420
FXUS65 KBOU 290851
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
251 AM MDT Sat Jun 29 2024

.KEY MESSAGES...

- Slightly cooler today, with scattered afternoon thunderstorms
  returning, strongest and most numerous south of I-70.

- Isolated to scattered thunderstorms this weekend, with a few
  strong to severe storms possible Sunday afternoon and evening.

- Decreasing chances for storms through the week, with warm
  weather persisting.

&&

.SHORT TERM /Through tonight/...
Issued at 148 AM MDT Sat Jun 29 2024

Temperatures are running approximately 5 to 10 degrees cooler than
this time yesterday for all but Summit and Park Counties following
the passage of the nocturnal cold front. Although most model
guidance remains steadfast in showing the development of a robust
yet transient low-level cloud deck around 750mb early this
morning, ACARS soundings from DIA show the moistening is, a
minimum, delayed. Have thus tapered the extent and persistence of
the cloud cover, but will continue to maintain some scattered to
broken low clouds through mid morning across much of the urban
corridor. In any case, any such obscuration should clear fairly
easily later this morning, so will lean toward the warmer end of
guidance still, with highs climbing into the low 80`s around the
Denver metro, with pockets of upper 70`s for higher elevation
areas like the Palmer Divide, high mountain valleys, and Cheyenne
Ridge. If cloud cover indeed proves more persistent and extensive,
upper 70`s will be more likely for lower elevations highs.

Come early to mid afternoon, low-level winds will shift to the
southeast in the plains, and south/southwest in the high country,
resulting in increased moisture advection with dewpoints progged
to climb into the 50`s for lower elevations. The last few days
have lacked this southeasterly surface component, and
thunderstorm coverage was more isolated across the I-25 corridor
as a result. Instability will be rather marginal today and mostly
below 500 J/Kg, maximized over the high country and southern tier
of our forecast area. The largely southerly low-level flow will
provide for some upslope enhancement across Park County and the
Palmer Divide this afternoon, hence considerably higher PoPs
along/south of I-70 for today. Thunderstorms should then progress
eastward into our southern plains in Elbert and Lincoln Counties,
where the strongest storms of the day will be favored. With
limited shear and somewhat reduced DCAPE, expecting a
comparatively lower threat for severe storms, although a stronger
storm or two can`t be ruled out completely. Low temperatures
tonight will rebound under enhanced warm southeasterly winds,
potentially boosted by evening outflows from convection pushing
into the SE Colorado plains.

&&

.LONG TERM /Sunday through Friday/...
Issued at 148 AM MDT Sat Jun 29 2024

An active weather pattern will likely continue into early next
week, before a general trend towards quieter conditions is
expected as we approach mid/late week.

A plume of above normal moisture (PWATs > 150% of normal) is
expected to remain anchored across Colorado, on the western
periphery of an expansive ridge across the south central U.S.
The mid-level thermal ridge axis is also expected to shift east
into the region during the day, which should lead to warmer
temperatures across the forecast area Sunday afternoon. The main
question for the day is what type of daytime heating/sfc moisture
combination we end up with, and how much instability that results
in. There should be sufficient deep layer shear across the region,
especially later in the day as 500mb flow increases ahead of a
weak shortwave trough. HREF again keys on the higher elevations
south of I-70, with decreasing PoPs into the plains. The SPC
marginal risk area looks sufficient with at least a couple of
strong to severe storms possible across most of our forecast area.

The previously mentioned upper ridge should shift east and weaken
by early next week, with a broad upper trough axis gliding across
the northern Rockies Monday into Tuesday. Some moisture should
linger across the region, with at least isolated/widely scattered
showers and storms during the afternoon hours. The storm threat
should shift east of the urban corridor by Wednesday as a dryline
sets up across the eastern plains, with considerably drier air
working into the high country. Temperatures should remain near or
a little above normal during this period.

The latter half of the week looks to be dry. Guidance is in
reasonably good agreement that a ridge should build across the
Pacific coast by Thursday, with a trough axis somewhere over the
northern Great Plains. Main question in this period is if a cold
front will find a way to push into the region Thursday or Friday.
There is quite a bit of spread among individual ensemble members,
but this will be worth watching for those with outdoor plans for
the holiday weekend.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1129 PM MDT Fri Jun 28 2024

Cold front imminent in next 1-2 hrs for Denver metro, and will
bring shift to north winds with gusts up to 20 kts at times.
Expect reduction in speeds after 1 to 2 hours post-front, with
generally north flow prevailing still. Some low clouds 025-035 may
trickle in after ~09Z Sat, but suspect any CIGS would be on the
patchier side, with better chances from KDEN eastward into the
plains. Any low cloud cover should dissipate near 16-17Z.

Winds will be out of the southeast for most of the day tomorrow.
Scattered convection will develop mid afternoon, with greater
coverage immediately due south of Denver. Leaning on bulk of
convection remaining south of KDEN, but do believe stronger TS are
possible relative to yesterday, so have replaced VCSH with VCTS
or -TSRA in TEMPO (terminal-dependent). Some outflow winds
possible (favoring southerly direction), but expect outflow threat
to be less than previous days. As convection moves into the
southeast plains, more robust south flow will take hold in the
evening and overnight, when gusts have a higher potential of
exceeding 30 kts. Also monitoring for potential intrusion of low
to mid-level cloud cover Saturday night under a moist environment,
but confidence is low.

&&

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

&&

$$

SHORT TERM...Rodriguez
LONG TERM...Hiris
AVIATION...Rodriguez