December 2017: End Of The Year Weather

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December 2017: End Of The Year Weather

Postby srainhoutx » Mon Nov 27, 2017 2:54 am

It looks like December will begin rather chilly as a strong shot of colder Canadian air arrives late this week. I am not seeing any significant rainfall chances in our sensible weather forecast into the coming weekend.

Changes are brewing during the first full week of December via the Ensemble Guidance suggesting significant pressure falls across the West Coast and Inter Mountain West as a deep trough and a winter like low pressure system exists the Southern/Central Rockies into the Plains and pulls some very cold and snow packed Canadian air well S into the Eastern 2/3rds of the United States near December 7th, +/- a day our two. There are strong signals via our Hemispheric Reconnection Indices suggesting a blocking regime may be possible. A - EPO/-AO/-NAO pattern with a hint of a + PNA suggests that a very deep and cold trough may become established by December 8th or so ushering in the coldest air of the season. We'll need to monitor for any unforeseen upper air disturbances rotating around that deep Central US trough or possibly a disturbance riding along the sub tropical jet stream atop that cold air at the surface next week. We will see.
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby tireman4 » Mon Nov 27, 2017 10:38 am

To further go with what Srain has alluded to...this is from NWS Hastings, NE..but...
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby sambucol » Mon Nov 27, 2017 1:55 pm

Any idea how cold it will be here next week with the front?
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby jasons » Tue Nov 28, 2017 5:19 pm

Gee we need some rain. It's either feast or famine for us. No in-between any more. Won't debate the causes, but I think our climate is permanently whacked.
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby srainhoutx » Tue Nov 28, 2017 6:32 pm

The afternoon Updated Extended Analogs/Upper Air Pattern continues to advertise a change is brewing around the 8th of December, +/- a day or 2.
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500hgt_comp_sup814.gif
814temp.new(3).gif
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby harp » Tue Nov 28, 2017 6:46 pm

Interesting.... ^^^^^
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby DoctorMu » Wed Nov 29, 2017 12:16 am

NOAA and the GEFS Ensemble holding strong for blue norther.

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GFS - not so much.

Canadian is bringing the heavy (firewood) lumber:

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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby DoctorMu » Wed Nov 29, 2017 12:21 am

The dreaded AccuWeather, but still...in agreement.

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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby srainhoutx » Wed Nov 29, 2017 7:57 am

Looking at the overnight GEFS/ECMWF EPS Ensembles for hour 192, I see a very similar Upper Air Pattern suggested by those computer schemes. Both suggest strong Ridging along the West Coast extending N into Alaska and portions of the Artic with a deep trough developing across Central and Eastern Canada into the United States along and East of the Rocky Mountain Chain. With a N to NW flow aloft, dense snow refrigerated cold air locked up in Canada should spill South with ease all the way down into Texas.
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11292017 00Z GEFS 192 gfs-ens_z500aNorm_namer_33.png
11292017 00Z ECMWF EPS 192 ecmwf-ens_z500aNorm_namer_9.png
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Re: December 2017: Pattern Change/Much Colder Weather Possib

Postby srainhoutx » Thu Nov 30, 2017 8:24 am

I don't see any significant changes in the Medium Range sensible weather forecast for next week other than an increase in our rain chances which will need to be monitored. Still looking like the first in a series of strong cold fronts arrive mid next week with rain chance slowly increasing Tuesday into Wednesday as the front nears our Region. There is a chance of some over running nasty cold rain Wednesday night into next Thursday with temperatures in the low to mid 40's.

The extended Ensemble Guidance advertises that each additional cold front will bring colder air each shot suggesting we step down and see potentially colder air with each of the Canadian Cold Fronts into mid December. Not going to attempt to make a forecast for the extended range as we know the models can't be completely trusted beyond 3 to 5 days, but let just say that if the current Upper Air Pattern projected via the ensembles hold, somewhere across the Northern Plains could see temperatures nearing the -40F range as we near the Mid December timeframe. It is looking like Winter is arriving in Texas.
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