Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 202132

Area Forecast Discussion
National Weather Service Denver/Boulder CO
332 PM MDT Thu Jul 20 2017

.SHORT TERM...(This evening through Friday)
Issued at 332 PM MDT Thu Jul 20 2017

The slowly evolving upper air pattern over the southern United
States will continue funnelling monsoonal moisture over Colorado
through tomorrow. This afternoon has seen another round of showers
develop over the mountains and move slowly north-northeastwards.
Moderate rainfall amounts and hail up to marble size has been
reported so far. The freezing level was 16,000 feet this morning,
showing how warm the airmass is. Precipitable water values along
the I-25 corridor now range from 0.85 to 1.10 inch, which is moist
enough for storms to produce periods of heavy rain. Satellite
imagery indicates that most of the plains should remain dry this
evening as a capping inversion is in place over the southern
plains into southeast Colorado. The shower activity over the
mountains this afternoon should begin taking a bit of a more
northeastward track this evening as the embedded short wave aloft
rotates around the strong upper ridge over the southern plains.
Shower activity will gradually diminish through the evening with
the loss of daytime heating.

For Friday, another round of convection is expected. The short and
medium range models indicate that moisture levels will be slightly
higher tomorrow, so the threat of heavy rain may be a little
higher. Temperatures are also forecast to be a couple degrees
cooler, owing to the slight increase in the amount of moisture
present. Like today, a sunny morning across the state will give
way to increasing clouds and showers through the afternoon. The
highest pops will be over the mountains and adjacent plains. Winds
aloft will remain weak, so that slow-moving storms will pose a
threat for locally heavy rain.

.LONG TERM...(Friday night through Thursday)
Issued at 332 PM MDT Thu Jul 20 2017

Upper level pattern has a persistent set of ridges with varying
shortwaves bringing an unsettled pattern for portions of the long
term. starting Friday night into Saturday the high pressure will
be over the Great Plains with a shortwave making its way over the
state as the ridge progresses eastward. Moisture PW values will
vary between 0.75 up to 1.5 further east over the plains. This
increase moist flow combined with NNE flow at the surface will
help to increase storm chances along the Foothills and Palmer
Divide Friday afternoon and evening. Storm motion will be slower
Friday evening so storms could drop a quick inch to 1.5 inches in
a short period of time increasing chances of flooding. Behind the
shortwave northerly flow will increase helping to usher in
slightly cooler temperatures for Sunday. This is due in part to
the high pressure over the plains transitioning eastward with a
ridge starting to build in over the Great Basin. Highs will drop
from upper 80s to lower 80s by Sunday. Subsidence will increase by
Sunday morning helping to dry out conditions through the
afternoon. There will only be a slight chance of storms for the
higher elevations

For next week the upper ridge over the Great Basin will make a
slow eastward progression moving over the state by Tuesday. Monday
and Tuesday will have storms over the higher country with
temperatures in upper 80s to lower 90s. Upper level flow will once
again be light, however PW moisture values will be slightly lower
then through the weekend with values from 0.75 to 1.0. by
Wednesday the upper ridge will shift east of the state helping to
bring another disturbance through CO. Increased storm potential is
possible by Wednesday afternoon with temperatures once again
getting into the mid 90s.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 332 PM MDT Thu Jul 20 2017

Scattered rainshowers and thunderstorms will be mainly over the
western parts of the Denver area this evening. Skies will clear
overnight, and then another round of showers are expected Friday
afternoon. Locally heavy rain will be possible from the slow
moving showers.


Issued at 332 PM MDT Thu Jul 20 2017

Slow moving storms this evening and again Friday afternoon will be
capable of producing locally heavy rainfall. Areas that have had
rainfall over the past couple days will be at the highest risk of
flooding, if more slow moving storms pass over.




SHORT TERM...Dankers
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