Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 221602
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1002 AM MDT Sat Jul 22 2017

.UPDATE...
Issued at 932 AM MDT Sat Jul 22 2017

Light showers developing in Elbert, Lincoln and southern
Washington counties this morning so will be including pops in
these areas. The main area of showers extends south and east of a
line from around Sterling to Strasburg to Larkspur. This appears
to be associated with weak mid level QG ascent associated with a
jet oriented southwest to northeast across the region. Elsewhere,
RAP and HRRR not developing much in the way of showers through
this afternoon, so will be backing off the pops especially to the
north and west of this line. There is a second weak system that
could push into the cwa from the north later this aftn, so will
continue with isolated pops through this evening to account for
potential redevelopment.
&&

.SHORT TERM...(Today and tonight)
Issued at 335 AM MDT Sat Jul 22 2017

Showers have dissipated in most areas except some lingering light
rain across the far northeast plains of Colorado. There is still
plenty of mid and upper level moisture lingering over much of
Colorado. Expect some partial clearing towards sunrise. Models are
persistent on showing a drying and more stable airmass moving in
from the west and northwest during the day. Having a hard time
buying off on this drying after looking at water vapor imagery
with the brunt of the dry airmass still well up northern Utah and
northwest wyoming. NAM/RAP continue to show mid level drying
through northwest Colorado between now and 18z this morning and
don`t see it. PW values are still around an inch over the Front
Range and past 3 hour trends do show some slight drying. Even if
we have the drying, moisture should still be plentiful enough for
at least a 20-30 percent chance of showers and thunderstorms
through mid afternoon. Certainly looks like more significant dry
later today and tonight as the ridge builds westward and Colorado
shifts under a light northwest flow aloft. current high temps look
too cool today and will raise them up close to 90 over lower
elevations.

.LONG TERM...(Sunday through Friday)
Issued at 335 AM MDT Sat Jul 22 2017

The upper ridge parked over the Great Plains past several days will
have collapsed by Sunday as another upper ridge gains strength over
the Great Basin/Intermountain West. Circulation around this building
dome of high pressure should redirect the core of the monsoon moisture
plume and its embedded waves westward away from Colorado on Sunday,
resulting in significantly less cloud cover and noticeably fewer
t-storms. Even with more hours of sunshine, should see little change
in temperatures as they remain slightly below average with weak
nwly flow aloft.

Monday and Tuesday...models show the Great Basin upper ridge slowly
returning to the Great Plains as they have indicated the past few
model iterations. The 500 mb ridge axis is progged to pass over
ern Colorado by late on Monday and with its passage should see the
light nwly flow aloft turning to a gradually warmer w-swly
component. Before this happens, some of the models show a weak
shortwave clipping the nern corner of the state Monday afternoon.
Will play it safe and introduce low PoPS out there during the
afternoon. This high based convection, should it form, will
probably produce more wind than rain. Will also hang onto the low
PoPs in higher elevations.

By Tuesday with the upper ridge east of Colorado, should see will a
return of the monsoon moisture conveyor, which should increase
the chance for t-storms in the high country, but not quite yet at
lower elevations. The shift to a warmer swly flow aloft and a
low-level sly gradient flow east of the mtns should return daytime
temperatures to the low/mid 90s on the plains both days.

Wednesday through Friday...models continue to struggle pinning
down the position of the upper ridge. Some show the ridge
retrograding back over the Four Corner region, while others show
it slipping southeastward over the lower Mississippi Valley. The
shift westward would return the forecast area to drier and
slightly cooler conditions, while the other scenario would open
the door to a moist and warmer swly flow which would potentially
increase storm activity across the region, especially in the high
country. Not really knowing which solution will pan out, will
weight the days 5-7 forecast more towards climatology, meaning
daily chances of t-storms and temperatures near to slightly below
average.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 932 AM MDT Sat Jul 22 2017

VFR conditions through the period with no restrictions. Potential
for shower development today on the low side, so will not mention
it in the terminals at this time. Southerly winds this morning
should transition to east/northeast by midday and continue into
early evening, generally at or below 10 kts.

&&

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

$$

UPDATE...Cooper
SHORT TERM...Entrekin
LONG TERM...Baker
AVIATION...Cooper



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