Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 140956
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
356 AM MDT Sat Oct 14 2017

.SHORT TERM...(Today and tonight)
Issued at 356 AM MDT Sat Oct 14 2017

GOES-16 satellite currently shows a stratus deck with isolated
areas of fog has moved into our far eastern zones, with 1/2 VIS in
Limon. Included areas of fog through 8 AM given latest
observational data trends. The downslope winds discussed below
will quickly wipe out any areas of fog not long after 8 AM.

A cold trough will dig south throughout the day today, with the
trough axis swinging across the Rockies by midday, shifting the
flow to northwest this evening, and remaining northwest into
Sunday morning. The trough does not dig far enough south to
generate much precipitation across our area. Despite significant
vertical motion ahead of the trough axis, Colorado looks to get
dry slotted today and the best chances of precipitation will
remain north of the state across Wyoming. Latest GOES-16 water
vapor imagery shows nicely the strong drying from the southwest
U.S. into Colorado on all three water vapor channels. Strong
northwest downslope winds late morning through the evening before
the trough axis passes will make precipitation close to
impossible west of the Continental Divide. Will however retain low
PoPs for the Park Range and the Front Range mountains of Larimer
County given a good westerly upslope component to the flow and the
glancing blow of ascent and moisture through early evening. The
trough axis swings by late afternoon into the early evening, after
which strong subsidence occurs and precipitation chances drop to
zero everywhere.

Despite a lack of precipitation for most of our area, the short
wave trough will impact today`s weather in several ways. The most
noticeable will be a Bora event west of the continental divide.
80 kts flow at 500 mb, combined with deep boundary layer mixing
and a strong frontal inversion between 700-500 mb will allow the
winds to howl at the surface throughout today. Strong northwest
winds will migrate out of the mountains and foothills this morning
between 9 and 10 AM or so with the passage of the 700 mb cold
front, then spread east across the Plains. Northwest winds will
blow 25G35 mph from midday into the late afternoon hours across
the I-25 urban corridor, with 30G40 mph across the far eastern the
eastern Plains. Winds across the mountains will be a bit
stronger, reaching speeds as high as 35G50 mph this afternoon.
Strong cold advection throughout the depth of the atmospheric
column will also occur with the shift to northwest winds. In
particular, 700 mb temps cool 11-14 degC in 24 hours across our
area, translating into much cooler temperatures today everywhere.
Expect highs in the upper 30s to mid 40s in the mountains and mid
50s across the Plains. An exception may be Lincoln County where it
could warm into the mid 60s before the frontal boundary arrives.

Winds should diminish late this evening as the surface ridge
builds across northeast Colorado and as the trough pulls further
northeast. Clear skies and light winds will result in cool low
temperatures tonight, with upper 20s outside of the urban heat
islands (near 30 there), and teens in the mountains.

.LONG TERM...(Sunday through Friday)
Issued at 356 AM MDT Sat Oct 14 2017

There will be an upper ridge to the west of Colorado Sunday
through Monday night, with northwesterly flow aloft for the CWA all
four periods. The jet level northwesterly winds will be in the 50
to 70 knot range all four periods. The QG Omega fields show
benign synoptic scale energy for the forecast area through Monday
night. The boundary layer flow should adhere to normal diurnal
trends through Monday night. There is little moisture progged on
any of the models through Monday night; maybe a bit of high
cloudiness Monday afternoon. There is no measurable precipitation
noted on the QPF fields. No pops Sunday through Monday night. For
temperatures, Sunday`s highs will be 7-10 C warmer than today`s
highs. Monday`s highs will warm up another 3-6 C from Sunday`s
readings. For the later days, Tuesday through Friday, models have
upper ridging and flat upper ridging in around Colorado Tuesday
and Wednesday. Southwesterly flow aloft is noted for Thursday and
Friday. There is an upper trough axis over the Great Basin Friday
night. Will keep pops out everywhere all the periods, with the
exception of the high mountains Friday afternoon.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 356 AM MDT Sat Oct 14 2017

Stratus and patchy fog has redeveloped tonight, though much
further east than last night. Upslope flow on the Cheyenne Ridge
has also developed a region of low stratus/fog across northern
Weld County. Do not think that will get advected into KDEN, as we
expect drainage winds and then West to Northwest flow to keep
them at bay. Expect VFR conditions through Sunday and no
precipitation. Only wx impacts today will be from winds. Strong
northwest winds to impact the metro area airfields around 15/16Z.
High res models indicating northwest winds 20G30 kts through about
23/00Z. After 00Z or so winds will weaken and shift more
northerly before going to drainage after 08Z and remain 10 kts or
less much of Sunday.


&&

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

$$

SHORT TERM...Schlatter
LONG TERM...RJK
AVIATION...Schlatter


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