436
FXUS65 KBOU 140541
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1141 PM MDT Mon May 13 2024

.KEY MESSAGES...

- Scattered showers and isolated thunderstorms over the mountains
  and foothills with isolated showers and storms over the nearby
  plains.

- Scattered afternoon/evening showers and thunderstorms Tuesday.

- Front brings cooler and wetter weather on Wednesday. Light snow
  for elevations mainly above 10,000 feet.

- Warmer and generally drier starting Thursday, with lesser but at
  least isolated daily afternoon showers/thunderstorm coverage,
  highest for the mountains.

&&

.UPDATE...
Issued at 802 PM MDT Mon May 13 2024

A few showers are still lingering across the high country and
eastern plains, but it`s generally a quiet evening. Showers should
diminish through the rest of the evening although a snow shower or
two will remain possible overnight across some of the northern
mountains. No significant changes to the previous forecast were
made as it was in good shape.

&&

.SHORT TERM /Through Tuesday/...
Issued at 217 PM MDT Mon May 13 2024

Radar showing scattered showers over the mountains and foothills.
Best instability resides over the higher terrain with ML CAPE to
around 500 J/kg, so still expect isolated storms to form.
Instability decreases eastward onto the plains. Weak ridging will
move across Colorado this evening and tonight. Expect this to keep
convection weak and isolated to scattered. The stronger storms
will be capable of produce small hail (pea sized), wind gusts to
40 mph, and brief heavy rain. Convection dies off early to mid
evening with the loss of daytime heating stabilizing the airmass.

For Tuesday, westerly flow aloft will prevail behind the exiting
ridge and in advance of a wave dropping southeast across Wyoming.
This wave should help produce at least scattered convection (more
than today). Instability will slightly increase with ML CAPE up to
700 J/kg. Still expect storms to stay sub severe, with brief
heavy rain and small hail under the stronger storms. Wind gusts
may be slightly stronger, up to 50 mph. Airmass warms a little
more with some locations topping 80F degrees over northeast
Colorado.

&&

.LONG TERM /Tuesday night through Monday/...
Issued at 217 PM MDT Mon May 13 2024

Tuesday evening into Wednesday, an upper level trough approaches
from the west with weak QG lift ahead it. An associated cold front
moves across the region, likely early Wednesday morning (midnight-
6am). North to northeasterly flow persists during the day Wednesday
post-front. The upslope component will provide an addition source of
moisture, especially in the favored areas such as the Palmer Divide,
Front Range, and adjacent plains. This will bring a cooler and more
unsettled day. In the cooler post-frontal airmass, high temperatures
likely stay in the 60s across the plains, considerably cooler than
Tuesday`s highs. Sounding profiles and instability fields show
marginal instability Wednesday afternoon (MLCAPE < 500 J/kg). Within
the weak upslope environment, this could support convective showers
and embedded storms.

With respect to amounts, ensemble means show a range of 0.20" to
0.60". There is notable small variations happening from run to run
and the GFS is appearing to be the wetter suite of solutions. The
higher amounts will likely be focused in those upslope favored
areas (Front Range, Palmer Divide, south foothills, Denver metro).
The cooler air stays north with the trough, but it be should
enough to bring snow levels down to 10,000 during the day and
around 9500 overnight. As a result, snow showers are possible for
the higher mountains/mountain passes. Ensembles show light
accumulations, so at this point not major impacts are anticipated.

On Thursday, the upper trough exits to the east putting northeast
Colorado under northwesterly flow aloft. Subsident flow should keep
dry out much of the region from Wednesday. Model cross sections show
some residual moisture in the high country with marginal instability
building in the afternoon to support scattered showers/storms. Given
the limited instability/moisture, coverage/chances will be less (<
25%) and mainly over the higher terrain. Temperatures recover from
Wednesday with highs pushing back into the upper 60s/low 70s for the
lower elevations and 40s/50s for the high country.

Friday into the weekend, expect weak ridging to zonal flow in the
upper level pattern. 700mb temperatures warm a degree or two each
day, supporting a gradual warming trend. Highs in the upper 70s to
low 80s Fri/Sat. Daily heating/instability should support scattered
afternoon showers and thunderstorms in the mountains with a low
chance for a few to stray onto the adjacent plains. Friday through
the weekend will be drier across the plains with relative humidity
values dropping into the 20 percent range in the afternoons.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 1128 PM MDT Mon May 13 2024

VFR conds expected to prevail for all terminals through at least
03Z Wed. Relatively light SSW drainage flow during the early
morning hours today will transition to a more robust NW wind
between 17-19Z with speeds 12-16 kts.

Scattered PM convection expected to develop over and south of the
Denver metro starting 20-21Z Tue, with SCT-BKN clouds bases near
080. Majority of SHRA/TS activity expected to remain due south of
KDEN although impacts to the terminal can`t be ruled out. The
larger potential may revolve around outflow winds from any
developing convection. These would have a greater likelihood of
coming from the south or southeast. Activity should dwindle
relatively quickly in the evening, with weakening of wind speeds
between 00-03Z Wed.

Finally, will need to monitor potential for lower CIGS after
06-08Z Wed in association with an approaching surface front, with
increased potential for bases 010-020 Wed AM for all terminals.

&&

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

&&

$$

UPDATE...Hiris
SHORT TERM...Meier
LONG TERM...Mensch
AVIATION...Rodriguez