National Weather Service Forecast Discussion

000
FXUS65 KBOU 250252
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
852 PM MDT Thu Sep 24 2020

.UPDATE...
Issued at 839 PM MDT Thu Sep 24 2020

Ridge continues to be in place across the Great Basin and
southwestern portions of the CONUS. The jet is pushed to the north
with a gradual southeast progression of a surface low through the
day Friday. The jet will dip south across the northern border
region with mid-level winds increasing through the day. This will
bring increased fire danger to the mountains and foothills by
Friday afternoon. With highs continuing to be above normal and
with the addition of downsloping provided by moderate mid-level
flow highs could reach another 90 and even another record if we
are able to meet or surpass 91 degrees. Overall, not many
adjustments were made to the forecast minus current conditons.

&&

.SHORT TERM...(This evening through Friday)
Issued at 222 PM MDT Thu Sep 24 2020

Summer just keeps hanging on. Warm and dry air will continue
advecting into the region through Friday as westerly flow aloft
strengthens. High temperatures on the plains have been in the mid
and upper 80s all week, so a couple degrees of warming tomorrow
should push many locations above the 90 degree mark. Mountain
areas should also see increasing winds through the day, due to the
increasing westerly flow aloft. This will have implications for
fire behavior tomorrow afternoon with a Red Flag Warning already
issued to cover the situation. Winds on the plains are forecast to
be out of the east through most of the day as the westerly winds
aloft will induce a lee trough of low pressure that stays right
along the foothills. This will help to keep the gusty winds in the
mountains and the foothills.

A record setting 75th 90 degree day at Denver International
Airport and windy conditions in the mountains that will effect the
behavior of the ongoing Cameron Peak wildfire are the primary features
of this, my last forecast discussion as a member of the Denver
forecasting team. It has been an incredible run that has
stretched almost 30 years. Thank you to my colleagues who helped
to make it a great career.

.LONG TERM...(Friday night through Thursday)
Issued at 222 PM MDT Thu Sep 24 2020

Spatial cross-sections show fairly strong downslope winds
developing in the foothills Friday night into Saturday morning.
Colorado will be on the subsident side of a strong westerly
jetstream stretching across the northern Rockies. NAM12 spatial
cross-sections show an amplified mountain wave developing around
09z Friday night, with a cross-mountain component of 50 kts at 700
mb. The wave breaks down fairly quickly but gusty westerly winds
will mix down the surface. High temperatures on Saturday will
again close to 90 again. Fire danger will again be high over much
of the forecast area on Saturday, reference the fire weather
discussion. A weak cold front pushes into the northeast plains
Saturday evening. Sunday into Sunday night, a stronger system is
expected to drop out of the northern Rockies and impact the
forecast area. Moisture is still limited with this system but
cooler temperatures will accompany the system Sunday afternoon.
The ECMWF is a little slower and deeper than the NAM12/GFS
solutions forecast continues to fluctuate at this time. Main
change was for bring in the cooler temperatures for Sunday. Gusty
northerly winds through the day, with gusty west/northwest winds
over the mountains. Snow level appears to lower to around 7500
feet by Monday morning, but will need to watch that as well.
Frost/freeze potential may exist with a cool and dry airmass in
place. Cooler northerly flow continues over the region through
Tuesday as a ridge reamplifies over the western U.S. Models
solutions not in very good agreement for next week but consensus
of the models is for more seasonal temperatures and generally dry
conditions. Happy trails Todd!

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 222 PM MDT Thu Sep 24 2020

No aviation impacts expected over the next 24 hours. Ceilings
will be nearly unlimited along with good surface visibilities.
Slant visibilities for approaches to KDEN may be slightly reduced
during the hours around sunset and sunrise. Winds will be
southerly overnight and then mostly east to southeasterly
tomorrow.


&&

.FIRE WEATHER...
Issued at 222 PM MDT Thu Sep 24 2020

Mountain areas will see increasing wind through the day, due to
the increasing westerly flow aloft. This will have implications
for fire behavior Friday afternoon with a Red Flag Warning
already issued to cover the situation.

Strong and gusty downslope winds are expected to develop late
Friday night into Saturday morning, strongest in the foothills of
Larimer, Boulder and northern Jefferson counties. Peak wind gusts
up to 50 mph will be possible at that time with minimal rh
recovery with the windier areas. The Red Flag Warning in effect
through early Friday evening, will likely need to be extended
through Friday night at some point.

On Saturday, strong and gusty continue over the higher terrain with
gusts. Fire danger will again be a concern with red flag conditions
possible in the afternoon, especially from the Front Range Foothills
eastward across the plains. There will be a slight chance of
showers Sunday afternoon and evening and a storm system clips
northeast Colorado. Gusty northerly winds will continue to keep
the fire danger elevated across the northeast plains, in spite of
the cooler temperatures and improved rh. Generally dry but more
seasonal temperatures are expected for early next week.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 8 PM MDT Friday for COZ211>218.

&&

$$

UPDATE...Bowen
SHORT TERM...Todd Dankers
LONG TERM...Cooper
AVIATION...Todd Dankers
FIRE WEATHER...Cooper

NWS BOU Office Area Forecast Discussion