Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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436
FXUS65 KBOU 212132
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
332 PM MDT Fri Jul 21 2017

.SHORT TERM...(This evening through Saturday)
Issued at 238 PM MDT Fri Jul 21 2017

A weak west to southwesterly flow aloft will be over the region
this evening. Slow moving thunderstorms developing over the higher
terrain this aftn, with the stronger storm producing one half to
three quarters of an inch of rainfall in 30 minutes. So far these
storms have been fairly localized with lesser rainfall with the
storms elsewhere. Some small hail also reported. Thunderstorm
coverage is still expected to increase over the mountains then
gradually spread eastward across the northeast plains overnight.
An upper level jet max will be passing across northern WY in the
vicinity of the right entrance region of the jet. As a result,
there will be some weak mid level QG ascent along the northern
border which could allow for some showers to persist over the
far northeast plains late tonight.

On Saturday, a drier and still weak westerly flow aloft will be
over the northern and western part of the cwa. The best chance of
thunderstorms will be south of I-70 so best coverage will be
there. Temperatures on the plains for Saturday will not as warm as
today but still dependent on how much precipitation falls
tonight. If the storms underperform tonight, then drier soils may
allow for warmer temperatures than the max temperatures currently
in the grids.

.LONG TERM...(Saturday night through Friday)
Issued at 238 PM MDT Fri Jul 21 2017

Drier air and weak subsidence will continue to advance southward
across the forecast area Saturday night. This occurs as ridging
begins to pop back up across the Great Basin. This drying will
bring an end to showers and storms during the evening.

For Sunday through Tuesday, the ridge axis amplifies a bit more
over the Great Basin and inches eastward toward Colorado. This
will bring mainly dry conditions to the plains, while the
mountain areas should still see isolated to scattered storms each
day. With the building ridge and somewhat drier airmass,
temperatures will undergo a warming trend with highs pushing back
into the 90s across the plains by Monday and Tuesday.

For Wednesday through Friday, the ridge axis is forecast to shift
slightly eastward. This may allow for weak passing short waves and
potential influx of a mid/upper level monsoonal moisture plume.
However, low level moisture may remain limited, so main threats
would be gusty outflow winds, lightning, and only brief heavy
rain from storms. We should see slight cooling during this period,
but temperatures will likely remain above normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 238 PM MDT Fri Jul 21 2017

Thunderstorms developing over southern Jeffco and Douglas
counties at this time so will impact primarily KAPA until 23z.
Still expect thunderstorms to move across KBJC and KDEN until
after 23z. Northwest winds around 10 kts possible after 01z, with
drainage by 06z. Overall will stick with -tsra and wind gusts to
35 knots for the thunderstorm threat through 01z. The storms are
expected to push east of the Denver area by 04Z.

&&

.HYDROLOGY...
Issued at 238 PM MDT Fri Jul 21 2017

Heavy rain from slowing moving thunderstorms will be the primary
concern for tonight and Saturday. The main concern will the
higher terrain and urban areas that are more susceptible to
flooding. Elsewhere the dry low levels and a lack of large scale
forcing is expected to limit the flooding threat.

&&

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

$$

SHORT TERM...Cooper
LONG TERM...DB
AVIATION...Cooper
HYDROLOGY...Cooper



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