Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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655
FXUS65 KBOU 141015
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
415 AM MDT Tue Aug 14 2018

.SHORT TERM...(Today and tonight)
Issued at 415 AM MDT Tue Aug 14 2018

Low level moisture has spread across most of northeastern
Colorado. Areas of low clouds and fog have developed over the
eastern tier of counties, with another patch from Limon south and
across the Arkansas River valley. Most of this is off the ground,
but there may be some patchy dense fog. Meanwhile convective
clouds from the area of moisture over the mountains have
dissipated.

The convective forecast for this afternoon is complicated. There
is a warm layer around 600 mb which will probably cap convection
over most of the plains. The air which is feeding in this morning
is a bit cooler, leading to more of an all-or-nothing situation.
Meanwhile there is a bit more mid level moisture over the
mountains, and that capping layer should be a bit weaker.
Yesterday there were thunderstorms over northwestern Colorado, and
this area should spread over the northern mountains today. Areas
just east of the mountains will likely be capped to surface-based
convection, but capped weakly enough that mountain storms will be
able to move off the mountains in the late afternoon/early evening
and with some increase in low level moisture they may sustain for
a while. Most of the mesoscale models move scattered storms over
the western portion of the plains, then dissipate them, which
seems reasonable. A couple have a storm that forms in southeast
Wyoming and moves more southerly towards Sterling then dissipates.
With several possibilities for how to get storms there, a slight
chance of storms in the evening is alright for the further eastern
plains. CAPEs look to be 400-800 J/kg over the area we expect
storms. We could get up to 1000 J/kg on the plains in the evening.
With limited shear, a storm with marginally severe hail/wind is
not out of the question, but does not appear likely today.

The smoke situation will likely be similar to yesterday. The more
concentrated smoke will remain north of us. The Silver Creek fire
south of Rabbit Ears Pass has remained hot overnight, so will
likely produce more smoke today. This should mainly affect parts
of Grand and Summit counties during the day, but it could be
spreading toward Denver by evening. There may be more significant
widespread smoke coming in on the northwest flow behind tomorrow`s
shortwave.

.LONG TERM...(Wednesday through Monday)
Issued at 415 AM MDT Tue Aug 14 2018

On Wednesday, upper level high pressure will stretch from Texas
across the southern Rockies and into the Intermountain West. A
potent short wave trough is forecasted to move east-southeast across
the central Rockies and northern Great Plains States through the day
into the evening. Northeastern Colorado will lie under the southern
end of the upper trough under the influence of a 40+ KT upper
level jet. In addition, models are showing a weak surge moving
across the northeastern plains during the late morning or early
afternoon hours. Isolated to scattered storms may develop in the
mountains by noon and then move southeast onto the plains and
Palmer Divide during the afternoon and evening. Any storms that
form across the Mountains, foothills and adjacent plains would
probably produce more wind than rain. Better moisture across the
plains east of Denver and the Palmer Divide could result in a few
marginally severe storms with hail, strong winds and brief heavy
rain possible.

The upper level ridge of high pressure is progged to build over the
Rocky Mountain Region on Thursday with another weak cool front
moving across the plains during late morning or early afternoon. The
stable airmass behind the front may inhibit any thunderstorm
activity across much of the plains and Front Range Urban Corridor.
The main focus for any shower and thunderstorms activity would
probably be across the mountains, southern foothills and Palmer
Divide, where better instability exists.

Precipitation chances may increase somewhat by late Friday as the
upper ridge begins to flatten and an upper level disturbance moves
across Colorado from the west. PW`s over an inch on the plains
would suggest the possibility of locally heavy rainfall with any
of the storms.

By Saturday, all the models are showing an upper level trough of low
pressure moving across Colorado with plenty of low level moisture
and wind shear available. This pattern may lead to an active weather
day with the potential for severe weather and locally heavy rainfall.

Sunday and Monday could see some lingering showers and storms as the
upper trough moves east of the state. Temperatures should be
somewhat cooler both days behind the passage of a couple of weak
cool fronts.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 415 AM MDT Tue Aug 14 2018

VFR conditions are expected through tonight, but widespread
diffuse smoke could limit slant visibilities enough to require
instrument approaches to KDEN. Isolated thunderstorms are
expected between 21z-03z so there is a chance of a few wind
shifts with gusts to 30 knots.

&&

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

$$

SHORT TERM...Gimmestad
LONG TERM...jk
AVIATION...Gimmestad



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