Updraft: December 1, 2011 Archive

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The feel of a winter day

Posted at 6:33 AM on December 1, 2011 by Craig Edwards
Filed under: Cold, Daylight, Snow

An east to west band of light snow accompanied an invasion of colder air into Minnesota overnight. Snowfall from Duluth to Alexandria southward tallied up to an inch in isolated locations. Most places accumulated a half inch or less, including the measurement at the Twin Cities International Airport.

The narrow band of light snow and remaining cloud cover will continue to push through the southeast corner of Minnesota this morning. Afternoon temperatures will hold close to seasonal normals. Colder air is poised to invade the Upper Midwest on the weekend and extend into Tuesday. Indeed, with the low sun angle and shortendaylight hours you'll experience the chill of a Minnesota winter.

Meteorologists are still pondering the model data to determine the northward extent of a snow system coming out of the Colorado region on Friday. Southeast Minnesota, from Albert Lea to Rochester and Hastings looks to be the most likely area for the potential for accumulating snowfall late Friday night through Saturday.

Current thinking from the NOAA Prediction Center on the favored region to receive four inches or more of snow on Saturday.

Forecasting snow amounts is problematic due to the lack of a definitive center of low pressure. Here is the graphic of the track of the lowest pressure for the next couple of days. Note the weakness of the surface low as the system moves through Iowa.

Let's see how this plays out in the next forty-eight hours. There is still plenty of time to refine the forecast before the first flakes fly.
CE

Crafting a forecast with the tools at hand

Posted at 3:34 PM on December 1, 2011 by Craig Edwards (1 Comments)
Filed under: Cold, Forecast models

It's times like these where a meteorologist gets pumped about the profession. Sorting through the computer models, matching the satellite data with previous computer model output and tracking surface weather make the job challenging and sometimes even rewarding.

Here's the infrared satellite imagery at mid afternoon. The large scale circulation over the southwest corner of the US appears to be more tame than the weather reported from southern California to Colorado. Winds have gusted from 60 to 80 miles an hour from near Los Angeles to Las Vegas in the past eighteen hours. The national news networks are delivering the details of this savage weather.

Meanwhile another surge of cold air is sweeping through Albert, tracking toward the Dakotas and Minnesota as indicated in the enhanced (red) cloud tops.

These two separate systems are likely to meet up from Minnesota to Missouri on Saturday.

Here's an image of the mid level jet stream from noon today. The wind field is approximately 18k feet.

The closed circulation of the upper low stands out over southern California and Arizona. Wicked winds have been induced at the surface as a result of the topography and the atmospheric dynamics of this system.

By noon on Saturday, as shown by the NAM, the low in the southwest has weakened and continues to track east, but no longer a closed circulation. At the same time a trough has been craved out in North Dakota. These two forces of nature will combine to create the problematic weather in southeast Minnesota.

The reflection of weather on the surface is what television weathercasters typically deliver to the viewers to keep the meteorology simple. But significant precipitation is induced by factors at cloud level of 5K and greater.

Here's the consensus track of the surface low from NOAA for the next couple of days. Indeed a favorable track for snow in our neck of the woods, but not a particularly deep center of low pressure.

Put this altogether and it still targets the best chance for accumulating snow over southeast Minnesota. NOAA's Environmental Prediction center indicates the most likely area for four or more inches of accumulation on Saturday.