144
FXUS65 KBOU 090612
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1212 AM MDT Sun Jun 9 2024

.KEY MESSAGES...

- More thunderstorms Sunday and Monday with a lower severe threat
  but a risk of heavy rain and localized flooding.

- Minor snowmelt impacts from rising streams, mainly in Grand
  County. Thunderstorms this weekend could further increase stream
  flow.

- Hot and mainly dry weather towards the middle to end of next
  week. There is potential for a day or two to need a Heat
  Advisory, most likely Thursday.

&&

.UPDATE...
Issued at 812 PM MDT Sat Jun 8 2024

Busy aftn which has finally calmed down early this evening. Still
have lingering non severe storms over portions of sern Elbert and
Lincoln counties which may produce some heavy rain.  Other weaker
showers and isolated storms were near the CO-WY border. Satellite
still shows another weak shortwave may move across nrn CO around
midnight with some additional activity from Fort Collins north to
the WY border. Thus will leave in some pops after midnight across
nrn areas of the plains.

&&

.SHORT TERM /Through Sunday/...
Issued at 200 PM MDT Sat Jun 8 2024

Early Forecast Discussion issuance for the short term to capture
the upcoming severe weather this afternoon.

Upper level trough will continue to progress east across Utah and
western Colorado this afternoon providing lift for thunderstorm
development. MLCAPE reaches 1000-1500 J/kg ahead of the convection
along the Front Range and up to 2000 J/kg over the plains. This
combined with 0-6 Bulk Shear to around 40 knots will lead to
strong/severe thunderstorms. A few supercell thunderstorms will be
possible at first with large hail (greater than 2 inches) and
damaging winds. Storms then grow into a line with strong winds
becoming the main threat. Hi-Res models in good agreement showing
bowing segments in the line of thunderstorms, which may lead to
very strong wind gusts (greater than 75 mph). The timing for the
strongest storms across the Urban Corridor looks to be noon to 3pm
and for the eastern plain, it will be a little later 2-6 pm.

Isolated/scattered showers and weak thunderstorms will remain
possible through mid evening once the strong/severe storms move
off to the east. Brief heavy rain and lightning are the main
threats with this. Low clouds and areas of fog move into eastern
Colorado overnight, which will result in mild overnight lows.

For Sunday, upper level ridging begins to build over the Four
Corners with weak northwest flow aloft over eastern Colorado. At
the surface, high pressure will be centered over the Northern and
Central Plains. Clockwise flow around the high will bring
southeast to east winds across eastern Colorado. This will
continue to transport low level moisture into the area. Low clouds
will form overnight and continue into Sunday morning. The moist
layer may be thick enough to produce light rain/drizzle over far
eastern Colorado. Some of these clouds will linger into the
afternoon. The reduced sun leading to cooler temperatures will
stabilize the airmass over the eastern plains. However, west of a
line roughly from Greeley to DIA to Colorado Springs, better
clearing will allow for more heating with highs in the lower 80s.
IF temperatures reach the lower 80s, MLCAPE climbs to 1000-1500
J/kg. Enough instability for strong to severe storms. Shear, will
be on the weaker side so no organized severe threat is expected,
but brief one inch or slightly larger hail will be possible. Heavy
rain may be a greater concern due to slower storm movement and
high running streams/rivers from snow melt. Still some uncertainty
how much and how far east the clearing will take place, but most
of the 12Z models runs show scattered thunderstorms late Sunday
afternoon across the Front Range (west of I-25).

&&

.LONG TERM /Sunday night through Saturday/...
Issued at 200 PM MDT Sat Jun 8 2024

A shortwave trough will pass to the north of Colorado on Monday with
light winds aloft over our forecast area. At the surface, there will
be cyclogenesis over eastern Montana with southeast winds across our
forecast area. These winds will hold in the low level moisture and
there will likely be low clouds in the morning on the plains. By the
afternoon, there will be modest instability that develops with a
strong cap forming around 700 mb. If convection overcomes this cap,
there could be a few strong to severe storms that form mainly along
and south of the Cheyenne Ridge and along the Palmer Divide.
However, a good portion of the area will be too stable for storms to
develop. Hail will be the primary threat.

Northwest flow aloft will move over Colorado on Tuesday on the
northeast edge of a broad ridge over the western US. There will be
warmer air aloft that arrives and with mostly sunny skies, highs
will warm to the mid 80s across the plains. There may be some
light showers and storms over the higher terrain but this
convection will be much weaker than previous days.

The broad ridge aloft will strengthen and the 500 mb heights will become
over 2 standard deviations above normal Wednesday and Thursday.
The subsidence along with plenty of sunshine will lead to
temperatures climbing well into the 90s. Thursday continues to be
the day to focus on as there may be heat impacts. There are
multiple ensemble members that show Denver hitting 100 F and given
the pattern and time of year, that would seem to be reasonable. If
that were the case, heat highlights would be needed as cooling
shelters would almost certainly be spun up. There are a couple
ensemble members that keep eastern Colorado much cooler on
Thursday as they have a cold front making it through the area.
While that is not likely, it is possible.

A shortwave aloft will move over Colorado on Friday with a cold
front at the surface. Friday should be much cooler with numerous
storms as a result. There does remain some uncertainty though as
the timing of the shortwave is not agreed upon in the models.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1212 AM MDT Sun Jun 9 2024

SW winds at the terminals will weaken by 09Z this morning. Still
seeing a chance for fog/low stratus near BJC and DEN in the
09-14Z timeframe. Most model guidance is keeping the fog and lower
clouds just at the edge of both terminals. Any fog or lower
stratus should erode by mid morning. There is potential for
showers and a few thunderstorms this afternoon, mainly after 22Z.
Chances are a little higher at BJC/APA compared to DEN. Nearby or
passing storms may bring brief gusty winds up to 35 kts and
outflow boundaries. Early evening, any remaining showers/storms
weaken and move eastward.

&&

.HYDROLOGY...
Issued at 200 PM MDT Sat Jun 8 2024

Elevated flows continue across the upper Colorado River basin and
additional rainfall this weekend could lead to further increase in
the flows. Remain cognizant of the dangers of these cold flows,
and be aware of any Flood Advisories.

Multiple rounds of thunderstorms are expected over the higher
terrain today. These storms will be moving quickly so the flash
flood threat will remain minor. It may increase the flow in the
Colorado River, though.

Storms will be moving much slower on Sunday and Monday. However,
they will likely be weaker than today. The primary threat during
the forecast period will be in Cameron Peak on Sunday as a
moderate threat for flash flooding will exist. The threat will be
minor again on Monday.

&&

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

&&

$$

UPDATE...RPK
SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...Mensch
HYDROLOGY...Danielson