Special Weather Statement, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
359 PM MDT Sat May 8 2021

.SHORT TERM...(This evening through Sunday)
Issued at 233 PM MDT Sat May 8 2021

Scattered showers and thunderstorms are developing in the pocket
of warmer air east of the Front Range that got sunshine early
this afternoon. Over northeastern Colorado the air is potentially
cooler, but there is probably enough warmth out around Limon to
maintain this activity for a while. The main threat from these
storms, other than lightning, is some amplification of the
background wind gusts. An isolated 60 mph gust isn't out of the
question, but we mostly expect gusts to be in the 30-50 mph range.

As the storms move east, we'll be left with drier air aloft at the
same time that low levels see increasing moisture with the cooler
air coming down from the north. This shold produce a stratus deck,
but that should be under an inversion so it's not clear if we'll
be able to produce any more showers. It may just become cloudy,
and if there is any precipitation overnight it would likely be out
of this shallow cloud deck and be pretty light. All of this is
still true for Sunday morning, though the clouds may be starting
to deepen a bit. By afternoon there will be a less stability, a
bit more moisture, and a little QG lift. Models look to be
overdoing the QPF from the showers they produce (the 12z NAM had a
foot of snow around Evergreen during the day). But increasing
light showers could produce some light accumulations in the
mountains. For now we cooled temperatures a few degrees to match
the middle of guidance, but with a solid cloud deck it could be
closer to the cooler NAM MOS which keeps the plains in the 40s.

.LONG TERM...(Sunday night through Saturday)
Issued at 233 PM MDT Sat May 8 2021

Sunday night...The airmass over northern CO will continue to
become increasingly moist with showers with some embedded
thunderstorms increasing in coverage across the forecast area.  The
snow level by 12z Monday will range from 6700-7200 feet MSL.  The
models weak to moderate qg ascent developing in the mid and upper
levels Sunday night and continuing across north central and northeast
CO Monday into Monday night.  One piece of energy appears to move
across the region late Sunday into Sunday night, with colder and
deeper main trough moving across northern CO Monday into Tuesday
morning. The most consistent feature associated with this system
will be steady mid and upper level QG ascent and deep moisture.
The upslope overall is deep but fairly weak through the period,
with moist adiabatic lapse rates in place. The best period of
upslope appears (E/SELY) to be Monday night through Tuesday
morning. Moderate to heavy snowfall most likely in the Front
Range mountains and higher foothills, heaviest Monday afternoon
through Tuesday morning. At this time, will hold off on a Winter
Storm Watch, but this will likely need to be issued at some point
with storm totals in the neighborhood of 8-16 inches possible.
The snow level will lower Monday night, 5000-5500 feet, which
could mean some light snow possible for portions of the urban
corridor by Tuesday morning. GFS has has been the coldest and much
more bullish regarding snowfall across the northeast plains, but
it also remains the biggest outlier. For this reason, will
continue with more of a blend with the other models as they seem
more reasonable regarding the precipitation. Mainly rain or
rain/snow mix for the urban corridor and northeast plains, with
the potential of a brief switch to snow around 12z Tuesday. By
Wednesday a drier and more subsident northwesterly flow aloft will
be in place ahead of a building ridge of high pressure. By the
end of the week, a broad ridge will be over the west with a
persistent northwest/westerly flow aloft over northern CO.
Temperatures will climb back above normal, in the mid/upper 70s by
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 233 PM MDT Sat May 8 2021

Thunderstorms will move east away from the Denver area in the late
afternoon. Scattered weaker showers are likely to develop by early
evening. The wind direction will continue to vary between west and
north, then become north behind a cold front by 00z. Instrument
approaches to KDEN will likely be needed after 00z. Areas of MVFR
conditions will develop by 12z as ceilings continue to lower,
with scattered showers continuing mainly south and west of Denver.
The showers will gradually increase with MVFR conditions becoming
more widespread on Sunday afternoon.

&&

.HYDROLOGY...
Issued at 233 PM MDT Sat May 8 2021

Only isolated weak showers are expected over the burn areas
through tonight. On Sunday the showers will become more numerous,
but precipitation is still expected to be light and the snow level
is expected to be between 7 and 8 thousand feet, so no flood
threat is expected.

For Sunday night thru Tuesday morning, there will be periods of
snow. Tuesday will see some snow in the morning with decreasing
chances by late afternoon. Since much of the precipitation is
expected to fall as snow, the flood potential is expected to be
low.

&&

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

SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Gimmestad
HYDROLOGY...Cooper/Gimmestad

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1111 AM MDT Sat May 8 2021

COZ030>051-091715-
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-
1111 AM MDT Sat May 8 2021

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

.DAY ONE...Today and Tonight

Scattered showers will develop this afternoon, mainly over the
foothills and eastern plains. An isolated thunderstorm is
possible. North to northwest winds gusting up to 40 mph over the
northern and eastern parts of the plains will eventually spread
into the Denver area for a few hours in the late afternoon and
evening. A chance for showers will persist overnight, mainly along
and south of Interstate 70. The snow level will be around 9000
feet today, but lower to around 7000 feet by Sunday morning. Any
accumulations in the mountains will be less than 2 inches.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Sunday through Tuesday there will be widespread showers and
storms. Cooler temperatures will arrive Sunday through Sunday
night and will allow the precipitation to fall as snow over the
mountains and foothills. The I-25 corridor may see some snow
Monday night into early Tuesday as well but accumulation should be
light if any snow accumulates at all.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.

Gimmestad/Cooper

Special Weather Statement
National Weather Service Denver CO
408 PM MDT Sat May 8 2021

COZ032>034-082230-
South and Southeast Grand/West Central and Southwest
Boulder/Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet CO-Grand and Summit Counties Below 9000 Feet CO-
South and East Jackson/Larimer/North and Northeast Grand/Northwest
Boulder Counties Above 9000 Feet CO-
408 PM MDT Sat May 8 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN GRAND AND
SOUTHWESTERN BOULDER COUNTIES UNTIL 430 PM MDT...

At 407 PM MDT, Doppler radar was tracking a strong thunderstorm near
Hot Sulphur Spring, or 60 miles southwest of Fort Collins, moving
east at 35 mph.

Wind gusts of 50 to 55 mph will be possible with this storm.

Locations impacted include...
Granby, Fraser, Winter Park, Hot Sulphur Springs, Grand Lake,
Parshall, Arapahoe Peak, Tabernash, Elkdale, Rollins Pass, Hot
Sulphur Spring and Williams Fork Reservoir.

LAT...LON 3992 10630 4005 10634 4026 10623 4033 10567
      3992 10563
TIME...MOT...LOC 2207Z 264DEG 31KT 4011 10605

DANIELSON