Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 182120
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
320 PM MDT Tue Apr 18 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 320 PM MDT Tue Apr 18 2017

Warm west/southwest flow aloft will strengthen tonight. In the low
levels, moisture will increase across the northeast plains in
southeasterly flow. There is some threat for elevated convection
overnight (mostly east of Fort Morgan) as the nose of a strong
100+ knot upper level jet approaches after 06z. A couple of these
storms may be strong with hail and brief heavy rain given
elevated CAPE near 1000 j/kg and strong wind shear. This speed max
and passing short wave with weak/moderate Q-G lift will also aid
shower production in the mountains, with the snow level advertised
to reach mountain valley floors by early Wednesday morning.
It still appears moisture is limited, but enough orographic lift
to support 1-3 inches of snow over the mountain peaks through
Wednesday morning.

Winds will increase across the mountains and foothills tonight
through early Wednesday, with peak gusts increasing to around 60
mph above timberline and higher exposed peaks. On Wednesday, the
flow is strong and well mixed, so the subsident post-trough
environment should bring gusty winds to all of the forecast area
including the plains. Peak gusts may reach 40-45 mph for a few
hours on the plains as suggested by using the max wind in the
mixed layer. Have increased wind speeds overall for this forecast
period. It will still be warm with low humidity readings...see
Fire Weather section below for more details.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 246 PM MDT Tue Apr 18 2017

Medium range models are now focusing on an upper trough/closed low
moving across Wyoming and Colorado Thursday night and Friday. The
trough appears that it will be coming through in a progressive
manner, but will be transitioning to a little more negative tilt
as it leaves Colorado. As the system approaches Colorado, the
surface low will draw moisture back into Colorado from the central
plains. Models are showing a decent shot of QPF on Friday morning,
centered over the northern plains. Until the system taps into
moisture from the central plains, it will only have modest amounts
of moisture that it brings from the north Pacific. Therefore,
snowfall amounts in the mountains should only be light.

Ahead of this system, weak ridging will be over the state with
moderate westerly flow aloft. Temperatures will be cooler in the
wake of a weak disturbance that moves over the state tomorrow
evening.

For Sunday through Monday, drier and warmer weather will return as
a high pressure ridge re-builds over the state. Each of the models
show good agreement in timing of moving the trough out of the
state and building the ridge over the Four-Corners region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 320 PM MDT Tue Apr 18 2017

Winds will be the biggest challenge through Wednesday. Denver
Cyclone is developing this afternoon, and this will likely bring
a period of variable/shifting winds and low confidence in wind
direction for a few hours this evening 23Z-04Z. Then more
southwesterly winds are eventually expected to develop overnight.
On Wednesday, gusty west/northwest winds will be developing in
the morning with peak gusts of 30-35 knots expected. This could
have crosswind limitations on north/south runways, but winds
should begin to transition to a bit more northerly in the
afternoon and gradually diminish in speeds. VFR conditions will
persist through Wednesday.

&&

.FIRE WEATHER...
Issued at 320 PM MDT Tue Apr 18 2017

Northwest winds will increase across Front Range Foothills late
tonight and then spread across the plains Wednesday morning.
Temperatures will still be warm, and humidities will drop into
the teens in/near the Front Range where the driest low levels are
expected. Strength of winds would easily reach criteria, but
humidity values are marginal for a Red Flag Warning, and some
green-up is also underway. For this reason will state elevated
fire danger conditions on Wednesday but no Red Flag Warning. Open
burning should be avoided due to the strength of winds.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Barjenbruch
FIRE WEATHER...Barjenbruch



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