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February 8-12 model discussion


Rankin5150

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Gotcha. but I have to ask why For the past two days my grid forecast showed snow, Now it shows rain and some mix? For the common folks who check this from day to day will get confused. Is this talked about in the office?

We try not to waft too much on the ext p/types...esp when there is a good chance of a some sort of winter storm in the offing. What happens most times is a forecaster may use a different scheme to generate the wx grids than the previous forecaster. The main tools used are: wx from nomogram, the top down method, ra/sn from sfc T, and ra/sn from Tw. Each of these will give a different sensible wx outcome.

We need a more coherent policy as to what tools we should consistently use depending on the wx expected and continuity with the previous fcst. This has been an issue and yes we do talk about it. I cringe when I come to work and there is chance -fzra (all alone) in the ext range. We need to either say sn or ra or some sort of mix...unless of course confidence is high with the pattern.

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Especially with the past two storms if you start sounding the alarms early it's a set up for major fail. Also given the Euro it makes total sense.

And this is the southeast after all..it's extremely rare to see a snowstorm on a model 5 days out and have it verify close to what the models are showing. GSP is doing the right thing by not committing to a snowstorm this far in advance.

12z Canadian has come further south. Weak LP south of AL gulf coast. But a good trend from it's TN/KY solution. :thumbsup:

http://www.weatheroffice.gc.ca/data/model_forecast/236_100.gif

Nice to see the canadian trend toward the euro (although it does transfer energy to the southeast close but later than the gfs). Very close call for atlanta/athens. Looks like it starts as snow but could go to a mix/rain..however keep in mind when seeing these maps that the 0c line is valid for the specific time period while the precip is over the past SIX hours. Most of the precip could fall with 850s cold enough. Even so, looks like mainly snow for areas along and north of 85. Of course this is assuming there isn't a substantial warm layer near the surface like isohume mentioned.

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A couple positive things for this system that should prevent an apps runner is the huge arctic cold pool over SE Canada. That really doesn't favor something too far west, neither does the amplitude of the PNA ridge, which favors this wave to dig south. The kicker coming into behind also usually hints at a more progressive solution. My only fear for a system like this is if it shears out into a weaker storm. I would like to see this trend towards a more cutoff look like the euro has at hour 96. If we could see this wave stay tight and cutoff and progress SE, then this could be the biggest snowstorm of the season. At least for TN/NC/S VA.

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this is whats crazy for two day NWS IN GSP has shown snow for next week in the mtns. and now a mix. i don't see how the mtns would be a mix from everything i'm seeing and reading.

That's not true. The mix is on wed...and all sn or snsh is for Thu.

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It's interesting to look at the seasonal trends thus far this winter and apply them to this system. This is all anecdotal, of course, although I've followed the model trends pretty darned closely. So far this winter, in my opinion, the trends have been:

1) Underestimate the staying power of shortwaves that are moving out of the desert SW across the lower Miss. Valley

2) The Euro and particular has been overestimating the penetration of cold air in the medium range. At some point around the 3-5 day range, the 850 0C line starts retreating NW during successive Euro runs as the event draws near.

3) Especially in the 4-7 day range, the models this winter seem to be too fast -- as the event draws nearer, the arrival of the main disturbance seems to be delayed.

Will be interesting to see if these perceived biases affect the coming system.

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We try not to waft too much on the ext p/types...esp when there is a good chance of a some sort of winter storm in the offing. What happens most times is a forecaster may use a different scheme to generate the wx grids than the previous forecaster. The main tools used are: wx from nomogram, the top down method, ra/sn from sfc T, and ra/sn from Tw. Each of these will give a different sensible wx outcome.

We need a more coherent policy as to what tools we should consistently use depending on the wx expected and continuity with the previous fcst. This has been an issue and yes we do talk about it. I cringe when I come to work and there is chance -fzra (all alone) in the ext range. We need to either say sn or ra or some sort of mix...unless of course confidence is high with the pattern.

Thanks for taking the time to answer.

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I am very encouraged by the trends- I am now convinced GA sees at least some snow, and probably ATL. The question is how much. Probably not over 2-4" since if the system is too positive tilt/too strong, it probably will go too far north and we get mostly rain. A lesser amount with a more suppressed solution is possible also, but a complete screw with total suppression seems less likely as the Euro ensembles were very adamant in s having some precip. Not a lock for accumulation, but at this point would be surprised to at least not see a few flakes. The 12Z Euro is an important run.

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ukmet is way south. It has the surface low crossing florida. I am now becoming worried we could miss this thing to the south.:yikes:

Also 12z nogaps, shears out the wave and basically has no storm at all now.

I would rather have every model south and east right now, I don't remember any storm that was modeled as inland/apps runner that drifted southeast at the very end, but there has been plenty that have started off southeast and in the last 48 hours trended stronger and north/west.

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The Euro looks about the same so far, except maybe further east at 84 hours with the eastern Maine/offshore low, which it still bombs. Cold air spills into much of the country in its wake, and there's good separation in the flow, with the Rockies system taking shape. At 90 hours, the 0 at 850 is roughly I- 20, and snow in Ok, Ks, Colo.

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