High Wind Watch 5, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
Issued by National Weather Service Pueblo CO
1118 AM MDT Wed Apr 20 2022

.UPDATE...
Issued at 900 AM MDT Wed Apr 20 2022

The Red Flag Warning over the northern border and Cheyenne Ridge
vicinity has been expanded one Fire Zone westward to include
Larimer County Below 6000 Feet and Northwest Weld County (Fire
Zone 238). Surface observations in this area indicate relative
humidity already falling into the middle 30s to the lower 40s.
With diurnal mixing increasing further, and additional
tropospheric drying aided by weakly subsident flow aloft,
confidence is increasing that relative humidity values fall to
13-15 percent across Fire Zone 238. Meanwhile, strengthening
vertical mixing into moderate midlevel winds is expected to
support 25-40 mph wind gusts combining the with the low relative
humidity -- warranting expansion of the Red Flag Warning. Forecast
conditions have been updated through the day across the foothills
and plains to account for the drier air, along with the latest
observational data. No other changes have been made to the ongoing
forecast.

&&

.SHORT TERM...(Today and tonight)
Issued at 354 AM MDT Wed Apr 20 2022

..Red Flag Warnings have been expanded to include the
northeast WY/NE border counties for this afternoon...

Upper trough will be exiting eastern CO this morning with gusty
north winds behind the front weakening before the Denver cyclone
sets up bringing southeasterly winds into the Denver area and
adjacent plains in the afternoon. To the north and west however,
gusty west winds in the wake of the system will bring elevated to
critical fire weather concerns back to portions of the area.
Relative humidity will be the determining factor for these areas
with Park, Logan, Sedgwick, Phillips and northeast portions of
Weld county having the best chance of seeing 3 hours or more of
combined gusty winds and critically low relative humidity.
Conditions look more marginal across Northwest Weld county and for
locations westward to along the foothills around Fort Collins
where humidity values come up just shy of the required 15%
threshold. Will hold off on fire weather highlights for this area.
But certainly gusty winds will be in place and will have to
closely monitor dew point trends through the afternoon. Red Flags
will run from noon to 8 PM before winds relax a bit.

Southeast winds increase across the plains overnight which brings
higher dew points westward and will serve to keep overnight lows on
the mild side with readings around 5-10 degrees above normal. -KT

.LONG TERM...(Thursday through Tuesday)
Issued at 354 AM MDT Wed Apr 20 2022

Southwest flow aloft increases Thursday and Thursday night ahead of
the next digging system along the west coast.  Return southerly flow
continues across the plains and winds will be gusty in the afternoon
once again both across the high county with southwesterlies and
across the plains with southeasterlies.  However with dew points on
the increase across the plains, this should keep afternoon humidity
values above critical thresholds so fire weather highlights do not
look needed at this point.

Models are in fair agreement lifting the upper trough through the
Great Basin on Friday and closing off the upper across WY Friday
night before ejecting it to the northeast into the Dakotas into
Saturday. Snow and wind will ramp up along the Continental Divide
on Friday, with gusty winds and extreme fire danger spreading across
the plains. The southeast tier of the area could see high wind
criteria gusts as strong southwesterlies aloft eject eastward
across and mix to the surface with the deepening surface low
Friday afternoon and evening. This will likely result in
widespread blowing dust across the eastern plains. Winds should be
a little lighter up against the foothills but still very windy
and with widespread relative humidity values below 15 percent,
this will be a high impact critical fire weather day for much of
northeast CO. It is still too soon to hoist highlights for winds
and fire concerns, but will continue to highlight these concerns
in social media and hazardous weather products. Suspect watches
will be hoisted in the next 12-24 hours.

