Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 132143
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
343 PM MDT Thu Jul 13 2017

.SHORT TERM...(This evening through Friday)
Issued at 343 PM MDT Thu Jul 13 2017

Cool and stable air has held in place over northeast Colorado
today, keeping the temperatures too cool to break any cap. Deeper
moisture has retreated to central and southeast Colorado with some
thunderstorms over those parts of the state. Scattered early
evening thunderstorms will continue through about 8 PM over Park,
Summit, southern Jefferson and Douglas Counties. Mostly clear
skies are expected after that.

The upper air pattern will remain nearly unchanged for tomorrow.
The upper level ridge will be centered over central Colorado with
moisture still in place over southeast Colorado. Weak flow aloft
will cause winds aloft to be light. At the surface, high pressure
over the central plains will keep easterly winds in place most of
the day. This will keep most of the plains too stable again for
any shower activity. The Palmer Divide and southern foothills
should be the only places to see any showers. A model sounding
around KLIC for tomorrow afternoon shows 1500-2000 j/kg of CAPE,
meaning that strong thunderstorms will be possible. The amount of
moisture over the northern mountains and northeast plains will be
fairly limited, considering we are supposed to be moving into the
Southwestern Monsoon season.

.LONG TERM...(Friday night through Thursday)
Issued at 343 PM MDT Thu Jul 13 2017

The large upper ridge wobbling over the center of the country
may play tricks with our weather during the extended pd,
particularly this weekend. Models differ quite a bit Saturday
with the GFS indicating a closed 700-500 low near the Denver metro
area early Saturday morning. GFS moves this low very slowly
e-newrd across nern CO during the day, along the way being fed by
a moist e-sely 850-700 mb flow. GFS soundings keep areas east of
the Front Range socked in with low/mid-level clouds nearly all
day, with scattered to likely PoPs acrs the area. In comparison,
the Canadian model shows a low nearly closed off over sern CO and
a moist e-sely low-level flow over sern sections of our CWA. The
EC and NAM models are significantly drier and warmer, esply over
nrn portions of the fcst area as they only hint at a low spinning
around near the CO-KS border during the day. Temp differences
really stand out amongst the models. For instance, NAM gives
Denver a high of 90 on Saturday, while the GFS a high of only 74
degs. NAM gives a 12-hr pop of only 5 percent, and the GFS an
impressive 54 percent PoP! With such a discrepancy in the models,
will avoid going with any one model and will use a middle-of-
the-road model blend for Friday night thru Saturday night.

Looking ahead to the rest of the extended period...latest models
shift the upper ridge east over the central Great Plains which
exposes Colorado to a moist south-southwesterly subtropical flow.
Moisture begins affecting the high country as early as Monday,
and gradually across the rest of the fcst area through the week.
Even though this moisture plume shifts east of the mtns next week,
low-levels may not moisten as much, and thus the risk for heavy
rainfall on the plains remains uncertain. Still daytime temps
likely to trend downward with greater cloud cover, while this
same cloud cover will likely warm overnight lows.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 343 PM MDT Thu Jul 13 2017

Cool and stabilizing easterly winds will continue across the
Denver area this evening, keeping any showers or thunderstorms
from developing. The exception is over KAPA where a little more
unstable airmass over the Palmer Divide may allow one or two
showers to drift over the airport. Shower activity should be
ending by 8 PM. Little aviation impact is expected overnight as
winds switch to drainage southeasterlies. On Friday, the upper air
pattern will be nearly unchanged with most shower activity
expected to be to the south and southwest of Denver.

&&

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

$$

SHORT TERM...Dankers
LONG TERM...Baker
AVIATION...Dankers



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