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Office: BOU

FXUS65 KBOU 130341
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
841 PM MST Tue Dec 12 2017

.UPDATE...
Issued at 833 PM MST Tue Dec 12 2017

No significant changes planned in the grids for tonight's
forecast. One short wave embedded in the flow aloft will pass to
the north and east of the state on Wednesday morning. It's
associated cold front is still expected to move into the Denver
area around sunrise, with increasing clouds over the northwest in
the afternoon ahead of a stronger system in the northern Rockies
dropping into the Front Range Wednesday night.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 310 PM MST Tue Dec 12 2017

Upper ridge upstream of Colorado will lead to a pleasant evening
and into the overnight hours. A few high clouds and light winds
tonight will allow overnight lows to cool off into the 20s across
the Plains, near 30 across the I-25 urban corridor, and teens in
the mountains.

A weak short wave trough will move across the northern Plains
early on Wednesday and force a cold front south across the Plains
of Colorado. Expect high temperatures to occur late morning to
near noon just before frontal passage as the front enters Colorado
around sunrise, reaches metro Denver mid-morning. Steady temps
around 50 should occur Wednesday afternoon. The mountains will
see similar temperatures compared to today, with 700 mb temps
cooling 1-2 degC, so expect highs in the upper 30s to low 40s
there.

Chances of precipitation increase significantly Wednesday
evening in the mountains (and eventually Plains) as a short wave
trough moves quickly south-southeast towards central Colorado. The
trough will dig south given a 100-120 kt jet on the backside of
the trough. These features will impact Colorado weather and the
potential for snow overnight into Thursday, discussed below.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 310 PM MST Tue Dec 12 2017

The upper trough passing over the state Wednesday night and
Thursday morning should produce a period of snowfall for the
mountains, with snow accumulations being limited by the short time
frame that the snow is expected to stick around. The upper trough
will be moving out of the state by Thursday afternoon, with strong
subsidence expected to be over the state by Thursday evening.
Surface high pressure will be building in from the north behind
the trough and this will tighten up the pressure gradients across
the plains. Gusty north-northwest winds are expected across the
plains, which might be approaching high wind criteria for a few
hours. The northerly winds will also be bringing in chillier
temperatures through the day.

On Friday, pressure gradients will relax and warmer temperatures
will move back in. Another stronger trough is forecast to drop
over the state Saturday night. The ECMWF and GFS are in good
agreement with the storm as it moves across the state in a track
similar to Thursday's trough. This trough will also be driven by a
110+ knot upper level jet. Plains areas may also pick up some
precipitation from this trough. After Sunday, the flow aloft will
become more westerly as it looks like the blocking ridge pattern
than has been over the western U.S. will begin a retrogression out
over the eastern Pacific. If the ridge does retrograde, then the
storm track over the Rocky Mountain Region may become a little
more active than we have had the past several weeks. In the
meantime, Monday and Tuesday still look dry.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 833 PM MST Tue Dec 12 2017

VFR through Wednesday evening. Diurnal winds tonight into early
Wednesday. Expect a weak cold front to impact the metro area
terminals with a wind shift to the north and northeast 15-16z,
and increase in speed to 10-15 kts through through 00Z.
Precipitation chances go up late Wednesday night along
with likely MVFR ceilings after 00z with a chance of rain/snow
turning to snow in the evening.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Cooper
SHORT TERM...Schlatter
LONG TERM...Dankers
AVIATION...Cooper



