635
FXUS65 KBOU 040539
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1139 PM MDT Fri May 3 2024

.KEY MESSAGES...

- A few showers and storms across the eastern plains this
  afternoon into tonight.

- Warmer and windy on Sunday.

- Active, cooler, and mainly windy pattern from late Sunday
  through most of next week. A few chances of accumulating snow
  across the mountains with isolated/scattered showers across the
  plains.

&&

.UPDATE...
Issued at 848 PM MDT Fri May 3 2024

We observed one severe thunderstorm in eastern Lincoln County this
afternoon which generated strong outflow winds measuring at least
62 mph in and near Hugo. All of that action has now pushed east,
with just some lingering light showers over the mountains where
there`s sufficient orographic lift to tap into a stream of mid-
level moisture. These should dwindle in the next few hours as this
corridor pushes east. Cloud cover appears less expansive than
initially indicated, so have made pertinent adjustments and also
lowered minimum temperatures for tonight by a couple degrees for
most areas. Breezy conditions remain in the plains following the
front, particularly in Lincoln County, but winds will gradually
subside as the lower levels decouple.

&&

.SHORT TERM /Through Saturday/...
Issued at 303 PM MDT Fri May 3 2024

Current analysis shows a lee cyclone across the Palmer Divide area.
From the north, a cold front is advancing southward with a push of
gusty northerly winds behind it. Gusts 35-45 mph are being reported
across the region from the front. Along this front, a line of
thunderstorms moves across the northeastern plains. SPC mesoanalysis
shows an axis of marginal instability across the far east plains (<
500 J/kg SBCAPE). This is overall supported by an shortwave trough
moving eastward just north of the Colorado border. For the
remainder of the afternoon and into the evening expect showers in
the mountains with another round of showers moving across the
northern border onto the plains. Areas such as Lincoln County
remain unstable ahead of the advancing front, so can`t rule out
any shower or storm development in those areas in the next hour.

Showers linger across the mountains this evening with remaining
showers/storms exiting the eastern plains. Behind the front,
temperatures cool sufficiently overnight with lows in the low to
mid 30s across the plains. We are approaching Frost/Freeze
headline territory for areas on the plains; however, given its
current rating of mixed susceptibility for vegetation and
closeness to average last freeze, we decided to hold off on
headlines. For tomorrow, expect cooler temperatures with highs in
the 60s across the plains, 50s for foothills/mountain valleys, and
40s for the mountains. Expect another round of showers and a few
storms in the afternoon (marginal CAPE), mainly over the higher
elevations and south of I-70.

&&

.LONG TERM /Saturday night through Friday/...
Issued at 303 PM MDT Fri May 3 2024

A strong upper low will be located near northern California on
Sunday morning, with increasing south-southwesterly flow
over our forecast area through the day. The result will be a
warm, dry, and breezy end to the weekend as the dryline shifts
towards the CO/KS/NE border. Temperatures should warm into the mid
to upper 70s. Model soundings suggest boundary-layer average
winds of 30-45kt, which would lead to wind gusts of 45-55 mph.
Some guidance keeps just enough moisture out in the far eastern
plains for an isolated shower or storm, though the models that
keep some moisture here also maintain a strong cap through the
day.

The closed upper low is expected to transition to a sharp,
negatively tilted trough axis by Monday morning... which then
ejects into the northern Great Plains from Monday into Tuesday. A
quick round of mountain snow is likely with the passage of the
trough axis, though cross-sections show somewhat sparse moisture
on this side of the trough. For the plains, a few showers will be
possible, but the main story will be wind. A bora-like event
appears likely as a colder westerly flow develops. Temperatures
will hover in the upper 50s/low 60s. Gusty winds will continue,
especially across the high country.

Zonal flow is expected to persist Tuesday into Wednesday as the
upper trough stalls over the far northern Great Plains. Guidance
shows a bit of moisture lingering in this flow, which would lead
to scattered snow showers across the high country while the plains
remain generally dry. With fairly strong mid-level flow, gusty
winds will be slow to subside in this period.

As we get into the latter half of next week, there is increasing
uncertainty in the overall synoptic pattern. Recent guidance
attempts to stall out the trough or even retrograde it back to the
south and west. Unsurprisingly, ensemble guidance lacks a clear,
definitive signal, with a substantial amount of spread for T/QPF
as we get into Thursday/Friday of next week. We`ll likely have a
ways to go until we see better agreement in this timeframe... but
at the very least, it does appear that a cool and unsettled
pattern will continue.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1134 PM MDT Fri May 3 2024

VFR conditions are expected through the TAF period.
Southeast winds should continue through Saturday afternoon.
Scattered showers will occur west of all terminals along the
higher terrain, but it is possible a shower or two could spread
into KBJC by Saturday evening. Models have favored this outcome
thus including a VCSH between 00-02Z. There is lower confidence in
this outcome for KAPA and KDEN due to unfavorable conditions for
thunderstorm development thus kept it out of the TAF for now.
Additionally, winds increase this afternoon gusting between
20-27kts briefly from 21-22Z until 00Z. Drainage winds are
unlikely by Saturday night and should remain south.


&&

.FIRE WEATHER...
Issued at 303 PM MDT Fri May 3 2024

Increasing fire danger is expected late this weekend into early
next week behind the strong storm system. Gusty winds should
develop on Sunday and continue daily through at least mid-week,
with a gradual drying trend from Sunday through Tuesday. Near-
critical to critical fire weather conditions appear likely across
portions of the lower elevations at times, especially south of
I-70. However, recent rainfall and ongoing green-up across the
plains may limit overall fire danger. Still a couple of days out
at this point, so no watches have been issued... but we`ll be
watching closely as we get into the weekend.

&&

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

&&

$$

UPDATE...Rodriguez
SHORT TERM...Mensch
LONG TERM...Hiris
AVIATION...AD
FIRE WEATHER...Hiris