significant winter storm for the plains, including parts of Minnesota and Wisconsin. The forecast models haven't come to an agreement yet on the placement/strength of it, with the GFS being the most sporadic of the models, and the European (ECMWF) being the most consistent. In fact, the National Weather Service said that if the consistent European model pans out, some areas could see a foot or more of snow by Christmas morning. It is something to watch of the next couple days. Like last time, winds will be an issue as the low passes, so the potential is there for a snowy, blustery Christmas. Below is the European's placement of the low Christmas morning.

Sunday, December 13, 2009

Snow accumulations on the way

After a couple days break from our last winter storm, it appears that our next snow maker is on its way. Radar image below at around 5:30pm already shows snow developing out to our west. HPC still has our area in a low risk of 4 inch snows, with a slightly higher risk just to the north of Eau Claire. Areas circled in blue are low risk (10%), green are moderate risk (40%), and red are high (70%). 18z GFS shows close to .3 inches of liquid, and higher snow ratios (close to 15:1) would put out around 4.5 inches of snow. However, snow may be slow to reach the ground with some drier air in place, so I think totals around 4 inches is possible...with 3-5 around the area. Winter Weather Advisories will remain in effect through the night tonight, and into the first part of our Monday. Areas shaded in purple are under the advisory. Cold air looks to be behind this system, so single digit highs are likely on Wednesday. Temps moderate again towards the end of the week, before perhaps another shot of cold air makes it down from Canada. Let the roller coaster ride continue.

Busy week of weather...snowy Monday?


Wow...what a crazy week it has been. The storm that was advertised by the forecast models for several day, and was mentioned in my previous post, actually came through pretty much as planned. This was a powerful winter storm that affected a very large portion of the United States, with the most significant impact in the higher terrain Colorado, northern Kansas, south central and southeast Minnesota, and pretty much all of Iowa and Wisconsin. The system came ashore in Southern California, trekked east through the four corners region then southeast through the Texas panhandle to eastern Oklahoma, before making a hook towards the northeast through eastern Illinois, to the southern tip of Lake Michigan, before exiting up into Canada. Systems that take this particular track are typically known as a "Panhandle Hooker" or "Texas Panhandler" due to their origination in the Texas Panhandle, then a sharp turn or "hook" towards the northeast. Think of these systems as a giant bucket, scooping up a lot of moisture from the Gulf of Mexico, and carrying it north. That is exactly what this system did, and was truly a classic winter storm. There was plenty of moisture, and plenty of cold air for it to be all snow. Below are three sets of maps. The top one shows the approximate path the storm took along with snow totals. The middle one is also snow totals, but with a closer look into the area. The bottom one is the low track, along with the millibar numbers. This system bottomed out at 976mb, which is quite impressive.







Snow was not the only issue with this system. Strong winds behind it whipped up the very light, fluffy snow, creating blizzard conditions across a large part of southern Minnesota and western Wisconsin. The highest gust reported was in Blue Earth, MN with a gust of 54mph. The winds also created very cold wind chills, as well as drifting snow, which made measurements difficult. The highest amount reported to the NWS in Chanhassen, MN was 13.3 inches in Zumbrota, MN in Goodhue Co., with Eau Claire, WI coming in a close second with 13.1 inches reported. Below is an animation of the storm, from start to finish. You can see how far north the precip made it, even when the center of the storm was well down to the south, and then see it as it deepens (strengthens) as it moves northeast. A typical sign of a storm strengthening is the isobars around the low tighten up, and create almost a spider web look to them.



Now, onto the next system that looks to affect central/southern Minnesota and west central Wisconsin. A low pressure system looks to come ashore in northern California, dip south towards Colorado (named a Colorado Low), then head north east towards Chicago. A band of accumulating snow appears likely over the areas mentioned above, with 2-4..perhaps even 5 inches of snow possible, if rain:snow ratios can get to be high enough, or if a bit more moisture can be tapped from the Gulf. In fact, even as I was putting this blog together, the National Weather Service issued a Winter Weather Advisory for pretty much the entire area Chanhassen covers, as well as a small portion that La Crosse covers. The counties in the advisory are shaded below. Expect the snow to begin late Sunday night, and last through the night into Monday morning. Many should expect a slow commute back to work on Monday. The HPC also highlighted an area, also shown in the map below, that has a low risk (10%) of seeing 4 or more inches of snow. It is the area that is to the south of the northern line, and to the north of the southern line (I hope that makes sense). If you're not a fan of the snow or cold, well, sorry. The snow looks to be around up through Christmas, as well as do the colder temps.

Friday, December 4, 2009

Colder air invades...potential Winter Storm next week

After a below normal October and above normal November, temps have, once again, dropped below normal numbers for our first week of December, and it doesn't appear the cold air is going anywhere anytime soon. In fact, long range models showing an even colder air mass heading our way for the end of next week. That cold air will help to stir up what appears to be the first significant snowfall of the season. Exactly where the snow will fall, and how much will fall is still way up in the air, but both the GFS and European models show this potent low, with the Euro being the stronger of the two. European models have great track records during winter months, and the GFS is coming into alignment with it. Some things in our favor...the cold air is here, and this system looks plenty cold. Surface temps will have a good week to cool off, so the snow shouldn't have a problem sticking. The models have also trended a bit north from where they were yesterday, bringing the low up close to Chicago, rather than across southern IL. If this system can nudge a bit further north and west, and track over Madison, then we would be in business. However, even now, accumulating snow looks possible. I think the kicker with this storm will be the timing of the very cold air mass behind it, with the low riding up the leading front. If the front moves slower, it should push the track further west. Faster movement means it would just shove the whole thing too far east, so there's still much to watch. Some other interesting facts about these systems...they are good wind makers, so even a little bit of snow, along with the wind can create very hazardous travel. Add a chill in the air, and you've got winter in Wisconsin. Second, snow ratios increase as the system progresses. The colder the temps are, the higher the ratio..so it could very easily start out around 13:1 snow:rain, and end up at 20-25:1 ratio. Higher snow ratios means it would take less liquid to accumulate snow, and the more powdery the snow is. (Example: .25 inches of liquid, 10:1 ratio would be 2.5 inches of snow...15:1 would be 3.75...25:1 would be 6.25 inches of snow...and so on.) Not great for snowman making, but simple to clear off a sidewalk or car. There are some downsides too, for those who like snow. Stronger systems can draw drier air into them, pretty much killing off any precip more quickly than expected. Also, if there's any strong/severe weather between here and the Gulf, then the potential is there for those storms to rob the moisture trying to make it up here. The good thing is that it looks like it will start far enough south that it will be able to draw the moisture down there and carry it north. Either way, this system will be closely watched, as many model runs are between now and Tuesday. In the shorter term, some accumulating snow is possible for southwest WI for the end of this weekend, mostly south of the I-90 corridor. COME ON SNOW!!