Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 281657
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1057 AM MDT Wed Jun 28 2017

.UPDATE...
Issued at 1057 AM MDT Wed Jun 28 2017

No changes to the forecast at this time. Westerly flow aloft will
continue over the state today with an upper level jet also moving
overhead this afternoon. Model soundings continue to show CAPE
values around 1000 j/kg. Isolated high based showers will be
possible over the plains through the afternoon. Better moisture
will be available for convective showers further to the east,
where SPC maintains a slight risk of severe thunderstorms.
Temperatures are running about 5 degrees cooler than yesterday, so
high temperatures should be in the upper 80s.

&&

.SHORT TERM...(Today and tonight)
Issued at 413 AM MDT Wed Jun 28 2017

Westerly flow aloft will prevail through tonight around an upper
level trough over southern Canada. A cold front pushed south last
evening and will bringing cooler, near normal high temperatures
today. A lee side surface trough will set up at the base of the
foothills today. This will result in east to southeast winds for
the Urban Corridor and the eastern plains. Moisture will increase
through the day under this pattern with precipitable water values
reaching three-quarters of an inch along the Front Range and up to
an inch across the eastern plains. CAPE values this afternoon and
evening will be up to 1000 J/kg. Isolated showers and
thunderstorms should move across the area this afternoon and
evening. A few could become severe with damaging wind and one inch
hail.

Airmass will remain dry over the higher terrain today. There may be
enough moisture and instability for a few high based showers and
thunderstorms with gusty winds and little rainfall. Highs will be
slightly cooler with 70s to lower 80s in the valleys.

Surface low pressure deepens over southwest Kansas overnight and
will bring another push from the north overnight. This is expected
to usher in slightly cooler temperatures and northeasterly wind
for Thursday.

.LONG TERM...(Thursday through Tuesday)
Issued at 413 AM MDT Wed Jun 28 2017

An upper-level trough is still slated to pass over Wyoming and
northern Colorado on Thursday, bringing with it another cold
front. The front is progged to drop south across nern Colorado
early that morning, possibly before sunrise, consequently lowering
daytime temperatures by another 4-6 deg f. The GFS is deeper and
more progressive than other models with the upper trough, while
the NAM is earlier with the cooler and deeper post-frontal nely
upslope flow east of the mtns. The ECMWF is warmest as it does not
indicate any low-level upslope flow during the day...it`s indicates
more of a nwly downslope flow off the Cheyenne ridge which would
account for the several degree warmer temps east of the mtns. NAM
also generates convection/QPF over the Front Range sooner than
other models which would also account for the cooler daytime temps
it offers. GFS and Canadian Global models eventually indicate a
brisk, relatively moist nely flow along the Front Range, but not
until late afternoon or early evening. Based on a blend of these
models, will introduce a slight chance of t-storms over/along the
Front Range mtns/fthls starting around midday on Thursday,
centered on the srn foothills where PoPs may be a bit higher.
Through the afternoon, should see isolated t- storms tracking
east-southeastward across the plains as the 700-600mb trough axis
passes overhead. May see the best chance for t-storms after 22z
along a convergence zone which the NAM and Canadian GEM show
stalled out across Elbert and Lincoln Counties. SPC indicates a
marginal risk for SVR storms in this area with large hail and
damaging winds main threats, but again only a marginal risk.

Thursday night, models, excluding the GFS, show the coolest air
aloft at the core of the upper trough passing over ern Wyoming/
northeastern Colorado. Model sfc-500 mb QG Omega fields indicate the
best lift over the area during the evening hours, though the NAM
shows the bulk of the precip/QPF occurring on the plains after
midnight and lingering through midday Friday. ECMWF and Canadian GEM
indicate a similar time line, but amounts are lower and not as
extensive in coverage. Friday appears to be the cooler of the two
days with upper 70s/lower 80s for highs on the plains. Should we
sock in with more low to mid-level clouds on Friday as the NAM and
Canadian GEM indicate, daytime temps east of the mtns may end up
being several degs lower.

Looking ahead to the weekend...the upper ridge gradually builds
across the region with temperatures rebounding Saturday and Sunday.
By Sunday should see lower elevation temps approaching 90 degrees
and in the 70s to around 80 in the high country. With relatively
weak flow aloft and weak pressure gradients at the surface, winds
will stay down most areas keeping the risk of wildfires at bay.

For Monday and the 4th of July, models are in general agreement with
mid and upper-level ridge anchoring over the central Rocky Mtn
region. Temperatures on the plains will have little problem reaching
the lower 90s both days, with 70s and lower 80s in the high country.
Thunderstorm chances will be quite low in the high country and near
zero elsewhere.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1057 AM MDT Wed Jun 28 2017

Minimal aviation impacts are expected today as high based shower
activity develops early in the afternoon. Wind gusts up to 35 mph
will be possible. Shower activity should be cleared out by 6 PM.
Winds will remain out of the north overnight as a surface low
develops over southeast Colorado, maintaining northerly pressure
gradients.

&&

.FIRE WEATHER...
Issued at 413 AM MDT Wed Jun 28 2017

Westerly flow aloft is expected to bring breezy to windy
conditions to the mountains and mountain valleys today. Airmass
will be slightly cooler, which will help increase relative
humidity. Overall, a dry and breezy day is expected. A few
locations should reach Red Flag criteria briefly, however long
duration and widespread Red Flag conditions are not expected.

&&

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

$$

UPDATE...Dankers
SHORT TERM...Meier
LONG TERM...Baker
AVIATION...Dankers
FIRE WEATHER...Meier



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