Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211615
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1015 AM MDT Thu Sep 21 2017

.UPDATE...
Issued at 1015 AM MDT Thu Sep 21 2017

Mostly sunny/sunny skies will persist through the day as a very
dry airmass remains over Colorado. Temperatures are on track to
challenge some record highs this afternoon. Do not expect to make
any changes to the current forecast.

&&

.SHORT TERM...(Today and tonight)
Issued at 522 AM MDT Thu Sep 21 2017

Today will be warm, dry, and becoming windy across most areas by
this afternoon. Only slight changes needed to the current
forecast. Model soundings indicate drier air aloft that will be
available to mix down this afternoon. Nudged the forecast toward
the NAM and NAM MOS guidance which has lower dew points and more
wind in the higher mountains. With a SSW flow some areas like
the west side of Denver will be sheltered, and the foothills from
Golden to Estes Park will also not be as windy as they usually are
in W-NW flow. Places open to this direction, like Kremmling,
Walden, South Park, and areas south of Denver should make the most
of the wind again today. Considered the need for expansion of the
Red Flag Warning, but it looks about right. Record high of 89 at
Denver today--it will be close.

Wind will ease some this evening with lack of heating and less
low level gradient. However the flow aloft will increase a bit and
we may even get a bit of a mountain wave setup overnight. With the
wind direction this will be spotty and mainly affect remote areas,
but could approach high wind criteria in favored spots.

.LONG TERM...(Friday through Wednesday)
Issued at 522 AM MDT Thu Sep 21 2017

Strong southwesterly flow aloft will cover the CWA Friday into
Saturday evening, then it becomes southerly but will stay pretty
strong. Jet level speeds are 80 to 110 knots that entire time. At
12Z Sunday morning, models show an upper trough stretching from
western Montana southward into the Gulf of California. There is a
closed upper low over the southern half of Utah. Fairly decent
upward QG Omega is over the forecast area in the synoptic scale
Friday through Saturday night. The low level pressure and wind
fields have south-southwesterly winds on Friday with only the GFS
showing a cold front and northerly winds Friday night. The rest
of the models keep normal drainage patterns going. There are some
easterlies progged on Saturday, with all the models showing a
cold front and upslope into the CWA later afternoon into the evening.
Upslope is progged all night Saturday through Sunday night.
Moisture increases in advance of the upper trough. Precipitable
water amounts increase by later Friday afternoon. They range from
0.50 to 1.25 inches from west to east Friday night through
Saturday night. There is not much CAPE around Friday, but it
increases overnight along the eastern border of the CWA. On
Saturday, there is pretty decent CAPE over the eastern half of the
plains and the southwestern quarter of the CWA. There are lesser
amounts over the rest of the forecast area. The QPF fields have no
measurable precipitation on Friday through mid day, then a bit
develops in the afternoon and overnight. Models have fairly decent
precipitation over much of the CWA later Saturday afternoon and
evening. For pops, will go with "chances" in the mountains Friday
afternoon into Saturday morning, with little or nothing over the
plains. Will leave in or go with higher pops Saturday and Saturday
night. "Likely"s are a good bet in most areas. Snow levels should
stay above 9,000 feet Saturday and Saturday night. For temperatures,
Friday`s highs should be 2-4 C cooler than this afternoon`s.
Saturday`s highs will cool down another 3-8 C from Friday`s. For
the later days, Sunday through Wednesday, the latest medium range
models still show a slow eastward progression with the upper
trough.  It gets into western Colorado on Sunday an then moves
slowly eastward into eastern Colorado by 12z Thursday morning.
There are various pieces of energy with it here and there as well
as some reinforcing shots of cooler air and upslope flow east of
the divide. One thing for sure, it will be a bit of an unsettled
period all four days with a better chance of precipitation than
we have had for many weeks. Temperatures will be cooler than
seasonal normals, but a freeze doesn`t look viable for the lower
elevations just yet.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1015 AM MDT Thu Sep 21 2017

VFR conditions through tonight and Friday under mostly clear
skies. South winds will gust to 30 knots at KDEN/KAPA. Winds will
be lighter and have some variability at KBJC.

&&

.FIRE WEATHER...
Issued at 522 AM MDT Thu Sep 21 2017

Little change to the forecast with Red Flag conditions expected
across the plains south of Interstate 76. Humidities will drop
as low as 10 percent with south winds gusting as high as 35 mph
this afternoon. In the mountain parks similar conditions are
expected, but the humidities will be a little higher. The
mountains north of I-70 have also had recent light rain and snow
and fuels are generally not as dry. On the plains north of
Interstate 76 winds are expected to be lighter, though it will
still be hot and dry.

Conditions will not be as extreme on Friday, though it will still
be warm and dry, and breezy in some areas.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM MDT this evening for COZ241-245>247-
249.

&&

$$

UPDATE...Meier
SHORT TERM...Gimmestad
LONG TERM...RJK
AVIATION...Meier
FIRE WEATHER...Gimmestad


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