Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 200217
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
717 PM MST Sun Nov 19 2017

.UPDATE...
Issued at 656 PM MST Sun Nov 19 2017

Main issue for tonight and Monday will be the wind. Latest NAM12
shows a developing mountain wave overnight, with a cross-mountain
component of 50 kts by 12z Monday. Current zone package appears to
be underdone regarding the wind so have increased them overnight
with gusts to 60 mph in particular for zones 33 and 35. The wave
weakens a bit by midday Monday then strengthens again toward 00z
Tuesday with 700 mb winds near 60 kts. Adjusted the winds for
Monday afternoon for the mountains and foothills to better reflect
this. No highlights at this time, but adjust the winds with
localized gusts 60-70 mph over exposed eastern slopes of Zones
33/34 by late Monday aftn. Will leave the Fire Weather Watch in
place at this time, with the strongest winds in the afternoon
likely favoring the fire weather zones bordering Wyoming and
Nebraska borders.

&&

.SHORT TERM...(This evening through Monday)
Issued at 257 PM MST Sun Nov 19 2017

.Short Term...Current observations are showing downsloping low
level winds over much of the CWA. Another batch of upper level
moisture is allowing more lenticular clods to develop from the
divide eastward. Models have the northwesterly flow aloft
increasing significantly on Monday. By 00Z Tuesday, 110 to 135
knot winds aloft are covering the CWA. The QG Omega fields have
downward energy overnight, and weak upward on Monday. The boundary
layer flow is all downsloping tonight and Monday; mostly
southwesterly tonight and westerly on Monday. For moisture, there
is a bit in the upper levels overnight into Monday afternoon.
Moisture increases and lowers by late Monday afternoon. There is
no measurable precipitation on the QPF field for the CWA tonight
and Monday. With the moisture increasing late Monday afternoon and
decent west-northwesterly mountain top flow, will go with
"chance"s in the high mountains after 21Z Monday afternoon.
Concerning the high winds; cross sections show a mountain wave
set up. Wind speeds come up over the Red Flag Watch area Monday
afternoon although they are marginal for the warning. The Red
Flag Warning GFE tool only point to elevated fire danger over the
northern plains by Monday afternoon. Will leave the Watch in
place this update. For temperatures, Monday`s highs are 1-3 C
warmer than this afternoon`s.

.LONG TERM...(Monday night through Sunday)
Issued at 257 PM MST Sun Nov 19 2017

Monday night a 120 kt northwesterly jet extends across Colorado,
while upstream a 150 kt jet streak jet enters northwest Wyoming.
Throughout the night the jet streak translates southeast across
the northeast quarter of Colorado. There is a decent mountain top
stable layer in place early Tuesday morning so expect high winds
across the northern half of the Front Range mountains, and east
of the Divide the high winds should extend down the foothills and
perhaps as far east as the favored windy locations like Boulder
and the CO-93 corridor to Golden. We do not expect the winds to
get very far east across the adjacent Plains. The cross barrier
flow isn`t terribly strong given the direction is northwest,
though synoptic (via the building ridge) and mesoscale (via the
jet streak) subsidence will also aid in bringing the winds down
the east slopes. Winds in the northern mountains and foothills
could gust to 60 mph Monday overnight into early Tuesday morning.
Elsewhere winds will be generally light until Tuesday afternoon.
The strong northwesterly flow will lead to a continuation of light
snow showers north of I-70, with the highest amounts occurring on
the west slope of the Continental Divide in Grand and Larimer
Counties, and the Park and Gore Ranges, for storm total snow
amounts 2-5 inches. I-70 corridor from Georgetown to Vail Pass
should see light accumulations through Tuesday evening. Will
remain dry elsewhere.

By Tuesday evening the core of the jet will be across Central
KS/NE and the ridge aloft begins a stranglehold across Colorado.
The last of the mid-level moisture and upslope snow showers for
the Park Range should be gone by Wednesday morning, and our area
will be dry for the foreseeable future under the influence of the
strong ridge across the lower Colorado River Valley extending
across Colorado. Unseasonably warm temperatures will be the main
weather story Wednesday through next Sunday. Temperatures will
likely exceed 70 degrees across the Plains Wed-Friday. The global
models bring a dry cool front across the Plains early on
Saturday, knocking high temperatures to around 60 Saturday and
Sunday, still >10 degrees above normal for this time of year.
Mountain temps should be consistently warm throughout given a lack
of any 700/500 mb cooling available, so expect mid 40s to mid 50s
Wednesday- Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 656 PM MST Sun Nov 19 2017

Models point to downsloping low level winds at DIA tonight and
Monday. There will be no ceiling issues. A lee side surface trough
is expected to hug the Front Range Foothills. At this time,
westerly winds at KDEN and KAPA will become south/southwesterly
overnight, then eventually increase with a west/northwesterly wind
component Monday aftn. Stronger westerly winds expected at KBJC,
with gusts 25-35 kts late tonight and Monday morning, then
increasing again by late Monday aftn.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday morning through Monday afternoon
for COZ238-242-248>251.

&&

$$

UPDATE...Cooper
SHORT TERM...RJK
LONG TERM...Schlatter
AVIATION...Cooper


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