Will also be watching the position of the dry line closely across
the far eastern counties Friday evening for the potential of
strong to severe thunderstorms near the eastern CO border, but
for now best parameters look to stay just east. Otherwise could
several inches of snow with the potential for winter highlights
along the Continental Divide Friday night through Saturday. For
now amounts are in the advisory range, though will have to take
into account blowing snow impacts as well. Some wrap around
precipitation may spread into the northeast plains Friday night
and Saturday, but with dry air entrained into the system, any QPF
looks light.

Trailing energy drops in from the northwest for Sunday which will
keep cooler and unsettled weather through the weekend.  Some
additional light snow will continue along the northern mountains
given continued favorable orographics. But with the cooler
temperatures will also come higher humidity values which should
put a damper on fire weather highlights.

Upper ridging takes hold for early next week which will bring
warming temperatures and the potential for spotty critical fire
weather conditions across the lower elevations, though it appears
winds may come up on the light side. -KT

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1103 AM MDT Wed Apr 20 2022

VFR conditions will continue the next 24 hrs, with e-se winds
until 22z. Main question after 22z regards wind direction, as
HRRR and NAM suggests w-nw winds will spread away from the
foothills and across the metro area 22z-02z. Given orientation of
surface pressure gradient, suspect this is a little overdone,
with better chance of a wind shift at KAPA and KBJC than KDEN.
After 02z, winds at KDEN return to e-se through the night, while
flow becomes light and variable at KAPA and KBJC before gradually
turning n-nw after 06z.

&&

.FIRE WEATHER...
Issued at 900 AM MDT Wed Apr 20 2022

...Extreme Fire Danger possible Friday...

Fire Zone 238 -- including Larimer County Below 6000 Feet and
Northwest Weld County -- has been added to the Red Flag Warning
across the Cheyenne Ridge today. No other changes have been made
to the ongoing Fire Weather Discussion.

Critical fire weather conditions will return to portions of
northeast CO today with Park county and the northeastern counties
seeing Red Flag conditions return in the Noon to 8 PM window.

Humidity values will stay higher for Thursday for most areas as
southeasterly surface winds advect moisture in from the southeast
across the plains.  Some spotty critical fire weather conditions
will be possible in and near the southern foothills but for now it
does not look like the 3 hour duration will be met.

Friday will be the most extreme day for fire weather as strong
southwest winds gusting to 40-60 mph will combine with humidity
values below 15 percent over a most of the lower elevation and
foothill locations.  The most volatile areas will be across the
eastern portions of the plains where the strongest winds and lowest
humidity values will juxtapose during the afternoon and evening.

Humidity values increase for Saturday and Sunday, then warming
temperatures into early next week will bring a return of lower
humidity values. Winds, however, appear to be the limiting factor
for critical fire weather conditions for early next week. -KT

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for COZ214-238-242-
248-250-251.

&&

UPDATE...COHEN
SHORT TERM...KT
LONG TERM...KT
AVIATION...EP
FIRE WEATHER...KT

Hazardous Weather Outlook...UPDATED
National Weather Service Denver/Boulder CO
Issued by National Weather Service Pueblo CO
826 AM MDT Wed Apr 20 2022

COZ030>051-211430-
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-
826 AM MDT Wed Apr 20 2022

...Critical fire-weather conditions this afternoon and early
evening across the Cheyenne Ridge as well as Central and Southeast
Park County...

...Widespread critical fire-weather conditions expected on
Friday...

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

.DAY ONE...Today and Tonight

Gusty winds and low relative humidity are expected to result in
critical fire-weather conditions today across Central and
Southeast Park County, as well as the Cheyenne Ridge. Elevated
fire-weather conditions are also likely today across the
foothills and plains.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Elevated fire-weather conditions are expected on Thursday across
the foothills and plains.

On Friday, strong winds, warm temperatures, and dry conditions
are expected to result in widespread critical fire-weather
conditions over the plains and lower foothills. Areas of blowing
dust will be possible over the plains on Friday.

Snow is expected over the mountains for Friday into Saturday,
with a few inches of snow possible particularly around the
Continental Divide.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.

Cohen