-- Discussion containing changed information from previous version are highlighted. --
850
FXUS65 KBOU 092044
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
244 PM MDT Thu May 9 2024

.KEY MESSAGES...

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- Some showers will continue over the mountains and higher
  foothills into Friday, with the heaviest snow expected along and
  south of I-70 including South Park and above 7500 ft in the
  southern Foothills. Some travel impacts overnight into early
  Friday morning above 8,000 feet.

- Cool and unsettled weather will be in place across the rest of
  the area into Friday with the best chance of showers along the
  I-25 Corridor and Palmer Divide.

- Gradual warming this weekend into early next week along with
  scattered late day showers and thunderstorms.
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&&

.SHORT TERM /Through Friday/...
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Issued at 206 PM MDT Thu May 9 2024

An upper level low will drift west/southwest across southern Utah
tonight and then retrograde to near Las Vegas by late tomorrow
afternoon. Current satellite shows somewhat bumpy stratocumulus/
cumulus over the forecast area, with showers now becoming more
numerous in/near the Front Range. Only isolated to widely
scattered coverage had developed on the plains so far, with higher
coverage in the Front Range mountains and foothills. Taking a
look at current temperatures, we`re estimating snow levels to be
around 7500 feet on average. Profilers show little if any upslope
contribution at the present time.

We will start to see a little better upslope component develop as
we head through the evening and overnight hours as the upper low
retrogrades through the Great Basin, and mid level flow turns more
easterly. This should result in more concentrated and persistent
precipitation in and immediately next to the Front Range.
However, the upslope component is quite weak, not to mention the
QG forcing. Those parameters are a bit better the farther south
one goes, so places like Park County and mountains south of I-70
will be favored for the heavier precipitation amounts. This goes
along with the current forecast, and overall not much has changed.
We still think the most impactful snow will generally fall across
Park County and especially in/near the Mosquito Range where
upwards of a foot is possible. Amounts will then taper off to the
north (4-10 inches in the rest of the Advisory area as long as we
get the upslope), and then taper off even further as we go north
of the I-70 Corridor. We probably won`t see a whole lot of change
to the snow level as temperature advection is weak and the airmass
is relatively moist, but may nudge downward to around 7,000 feet
given night-time. Most impacts for travel will likely stay above
8000 feet. The foothills west and southwest of Denver may be a
stretch for the Advisory, but again those higher foothill
elevations (officially go up to 9000 feet) will be more prone so
will word that accordingly.

The Denver area will likely remain on the edge of the more
numerous showers in this weak upslope pattern, so the eastern
side of town will likely stay dry, or at least drier, than the
western suburbs. The eastern plains will see only isolated
showers.

On Friday, the forcing in all aspects weakens with the upper low
drifting farther away from us. Thus, it will likely turn into a
day with decreasing precipitation early in the morning, lifting
cloud bases, and then scattered showers and a rumble or two of
thunder redeveloping in the afternoon. Due to the clouds and
scattered precipitation, temperatures will only moderate slightly
from today`s cool readings.
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&&

.LONG TERM /Friday night through Thursday/...
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Issued at 206 PM MDT Thu May 9 2024

Ensemble guidance is in agreement with a continued unsettled pattern
through the weekend. The foundation for this will be a slow moving
cut-off upper low and positively tilted trough that slowly moves
toward Colorado. The main low will track south of the region, but
will remain north enough to provide weak synoptic ascent with
periods of increased moisture combined with steepening afternoon
lapse rates. All elements to support at least scattered
showers/storms. There are a few smaller differences between
deterministic solutions, particularly revolving around the speed
that the upper low/trough exits the region at the end of the
weekend.

Saturday, there will be sufficient moisture and CAPE to support
scattered showers and storms for the high country and plains. MLCAPE
values stay marginal (< 500 J/kg)  Despite the trough aloft, 700mb
temperatures increase a few degrees, supporting warmer highs than
Fri. Temperatures rise into the mid to upper 60s and a few 70s
across the lower elevations and 30s/40s in the mountains.

Sunday into early Monday, the upper level system exits the region.
Some model solutions (GFS) show a quicker exit of the trough, which
could push the instability more eastward along with the higher
precip chances. Others show Sunday to be similar to Saturday with
warmer temperatures and moisture/afternoon instability to support
scattered showers/storms Sunday afternoon. Snow showers for the
higher mountains.

There is general agreement among ensemble guidance that a weak upper
ridge moves in for Monday with a transition to more zonal/weak WNW
flow aloft Tuesday and Wednesday. There are indications of a
shortwave trough or two moving through around mid-week, but the
certainty decreases in the details. The weak ridging will support
further warming temperatures with ensembles showing a good chance at
70s across the lower elevations early next week. Marginal
instability and moisture will support scattered chances for
showers/storms each afternoon. Snow will remain more confined to the
the higher mountains. If the wave timing lines up, this could bring
higher shower/storm chances with even a few strong storms, but we`ll
have to see how this lines up as we get closer.
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&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1138 AM MDT Thu May 9 2024

MVFR conditions and/or IMC will prevail at KDEN through this
period. There is a chance we lower down to IFR after 06Z tonight
if we see more numerous showers develop in the area, but for now
the greatest potential for that would be closer to the foothills
including KBJC and KAPA. There could be scattered and mostly light
showers without visibility restriction at nearly any time, so
it`s hard to pin down anything so generally VCSH or PROB30 is
appropriate at KDEN, while KAPA and KBJC would be more prone for
showers overnight so will have some TEMPOs there.

Ceilings are expected to gradually lift again Friday with daytime
heating, but destabilization will lead to more scattered shower
development. The chance of any thunder is 10% or less.

Light northerly winds will prevail through most of this period,
although there is a 20-30% chance of variable winds near showers
and during the late night hours.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory until noon MDT Friday for COZ034-036-037.
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&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Mensch
AVIATION...Barjenbruch