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Saturday, November 26, 2011
We do believe there is potential for over 4 inches of rain to fall in the Ohio Valley and parts of the Southeast. It looks like the instigator for this rainfall will be the cold front currently progressing east over the East US. After that, another factor will be a piece of energy associated with the front moving north, deepening and being cut off from the jet stream for a little while, leaving rain to move over the same areas for a while.
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At this point, it is unlikely that another huge warm burst will occur in the next week, signaling that the transition into winter is beginning. Meteorological winter does start on December 1st, so I guess it is about time for winter to start.
The rain this cold front will be putting down is fairly large- check out the forecasted total precipitation from the same model as the image above.
This forecast is NAM-biased. The only reason it is is because the NAM is showing this amount of snow shown while the GFS does show an area where snow could fall, but for some reason shows no accumulation where snow is clearly falling.
I never had a good feeling about this system and still don't, but I would rather have put out a warning and be wrong than not put out a warning and be drastically wrong.
That said, use this map with caution as this may be subject to drastic changes.
It appears that the cold front moving east will ignite an area of low pressure out by the Tennessee region. This area of low pressure will be cut-off from the jet stream, thus keeping the system in place. When the low does form, the 700mb relative humidity values will also deepen within the low, and will thus increase chances for precipitation.
This low will stay in position until a weak piece of energy will force the low northward and back into the jet stream. While the low is in position, however, models are predicting a piece of cooler air coming from the cold front to be cut off from the original cold air that the cold front is pulling. This colder air will turn counter-clockwise around the low and may produce some wet snow. Up to 4 inches of snow may be possible in Mississippi if this turns out as is projected.
We are currently producing a snow map for this system.