Damaging Wind in Colorado, September 10, 2018

Area Forecast Discussion
National Weather Service Denver/Boulder CO
310 PM MDT Mon Sep 10 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 310 PM MDT Mon Sep 10 2018

Dry southwest flow continues across Colorado with a potent trough
off the coast of Washington state.  This trough barely moves over
the course of the week as it looks to cut off mid week and the ridge
across the eastern 2/3 of the U.S. elongates southwest to
northeast, essential blocking the troughs eastward progress. The
forecast theme for this week continues to be well above normal
temperatures (hot for September) and dry. Based on GOES-16
satellite trends and a zone of weak instability across the Palmer
Divide and Lincoln County, a stray thunderstorm or two is
possible the remainder of this afternoon and early evening, mainly
across the central Mountains south of I-70. We do not expect much
rain from any storms that form. Tonight, clearing skies with
temperatures remaining quite warm most areas, with lows in the
mid to upper 50s Plains and mid 30s to 40s in the mountains.

On Tuesday 700 mb temps warm almost 1 degC, so high temperatures
at the surface are likely to be just a tad warmer than today,
especially given the likelihood of less cloud cover. There is a
small amount of mid-level moisture across the central Mountains,
resulting in another isolated chance of a thunderstorm or two
along and south of I-70. The plains and metro area will almost
certainly not receive a drop of rain Tuesday afternoon. Expect
highs in the low to mid 90s, and with Denver's record for Tuesday
at 92, a record high is possible. Mountains will be in the 70s to
low 80s. The main concern Tuesday is the elevated fire danger
across the northern mountains. It will be warm/hot and very dry
across the higher elevations and west slopes of Jackson, Grand,
and Larimer County, but winds should remain below red flag
criteria until Wednesday afternoon (details below). The Plains
will also be hot and dry but winds should remain be below RFW
criteria there as well.

.LONG TERM...(Tuesday night through Monday)
Issued at 310 PM MDT Mon Sep 10 2018

As a low pressure center sets up along the Pacific Northwest
coast, the flattened upper level ridge over the Central Great
Plains will begin to transition into a troughing pattern. This
will allow zonal upper level winds to begin carrying more of a
southwest component Wednesday through the weekend.

Conditions will be warm and dry through Saturday with good
agreement in the models. The cooler air will remain farther
northwest of the state with flow from the desert southwest
continuing to pump warm air into the region. The 700 mb
temperatures are expected to remain between 13 and 17 degrees
Celsius through the week. This will keep daily highs near the mid
to low 90s on the plains, while the mountains reach the upper to
mid 70s. See the fire weather section below for more details on
Wednesday's Red Flag Warning.

Come sunday, the ECMWF indicates the flow will again become more
zonal with the GFS showing continued troughing. The change in
source region for the winds will bring cooler temperatures from
Utah allowing high temperatures to drop considerably.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 310 PM MDT Mon Sep 10 2018

VFR through Tuesday and no precipitation expected at the metro
area terminals. Winds this afternoon at DEN have been rather
chaotic but for the most part the speeds have been less than 10
kts. Convection to the south has generated NW flow across DEN.
Expect weak northwest flow to continue for another hour or two
given the low- level pressure trends pattern and convection to the
south and southeast. Winds should shift to easterly early this
evening before turning to drainage.  Drainage winds out of the
south will return to APA and DEN after 04Z or so, and be in the
10-15 kt range. BJC will be west tonight and less than 10 kt.
Tuesday more of the same weather though there shouldn't be as much
convection to the south of the metro area terminals. Expect light
easterly flow by midday lasting into the evening hours before
once again drainage winds kick in.

&&

.FIRE WEATHER...
Issued at 310 PM MDT Mon Sep 10 2018

On Tuesday the higher elevations of Jackson, Grand, and Larimer
Counties will be hot and dry during the afternoon. Decided not to
issue any fire wx highlights because winds should remain below 20
mph. Continued dry conditions will carry over into Wednesday and
with another day of fuel curing and increasing west winds, a Red
Flag Warning has been issued for Wednesday from 11 PM to 8 PM due
to warm temperatures, low relative humidities, and gusty winds
over 25 mph. This could lead to rapid fire spread and erratic
winds leading to unpredictable fire behavior.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 8 PM MDT Wednesday for COZ211-213-
217.

&&

SHORT TERM...Schlatter
LONG TERM...Sullivan
AVIATION...Schlatter
FIRE WEATHER...Schlatter/Sullivan

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1022 AM MDT Mon Sep 10 2018

COZ030>051-111630-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1022 AM MDT Mon Sep 10 2018

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Hot and dry today with highs around 90 across the Plains, and 70s
in the mountains.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Dry weather with above normal temperatures are expected this week
into the weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.