Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 140255
AFDBOU

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

.UPDATE...
Issued at 855 PM MDT Thu Jul 13 2017

Airmass is stabilizing in all areas except for Lincoln county.
There is enough instability to keep a few showers and storms
going there for the next few hours, before diminishing or ending
overnight. Park county could also be on the edge of a few showers
as they rotate around weak/small circulation center over southwest
Colorado. Otherwise dry conditions will persist overnight.
Mostly clear skies over the northern tier of counties and moist
boundary layer is expected to bring some patchy fog late tonight.
Updates made for latest trends.

&&

.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 00Z TAFS through 00Z Friday evening)
Issued at 855 PM MDT Thu Jul 13 2017

Isolated thunderstorms in the Denver area ended earlier this
evening as airmass stabilized. VFR conditions will persist
overnight through Friday. Isolated showers and storms on Friday
should stay just south of the Denver metro area, with only a
slight chance of a storm reaching KDEN after 22Z. Normal diurnal
wind patterns expected around 10 knots or less through Friday.

&&

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

$$

UPDATE...Barjenbruch
SHORT TERM...Dankers
LONG TERM...Baker
AVIATION...Barjenbruch



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