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January Banter


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if anyone (besides me) would like to read up on this "trowal" feature, there is some good information here:

 

Mesoscale Snow Banding

 

http://www.theweatherprediction.com/weatherpapers/023/

 


 

Richard Pollman, Lead Meteorologist at the National Weather Service Office in Detroit says strong convection is the basic building block for frontogenesis forcing. “You might have a trough of warm air aloft within and stacked occluded system combining with TROugh of Warm air ALoft (TROWAL). All of these things work together to create instability.” Pollman also notes that it is important to consider Conditional Symmetric Instability where the movement of the parcel slanted, rather than straight up.

“Storms occluding on top of you are in the deepening phase, causing a deeper storm than one that occludes to the left of you,” Pollman says. His forecasting team looks for warm or occluded fronts as the first building block for frontal forcing. He says the extreme forcing occurs because the convergence and lift is over a concentrated area. “Lifting the moist, unstable air with added lift from convection helps the parcel to precipitate out,” he adds.

TROWAL is defined by Professor James T. Moore of the Cooperative Institute for Precipitation Systems at St. Louis University as a 3D sloping intersection of the upper cold front portion of the warm occlusion with the warm frontal zone. It is a wedge of warm air on top of cold air. He points to the exact location of TROWAL is usually along the ridge of high Theta-e values. It is the cyclonic portion of the warm conveyor belt that wraps around to the NW of the cyclone.

Pollman says, “TROWAL is between 700- 500 mb level. Frontal forcing is usually stretched from the surface up through to the 500 mb level, but most commonly found around 850 mb. It is a ridge of theta e extending into the cold sector of the storm. You can find it by looking at the 500-700 mb plan view of theta e. Trowel does enhance the lift, like summertime CAPE. And often, the TROWAL and forcing is accelerated within this winter instability. He says it is hard to forecast. “Usually there are three or four f-gen bands, but only a couple of them really come active.”

This banding can result in a blown forecast. Meteorologists may be able to forecast the large scale synoptic event, but locating the meso bands is more difficult until the storm is about two hours away. Weather balloon measurements may miss the entire event. This is another cause for missing the banding effect. Since balloons are released only every 12 hours, the banding event could have occurred in the middle of the launchings and go undetected until it shows up on radar. Meteorologists may have forecasted two to three inches of accumulation, when the stationary frontal forcing caused over six inches to fall. Pollman says there isn’t one specific thing that can be done to accurately predict where the heaviest snow fall will be. He says, “ You have to keep monitoring them on radar hour by hour.”

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I honestly hope for the snow, but I really hate the thoughts of that level of cold. It's probably not going to happen, but no one would have believed January 1985, December 1989, January 1994, or other big cold outbreaks would happen either. The timeframe around the 28th when the highs are 5 to -5 across the entire Tennessee Valley are just brutal. the -15 degree lows also dip into East Tennessee with the whole region below zero. 

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I would like to see one of those at 96 hours. It's bouncing around storms in a 2-5 day window. Hopefully one of them actually starts getting closer. It had a 300hr storm several days ago. I thought it was reeling it in earlier but seems like it's back at 300.

 

Possibly a good pattern, hopefully we cash in at least once.

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I would like to see one of those at 96 hours. It's bouncing around storms in a 2-5 day window. Hopefully one of them actually starts getting closer. It had a 300hr storm several days ago. I thought it was reeling it in earlier but seems like it's back at 300.

 

Possibly a good pattern, hopefully we cash in at least once.

 

When was the last time the GFS bounced around storms, even in fantasy land, for this many days in a row?  I recall 2010ish GFS showing some whoppers but this regularly, I think this is unique.

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Stovepipe, thank you for the link in the patterns thread (the Atl met). I liked his blog because even I could understand most of it.

 

-That blog says they're better able to forecast cold at ~10 days than they are storms. Does that mean within the next few days we will know if we're getting the really cold like we did last week? I can't remember how many days out we knew that was coming, but it seems like I was warning my brother by Thursday to go to my late mom's home and cover her outdoor faucets, etc. I guess I'm wondering HOW much better are they at temps than they are rain/snow.

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Patterns vs smaller storms makes sense, John. IF it happens, would it be similar to the temps you posted earlier? I may get another run of propane. I only use it when it's really really cold or I want a fire and use the heat pump the rest of the time. I have enough left for what our normal winters are, but this doesn't sound normal, at least lately.

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