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Cold Fronts

Hello Everyone,

What a difference a day can make. On Monday, we saw record highs all across the eastern two-thirds of the nation, with over 400 record highs in December set. On Tuesday, temperatures began to fall as the month of December decided to actually make itself known. On a related note, the nation hasn’t seen much snow to start the month and we are well below normal in terms of snow cover. However, that is all about to change this weekend, as a large storm develops in SE Colorado in response to upper level forcing in place, as a large trough digs out in the western United States. With moisture in place, and the Gulf of Mexico open for business, this storm will likely be the precursor to future storms for mid to late December.

For the most part, we have seen a very mild November and early December, but temperatures will return to normal/below normal for mid-December after this storm moves through this weekend. An arctic cold front will dive south and eastward, bringing with it much colder air that has been trapped up in Canada for weeks. With this pattern change, the storm track, which has been predominantly to the north in Canada over the past month, will drop further south, bringing more unsettled weather to the eastern two thirds of the nation. In fact, much of the central plains states have been dealing with an exceptional drought, and hopefully, a more active with pattern will bring much needed precipitation to the region. The image below can give you an idea of just how dry it has been.

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The one thing that sticks out is the lack of drought seen in southwestern Texas as compared to last year at this time. Unfortunately, where one place receives rain, another place often doesn’t and that looks to be the case over much of the front range and central plains. If only the central US could pick up the type of rainfall that the west coast has been seeing. We’ll have to wait and see, but as the 6-10 day precipitation outlook shows, the central part of the US won’t be seeing much in the way of serious precipitation until late next week.

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Now, I realize I may have drifted off topic slightly, so, here’s a look at the forecast for the snowfall. Right now, it looks as if much of the snowfall will remain north of the Interstate 80 line. Much of the Dakota’s, Minnesota, Wisconsin, and Michigan will see the bulk of this snow from this storm, however, on Monday, if temperatures are able to cool enough into northern Illinois and Indiana. The first measureable snowfall of the season is on tap for the Minneapolis Metro, and Chicago could even see a couple of inches by the time all is said and done. In fact, according to long time Chicago Weatherman, Tom Skilling, Chicago is on track for a record longest period without measurable snowfall. It would tie the record (280 days) on Sunday, and perhaps break the record (281 days) on Monday. However, it is possible that Chicago could see measurable snowfall on Sunday, but the most likely chance of measurable snow would be more likely on Monday.

The following graphic depicts the probability of seeing snowfall with this upcoming system, both Sunday night and Monday. The heaviest snows will likely fall in North Dakota and central and north central Minnesota on Sunday. I believe these areas will see about 4-8” of snow by Monday. Minneapolis should see around 3-7” of snow, with places in the northern metro seeing the totals on the higher end.

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Those colder temperatures will follow the arctic cold front, bringing an end to the mild weather we have been seeing so far in December. I’ll bring a few updates on the storm as it evolves tomorrow and Saturday.

Until next time,

Meteorologist Mack

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Happy Thanksgiving everyone!

What a beautiful day for a great American Holiday. Many places in the US are experiencing record breaking Thanksgiving warmth, with temperatures in the 60s and 70s in the great lakes and plains states.

All that will come to an end as a powerful cold front charges east southeast tonight and tomorrow. Black Friday will be a chilly one for many people, but that won’t stop the shopping craze. Be safe out there and stay warm.

That fog that caused a travel headache in Chicago yesterday will be a topic for Saturday when I return home from the holidays. Stay tuned

Until next time

Meteorologist Mack

Last weekend, we saw very warm temperatures throughout the Eastern US before a powerful cold front swept those warm temperatures out the door and with it brought the coldest air mass of the season.

Before the big cool down, a few thunderstorms, some severe, brought hail and even a few tornadoes in the Minneapolis metro area. Now, you may be asking, how can there be tornadoes at this time of year?

Well, the setup for this event was quite interesting. I’m going to share with you a few graphics of the meteorological setup for this event.

