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Dec 24-25 Snowstorm part 2


jhamps10

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Height field amplification can happen quite rapidly, and considering this run of the NAM has yet to phase the PV and eject it NE, low level CAA has yet to increase. Once that does, the 850 low will take little time forming along that thermal gradient. Incipient cyclogenesis will happen very fast and the upper level height field will respond. That EC vortex is playing a role but if you look at the height field it is quite weak overall even though it looks like a deal-breaker. This type of storm development is a great example of non-steady development/rapid amplification of a disturbance. Things can change quite quickly.

Last 3 NAM runs all have a PV max of 51-57 somewhere in the run. I am very surprised that it is not initiating the creation of a surface low, and a strong one at that.

Let's just say that if any storm has the possibility to surprise, this one's it.

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In recent history I notice we have shifts inside 54hrs... Thats why I am not on the bus. 2 nights before the 12th snow event it showed nothing then a day later BOOM... We got 6 out of that but 2 days before it showed nada.... So I hold out hope for that very reason. The models will catch something at the last minute I feel it may be that we get 2-4 but hell I will take it at this rate.

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Last 3 NAM runs all have a PV max of 51-57 somewhere in the run. I am very surprised that it is not initiating the creation of a surface low, and a strong one at that.

Let's just say that if any storm has the possibility to surprise, this one's it.

I was just looking at that while looping the H5 vort map..This is def a tough one to understand and forecast for but fun as always.

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Last 3 NAM runs all have a PV max of 51-57 somewhere in the run. I am very surprised that it is not initiating the creation of a surface low, and a strong one at that.

Let's just say that if any storm has the possibility to surprise, this one's it.

Remember a trough and/or a S/W is a depression in the height field. While the PV looks intense migrating through the flow field, if you look at the heights alone, it is really not impressive at all. 564 dm heights are not that low, and almost all of that cold air aloft/energy is wasted over the moist baroclinic zone through latent heat processes. All that qpf over MO/AR acts to weaken the disturbance aloft through even more warming in the mid levels. Height rises occur and this PV weakens more.

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Remember a trough and/or a S/W is a depression in the height field. While the PV looks intense migrating through the flow field, if you look at the heights alone, it is really not impressive at all. 564 dm heights are not that low, and almost all of that cold air aloft/energy is wasted over the moist baroclinic zone through latent heat processes. All that qpf over MO/AR acts to weaken the disturbance aloft through even more warming in the mid levels. Height rises occur and this PV weakens more.

Expanding on this. Look at the upper level temperatures associated with the PV. Note how cold they are at 500 hpa at 36 hours over Arizona.

post-999-0-87084400-1292989638.png

by 72 hours, after interacting with the moist baroclinic zone, note how much temperatures have risen at 500 hpa. Heights rise and the PV weakens because it is detached from the polar jet stream. The upper level cold front weakens, and therefore the baroclinity of the PV itself weakens and is therefore insufficient to incite strong cyclogenesis on its own. If the northern stream didn't phase with this weak PV, it would slowly "disintegrate" with heights continuing to rise/temps warming until there was just a remnant circulation.

post-999-0-46140800-1292989642.png

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I guess it could be worse. Atleast we have stale snow cover for christmas.

Actually the snow doesnt even look stale at all (save for some snowbanks near the busy roads), still fresh looking in residential areas, and that is downright amazing considering its been 10 days since the snowstorm with nothing but a slight dusting (19th) and a handful of traces since.

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