Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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986
FXUS65 KBOU 181028
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
428 AM MDT MON JUL 18 2016

.SHORT TERM...(Today and tonight)
Issued at 428 AM MDT Mon Jul 18 2016

Main concern today will be for thunderstorms with locally heavy
rainfall, and isolated severe storm threat. Current precipitable
water (PW) values are near 1 inch on the plains, and a plume of
deeper mid and upper level moisture is now just beginning to work
into the state from the southwest. As a result, PW values will
continue to climb through the afternoon and early evening hours
with values likely reaching 1.25 inches along portions of the I-25
corridor and up to 1.5 inches in the lower elevations of the
eastern plains. There is weak Q-G forcing noted by afternoon so
coverage should expand rapidly over the mountains by 11 AM - Noon
and then spread northeast across the plains through the afternoon
and early evening as airmass destabilizes and cap is broken.
Considering the high PW values and weak synoptic scale lift, have
increased PoPs across the board. However, still think there will
be more of a focus toward the Palmer Divide and eastern plains
thanks to a weak Denver Cyclone and convergence zone. See hydro
discussion below for more heavy rain potential details.

CAPES increase to around 2000 J/kg on the eastern plains and near
1000-1500 J/kg possible along the Palmer Divide. As a result,
could see a couple severe storms as well with large hail and
damaging winds the primary threats. Hail size will likely be
limited however by the ever increasing moisture and skinny CAPE
profile as we head into the evening.

Storms are expected to decrease this evening from west to east as
downslope southwesterlies develop off the Front Range.

Finally, low levels are very moist early this morning with
current dewpoints in the upper 60s over the northeast corner of
the state behind a weak surge. That area will be most favored for
fog and widespread stratus early this morning, but can`t rule out
patchy fog farther west toward the I-25 corridor.


.LONG TERM...(Tuesday through Sunday)
Issued at 428 AM MDT Mon Jul 18 2016

Showers and thunderstorm chances should gradually decrease beyond
Tuesday with drier and warmer air spreading eastward over the
state as the upper ridge begins its westward migration from its
present position over the southern Great Plains. On Tuesday...the
forecast area will still be under the influence of a moist and
unstable southwesterly monsoonal flow with the 700mb specific
humidity remaining up around 8 g/kg...a value commonly associated
with the monsoon and enhanced thunderstorm activity around here.
With storm motions forecast to be in the 20-25kt range...some
late day storms along the Front Range and Palmer Divide could
produce rainfall amounts in excess of an inch in a short period of
time...possibly resulting in localized flooding. With late day
CAPES not expected to be much greater than 1500 j/kg...severe
weather is not expected to be a big concern. Although still can
not rule out an isolated severe storm or two capable of large hail
on the plains.

By late on Friday and Saturday...t-storm chances may increase
again...particularly over and along the Front Range following the
passage of a weak cold front. Post frontal upslope flow on
Saturday will pool low-level moisture up against the terrain
creating a favorable environment and vertical shear profile for
isolated moderate to strong storms. Farther out across the
plains...the post frontal airmass looks pretty capped. So storm
chances out there appear low at best. There is also a chance of
afternoon and evening storms on Sunday both in the mountains and
on the plains with the passage of an upper level shortwave trough
during the afternoon. By Sunday flow aloft should be northwesterly
with the upper ridge retrograding over the lower Great
Basin/Desert Southwest.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 428 AM MDT Mon Jul 18 2016

Main concern today is for occasional thunderstorms in the 20Z-04Z
time frame. High confidence we will see thunderstorms from 21Z-
23Z, and then may see a few breaks but still a rather high storm
threat continue thereafter until around 04Z when storms should be
moving off to the east. Enough precipitable water for significant
reductions to visibilities of 1-2SM in the core of storms and
wind gusts to 40 knots. With regard to fog threat this morning, as
long as southerly winds hold then we should keep fog and stratus
just to the east and north of KDEN. If weak cyclone forms, then
could see a quick reduction to LIFR conditions 12Z-14Z before VFR
redevelops.

&&

.HYDROLOGY...
Issued at 428 AM MDT Mon Jul 18 2016

Precipitable water values climbing to 1.25-1.5 inches on the
plains will bring locally heavy rainfall and a flooding threat
today. A few areas saw heavy rainfall last night already, so those
areas would be more prone to flooding. Warm cloud depth is limited
to about 3000 ft due to high lifting condensation levels, but
soundings also point to a skinny CAPE profile developing through
the evening hours. At this point, storms are expected to roll
along near 20 mph, so main flooding threat would occur with any
training storms which seems more likely east of the I-25 corridor.
Will mention locally heavy rainfall in the forecast and localized
flooding in the hazardous weather outlook, but not issue a flash
flood watch at this time. Will continue to monitor.

&&

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

$$

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



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