Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 260150
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
750 PM MDT Tue Sep 25 2018

.UPDATE...
Issued at 743 PM MDT Tue Sep 25 2018

Only minor adjustments planned for the grids this
evening, current forecast appears on track.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 226 PM MDT Tue Sep 25 2018

Skies have clear as seen on GOES visible with clouds increasing
to the south with the help of lift from the warm conveyor belt
at the base of the elongated upper trough. Increasing NW flow
through the day has helped to clear out morning stratus leaving
sunny skies under cooler post-frontal temperatures. Surface high
pressure will build in over the far eastern plains pulling winds
from the North to a more easterly direction by the late evening
hours. This more favorable upslope wind direction combined with
some mild QG ascent provided by a piece of energy moving north
from AZ will increase cloud cover around midnight and into the
early morning hours Wednesday. Some areas will see some radiational
cooling and bring overnight lows into the lower to mid 30s on the
plains and low 20s in the mountain valleys overnight. A frost
advisory continues for the northern half of Weld County near the
Wyoming border, including the Pawnee Grasslands. Temperatures will
be just getting into the range for sensitive plants overnight.
Elsewhere, cloud cover will be enough to help keep lows out of the
front advisory range. Some areas could get close if cloud cover
is patchy.

For Wednesday, the upper trough will push into western CO with
westerly flow increasing over the mountains. Drier WNW flow will
bring RH levels down over the high country with some clouds
lingering over the SE portions of the state. Temperatures will be
warmer than today with highs in the mid 70s under partly cloudy
skies.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 226 PM MDT Tue Sep 25 2018

There will be a dry northwest flow pattern across Colorado for
Wednesday night and Thursday. Expect warmer temperatures as well
as 700mb temperatures increase to around +10c over the Front Range
by Thursday afternoon. Strong surface high pressure building
southward into Montana will send a cold front across the plains of
northeast Colorado Thursday night and early on Friday. The
coldest temperatures will be along the far northeast plains where
temperatures may only be in the 50s for afternoon highs on Friday.
Given some weak QG ascent would no be surprised to see a few rain
showers as well over the far plains as low level moisture depth
may be sufficient for drizzle or light rain.

For this weekend, high pressure ridge aloft will build across
Colorado in response to an upper low developing along Pacific
Northwest. Given this pattern change, the flow aloft will shift west
and then southwest through later this weekend. This will also
result in warmer temperatures as 700mb temperatures climb back to
the +12c to +14c range.

The longer range becomes even more muddled for next week as
model players present quite varied scenarios. Some of the
different paths also depend on track of Tropical Storm Rosa. The
GFS is most bullish in steering the track towards Baja and
results in quite a bit of moisture advecting northeast into the
desert southwest and just into Colorado by late Monday. In the
mean time the tropical system gets advected into the west coast
trof which swings through the region on Tuesday and into
Wednesday. The European solution keeps the tropical system and
much of the moisture further offshore with a much drier solution
for Colorado. The Canadians drop the deepest solution into the
Great Basin on Wednesday. So solutions generally span about 1500
miles apart. For now, will keep slight to chance of showers mainly
in the mountains by late Monday and Tuesday time frames.
Temperatures through these late periods will be slightly above
normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 743 PM MDT Tue Sep 25 2018

VFR conditions are expected for the period. Expect southeast winds
7-12 kts to continue then gradually transition to drainage, with
speeds of 5-8 kts.



&&

.FIRE WEATHER...
Issued at 226 PM MDT Tue Sep 25 2018

Fire danger will remain elevated for both Thursday and Friday
afternoons and possibly into the weekend for the high mountain
valleys. Humidity levels will be down in the 10-15 percent range
but wind gusts will be more marginal for red flag conditions,
usually in the 10-22 mph range. No fire weather watches are
planned for now.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 10 AM MDT Wednesday for COZ038-042.

&&

$$

UPDATE...Cooper
SHORT TERM...Bowen
LONG TERM...Entrekin
AVIATION...Cooper
FIRE WEATHER...Entrekin


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