Saturday, February 25, 2012

Brief Look into Winter 2012-2013

Here are forecasted precipitation and temperature anomalies (respectfully) for DJF (December, January, February). These forecasts are from the Ensemble Canonical Correlation Analysis (ECCA) forecast system at the Climate Prediction Center.

For precipitation, the ECCA is projecting above normal precipitation across the northern US, but also majorly in the West US, where a 40% chance is present. For the North US, it looks like widespread areas of up to 10% are present. The same is present in the Northeast.

As for temperatures, it appears a major area of below normal temperatures are forecasted in the Plains, Midwest, Ohio Valley, South Plains, Southeast, Northwest, Southwest. The High Plains and Northeast are slightly above normal, though.

This is simply a look into next winter and not a forecast.

February 28-29 Storm Discussion

"Dynamic System Signals Spring's Commencement"

A dynamic system is poised to strike the US and bring everything from snow to possible tornadoes. Here's the latest:

The strong system that comes through will be cold on the north part, indicating that the event will be quite a snowy one. Accumulations at this point look to be pretty substantial, with this strong a system not keeping 12 inches+ out of the question. Then again, it is a bit too far out to forecast snowfall. Any snowfall should be wind driven, with this strong a system making for possible blizzard conditions in the Dakotas into Minnesota.

Severe Weather
There does look to be some severe weather possible with this system. Lower, middle, and upper level winds look to be pretty strong during this event, with 700mb winds possible reaching above 70 knots (80 MPH). A strong jet stream (over 130 knots (150 MPH) are possible) combined with a strong lower level jet stream (70 knots + possible) makes for a very potent tornado set-up in the spring and summer. However, it is late February. Thus comes the issue of lack of instability. Without instability and lifting mechanisms, it looks like this event will cause some possible brief spin-ups in north parts of the rain area, with some more potent rotation in the severe weather area.

Questions can be asked below.

Potential Severe Weather Event Feb. 28 (Issued 2/25/12)

Top left image: 700mb winds
Top right image: 300mb winds
Bottom left image: 850mb winds
Bottom right image: Precipitation
The set-up for severe weather continues to intensify with major wind speeds at heights that are monitored for tornado development. If winds at any of the 3 wind images are high, it usually indicates a risk for some spinning motion in the air which could then cause tornadoes.
What the GFS is currently showing is a few clusters of storms that would then evolve into a squall line. Squall lines are traditionally unfavorable for tornadoes as they are cells in a linear formation, like trying to have car wheels turning inside a box. It just doesn't work.

It looks like this level of wind shear would be favorable for some tornadic activity, but it is impossible to predict where tornadoes will occur. These are just guesses.

There is the issue on how there is virtually no CAPE, or instability, forecast for the storms to use. Additionally, the Lifted Index (lift) and CINH (Cap that stops instability) are next to nothing, if nothing. The non-presence of those indices pretty much cancels any potential of severe weather. However, the way that this is mapped out tells me that a brief, weak tornado is possible. Thunderstorms will be likely as this is a squall line when you come down to it.