Office: PUB FXUS65 KPUB 130516 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 1016 PM MST Tue Dec 12 2017 .SHORT TERM...(This evening through Wednesday) Issued at 307 PM MST Tue Dec 12 2017 Dry northwest flow aloft will remain over the area tonight and into Wed. Winds tonight will start to increase, mainly over the higher elevations, but some of the lower elevations east of the mountains are expected to see westerly surface winds develop overnight. In areas where the westerly winds develop, overnight temps should be relatively mild. Wed morning a weather disturbance will be moving from NE into KS and will send a front thru eastern CO. This front will bring northerly winds to eastern portions of CO, and the winds could be a bit gusty over the far southeast plains. The winds will cause an elevated fire weather concern, but the RH values are expected to be too high for any fire weather highlights. At this time, it looks like the winds will decrease thru the afternoon hours, and will become easterly along the I-25 corridor. It looks like the weather will remain dry across southeast and south central CO thru Wed afternoon, however increasing cloud cover is expected, spreading from north to south over the area as a weather disturbance moves southward from WY toward CO disturbance will be approaching the state from the north. High temps on Wed are expected to be cooler than today, with mostly 50s acrs the southeast plains and the upper Arkansas River valley, and in the 40s or around 50 in the San Luis Valley. .LONG TERM...(Wednesday night through Tuesday) Issued at 307 PM MST Tue Dec 12 2017 Wednesday night and Thursday...Latest model runs indicate an intensification of the next incoming shortwave Wed night through Thu, which will bring a shot of colder air as well as some pcpn for a good portion of the forecast area. Snow showers will increase across the central mts and Rampart Range by midnight Wed night, then as the shortwave drops to the southeast showers will spread across all of the higher terrain as well as much of the plains through the day Thu. Snowfall amounts are expected to remain minimal, with an inch or two of new snow possible over the higher peaks. Pcpn will then taper off by midnight Thu night. Highs are forecast to only climb into the upper 30s to mid 40s on Thu, then min temps Thu night will likely be the coldest of the extended period with readings in the single digits for the high valleys, and teens to lower 20s for the plains. Friday...Temporary ridging over the western US will again produce dry and slightly warmer conditions across the state for Fri, with highs in the mid 40s to mid 50s for the high valleys, and 50s to near 60F for the plains. The next upper disturbance to affect Colorado will be crossing the Pacific NW Fri evening. Saturday through Monday...The next incoming shortwave will follow a similar path, bringing the chance for pcpn to initially the higher terrain Sat morning and then the remainder of the forecast area through Sun. Increasing westerly sfc winds will help boost temps on Sat into the 40s to around 50F for the high valleys, and into the 50s for the plains. A sfc cold front late Sat will drop temps on Sun into the 30s to mid 40s, then ridging for Mon will bring a return of dry conditions and 5 to 10 degrees of warming. Moore && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1014 PM MST Tue Dec 12 2017 VFR conditions the next 24 hrs at all taf sites. Cold front arrives just after the end of the taf valid period, with lowering cigs and a chance for snow and IFR conditions at KPUB and KCOS by early Thu morning. && .PUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...28 LONG TERM...MOORE AVIATION...PETERSEN
Office: GJT FXUS65 KGJT 130515 AFDGJT Area Forecast Discussion National Weather Service GRAND JUNCTION CO 1015 PM MST Tue Dec 12 2017 .SHORT TERM...(Tonight through Wednesday night) Issued at 322 PM MST Tue Dec 12 2017 Yet another pleasant day on tap thanks to the high pressure to our west while temperatures are running anywhere from 1 to 6 degrees warmer than yesterday. For the overnight, we can expect similar temperatures to what we've seen recently as minimal cloud cover will allow for decent radiational cooling. On Wednesday, clouds will be on the increase across the CWA from north to south as the jet stream starts digging southward. The jet will support a short wave that is progged to move through the area from Wednesday evening through midday Thursday. These clouds may keep temperatures a few degrees cooler than those seen today but not much modification anticipated. Since the short wave will be dropping down from Canada, there won't be significant moisture for the wave to work with. Having said that, models continue to show 1 to 2 inches, maybe as much as 4 inches for the higher elevations of the northern and central mountains, less for the San Juans. The northern valleys may also see a few snow showers but minimal to no accumulations expected at this time. .LONG TERM...(Thursday through Tuesday) Issued at 322 PM MST Tue Dec 12 2017 Some lingering snow showers will continue for the Rockies during the day Thursday but significant accumulations are not expected. Some clearing will commence from noon onwards Thursday but high temperatures will drop 3 to 5 degrees thanks to the short wave ushering in some cooler air to the area. Friday looks to be a nice day with some high clouds moving overhead from time to time. On Saturday, another shortwave will set its sights on eastern Utah and western Colorado. Upper level support for this feature will be a bit more robust than the wave on Thursday with a deeper trough and upper level jet eventually forming a closed low over the four corners region before moving into Arizona and New Mexico. Precip looks to start around noon Saturday up north before slowly shifting southward through Sunday evening. High temperatures also look to drop off by about 5 to 10 degrees as another shot of cold air moves in. Of course, the European is showing another quick wave moving through with minimal moisture so the end result remains up in the air. More to come on this next system. Conditions improve Monday giving way to sunny skies Tuesday with the next chance for any significant precipitation looking to be the end of next week. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1014 PM MST Tue Dec 12 2017 VFR conditions will prevail over the next 24 hours. Mid to upper level clouds will increase from north to south after 12z Wednesday morning throughout Wednesday evening. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...TGR LONG TERM...TGR AVIATION...CC