Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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344
FXUS65 KBOU 302036
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
236 PM MDT SAT JUL 30 2016

.SHORT TERM...(This evening through Sunday)
Issued at 236 PM MDT Sat Jul 30 2016

Current satellite imagery and radar shows weak convection
developing over the mountains and southeast Colorado. Meanwhile,
the airmass on the plains of northeast Colorado remain capped,
but temperatures reaching the lower 90s in a couple spots could be
just enough to pop one or two storms. Will keep low PoPs in place
to account for this, as well as the slight increase in mid level
moisture through the evening. After midnight, only a few mid/high
level clouds expected with moisture plume advancing into the
state but no forcing to keep any showers going.

On Sunday, mid level moisture plume will continue to shift into
the area as seen in the specific humidity charts. There is no real
synoptic forcing seen so main driver to afternoon convection will
be the terrain. Will continue the idea of higher PoPs in the
mountains and Palmer Divide area, where at least scattered storm
coverage is expected. CAPES are limited to around 500 J/kg in all
but the far northeast corner of the state so main threats would be
cloud to ground lightning, gusty outflow winds, and just brief
heavy rain.

.LONG TERM...(Sunday night through Saturday)
Issued at 236 PM MDT Sat Jul 30 2016

Synopsis: Light quasi-zonal flow aloft Sunday night atop an upper
ridge stretched across the southern half of the U.S. is progged by
models to gradually expand northward during the first half of the
week. This places the forecast area under a lighter, variable flow
on Monday. The upper high centered over SOCAL and the other over
central New Mexico merge in the vicinity of the Four Corners area
on Tuesday. NAM and GFS show a weak shortwave trough pinwheeling
over the top of this anticyclone and moving across northern
Colorado during the day. In advance of this wave models show a
narrow ribbon of subtropical moisture hanging over the Front Range
during the afternoon and early evening hours. On Wednesday...drier
air aloft coincident with the 500 mb ridge axis is forecast to
pass over the state during the morning hours. After passage of the
ridge, 700-500 mb flow trends southwesterly which begins advecting
mid and high level moisture up over western Colorado by nightfall.
Meanwhile models show southerly low-level winds strengthening on
the plains overnight which elevates sfc dewpoints/mean layer
precip water. By Thursday, the upper ridge and sfc high shift east
of the state resulting in a deep south-southwesterly flow over the
state. Such a flow appears to advect an increasing amount of moist
and unstable subtropical air northward up into the Four Corners
region during the day. From there the plume spreads northeastward
over the remainder of Colorado Thursday night and Friday. While
this is happening, models show a cold front backing into northeast
Colorado Thursday afternoon, with the main push of cooler air and
low-level moisture later that night and Friday morning. Layer
precipitable water along the Front Range climb from around an inch
as of 00z/Friday to 1.4-1.5 inches on Friday with a continuation
of and northeasterly-upslope flow. A mid-level disturbance
approaching for the Desert Southwest may also account for the
increase in moisture.

As for forecast trends...should see t-storm chances diminish
somewhat Monday, Tuesday and Wednesday...and then increase across
the high country during the day Thursday and over the entire CWA
Thursday night and Friday for the reasons mentioned above. Would
expect to see temperatures at to slightly above average through
Thursday...then fall below average Friday and Saturday, particularly
east of the Front Range with ongoing upslope flow and greater cloud
cover. Storms on the plains Thursday evening could go severe and
produce locally heavy rainfall. A moisture rich atmosphere on Friday
would more support heavy rain makers and a reduced chance for severe
weather.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 236 PM MDT Sat Jul 30 2016

VFR conditions will persist through 18Z Sunday. There is still a
slight 10-20% chance of a thunderstorm affecting the airports
01Z-05Z with gusty outflow winds but no restriction to
visibility. Otherwise winds will turn from easterly this afternoon
to southeast and southerly 03Z-07Z. On Sunday, thunderstorm
chances will increase to 20-30% as airmass destabilizes
sufficiently after 20Z. Those storms would be high based with
gusty outflow winds to around 35 knots the main threat.

&&

.BOU Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Baker
AVIATION...Barjenbruch



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