Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 300306

Area Forecast Discussion
National Weather Service Denver/Boulder CO
906 PM MDT Thu Sep 29 2016

Issued at 843 PM MDT Thu Sep 29 2016

Moisture is increasing over the mountains and foothills, which
will aid in cloud cover overnight. This moisture will move onto
the plains and over the Palmer Divide tomorrow before noon.
Pulled back on snow in the mountains to correspond with modeled
wet bulb temperatures. Sky cover also updated to be more
representative. No other changes to the forecast this evening.


.SHORT TERM...(This evening through Friday)
Issued at 313 PM MDT Thu Sep 29 2016

Radar pictures and surface observations show a decent boundary
pushing northwestward across the metro Denver area at this time.
South and southeast winds behind it have speeds up to 25 knots.
Upstream radars show that there is perhaps some light showers
getting into the far western CWA right now. There is better shower
coverage over western Colorado. Models have a weak upper trough to
move across Colorado later tonight into Friday morning, but it is
pretty weak. The flow aloft is west-southwesterly tonight and
Friday, with speeds decreasing on Friday. The QG Omega fields show
weak upward to neutral motion tonight and Friday. Normal diurnal
wind trends are expected for the CWA tonight and Friday. Moisture
is progged to increase through the first period, then decent
moisture is progged for all the CWA on Friday. It never gets into
the lower levels for the plains on Friday. There a tad of CAPE
over the mountains this evening. On Friday, there is limited CAPE
over all of the CWA. The QPF fields have limited measurable
precipitation over the mountains and foothills tonight and Friday.
There is a tad over the western half of the plains on Friday. So
there is increasing, mostly mid and upper level moisture and weak
lift with a meager trough. For pops will go with "chance"s in the
mountains this evening and again on Friday. Pops will be a bit
less over the foothills and "slight chance"s over the western
plains on Friday only. For temperatures, Friday`s highs should be
1-5 C cooler than this afternoon`s readings.

.LONG TERM...(Friday night through Thursday)
Issued at 313 PM MDT Thu Sep 29 2016

Blocking ridge-trough pattern across the continental U.S. next
36-48 hours as a massive closed off trough over the Mideast
begins its slow shift eastward. A weak upper air disturbance
riding over the top of the shortwave ridge over Colorado is
progged to generate scattered showers across the high country
Friday night. Precip amounts should be on the light side due in
part to limited forcing. Amounts anywhere from a few hundreds to a
couple tenths of an inch in west slope areas. East of the
Continental Divide precip chances much lower and largely confined
to areas near the base of the foothills during the evening hours.
Will stick with low pops /10-20 pct/ in this area. This shortwave
shifts east of the area with the upper ridge on Saturday returning
drier conditions to the plains with west-southwesterly downslope
flow. Mtn areas may still see a few showers during the day with
weak instability and orographic lift. Temperatures on Saturday
expected to be similar to those on Friday.

Sunday through midweek...upper ridge in the area regains its
strength as it back builds over the state. Sunday looks dry except
for a few late day showers in the mtns. Temperatures also slightly
warmer with more sunshine. By Monday with the upper ridge shifting
east of the area again...flow aloft goes southwesterly and
through the day speeds increase in magnitude ahead of the upper
low diving southeast over the central Great Basin. Models show a
deep upper trough carving out over the Inter Mountain West Sunday
night into Monday. From there models diverge from each other with
most showing the deep upper low tracking northeastward across
Wyoming on Tuesday, while the GFS shows this low taking an eastward
path across Colorado. By midday Tuesday the GFS shows the 500 mb
low passing over the Denver metro area...while the ECMWF...
Canadian GEM...SREF and GDEX show the low much farther north over
northeast Wyoming. The GFS solution would give us a better chance
for wetting rainfall and even some high country snowfall Tuesday
into Tuesday night. Whereas the alternative solution would pretty
much keep things dry on the plains and some orographic rain/snow
showers going in the mtns. Gusty west-northwest winds also a
strong possibility with this second scenario. Right now am
leaning more towards this drier and windier forecast and and so
will keep pops on the low side esply east of the mtns Tuesday and
Tuesday night.

Beyond Tuesday night...the general consensus is for drying and
warming as a large upper ridge builds over the Great Basin.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 843 PM MDT Thu Sep 29 2016

Partly cloudy skies will continue overnight with increasing cloud
cover through the period tomorrow. Winds will continue to stay
southerly over the next few hours then turn to drainage through
the evening. By 14z tomorrow morning winds will switch to a more
Northwesterly then North direction but will stay relatively light
at 5 to 10 mph. Ceilings will move in by 08z and continue through
the period with increasing mid level moisture. Large dewpoint
depression near the surface will help to keep conditions dry so
confidence is low on precipitation for tomorrow.




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