Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220324
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
924 PM MDT Sat May 21 2022

.UPDATE...
Issued at 922 PM MDT Sat May 21 2022

Precipitation has decreased significantly and continues to
gradually decrease. Isolated to scattered, light showers are still
expected to persist overnight over the terrain in the southern
part of the forecast area, mainly Park County, the southern Front
Range mountains and foothills, and the Palmer Divide. The next
shortwave is moving over the Pacific Northwest. Temperatures are
running just a few degrees warm in some areas but the forecast is
close to observations in most areas and it looks like skies may be
clearing out a bit more than expected - at least on the northern
plains. The southern plains likely maintain cover. Overall, there
still seems to be a good chance for freezing temperatures
overnight so we have maintained our Freeze Warning for all of the
plains of northeast Colorado valid 9 PM this evening through 8 AM
tomorrow morning. The forecast is performing well with only minor
updates this evening.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 251 PM MDT Sat May 21 2022

Snow is melting across the plains this afternoon with partly cloudy
skies evident on satellite. In places with little or no snow cover,
temperatures have made it back into the 40s to low 50s. In the
southwest metro, temps are generally stuck in the upper 30s. Day-
cloud phase satellite clearly reflects the thicker snowpack in South
Park, the southern Foothills, and Palmer Divide where 1 to 2 feet of
snow fell over the past 36 hours. A few snow showers are continuing
across Clear Creek county, but activity is expected to wane by the
late afternoon hours as instability decreases.

Tonight should be quiet in between storm systems, with some
scattered light snow showers for South Park and the Palmer Divide
where there`s still some synoptic support from the upper jet
streak. Across most of the plains, partly to mostly cloudy skies
are expected with temperatures near freezing. The cloud cover and
weak warm air advection will both be working to prevent
temperatures from falling too much, but still think there will be
subfreezing temperatures tonight, especially east of I-25. Have
opted to keep it simple and go with another Freeze Warning, but
it`s possible the Denver metro stays in the 33-35F range
overnight.

Moisture will return to the forecast area again on Sunday as
another weak shortwave approaches from the west. We should see a
gradual increase in showers (and possibly a thunderstorm or two)
through the day as better QG support slowly arrives while we
remain in the right entrance region of a 90kt jet streak. Snow
levels will rise above 9000 feet by the afternoon, so most of the
precipitation will fall as rain. Total precip/snow amounts through
the evening hours will be relatively light, with snowfall amounts
less than 2 inches possible above 10000 feet.

.LONG TERM...(Sunday night through Saturday)
Issued at 251 PM MDT Sat May 21 2022

There is good agreement that the region stays under the influence of
an upper level trough through mid-week next week bringing periodic
chances for precipitation. An approaching shortwave trough brings
the first round of precipitation Sunday afternoon with broad
synoptic ascent over the region coupled with sufficient moisture
(700-500 mb spec. humidity 2-4 g/kg). Most of the instability stays
confined to the higher elevations with MLCAPE values 100-300 J/kg.
This will promote development of convective showers over the high
terrain Sunday afternoon, later spreading onto the plains. Scattered
showers continue through the evening hours with snow showers
possible for the higher mountains overnight as snow levels drop to
around 9000 feet.

Upper level troughing persists Monday, with the axis of the
shortwave trough and an associated cold front sweep across the
plains. With the system exiting to the east, there will be less
large-scale ascent and moisture over the area decreasing shower
coverage. A jet max positioned to the west and cooling aloft will be
enough to support some lift and instability for showers. Another
shortwave moves through the region during the Tuesday-early
Wednesday timeframe bringing another round of showers/thunderstorms.
Higher heights slowly build into the region Wednesday with dry air
and synoptic descent working into the region.

Ensemble guidance indicates general agreement with the transition to
a dry and warmer pattern as the main ridge axis moves over the
region Thursday. Temperatures across the plains rise back into the
80s the end of the week. Relative humidities will trend downward
in the 18-25 percent range Thursday and potentially lower Friday
over the foothills/plains. Recent precipitation should keep the
potential for fire weather conditions lower, although it warrants
watching especially in areas that have received less water such
as Weld County. Into the weekend, flow aloft becomes southwesterly
ahead of an upper level trough. There is is uncertainty in the
the strength and available moisture of this system, leading to
more of a spread in solutions in regards to precipitation
potential.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 540 PM MDT Sat May 21 2022

Expect VFR conditions to persist this evening through tomorrow
morning, and likely then through the TAF period. Winds should
turn to drainage this evening and persist overnight, then there
will be an increasing southerly flow tomorrow morning. In the
afternoon, a Denver Cyclone is likely in response, which may lead
to variable winds at some terminals. Scattered showers and
isolated thunderstorms may initiate over the high terrain in the
afternoon, but this is low confidence due to low instability and
has been kept out of the TAFs. ILS conditions are possible but
also low confidence and cloud bases have been kept at 6 kft for
now. In the evening, showers will become more widespread and we
have included vicinity showers at KDEN. Models currently suggest
drainage winds again in the evening and overnight, which seems
likely given more widespread precipitation across the high
terrain.

&&

.HYDROLOGY...
Issued at 251 PM MDT Sat May 21 2022

There is a very limited threat of heavy rain on Sunday with
scattered showers and couple of thunderstorms possible in the
afternoon hours. Instability and precipitation coverage are both
marginal and precipitable water amounts are near or below normal,
and snow is generally still covering the burn areas at this time.
The threat on Sunday will be nonzero but very low.

An upper level trough with the passage of a few embedded shortwaves
will contribute to a more unsettled weather pattern Sunday through
mid-week. Marginal instability will be in place over the higher
terrain which will support showers/thunderstorm chances each day.
This may bring a "limited" threat for burn area flooding, mostly
the Cameron Peak/East Troublesome burn areas. The main uncertainty
is the snow coverage in those areas from the recent storm, so
this will depend on the degree of melting over the next few days.
Conditions trend dry Thursday and Friday as an upper level ridge
moves into the region.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Freeze Warning until 8 AM MDT Sunday for COZ038>051.

&&

$$

UPDATE...EJD
SHORT TERM...Hiris
LONG TERM...Mensch
AVIATION...EJD
HYDROLOGY...Hiris/Mensch


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