In the second surface map, around sunset in Minneapolis, a stationary warm front is situated over central Minnesota and a cold front extends from the area of low pressure just to the west of the Twin Cities, somewhere around the St. Cloud area. The Twin Cities happen to be in a favorable region for tornadoes to develop, as winds at the surface are southerly and winds in the mid-levels (not shown) are from the west. This creates what is known in the world of meteorology as shear. Shear is key to the development of tornadoes, along with moisture, instability, and a source of lift. On this day, the main ingredient that was lacking, was instability. If this system had had a more warm, moist unstable airmass to tap into, their may very well have been a much greater tornado threat.

In the first surface map, around 9PM, the system begins to occlude, meaning the low pressure at the surface begins to become displaced with the center of the storm in the middle and upper levels of the atmosphere. The area where the warm front and cold front intersect with the surface low, is called the triple point. This is often a place where the greatest shear and instability are located, and it is no coincidence that it is over the area where these tornadoes occurred.

Take a look at the links below to see the surface maps from this event.

Ultimately, these tornadoes occurred because of they formed in an environment that was favorable for development. However, if there was more lift and instability in the atmosphere on this day, things could have been much worse.

Take a look at a few images of the damage from the NWS in Chanhassen. They surveyed the damage and determined the EF ratings for the tornadoes.

For more on this event, check out the National Weather Service’s damage assessment on their webpage at the link below.

http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=mpx&storyid=89269&source=2

Keep watching for new posts!

Until next time.

Meteorologist Mack

Hey everyone,

I know I haven’t been posting much lately, but I’ll be back at it in full swing now. Not much weather to talk about this week except for the “true” return of winter-like temperatures to much of the United States. Early this week, we saw a large and expansive storm develop in Colorado in a process called lee-cyclogenesis, a process in which low pressure develops in the lee of the Rocky Mountains and strengthens as it moves ENE into the Midwest and Northern Plains States. With that came some very heavy rain, and even severe weather for parts of the Southern and Central Plains, as storms erupted in a line along the eastward advancing cold front. Damaging winds and even hail were seen in places such as Minneapolis and even Chicago. Take a look at some of the pictures below.

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The picture above is from North Minneapolis on November 10th. Some of the hail was up to quarter size.

Naperville, a suburb of Chicago, saw hail as well:

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And a video as well:

Now, certainly, hail isn’t typically seen in November in places such as Naperville, or Minneapolis, but in this case, there was enough cold air aloft to form the hail and a very shallow layer of warm air at the surface in the form of a northward moving warm front. With that, storms broke out and small hail was seen in both locations on the 10th.

Behind this front, many places saw a temperature drop of over 50 degrees in just 24 hours!!! Now that’s a cold front!

Over the next few weeks, temperatures will, in fact, be warmer than normal, but don’t expect to see in temperatures in the 60s and 70s anytime soon in the upper Midwest. However, there does not appear to be any snowstorms looming for Thanksgiving week, but it is still over a week out, so I’ll be sure to keep you updated and let you know if that changes.

Until next time,

Meteorologist Mack

Good Evening,

What a difference a day makes! Or for that matter, an hour. After experiencing temperatures in the upper 70s and low 80s, early this week, temperatures have taken a nosedive following the passage a powerful cold front. Some extreme examples of 1 Hour temperature drops include the Quad Cities area, with multiple places experiencing a drop of over 20 F! Temperatures in Chicago plummeted from 75F to 57F in only 1 hour this evening. A few places even saw snow, as the atmosphere rapidly cooled, conditions were just right for light snow to form in much of Minnesota and Wisconsin. Minneapolis saw its first snow of the season, although little to no accumulation was seen.

Expect this powerful fall cold front to continue pushing off to the east and bring with it a much colder continental polar air mass to replace the much warmer air mass out ahead of it.

With a final look at those temperature drops, take a look at the 3 Hour Temperature Changes observed by the National Weather Service over the Midwest this evening. Incredible that some places have seen drops of over 20F. Image

Tomorrow’s blog will focus on the impact that Hurricane Sandy could have on the East Coast this weekend. Until next time.

Meteorologist Mack