Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 301110
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
510 AM MDT Fri Jul 30 2021

.SHORT TERM...(Today and tonight)
Issued at 201 AM MDT Fri Jul 30 2021

Temperatures today will be very similar to those yesterday as the
ridge holds fairly steady over the region, with heights
persistent over northeast Colorado. Expect highs in the 90s across
the plains and maybe a few degrees cooler across the high country
following precipitation yesterday and better cloud cover earlier
this afternoon, in the upper 60s in the mountains and upper 70s
and lower 80s in the foothills and parks.

Storm coverage and intensity should continue to increase today as
mid level moisture over the mountains continues to increase.
Models consistently show high precipitable water across the area,
above 0.75 in over much of the mountains and 1.25 in for the lower
elevations, and high specific humidity in the low to mid levels
particularly over the mountains. Expect widespread showers and
storms over the mountains and foothills this afternoon and
evening, and lesser chances for the lower elevations. A front will
move through the area in the late afternoon and evening, bringing
some cooling and an increase in low level humidity. It will
provide lift on the plains with instability at the boundary, but
increased stability behind, and shallow upslope flow into the
foothills and Palmer Divide in the late evening and night. This
will lead to a better chance of thunderstorms for the lower
elevations in the evening and enhanced precipitation in the
foothills in the evening and night. Weak winds aloft will mean
slow storm motions and an elevated threat of flash flooding across
the high country, especially for the new burn areas, considering
the substantial increase in moisture. We have maintained the Flash
Flood Watch for the Front Range mountains, northern foothills and
Middle Park and added North Park and the mountains of Jackson and
Grand Counties as well. Weaker showers will probably continue
into the night in many areas. Lows tonight will also be similar to
those yesterday, insulated by cloud cover but cooled by
precipitation, maybe a few degrees cooler following slightly
cooler highs.

.LONG TERM...(Saturday through Thursday)
Issued at 201 AM MDT Fri Jul 30 2021

No changes in the current trends for the upcoming weekend with
cooler and wetter conditions expected. Saturday into Saturday
night, a weak north to northeast flow aloft will be in place with
the upper level ridge axis extending from west TX into the
northern Rockies. A fairly strong cold front will push south and
west into the Front Range with a deepening upslope developing in
the afternoon and evening. The combination of monsoonal moisture
in the mid and upper levels, a the upslope in the flow levels will
increase the likelihood of thunderstorms producing localized
heavy rainfall in and near the Front Range. Forecast soundings
Saturday afternoon continue to generate PWAT values 1-1.3 inches
from the Front Range Foothills eastward into the urban
corridor/Palmer Divide. No plans to issue a Flash Flood Watch yet,
but another one will be issued at some point for Saturday.
Forecast CAPES 500-1000 j/kg Saturday afternoon west of the front,
but increasing stability following fropa could significantly cap
the northeast plains late Saturday afternoon and evening. Some
nocturnal showers/storms will likely continue Saturday night but
weaken in overnight. On Sunday into Sunday night, similar
conditions are expected with high PWAT values at or above one
inch, with weak storm motions. The models still show a slight
decrease however with the highest moisture getting shifting
slightly south. Flash flood threat in the burn areas will remain
elevated, with the best instability over the higher terrain, with
greater stability over the northeast plains. The trend for the
upcoming week will be for a gradual decrease in moisture, coupled
with gradual warming trend. Locally heavy rainfall will still be a
concern in the burn areas, but overall thunderstorm coverage
should decrease into the middle of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 201 AM MDT Fri Jul 30 2021

Expect VFR conditions through the TAF period. Drainage winds this
morning will turn northwesterly to northerly quickly behind a weak
push around 16Z. Winds will turn more northeasterly through the
afternoon before returning to northerly as a front moves through
around 00Z Saturday. Expect showers in the vicinity of the
terminals by the early evening, and increased change of
thunderstorms behind the front. Passing storms will bring
lightning, moderate precipitation, and gusty outflow winds to
around 30 knots. Showers in the vicinity of the terminals may
persist into the night.

&&

.HYDROLOGY...
Issued at 201 AM MDT Fri Jul 30 2021

The threat of flash flooding will be elevated today due to greater
storm coverage and intensity with increasing mid level moisture
and slow storm motion with weak winds aloft. Stronger storms may
be capable of producing an inch of rain in 30 minutes, and thus a
considerable flash flood threat especially for the burn areas.

Moisture will increase even further on Saturday, especially in and
near the Front Range mountains and foothills, which will elevate
the flash flood threat through Saturday night. Precipitable water
values will be well above normal. Coupled with weak flow aloft
and upslope flow, this will promote a favorable environment for
localized heavy rainfall. Model profiles depict a deep moist
environment with sufficient instability to support showers and
storms. Threat for flash flooding over the burn areas will be
elevated or possibly even significant given the environment if a
stronger storm were to occur in those areas. Sunday will feature a
similar threat with rich moisture likely staying in the area,
although the main risk could shift slightly southward.

Showers and storms will be possible Monday through mid-week,
although the upper level pattern supports a gradual drying trend.
This will result in a decrease in coverage of showers/storms. It is
also important to note that given the several days of rainfall, the
burn areas may be saturated and potentially more sensitive to
rainfall.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 11 AM MDT this morning through this
evening for COZ030>035.

&&

$$

SHORT TERM...EJD
LONG TERM...Cooper
AVIATION...EJD
HYDROLOGY...EJD/Cooper


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