Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 131622
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1022 AM MDT Wed Sep 13 2017

.UPDATE...
Issued at 1021 AM MDT Wed Sep 13 2017

Today`s forecast looks on track and no significant changes were
made. Temperatures near the foothills have already mixed out the
overnight inversion and are well into the mid 80s. Denver and
areas below 6500 feet should easily reach 90 degrees today. For
Denver, this will be day 46 in 2017 with high temperatures at or
above 90 degrees. We are still not very optimistic in rain chances
today outside of the Front Range mountains and foothills. Surface
dry area across the Plains will inhibit rain chances elsewhere
and at best a sprinkle or two with gusty winds east of the
mountains and off the Palmer Divide.

&&

.SHORT TERM...(Today and tonight)
Issued at 405 AM MDT Wed Sep 13 2017

Upper level ridge will remain over the Central and Southern
Rockies today, but there will be a slight increase in mid level
flow as ridge flattens. Current GOES 16 low/mid level water vapor
imagery actually shows some moisture moving our way from the
Western Slope of Colorado. While it remains very warm aloft, the
slight increase in moisture and strong daytime heating will be
enough to generate afternoon/early evening convection. Coverage
should be slightly higher than yesterday, but still limited due to
the dry low levels. As a result, expect fairly widespread gusty
outflow winds today, but only light rainfall from any storms.

Temperatures will be very warm once again, with readings expected
to be another degree or two warmer on the plains. That should push
us into the lower to mid 90s over most of the plains, but probably
just a couple degrees shy of records. Record for Denver is 96F.
Lee troughing and shallow inversions will also mean a quick
warmup this morning.

Convection ends this evening with a stabilizing airmass and lack
of any synoptic support. Overnight lows will once again be quite
mild with readings in the mid 50s to lower to mid 60s on the
plains, warmest near the foothills including Metro Denver.

.LONG TERM...(Thursday through Tuesday)
Issued at 405 AM MDT Wed Sep 13 2017

SW flow aloft will be over the area on Thu ahead of an upper lvl
disturbance which will affect the rgn Thu night into early Fri.
There will continue to be some subtropical moisture embedded in the
flow, which combined with favorable lapse rates, should lead to
sct showers and tstms over the higher terrain by aftn with some of
the activity spreading across nern CO. As for highs, 850-700 mb
temps change little so readings over nern CO will be in the upper
80s to lower 90s.

For Thu night into early Fri the disturbance will move across with
some minor mid level ascent.  Thus will continue to see a chc of
showers mainly over the higher terrain with a slight chance across
the plains. As for highs, there will be some slight cooling in
the 850-700 mb layer so readings across the plains will be mainly
in the lower to mid 80s.

By Fri night into Sat swly flow aloft will increase as a stg upper
level trough moves into the nrn Rockies.  There will be some mid lvl
ascent across nrn CO mainly Fri night with an increase in moisture
especially over the higher terrain north of I-70.  Thus will see
another chc of showers with some snow possibly mixed in overnight
abv 11000 ft.  Across nern CO a cold front will move across the
plains by Sat morning which will drop temperatures into the 70s for
aftn highs. At this point it looks generally dry across the
plains although there could be a slight chc of showers near the WY
border.

By Sat night the upper level trough will move into the nrn Plains
with wsw flow across nrn CO.  Both the ECMWF and GFS show an
increase in moisture across nern CO with the right rear exit rgn of
an upper level jet affecting the plains.  As a result this could
lead to a chc of showers over the plains Sat night although
confidence this far out is rather low.  Thus will just mention a
slight chc of showers for now.

On Sun wsw flow aloft will remain over the area as sfc high pressure
begins to move east into the cntrl plains.  At this time it looks
mainly dry with highs in the 75 to 80 degree range across nern CO.

For early next week a stg upper level trough will dvlp over the
Pacific NW with swly flow aloft over nrn CO. Thus will see
generally dry conditions with above normal temperatures both days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1021 AM MDT Wed Sep 13 2017

VFR with just scattered mid level decks today through Thursday. Expecting
a wind shift to 300 deg at KDEN midday, then outflow from
thunderstorms across the mountains and foothills may increase the
WNW flow at all Denver metro area airports. Have kept a TEMPO
group in there to account for variable gusty winds, but we hope to
provide a robust wind direction this afternoon once convection
gets going and we can identify and track the gust front(s). We are
not expecting any precipitation or lightning at the TAF sites
this afternoon. Tonight winds will go to drainage after 04/05Z and
then variable after 14Z. Best bet for wind direction tomorrow
from midday on is west and west-northwest, with winds around 10-15
kts in the afternoon.

&&

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

$$

UPDATE...Schlatter
SHORT TERM...Barjenbruch
LONG TERM...RPK
AVIATION...Schlatter



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