Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 261445
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
845 AM MDT Tue Sep 26 2017

.UPDATE...
Issued at 845 AM MDT Tue Sep 26 2017

Stratus and fog is slowly burning off and this slow erosion will
continue through the early afternoon hours. Short range Hi-res
models show showers developing in the mountains, and there may be
a chance that some of these spread northeast onto the nearby
adjacent plains late in the day before dissipating in a more
stable environment. Will monitor that potential through the rest
of the day.

&&

.SHORT TERM...(Today and tonight)
Issued at 321 AM MDT Tue Sep 26 2017

A short wave ridge aloft will be over the region today with one
trough exiting into the the upper Midwest while another drops
into the Great Basin. Stratus remains over the Urban Corridor and
Palmer Divide with clearing around Morgan, Washington and Logan
Counties at this time. Spatial cross-sections and forecast
soundings maintain moisture at or below 700 mb through the day.
Will keep patchy to areas of fog in the grids in the 10-15z
period, then partly to mostly cloudy the rest of day. In addition
to fog, patchy drizzle may linger over southern portions of Elbert
and Lincoln Counties this morning. This afternoon, the models do
generate some weak shower activity around Summit and Park
Counties. Will lean more toward showers vs tstms this aftn and
evening as the airmass is still quite cool. Not as cold today with
highs near 60, but still well below normal. Although drier in the
mid levels, the models do maintain some low level cloudiness
around the region tonight as well. Mid and upper moisture will
spread southwest to northeast across the cwa overnight, with
isolated showers redeveloping in the central mountains toward 12z.

.LONG TERM...(Wednesday through Monday)
Issued at 321 AM MDT Tue Sep 26 2017

Upper level low over the Desert Southwest Wednesday morning will
slowly lift northeast and be over Utah Thursday, and then Wyoming
Friday. The southwest flow aloft ahead of the low and easterly low
level winds around a surface high over Central Plains will
increase moisture over the area Wednesday and Wednesday night. The
airmass becomes slight unstable over the higher terrain and along
the Front Range due to cooling aloft. This combined with the
moisture should produce scattered showers Wednesday.

Expect rain and high mountain snow to increase Wednesday evening and
become widespread overnight. Diffluent flow aloft will prevail over
the area late Wednesday and Wednesday night. Increased pops into
the 60-80 percent range. With this system coming out of the
southwest, snow levels will remain high, above 10,500 feet MSL and
in many cases above 11,000 feet. Lift and rain showers decrease
Thursday. However, a moist easterly flow will keep cloudy and cool
conditions over most of the area with a few showers. With the
expected increase in cloud cover, lowered highs into the 50s for
Wednesday and Thursday for most of northeast Colorado. Did keep
some low 60s for the eastern plains where more sun may prevail
Wednesday.

Drier air will move into the area Friday. Increased sunshine will
bring warmer temperatures. There will be a chance for showers
mainly over the mountains.

For the weekend, an upper level trough moving across the Pacific
northwest and Northern Rockies will produce a west to southwest
flow aloft over Colorado. Expect warmer temperatures for Saturday
and perhaps into Sunday. As the trough axis passes to the north of
Colorado, a cold front will push south into the state. This will
bring cooler temperatures along with a chance for showers Sunday
and Sunday night. Northern areas are expected to be favored under
this pattern.

Monday should be dry with subsidence behind the trough. Not much
agreement among the models on how the pattern evolves early next
week, so confidence in temperatures and pops are low.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 845 AM MDT Tue Sep 26 2017

IFR/MVFR ceilings are slowly eroding and expect mostly VFR
conditions by 18Z. Patchy fog with visibilities 1SM or less
confined to areas from KGXY-KFMM, but that is slowly dissipating
as well. We do anticipate local ceilings around 5000 feet after
18Z so possible ILS landings may continue. Light winds will turn
easterly 18Z-21Z with speeds holding 10 knots or less.

&&

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

$$

UPDATE...Barjenbruch
SHORT TERM...Cooper
LONG TERM...Meier
AVIATION...Barjenbruch


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