537
FXUS65 KBOU 172059
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
259 PM MDT Fri May 17 2024

.KEY MESSAGES...

- Warm through Sunday. Isolated to scattered high based showers
  and storms this evening, and then again Saturday.

- Breezier Sunday into Monday.

- Cooler, unsettled pattern with increasing precipitation chances
  across the region early next week.

&&

.SHORT TERM /Through Saturday/...
Issued at 259 PM MDT Fri May 17 2024

Satellite shows shallow cumulus developing across the area. There
is a little deeper growth noted over northwest Colorado, with a
few showers starting to develop. With just enough destabilization
but dry low levels, we expect isolated to scattered high based
light showers/sprinkles in the high country/northern border area
through this evening, with only a rumble or two of thunder
possible. The rest of the plains and I-25 Corridor will only see
some virga, but can`t rule out some gusty outflow winds due to
well mixed and relatively deep sub-cloud layer.

On Saturday, both moisture and instability build a little more
with a weak shortwave noted in the QG fields. At the surface, a
weak cold front backdoors across the plains late tonight/early
Saturday morning. There is slight cooling noted in the boundary
layer, but enough daytime heating still expected to weaken the cap
and allow scattered showers/storms in the mountains to eventually
spread onto part of the plains late in the afternoon. There is a
little more MLCAPE with 200-400 J/kg noted, so expect a few more
lightning strikes and rumbles of thunder. The most favored
locations would stay generally south of I-76. Temperatures should
be a few degrees cooler behind the front, but still a few degrees
above normal. Southeast breezes will increase through the
afternoon.

&&

.LONG TERM /Saturday night through Friday/...
Issued at 259 PM MDT Fri May 17 2024

Scattered showers and thunderstorms should continue along areas
south of Denver Saturday evening. It is likely areas will lack
instability especially after the front thus leading to weak high
based showers spreading into the plains through southerly flow until
Sunday night. Low temperatures range between 45-55F for the
Palmer Divide and plains. For the higher elevations, temperatures
drop between 30-39F. Partly cloudy skies persist through Sunday.

Cross sections display drier air and weak mid-level moisture
mainly in the high country Sunday. Zonal flow will increase
resulting in wind gusts up to 25-35 mph for foothills below
timberline through Sunday afternoon. NBM retains too much PoPs for
weak mid-level moisture afternoon for the foothills and plains
thus this forecast update reduced PoPs for likely (35-50%)chances
of showers mainly in Jackson and northern Larimer counties.
Expect light rain and gusty winds up to 40-45 mph if a shower
collapses.

High uncertainty lingers for Monday night and Tuesday synoptic
pattern. 500mb heights across ensembles favor a shortwave trough
entering no eastern Colorado mainly Monday through Tuesday. ECMWF
seems to favor a less robust system with an open broad trough
sweeping north of our region while the GFS favors a deeper trough
entering the western mountains then pushing into the center of our
CWA. Timing seems to be delayed where majority of this system
occurs Tuesday. Given this pattern, it is possible PoPs may have
to be reduced Monday afternoon. Higher confidence remains in the
general outcome of numerous showers and storms Monday night into
Tuesday late morning. This pattern would likely lead to impacts
such as brief heavy rainfall and small hail. Additionally, cooler
temperatures are possible each afternoon Tuesday and Wednesday.
Overall, this cool down seems short lived as temperatures bounce
back near normal Thursday.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1153 AM MDT Fri May 17 2024

VFR through the TAF period. Winds will be the biggest challenge as
usual. We`re already seeing signs of channeling of west winds,
which means some places will see northerly or even light easterly
winds, while others in the channels will see gusts to 20-25 knots
through the afternoon. We`ll mention some of this variability in
the TAFs for now, but then shoot for more dominating WNW winds
after 21Z with further mixing. Some virga is also possible which
could bring a few VRB gusts to 30-35 knots (20-30% chance) given
the deep and well mixed sub-cloud layer.

Winds are expected to weaken again by about 02Z, and then return
to fairly normal south/southwest flow. A weak cold front will try
to push towards the terminals overnight with a shift to the north
or northeast possible after 10Z, but there are equal odds of just
variable winds until a stronger anticyclone develops 12Z-18Z with
an increase in southeast winds to 10-15 knots. Southeast winds
will likely strengthen further on Saturday afternoon with gusts
upward of 25 knots possible. Isolated to scattered high based
showers/storms will develop late in the afternoon and evening,
warranting a PROB30 of VRB gusty winds and -TSRA after ~22Z.

&&

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

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...AD
AVIATION...Barjenbruch