Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 150423
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
923 PM MST Tue Nov 14 2017

.UPDATE...
Issued at 923 PM MST Tue Nov 14 2017

Tonight`s cold front is in several pieces, but the strongest winds
are now over northeastern Colorado and this surge should be moving
past our area by midnight. Temperatures are much colder behind it,
with 30s in SE Wyoming, and 20s in central Wyoming. With the winds
turning around quickly by morning, the coldest air shouldn`t make
it this far south. Only minor adjustments needed for a bit
stronger winds on the plains this evening and also over the
mountain ridges, and a little colder lows in the mountains.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 249 PM MST Tue Nov 14 2017

A cold front is moving south through northeastern Wyoming this
afternoon, and is on schedule to push across the plains late this
evening. Temperatures will turn colder but moisture is rather
limited, so dry conditions will persist.

Temperatures will turn colder behind the front, with cooler
readings persisting through Wednesday. While high temperatures
will be about 15 degrees cooler than today, they`ll be near normal
for this time of year.

Upper level cloudiness associated with passing short wave in the
northern plains will be clearing early this evening. Then mostly
clear skies should prevail tonight, with only patches of stratus
possible due to marginal amounts of low level moisture in the weak
upslope behind the front.  On Wednesday, high level clouds are
expected to increase late morning into the afternoon as next wave
of upper level moisture streams off the eastern Pacific.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 249 PM MST Tue Nov 14 2017

...Snowstorm to impact the mountains Thursday night into Friday
afternoon...

Winds aloft will increase Wednesday night as a jet strengthens
ahead of a deepening Pacific trough. This will induce a surface
trough to the lee of the mountains creating gusty winds for the
high country including the foothills. Model cross sections show
cross mountain flow of 55 kts overnight, however not much downward
QG motion to push it down over the plains.

For the Thursday through Friday weather system to impact the
state, the newest 12Z GFS has slowed the progression of the
system, but still remains the fastest outlier. Other latest models
have slowed as well, trending toward the slower ECMWF solution.
Forecast will adjust toward this slower solution. Cross mountain
flow will be increasing to 65 kts Thursday as the Pacific trough
pushes inland into the Pacific Northwest. As the surface trough
continues to deepen, west-southwesterly surface to 700mb flow will
increase, with warm and dry conditions expected. Fire weather
concerns will increase, especially along the Palmer Divide, east
central plains and possibly into eastern South Park depending on
the speed of the system. The jet max will push over northwestern
Colorado and into Wyoming Thursday night increasing rain and snow
showers over the high country as QG vertical motion increases.
Snow levels will start high, around 10kft decreasing to around
8500 ft up hear the northern state border.

On Friday, the jet max will sink south and be stretched from southwestern
Colorado into northeastern Kansas. Upward QG motion will continue
to increase as colder air moves in from the upper trough
stretched from the northern Great Plains down into the Great
Basin. Snow levels will be lowering to 5000 to 7500 ft by evening
with the lowest levels over the northern mountains. Snowfall rates
will likely be peaking during the day over the mountains due to
the jet dynamics and cold advection. Overall, snowfall amounts
could be in the 8 to 16 inch range over the northern mountains,
and 5 to 10 inches in the mountains near I-70. Snowbanding will be
likely due to the jet dynamics, so large differences over a short
distance will likely happen. Not sure we`ll see much if any
precipitation over the plains until Friday morning. Taking a
slower forecast solution, currently thinking the cold front won`t
push into northern Colorado until around noon. This will be when
the plains will start to have the best chance for precipitation.
It should remain mostly rain until the evening
- though this is when the trough axis should move east of the area
and strong subsidence on the back end will clear things out
quickly. The far eastern plains would have the best chance of
getting any accumulating snow, but it would be low amounts.
Saturday should be dry with highs in the upper 40s for the plains
and in the upper 20s and 30s in the high country.

A large ridge will build over the western US Saturday to Monday
putting CO under northwest flow. This will allow for dry
conditions and a gradual warmup. A weak disturbance may bring a
slight chance of light snow to the mountains on Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 923 PM MST Tue Nov 14 2017

VFR through Wednesday. North winds gusting to 20 knots should
diminish by 06z, then turn east and then southeast by morning.

&&

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

$$

UPDATE...Gimmestad
SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...Gimmestad



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