Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 112118
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
318 PM MDT Wed Oct 11 2017

.SHORT TERM...(This evening through Thursday)
Issued at 318 PM MDT Wed Oct 11 2017

A west-southwest flow aloft will persist through Thursday as an
upper level trough moves across the Pacific Northwest and into
the Northern Rockies. This will usher warmer air into Colorado.
Lows tonight should stay above freezing except over the higher
terrain and mountain valleys. Airmass will remain dry with only
some high clouds.

Highs are expect to climb into the 70s over most of northeast
Colorado Thursday. A weak cold front may sneak into far northeast
Colorado late Thursday afternoon bringing slightly cooler air
late in the day. Moisture is expected to increase over the
northern mountains after noon. Doesn`t appear there will be enough
moisture or lift for precipitation, but clouds should increase
because of this.

.LONG TERM...(Thursday night through Wednesday)
Issued at 318 PM MDT Wed Oct 11 2017

A weak shortwave will move north of Colorado Thursday night,
dragging a cloud band across our northern border areas with a bit
more wind over the mountains and a puff of northerly winds on the
plains. Friday will be a bit cooler as a result, despite little
change in the air aloft. A stronger trough will come over late
Saturday. There has been a little convergence between the models
on the details, but the operational ECMWF is still a bit stronger
and about 6 hours slower than the GFS. GFS ensembles are mostly
like the operational run or a bit stronger/slower so a compromise
looks good. Models are picking up on colder temperatures coming
ashore in the Pacific northwest and are showing stronger cold
advection. This could lead to a bit stronger forcing, and also a
lower snow level. While the EC has stronger lift, this wave is
still moving through a dry low/mid level environment, which will
reduce the chance of showers. Our forecast still has just a chance
of showers with the front in the late afternoon and evening. With
the colder temperatures, the snow level drops to near 6000 feet by
the time the showers end. We could get a couple inches in the
mountains, but there shouldn`t be any impact on the plains.

Warmer air aloft moves back in quickly, with subsidence and dry
westerly flow aloft. There`s about a 10 degree spread in the model
ensembles for temperatures Sunday through Wednesday, based on the
amount of upstream ridging versus flat westerly flow continuing.
Our current forecast shoots down the middle. There should be a
weak shortwave in the middle of the week, but timing is unclear
and it should be moving through a very dry environment.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 318 PM MDT Wed Oct 11 2017

VFR conditions will prevail through Thursday with a few high
clouds at times. Light northerly winds are expected to settle at
a south- southwest drainage direction around 02Z. Wind speeds are
expected to remain less than 15 knots. Weak winds are expected
again for Thursday.

&&

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

$$

SHORT TERM...Meier
LONG TERM...Gimmestad
AVIATION...Meier



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