Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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796
FXUS65 KBOU 240159
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
759 PM MDT Sat Sep 23 2017

.UPDATE...
Issued at 743 PM MDT Sat Sep 23 2017

Radar and observations showing heavier band of rainfall now
shifting east of the Denver area and rain showers gradually
expanding over the northeast plains. The main upper low is has
dropped into Southern Utah while jet streak across Central
Colorado lifts northward. This will take much of the precip into
far northern and eastern portions of our CWA after midnight. Only
expecting scattered showers in the mountains for the rest of the
tonight as even some drier air moves into the area by later this
evening. Web cameras showing some slushy snow on high mountain
passes so could be some slick spots through the night. Any
additional snowfall tonight would be less than an inch. Will trend
forecasts for drying conditions from west to east overnight.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 410 PM MDT Sat Sep 23 2017

Moist and unseasonable cool air has become entrenched east of the
mountains today as the deep upper level trough presently over the
Great Basin creeps towards Colorado. Models generally agree on
the timing of this trough, but differ on the amount of lift,
cooling and QPF it generates during the next 24 hours. The sharp
baroclinic zone moving over nwrn Colorado attm evident on GOES-16
satellite imagery is in the vicinity of 70-90kt sly jet. Models
generally show this feature shifting east over north central
Colorado this evening. A steep 700-500mb lapse rate and favorable
shear along this jet, together with a deep fetch of moisture are
likely to produce several hours of light to moderate precipitation
over the high country overnight. It appears sufficiently unstable
for at least isolated t-storms which may produce bursts of heavy
precip. As for the snow level, its already snowing on top of many
of the high passes according to CDOT CAMs and spotter reports.
Expect to see the snow level lowering to around 9000-9500 feet MSL
overnight, with anywhere from 1-4 inches of accumulation in areas
above 10500 feet. On the plains, showers should become more
widespread this evening accompanied by a few thunderstorms.
Although over the eastern fringe of the CWA in the vicinity of yet
another stronger jet, should see scattered t-storm coverage with
locally heavy rain and small hail possible this evening.

On Sunday...Models indicate rapid drying at mid-levels during the
morning hours as the upper trough moves over Utah. Should see a
drop off in precip in the high country as well as on the plains to
start the day. However model cross sections and soundings show
areas east do the Front Range staying socked in with low clouds
pretty much all day. Later in the day, a shortwave disturbance
rounding the bottom of the approaching trough is progged to lift
north over the CWA generating showers first over the high country
and eventually over the northeast plains during the afternoon.
Precip amounts not expected to be no where as great as those
tonight. Lastly with the cooling aloft and extensive low cloud
cover should keep high temps on the plains in the 50s tomorrow.

.LONG TERM...(Sunday night through Saturday)
Issued at 410 PM MDT Sat Sep 23 2017

Sunday night the upper trough remains over the Rocky Mountain
Region...with the center of low pressure over northeastern Utah. The
upper low weakens as it lifts into Wyoming overnight. This pattern
should result in a continued cool and unsettled weather pattern
across north central and northeastern Colorado through Monday.
Increased upslope flow...combined with QG Forcing from an 80KT+
upper jet...may lead to increased precipitation chances east of the
mountains Sunday evening. Therefore...have raised pops for those
areas.

On Tuesday...the upper trough moves over the northern Great Plains
States...while a secondary low pressure system deepens over the
Desert Southwest. Colorado will lie between these two
systems...under the influence of a drier westerly flow aloft. This
pattern should result in dry weather and moderating temperatures
across the area.

Models show the upper low lifting northeast towards Colorado on
Thursday then washing out over the Four Corners Region Region over
the weekend.  As the upper low approaches Colorado...we could see an
increase in shower and thunderstorm activity...especially across
southern sections of the CWA Thursday and Friday. In addition...the
GFS is showing another cold front moving cold front moving across
the northeastern plains on Thursday...which could enhance
precipitation chances. Warmer and drier weather is expected by
Saturday as upper level high pressure builds over the central and
northern Rockies.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 743 PM MDT Sat Sep 23 2017

Heavier rainfall over kden now but this will be shifting east by
03z with rainfall diminishing to just scattered light showers or
drizzle. Expect ceilings to stay below 1000 feet agl for the rest
of the night. Expect the low stratus to remain over all terminals
through much of Sunday.

&&

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

$$

UPDATE...Entrekin
SHORT TERM...Baker
LONG TERM...Kalina
AVIATION...Entrekin



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