Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 181046
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
446 AM MDT Wed Oct 18 2017

.SHORT TERM...(Today and tonight)
Issued at 446 AM MDT Wed Oct 18 2017

A jet streak will move across northern Colorado this morning.
There is a band of high clouds associated with this. It is mainly
thin, but thicker in a mountain wave over the Front Range. This
should diminish later today, but there is still some high level
moisture upstream. There is a little reflection of the passing
feature at low levels, with some enhancement of westerly flow
occurring this morning, then a wind shift on the plains behind the
jet streak this afternoon. The pressure rises will be sliding from
north through east of us, but will turn the low level winds on the
plains around to the north and then east. We won`t really be in a
different airmass, so this should only produce slight
cooling/moistening over the plains this afternoon. With mostly
clear skies and continued very dry air, it will be another cool
night in the mountain valleys tonight. I dropped low temperatures
in the colder areas to values similar to this morning, a
compromise between the previous forecast and the MOS guidance.

.LONG TERM...(Thursday through Tuesday)
Issued at 446 AM MDT Wed Oct 18 2017

Thu and Thu night...a weak southwesterly flow aloft will be
over CO ahead of the next Pacific trough. The trough axis will move
into western CO by 00z Friday then into the Nebraska Panhandle by
12z Friday.  GFS and NAM cross-sections show limited moisture in the
the mountains on Thu, with minimal qg ascent present as the system
passes across the cwa Thu night. Unseasonably warm temperatures will
keep the Fire Danger high over the northeast plains Thu aftn. The
models continue to show gusty southerly winds in the 25-30 mph range
with highs in the mid to upper 70s. The strongest wind gusts however
will be offset by relative humidities in the mid 20s. Consequently,
not all the parameters meet critical fire weather conditions so we
still do not yet anticipate fire weather highlights for these areas.
Spatial cross-sections indicate gusty downslope winds in the
mountains and higher foothills for a brief time around 12z Friday,
with gusts in the 40-45 mph range. On Friday, an increasing
west/southwesterly flow will develop with weak to moderate qg
ascent by 00z Saturday ahead of next incoming trough. This
stronger Pacific trough will pass across northern CO Friday night.
Overall timing and intensity has been pretty consistent from run
to run. In the mountains, the deepest moisture and strongest lift,
albeit brief, will occur in the 03-09z window. Weakening mid
level ascent will occur Saturday morning, followed by moderate qg
descent and drying by Saturday aftn. 700 mb temperatures around
+10c Thu and Fri aftn, then around -5C Sat aftn. Increasing mid
level subsidence and strong cold air advection will allow for dry
and cool weather across the northeast plains Saturday barring an
isolated shower or two in the morning. The cold front will push
through northeastern CO around 06z Friday night, with northwest
winds 10-20 mph through the day Saturday. In and around Denver, an
anticyclone may occur with weaker east/northeast winds in the
aftn. On Sunday, a dry northwesterly flow aloft will be in place
with a ridge aloft overhead. Warmer temperatures can be expected
going into early next week as a ridge builds over the west coast.
Gusty west/northwest winds likely at times especially in the
mountains and foothills. There may be a little cooling on Tuesday,
following a weak frontal passage Monday night. The flow aloft is
expected to remain northwesterly through the middle of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 446 AM MDT Wed Oct 18 2017

VFR through tonight. Winds will shift to north-northeast around
16z- 18z, then through southeast and back to south in the late
afternoon and evening.

&&

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

$$

SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Gimmestad



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