Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 142205
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
405 PM MDT Thu Sep 14 2017

.SHORT TERM...(This evening through Friday)
Issued at 318 PM MDT Thu Sep 14 2017

Current water vapor satellite pictures are showing and upper
trough getting into the western CWA. There is a more substantial
upper trough and upper circulation over southern Nevada. Local
radars are indicating around 20% convective coverage over the
mountains and foothills right now. There is less over the Palmer
and Cheyenne ridges. There is also a few cells developing over
the far eastern plains where the dew points are actually above 40
F. The western plains are dry with dew points in the 30s F. A
decaying upper trough moves across the CWA later overnight into
Friday morning. Southwesterly flow aloft is over the CWA on
Friday. There is some weak upward energy on the QG Omega fields
this evening, a bit stronger overnight with the second trough. But
it too is to weaken and move to our north. There is neutral to
weak downward energy on Friday. The boundary layer winds will tend
to normal drainage overnight, then downsloping low level winds
are noted. By mid afternoon, a cold front and upslope behind it is
progged into the plains. There is decent moisture for the western
CWA much of tonight. The plains will dry out after midnight and
stay pretty dry much of Friday. Moisture will be limited in the
mountains on Friday but increase over the west late in the day.
CAPE is minimal this evening over the plains, better in the high
country. So will keep decent pops going in the mountains this
evening, with 0-20%s for the plains. On Friday, no pops for the
plains and foothills, with limited pops in the high mountains. For
temperatures overnight, lows will be 2-4 C cooler Friday morning
than this morning`s readings. Friday`s highs should be highs
should be 1-4 C cooler than this afternoon`s.

.LONG TERM...(Friday night through Thursday)
Issued at 318 PM MDT Thu Sep 14 2017

Still a bit of timing difference on the front and trough for
Friday night. Prefer the slightly faster GFS, especially with the
timing of the cold front. Sharp gradient in PoPs over the
mountains from dry south to wetter north. Still some differences
between the models on whether Summit county will be in the
moisture or not. Either way, the snow will mainly be above 10
thousand feet and with a warm ground there probably won`t be any
accumulation at or below pass levels. On the plains there will be
sharp cooling and a burst of winds overnight. As usual, the wind
will probably be a bit more than forecast by most of the models,
so I raised them a little. For Saturday, there could be a thin
layer of stratus, otherwise dry air. Models continue to show more
cooling and with dry air and clear skies, I dropped temperatures
Saturday and Saturday night a little more. Lows will be mainly in
the 40s on the plains, and there could be some 30s near the
northern border.

Warming in dry southwest flow for Sunday through at least Tuesday.
There is quite a bit of disagreement on the shortwaves passing
through the mean trough near the west coast. With the southwest
flow, the early part of the week should get warm again, probably
80s and a 90 on Tuesday or Wednesday is not out of the question.
This could present fire weather issues as the fuels are now
getting dry enough, especially west of the Front Range. We could
get a shortwave pulling in cooler air from the west or northwest
on Wednesday or Thursday. Still looking like good moisture will
likely be north of us, or a quick shot with the trough, so we will
just go with the model blend trend of cooling with low mainly
mountain PoPs on Wednesday and Thursday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 318 PM MDT Thu Sep 14 2017

The southeasterlies did kick in at DIA.  As mentioned above, it is
pretty dry, so will keep an mention of -TSRA out of the DEN TAF.
Drainage winds are expected overnight with a downsloping component
around much of Friday. No ceiling issues. A cold front with
upslope behind may get into DIA around 23Z Friday afternoon.

&&

.FIRE WEATHER...
Issued at 318 PM MDT Thu Sep 14 2017

There will be elevated fire danger on Friday as the airmass over
much of the area will dry out some more. Temperatures are
expected to be a bit cooler then today`s readings however. A cold
front will bring some high gusty winds to the plains late in the
day Friday.

The weekend will be dry but cooler. Southwest winds aloft will
bring warm and very dry weather for the early part of next week.
Breezy conditions are likely, especially in the foothills and
west of the Front Range. A windy day is possible, more likely in
the middle of the week. Red Flag conditions are possible with the
main question mark the amount and timing of the wind. Any
thunderstorm activity should be very limited.

&&

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

$$

SHORT TERM...RJK
LONG TERM...Gimmestad
AVIATION...RJK
FIRE WEATHER...Gimmestad/RJK



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