Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 141719
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1119 AM MDT Thu Sep 14 2017

.UPDATE...
Issued at 1114 AM MDT Thu Sep 14 2017

Area radars show convection developing and moving northeastward
across western Colorado. There is some synoptic scale energy
moving this way on the water vapor pictures. Morning soundings did
show a bit of cooling aloft, but surface dew points are not great.
Perhaps the showers and storms developing over the mountains will
survive over the plains late in the day. Will leave forecast pops
as is for now.


&&

.SHORT TERM...(Today and tonight)
Issued at 351 AM MDT Thu Sep 14 2017

Weather maker today and tonight will be the upper level low
opening up and ejecting out of the Desert Southwest. There has
already been convection firing on the periphery of the best lift
and mid level theta-e advection in southern Nevada and southern
Utah overnight.

In advance of this feature, mid level moisture and precipitable
water values will slowly increase over our forecast area through
the day. The mid level moisture arrival (seen in the 700-500 mb
specific humidity charts) will result in higher convective
coverage and a little increase in strength. We will continue the
idea of higher PoPs in the mountains this afternoon and evening
with the increasing moisture and destabilization, with scattered
coverage gradually spilling out onto the plains. Overall, the
plains convection will be dominated by strong gusty outflow winds
given the still dry low levels, as well as the increasing mid
level flow. Could see a few gusts to around 50 mph in this
environment, but mainly light rain. Stronger storms in the
mountains may produce brief heavy rain and small hail, and gusty
winds. Timing of the storms is a bit difficult, as there may be
one batch of storms in the afternoon, with a possible break before
another organized band of showers and thunderstorms from stronger
redevelopment in/near the Four Corners regions spreads in this
evening.

Temperatures will be a couple degrees cooler today with slight
cooling aloft and increased convective coverage and outflows
during the afternoon.

For tonight, the main shot of Q-G lift associated with the
shearing ejecting trough will push off to the north late. That
should bring a decrease to the shower/storm activity later tonight
as long as model timing is ok with the convection. Will decrease
those PoPs accordingly with a potential dry slot moving in
overnight.

.LONG TERM...(Friday through Wednesday)
Issued at 351 AM MDT Thu Sep 14 2017

The upper level disturbance will exit nrn CO early Fri morning
with only a slight chc of showers mainly in zn 31. By late aftn
into Fri evening a stg upper level trough will move eastward into
the nrn Rockies with increasing swly flow aloft. There will be
some moisture embedded in the flow which will combine with mid lvl
ascent to produce a good chc of showers mainly across zn 31. As
for highs, temperatures across the plains will drop into the lower
to mid 80s.

Meanwhile late Fri night into early Sat the main upper level trough
will move across Wyoming however there is still some mid lvl ascent
fcst across nrn CO.  Thus will continue to see a chc of showers over
the higher terrain overnight especially north of I-70. Some snow
will be possible above 10000 ft.  Across nern CO a cold front will
move across the plains Fri night and with some mid lvl ascent there
will be a chc of showers especially closer to the WY border.  By Sat
aftn subsidence will develop over nrn CO as drier air spreads
across in wly flow aloft. Thus shower threat will diminish. As for
highs readings will cool into the lower to mid 70s over nern CO.

By Sun wsw flow aloft will be over the area as sfc high pres begins
to move into the cntrl US.  There could be a slight chc of showers/
tstms over the nern plains as a warm air advection ptrn begins to
develop. Over the higher terrain will mention isold aftn tstms.  As
for highs, readings will be near seasonal normals across nern CO.

For Mon a stg upper level trough will move into the Pacific NW with
increasing swly flow over nrn CO.  At this time it looks dry and
warmer with above normal temperatures. By Tue, differences begin
to develop between the ECMWF and GFS. The ECMWF keeps the stg
upper level trough over the nwrn US while the GFS begin to move it
into the nrn Rockies. At this point have more faith in the ECMWf
solution so will keep a dry fcst with above normal temperatures.

By Wed the ECMWF has a stg upper level low developing over the Great
Basin with stg ssw flow aloft over the area.  Meanwhile the GFS has
stg wly flow aloft as it has a broad upper level trough extending fm
the nwrn US into the nrn Rockies.  The GFS solution would lead to
mainly dry and windy conditions with seasonal temperatures.  The
ECMWF ptrn would be windy as well with abv normal temperatures. In
addition there would be a chc of showers in the mtns.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1114 AM MDT Thu Sep 14 2017

Models are showing southeasterlies at DIA by mid afternoon, then
normals drainage by mid/late evening. There could also be some
thunderstorm outflow winds to 40 knots with the storms later this
afternoon. Will keep the VCTS in the TAF. There should be no
ceiling issues.


&&

.FIRE WEATHER...
Issued at 351 AM MDT Thu Sep 14 2017

Higher coverage of showers and thunderstorms is expected today.
Due to the recent dryness, a few of these storms may spark new
fires in addition to gusty winds. Mountain areas above 7000 feet
are expected to see more rain with storms, but lower elevations
will likely see lighter rains and stronger wind gusts. Still
enough potential for wetting rains to preclude a Red Flag Warning
at this time.

&&

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

$$

UPDATE...RJK
SHORT TERM...Barjenbruch
LONG TERM...RPK
AVIATION...RJK
FIRE WEATHER...Barjenbruch



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