Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 262131
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
331 PM MDT Tue Sep 26 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 330 PM MDT Tue Sep 26 2017

Satellite shows a very stable airmass in place across the plains.
That stable layer is advertised to remain overnight, so while
a few showers are expected to develop across the mountains, the
models may be overdoing the extent of those spreading onto the
plains. That said, there is a departing speed max with some lift
potential in the right rear entrance region of that jet. We`ll
continue to monitor the potential of rain into the I-25 corridor,
but so far even the returns in the mountains have been very
limited. It will be another cool night, but increase in clouds
should hold temps a couple degrees warmer than last night.

On Wednesday, Q-G lift will begin to increase from the southwest.
At the same time, there is weak mid level theta-e advection across
the forecast area. This should bring more numerous showers into at
least Park and Summit Counties through the day, with showers also
spreading onto the plains. The highest coverage and heavier
showers will hold off until Wednesday evening, see details in
Long Term section below. Another cool day is in store with
thickening clouds and developing showers. Should see an inch or
two of snow from a couple heavier showers above 10,500-11,000 feet,
but only light rain showers in lower elevations.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 330 PM MDT Tue Sep 26 2017

Operational models have come into better agreement today with the
location and track of the upper low deepening over the Desert
Southwest. NAM, GFS, ECMWF and Canadian models track the upper low
nearly due north across Utah Wednesday night/Thursday morning. A
very moist southerly flow on the warmer east side of the upper
trough spreads over the area during the period, giving us our best
chance for measurable precip. This warm southerly flow will likely
keep the snow level high, even overnight. Could see the snow level
anywhere from 11800 ft MSL Wed evening to around 10600 ft MSL by
Thursday morning. 24-hour snow totals in the high country ending
00z/Friday generally less than 5 inches, while higher areas up
around timberline in Summit and Park Counties could see locally up
to 10 inches. Road sfcs on the high mtn passes will become slushy
and even snow covered Wednesday night when snowfall rates will be
at their greatest. At this time, not considering any winter
weather highlights, but higher portions of zones 33 and 34 may
eventually come under a winter weather advisory for snow.

Models show the upper low/trough lifting northeast over Wyoming on
Friday which allows a drier westerly flow to set up over Colorado.
However, still see enough moisture around for afternoon and evening
showers and mainly across the high country. By Saturday, models wash
out the low over Montana and positions Colorado under an even war
mer and drier zonal flow aloft. Should see precip chances near zero
on the plains this weekend and in the 10-20 percent range in the
high country. By Sunday night, could see isolated to scattered
showers return to the area with the tail end of weak upper level
system sweeping over the area. Even high elevations in the nrn mtns
could see a bit of snow overnight.

This quick hitting disturbance moves out before Monday morning,
opening the way to a couple of days of near average temperatures
and dry conditions beneath near zonal flow aloft.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 330 PM MDT Tue Sep 26 2017

Generally broken ceilings around 5000 ft AGL should hold in
place, perhaps rising a bit more through the evening as southerly
flow develops. ILS landing conditions should prevail for the most
part through Wednesday. Despite cool temperatures and close T/Td
spreads later tonight, fog threat should be limited by the mid
level clouds as long as they hold in place. Chance of showers will
increase after 18Z Wednesday but no visibility restrictions
expected until Wednesday evening. Then perhaps a slight chance of
a thunderstorm.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Baker
AVIATION...Barjenbruch


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