Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 172131

Area Forecast Discussion
National Weather Service Denver/Boulder CO
331 PM MDT WED AUG 17 2016

.SHORT TERM...(This evening through Thursday)
Issued at 331 PM MDT Wed Aug 17 2016

Weakly organized upper low centered just south of Trinidad is
progged to slowly track northeast and open up into an open trough
over northeast Colorado this evening. The light east-southeast
mid-level flow aligned with west-east cloud band hanging over
e-central Colorado at the moment will likely shift northeastward
with the low next several hours. Along the northern edge of this
cloud band beginning to see convection in the from to CU and TCU.
High res models continue to show an increase in sfc based CAPES
along a nern Denver-to-Sterling axis over the next few hours.
Values in the 400-800 j/kg range. Helicity values off model
soundings not all that impressive. Overall any t-storms that form
in this area should be upright and therefore of short duration.
Brief heavy rain and gusty outburst winds main produce of these
late afternoon and early evening storms. Meanwhile...widely
scattered showers/t-storms going up in the high country should
continue to increase in coverage particularly south of the i-70
corridor next few hours. East-southeast flow and weak mid-level
dynamics on the north side of the upper low should focus most of
the high country convection over and near Park County. Weak
transport winds may lead to locally heavy rainfall in this area.
Small hail and strong gusty outflow winds also possible. Most of
this activity should exit the forecast area by mid to late evening
with a loss of solar heating and departure of the upper low.
Should see partial clearing after midnight with drier northwest
flow on the back side of the upper low/trough.

On Thursday...skies should start out fairly clear but with cooling
aloft associated with the passing shortwave trough...with steeper
mid-level lapse rates by afternoon. This should set off another
round of showers and t-storms by early afternoon...first over the
high country. Downslope flow off the Front range should delay any
convection on the nearby plains until mid-afternoon. Shower/t-storm
chances should then increase east of the mtns with a shift to a
wetter northeast flow. Scattered pops seem reasonable for the
plains at this time. Temperatures also slightly cooler than today.

.LONG TERM...(Thursday night through Wednesday)
Issued at 331 PM MDT Wed Aug 17 2016

The primary challenge in the extended forecast are temperatures on
Friday and Saturday. A short wave trough moves across the northern
Plains on Friday placing CO in northwest flow aloft. At the
surface a cool front will enter across CO from southeast WY late
Thursday into early Friday and bring north winds that should
reach 20 mph for a several hours. The general features impacting
CO weather are the similar on all the numerical models but the
strength of the cooling behind the front is something they
disagree on. On Friday given the expected cloud cover and decent chance
of showers and thunderstorms, high temperatures will only be in
the low 70s across the Plains. Cloud cover will keep overnight
lows in check Friday night with lows in the Plains around 50. On
Saturday the NAM and EC are in agreement while the GFS is an
outlier in terms of high temperatures. The GFS is quicker than
other models in moving the northern Plains storm system to the
northeast and initiating downslope winds by midday on Saturday.
The GFS also has a weaker surface high (MSLP of 1020 mb for GFS vs
1024 for the EC and NAM) than the NAM and EC. Temperatures are 4C
warmer at 700 mb and 5-7F warmer at the surface in the GFS on
Saturday. Sided with EC and NAM and do not think downslope will
occur on Saturday early enough to warm temps much above 70
degrees if at all. Afternoon showers and thunderstorms will be
isolated on Saturday as the best instability is confined to the
south and east of the CWA.

Light northwest flow aloft continues on Sunday but the atmosphere
will dry out and only isolated thunderstorms are expected driven
by daytime heating. Monday through Wednesday the flow aloft is
weak and the storm track remains north of the border in Canada.
Precipitation chances will be low across the CWA, with the highest
(but still low) chances confined to the mountains. High temperatures
will return to seasonal norms in the mid 80s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 331 PM MDT Wed Aug 17 2016

Light east-southeast sfc winds in the Denver area will gradually
shift to a south-southeastward direction overnight. Speeds
generally under 10 kts. Isolated thunderstorms in the area from
23z-02z could produce gusts to around 30kts. Storms should end
this evening with partial clearing overnight. On thursday...VFR
conditions with a 20-30 percent chance of thunderstorms in the
Denver area after 3 pm MDT. Drainage winds of 4-9kts in the
morning will go north-northeast 8-15kts by early to mid afternoon.


.BOU Watches/Warnings/Advisories...


LONG TERM...Schlatter
AVIATION...Baker is the U.S. government's official web portal to all federal, state and local government web resources and services.