Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 160535

Area Forecast Discussion
National Weather Service Pueblo CO
1035 PM MST Tue Jan 15 2019

Issued at 928 PM MST Tue Jan 15 2019

Updated lows across the area, with lows likely being achieved at
this time across the the valley locales, as clouds continue to
increase from the west through the rest of tonight.


.SHORT TERM...(This evening through Wednesday)
Issued at 251 PM MST Tue Jan 15 2019

An upper level disturbance moving across the area tonight will bring
snow to the CONTDVD.  Favorable southwest orographic flow over the
Eastern San Juan Mtns will result in this area likely seeing the
highest accumulations overnight, but the central mtns will see a few
inches as well.  Some light snow is also expected to spread to the
eastern mtns tonight, with the potential for just some light
accumulation.  The high valleys may just see some scattered light
snow overnight, and the eastern plains should remain dry.

Another disturbance affects the area on Wed, and snow will continue
to fall along the CONTDVD, but by the afternoon additional
accumulations are expected to be light.  The rest of the area is
generally expected to be dry on Wed.  Westerly winds will increase
over the higher terrain on Wed, and over the Upper Arkansas River
Valley, Fremont county and mainly southern portions of the I-25
corridor, from about Pueblo and southward.  Southern portions of the
San Luis Valley should also see some westerly breezes Wed afternoon,
which should help the temps warm, probably to around average.  Temps
across most of the southeast plains should be in the 50s.  Gusty
winds over the mtns are expected to cause area of blowing snow on
Wed, so will keep that in the forecast.

The current Winter Weather Advisories still look reasonable, and
snow amounts in other mountain locations still look like they will
remain below advisory criteria.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 251 PM MST Tue Jan 15 2019

Wednesday night - Thursday...

Behind the Wednesday shortwave, heights rise, flow becomes
westerly, and the atmosphere dries as a shortwave ride builds over
the Rockies. This will bring an end to the snowfall over the high
terrain during the evening on Wedensday. Additional accumulations of
1-3 inches are expected in the central mountains, and up to 1 inch
over the eastern San Juans. Wednesday night low temperatures will be
in the mid 20s across the plains and single digits to teens in the
high valleys.

The ridge will bring a brief period of dry and pleasant weather to
the forecast area during the day on Thursday. High temperatures will
be in the mid to upper 50s across the plains, and mid 30s to mid
40s in the high valleys.

Thursday night - Friday night...

Attention turns to the next significant storm system that will
impact all of the forecast area. Deterministic and ensemble models
agree on the general evolution of the key synoptic scale features.
Uncertainties lie in the exact track of the wave and precip
chances/amounts across the plains and eastern mountains. A shortwave
trough will dig into the Four Corners region from the northwest
Thursday night to somewhere near or south of the Colorado/New Mexico
border by late Friday morning. An associated northwest to southeast
oriented 130+ knot 300 mb jet will become more amplified as a ridge
builds over the west coast. The exit region of the jet will round
the base of the trough into New Mexico during the day Friday,
increasing shear and curvature vorticity in the shortwave. Large
scale forcing for ascent associated with the left jet exit region
and the strengthening shortwave will expand and increase over
Colorado from northwest to southeast Thursday night into early
Friday evening. This will deepen a surface low somewhere near the
TX/OK Panhandles region, and drive a cold front down the eastern
Colorado plains, behind which moisture increases.

Confidence is high that the Continental Divide will see advisory to
warning criteria snowfall with this system, regardless of minor
shifts in storm track that still appear possible. Confidence is
still low in precip evolution across the plains and eastern
mountains considering run-run inconsistencies on the exact position
of the upper low by Friday evening. Slight meridional shifts change
the position of the surface low, surface wind direction, and
greatest large scale lift. The current storm track (closed upper low
over northeast New Mexico) would support at least a period of
snowfall (or rain changing to snow) across much of the plains behind
the front when large scale forcing is focused over southeast
Colorado during late Friday afternoon into early evening. The
greatest potential for accumulating snow would be along the Palmer
Divide, Raton Mesa and Wets where the north/northeasterly flow would
be upslope. Snow chances across much of the rest of the plains would
decrease as the greatest large scale lift quickly exits and
downslope flow dominates (especially from KCOS to KPUB).

We can be confident that it will become quite windy behind the cold
front. Latest guidance indicates sustained winds of 20-30 mph with
gusts to 50 mph will certainly be possible Friday evening,
especially over the far eastern plains where the surface pressure
gradient will be tightest. Friday high temperatures should reach
around 50 across the plains, and will depend on the timing of the
cold front passage.

Saturday - Tuesday....

Behind the Friday storm system, a ridge will build over Colorado
leading to dry weather for the weekend. Residual breezy winds
Saturday morning should become light during the afternoon.
Temperatures will be cooler on Saturday, with highs only in the 30s
across the plains, and 20s to 30s in the high valleys. Temperatures
will warm to near 50 across the plains on Sunday.

Models hint at the next trough impacting the forecast area on
Monday, but deterministic and ensemble spread is too great to have
any confidence in an outcome.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1035 PM MST Tue Jan 15 2019

VFR conditions with bouts of high clouds expected at COS and PUB
over the next 24 hours. Light winds overnight will become breezy
westerly 10-20kts aft 16Z.

Moist southwest flow aloft ahead of a passing upper level
disturbance will bring snow to the higher terrain west of ALS
through the day tomorrow, with isolated showers possible across
the San Luis Valley through 12Z. Low VFR and MVFR cigs expected
at ALS, with patchy IFR status possible through the early morning
hours. Breezy southwest winds of 10-15kts looks to break strong
inversions across the valley and help melt snow this afternoon,
though still will likely lead to IFR and LIFR cigs and fog
redeveloping at ALS aft sunset.


Winter Weather Advisory until 8 PM MST Wednesday for COZ068.

Winter Weather Advisory until 11 PM MST Wednesday for COZ060.



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