Zig-Zag: Saturday snow threat shifts south toward Metro!

Updraft Headlines:

13 degrees – dew point in the Twin Cities Wednesday

45 degrees – dew point in Phoenix, AZ Wednesday in the Sonoran Desert

(More than twice the moisture in Phoenix vs. the Twin Cities)

60 – 90 miles – southward shift on storm track for Saturday’s potential snow event

50% chance – Latest Weather Lab estimate for a plowable snow in Brainerd & Duluth Saturday

60% chance – Latest Weather Lab estimate for the first 1″ snowfall at MSP Airport Saturday night

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Growing metro snow chances Saturday?

This is why responsible meteorologists don’t make specific snowfall predictions 3 days to a week in advance of a potential snowfall. It’s also why we usually turn prematurely gray!

In the latest forecast model twist, the GFS and NAM models have locked on to a “southern solution” for our potential Saturday snow event. That shift would put the center of accumulating snow close to or right over the Twin Cities metro.

Here’s the latest thinking from the weather lab on our growing snowfall chances this weekend.

The System:

The same “Colorado Low” I’ve been tracking all week. Low pressure spins up in Colorado Friday, and quickly races northeast on a fast moving jet stream toward the Upper Midwest Saturday.

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Storm Track:

The latest model runs shift the storm track 60 to 90 miles south. If it verifies, that would bring the rain snow line south of the metro, meaning accumulating snow for the highly populated Twin Cities.

The latest model tracks bring the surface low through Iowa to south of La Crosse by late Saturday.

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GFS model 6pm Saturday shows surface low in NE Iowa. Rain snow line (white) is south of the metro with snow in metro.

This is a far more favorable track for accumulating snow in St. Cloud and the Twin Cities.

Timing:

Rain and snow should develop Saturday and linger into Saturday night.

Temperature Profile:

The southward track shift brings the critical rain-snow line south to a Mankato-Twin Cities line around midday Saturday. As the system swings by, any rain or mixed precip would quickly change to snow Saturday afternoon in the metro.

Potential Accumulations?

With 48 to 60 hours until the core of event, It’s still too early to pinpoint or issue credible specific snowfall forecasts.

The models have already shifted the track of Saturday’s system a few times, and may do it yet again over the next 48 hours.

I could tell you there is going to be 6″ of snow in Brainerd or Duluth, but it’s just not credible to say that reliably yet. In fact the latest model runs are leaning lower than that total.

The best thinking/advice at this point is to say there is a growing chance of accumulating snow Saturday and Saturday night for the metro and south central Minnesota cities like Willmar, Mankato and St. Cloud. You may want to locate your shovel just in case!

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GFS 120 hr snowfall shifts accumulating snow into metro!

One key observation of this system so far is that the models are consistent in keeping it as an “open wave.” This means the system would move through faster than a “closed low” keeping potential snowfall totals down.

The Weather Lab philosophy is to issue specific snowfall forecasts about 24 hours in advance of anticipated snowfall. This is generally the peak window between letting the models reach peak accuracy, and giving listeners enough time to react accordingly.

Even with great advances in forecast models, forecasting snowfall is among the most difficult forecasts a meteorologist has to make. It’s just not credible to throw out specific totals days or a week in advance. I wish it was different, but the state of the science of meteorology just isn’t good enough to make consistently accurate snowfall forecasts days in advance. Anyone who tells you otherwise is blowing smoke.

Stay tuned as new model runs come in through Thursday & Friday. This system will probably throw a few new twists at us yet!

NOAA “Greehouse Gas Index” on the rise in 2010:

Measurements by NOAA confirm what we already know. We’re putting more greenhouse gasses into our atmosphere every year.

According to the index, earth’s greenhouse gasses have become 29% more efficient at warming the planet since 1990.

One interesting twist is that while CO2 continues a steady rise, atmospheric methane is rising after a decade of holding steady. Some climate scientists fear that Arctic warming is releasing more methane into the atmosphere. Methane is a very efficient greenhouse gas.

From NOAA:

•A continued steady increase in carbon dioxide: Global carbon dioxide levels rose to an average of 389 parts per million in 2010, compared with 386 ppm in 2009, and 354 in the index or comparison year of 1990. Before the Industrial Revolution of the 1880s, carbon dioxide concentration in the atmosphere was about 280 ppm. Carbon dioxide levels swing up and down in natural seasonal cycles, but human activities – primarily the burning of coal, oil, and gas for transportation and power – have driven a consistent upward trend in concentration.

•A continued recent increase in methane: Methane levels rose in 2010 for the fourth consecutive year after remaining nearly constant for the preceding 10 years, up to 1799 parts per billion. Methane measured 1794 ppb in 2009, and 1714 ppb in 1990. Pound for pound, methane is 25 times more potent as a greenhouse gas than carbon dioxide, but there’s less of it in the atmosphere.

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PH

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