Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191734

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1134 AM MDT Thu May 19 2022

Issued at 842 AM MDT Thu May 19 2022

Warm start to the day with 8AM temperatures in the 60s and lower
70s. Forecasted highs of upper 80s to around 90F should be good.
Temperatures could over perform today with downslope winds ahead
of the approaching storm, so lower 90s are not out of the
question. Gusty winds are beginning to develop in/near the
foothills. The gusty west winds will become widespread by early
afternoon. Red Flag Warning conditions still on track for today.
Cold front races south across the area mid to late evening. Should
see gusts to around 45 mph as the front pushes through. The upper
level trough continues to progress southward tonight. Rain and
mountain snow spreads south across north central Colorado
overnight. By Friday morning, expect snow to falling in the
northern mountains/foothills with a cold rain for the Fort Collins
area. Going forecast is in good shape. Will take a look at the
12Z model runs and likely upgrade most of the Winter Storm Watches
to Warnings.


.SHORT TERM...(Today and tonight)
Issued at 410 AM MDT Thu May 19 2022

An increasing zonal flow aloft will be over the region today,
ahead of a very potent late season storm system that will drop out
of the Northern Rockies late tonight. The models stretch a 120+
kt jetstream from the Pacific Northwest, across WY and into the
northern Great Plains by 00z this evening. South of the jetstream,
weak downward QG will be over CO in the mid and upper levels, and
dry downslope winds are expected ahead of this approaching
system. For today, it will be very warm, dry and windy by this
afternoon with critical fire weather conditions expected. In
short, refer to the fire weather section for those details. High
temperatures in Denver today will climb into the upper 80s, which
should fall just short of the record of 92 for this day in Denver
set back in 2020. For tonight, the jetstream will drop southward
across northern UT/northern CO by 12z. A strong cold front will
bring gusty northerly winds and much colder temperatures into the
Denver area starting around 10 pm. In the mountains, light to
moderate snowfall will develop in mountains north of Interstate
70 after midnight. Main area of concern will be zone 33 and maybe
35 as well. Those areas will initially experience the best
combination of deepening moisture/upslope tonight, primarily after
3 am.

.LONG TERM...(Friday through Wednesday)
Issued at 410 AM MDT Thu May 19 2022

A late Spring storm will impact much of North Central and
Northeastern Colorado Friday into the weekend. This will be due to a
large upper level trough deepening over the Central and Southern
Rockies and an associated strong upper level jet sagging south over
Colorado. At sunrise Friday morning, snow should be ongoing
across the Northern Mountains and foothills with possibly some
rain showers across the northern sections of the Front Range Urban
Corridor. The precipitation should gradually shift southward
through the morning and move into Metro Denver by noon. Model
cross sections are showing a deep upslope flow developing east of
the mountains by early afternoon as another frontal surge moves
across Northeastern Colorado. The majority of the deterministic
and ensemble members are showing deep upslope flow continuing
through about noon Saturday with the strong upper jet remaining
parked over Colorado. The combination of the upslope flow, QG
ascent and possibly some CSI banding from a 120KT upper jet will
lead to significant and much needed precipitation across the Front
Range Mountains, Foothills, adjacent plains and Palmer Divide.
The Front Range Foothills and mountains above 7000 will likely see
significant snowfall from this event with one to two feet of
accumulation expected with locally higher amounts possible. West
of the divide, snowfall amounts should be quite a bit less due to
unfavorable orographics.

When looking at the lower elevations, forecasted snowfall amounts
get much more complicated and uncertain. This is primarily due to
the following factors.

Factor #1 How cold will it actually get across the Front Range Urban
Corridor. This will affect the timing, duration and intensity of the
snowfall. latest models have trended colder which would favor an
earlier change to snow and higher snowfall amounts.

Factor #2 How much melting will occur. It is late May and
temperatures have been unseasonably warm. Therefore, quite a bit of
melting is expected as the snow falls.

Factor #3 snowfall intensity. How intense will the snowfall be
across the lower elevations. There will a little instability which
may lead to some convection. In addition, the potential exists
for CSI banding due to the location of the strong upper jet. Both
of these would increase snowfall intensities and would affect
snowfall accumulations.

For now the consensus of the models is that 4 to 10 inches of snow
will fall across Metro Denver, highest in the southern and
western suburbs. The Palmer Divide should receive higher amounts
with forecasted accumulations ranging between 8 and 12 inches by
Saturday afternoon. If these amounts verify, there would likely be
some tree damage and downed power lines across the area. Further
east across the plains, much lighter amounts are expected. Once
again, there is still quite a bit of uncertainty with this system
and the amounts above are just estimates and could change due to
the factors above.

In addition, a hard freeze is looking more likely with lows
expected to drop into the mid to upper 20s both Saturday and
Sunday morning.

For Sunday into early next week, we should see a warming trend.
However, the cool and unsettled weather is expected to continue as
another upper level storm system moves across the region.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1133 AM MDT Thu May 19 2022

Gusty west winds still on track to develop between 19-20Z with
gusts to 35 knots possible. These winds continue until sunset and
may briefly decrease before a strong cold front pushes through.
This front is expected around 0230-0300Z with northeast winds up
to 40 knots. Winds quickly decrease behind the front, but remain
breezy with gusts to 25 knots possible overnight. As the storm
system nears, ceilings fall below 6000 feet 0800-1000Z. Rain
showers form mid to late morning. Snow will be possible 18z Friday
and likely after 21Z. Moderate to heavy snow is then expected for
DEN Friday night and early Saturday with 4-8 inches of heavy
slushy snow expected.


Issued at 410 AM MDT Thu May 19 2022

Critical fire weather conditions will occur after 11 AM this
morning and will continue through 8 PM this evening evening.
Widespread 10-15 percent low relative humidity levels will impact
parts of South Park, the southern Front Range Foothills, urban
corridor and northeast plains. The wind will let up this evening
ahead of a strong cold front. The cold front will move north
south across the region late this evening. Gusty north to
northeast winds and much colder temperatures will accompany the
front, with snow developing in the mountains north of Interstate
70 after midnight.


Issued at 410 AM MDT Thu May 19 2022

A snow storm will be moving into the region Friday morning with
increasing precipitation along the foothills by Friday afternoon
and continuing through the day Saturday. Snow levels will drop to
6500 ft by Friday night with the possibility of 0.02-0.10 inches
in a hour. There is currently not a flash flood threat for the
burn scar areas.


Red Flag Warning until 8 PM MDT this evening for COZ214-216-

Winter Storm Warning from midnight tonight to noon MDT Saturday
for COZ033-035.

Winter Storm Watch from Friday afternoon through Saturday
morning for COZ030-032-034-036>041.

Winter Weather Advisory from midnight tonight to noon MDT
Saturday for COZ031.



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