Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 160254

Area Forecast Discussion
National Weather Service Denver/Boulder CO
854 PM MDT Sun Oct 15 2017

Issued at 854 PM MDT Sun Oct 15 2017

Clear skies and light winds prevail across the forecast area this
evening. Only the high mountain areas are seeing some gusts, but
those will become stronger by Monday morning as flow aloft
strengthens. A few high clouds will also drift into the area, with
some mountain wave enhancement (generally in a narrow ribbon)
along the Front Range for Monday. This should do little to slow
the warming in most spots so overall forecast for warmer
temperatures on track. We did knock down temps tonight in the
normally cool valley locations due to the dry airmass, light
winds, and strong radiational cooling.


.SHORT TERM...(This evening through Monday)
Issued at 235 PM MDT Sun Oct 15 2017

A dry and stable post-trough airmass covers the region today
evident by the severe clear conditions. A weak sfc pressure
gradient also resulted in significantly lighter winds. Winds on
the mtn ridges have also trended downward through the afternoon
with the axis of strongest winds aloft shifting north over

Tonight, dry air will remain in place and the beginning of
warming aloft in advance of the shortwave ridge will result in two
things, warmer overnight lows and strengthening of the mtn top
inversion late. Models also indicate an increase in 600-500mb nwly
flow and the formation of a lee side mtn wave. Therefore, should
see an increase in the cross mtn wind component late tonight and
continue through Monday morning, then a decrease in speed Monday
afternoon with the mtn wave relaxing. Look for gusts in the
25-35 mph in the foothills and near 50 mph on the ridges. A
lighter downslope flow on the plains Monday will push afternoon
temps into the low to mid 70s. Warm yes, but still well below the
record max temps for the date. Lastly, the gusty west winds and
low RH in the foothills and higher area along the Cheyenne Ridge
will elevate the fire danger for a few hours during the afternoon,
but not long enough or extensive enough to warrant a fire weather
watch at this time.

.LONG TERM...(Monday night through Sunday)
Issued at 235 PM MDT Sun Oct 15 2017

WLY flow aloft will be over the area on Tue and then become more
WNW on Wed. Cross-sections only show some higher level moisture
embedded in the flow so it will be dry both days. As for highs,
temps will warm into the mid to upper 70s on Tue over nern CO. On
Wed a weak fnt may affect nern CO with highs a few degrees cooler
in the lower to mid 70s.

On Thu the flow aloft will become more WSW with downslope low lvl
flow.  Thus it will remain dry with temps fm 10 to 12 degrees abv
normal.  By Fri WSW flow aloft will increase ahead of an upper level
trough.  There may be just enough moisture for a few aftn showers in
the mtns, otherwise, it will remain dry with temps remaining 10 to
12 degrees abv normal across the plains.

For Fri night into Sat the ECMWF has a progressive upper level
trough moving across the area.  Meanwhile the GFS has a slower
system which affects the area Sat thru Sat night.  The GEM`s
solution favors the ECMWF solution.  For now will just mention a chc
of showers in the mtns with a slight chc over the plains.  Meanwhile
temps will become cooler as well as a cdfnt moves across with
readings dropping back to seasonal levels.  On Sun dry NWLY flow a
loft will be over the area with seasonal temperatures.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 854 PM MDT Sun Oct 15 2017

VFR conditions will persist with only a few high clouds above 20
thousand feet Monday. Light and variable winds this evening will
turn to normal south/southwest winds toward 06Z tonight and
continue through 15Z Monday. Then winds should gradually turn
clockwise to west/northwest by 18-19Z Monday, and then north to
northeast by 21Z-00Z. Speeds should hold 5-12 knots through most
of this period.


Issued at 235 PM MDT Sun Oct 15 2017

The foothills in Boulder and Larimer Counties and higher areas of
northern Larimer and Weld Counties up along the Cheyenne Ridge
could see west winds gusting 15-30 mph and min RH values of 8-15
percent for a few hours tomorrow afternoon. These conditions will
elevate the fire danger in these areas. However, a fire weather
watch will not be issued at this time because of the short
duration of these conditions and their limited extent.




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