538
FXUS65 KBOU 210006
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
606 PM MDT Thu Jun 20 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms through Friday evening. A
  few storms could be strong to severe, and also produce locally
  heavy rain. Burn scars would be most susceptible to flood risk.

- Hotter and drier this weekend into early next week. Potential
  for heat impacts starting Monday, but some relief toward
  Wednesday.

&&

.SHORT TERM /Through Friday/...
Issued at 1053 AM MDT Thu Jun 20 2024

Current radar trends show scattered thunderstorms continuing to
initiate off of the higher terrain then moving northeastward across
the adjacent plains this afternoon. While sub-severe storms are more
likely as activity continues to spread onto the plains, still can`t
rule out a few severe storms within the moist, unstable environment.
Most storms will yield brief heavy rainfall, gusty winds up to 50
mph, and small hail. Within any of the severe storms, hail up to
1.5" and severe wind are possible. With boundaries present, can`t
rule out landspouts initially on the plains as well. Storms continue
to move eastward onto the plains this evening. Some CAMs models
continue to show potential for another round or two of lower
coverage showers and storms mainly in the early evening to midnight
timeframe. There isn`t a ton of agreement among the high-res suite
of models, so this remains lower confidence still.

Friday, the region stays under a weak upper level ridge. The ridge
will gradually slide eastward inducing WSW flow aloft while
transporting in a plume of above normal moisture (140-170% of
normal). The region remains under weak synoptic ascent to provide
additional support for scattered showers/thunderstorms in the
afternoon/early evening. MLCAPE values build into the 500-1000 J/kg
range. High-resolution guidance highlights an area mainly north of a
line from Denver to Fort Morgan and through the northeast corner for
potential for a few severe storms with higher probabilities for CAPE
>500 J/kg and 0-6km bulk shear >30kts. With above normal moisture
around, localized heavy rainfall will be a threat again Friday.
Soundings indicate potential for drier air to remain in the lower
levels which would reduce a higher coverage heavy rain threat.
Temperatures will be a degree or two cooler than Thursday with highs
in the mid to upper 80s for the plains, 70s in the foothills, and
50s/60s for the mountains.

&&

.LONG TERM /Friday night through Thursday/...
Issued at 230 PM MDT Thu Jun 20 2024

The more active weather pattern of late will taper down late
Friday evening and overnight as a shortwave pushes east across the
area. There are now indications the shortwave and weak synoptic
support will be a little faster, adding to shower/storm coverage
into Friday evening. A couple stronger storms would still be
possible into the evening hours, with locally heavy rain and
isolated severe storm threat.  Then, subsidence builds in from
west to east after midnight, effectively taking most convection
with it.

Saturday will then feature drier weather with less and weaker
convection. Temperatures will also be warming as the drier airmass
takes hold.

The trend to hotter temperatures will continue through Sunday and
Monday as an upper level ridge builds over the Central and
Southern Rockies. We see high temperatures pushing into the mid
to upper 90s on the plains and I-25 Corridor, with a couple spots
near 100. Thus, we may need Heat Advisories for a good chunk of
the plains/I-25 Corridor by Monday as the heat load builds.
We`ll be on the northern fringe of moisture, so still expect a few
high based showers and storms each afternoon and evening, with
the mountains and Palmer Divide area seeing the main chance.

For Tuesday and Wednesday, there are a couple signs of change in a
few of the ensemble members showing a stronger shortwave moving
across the northern U.S., pushing a backdoor cold front across the
High Plains. Typically, these types of waves eventually result in
some cooling across the northeast plains, so hopefully some heat
relief is in the cards by midweek and more than what the current
National Blend of Models would suggest. A backdoor front would
also support a little uptick in the chance of thunderstorms each
afternoon and evening.

&&

.AVIATION /00Z TAFS through 00Z Friday/...
Issued at 547 PM MDT Thu Jun 20 2024

Scattered thunderstorms are currently impacting all DEN area
airports. Variable gusty winds are expected to continue for the
next few hours. While thunderstorms will likely diminish in the
next few hours, some showers may linger until the 06Z time frame.
Winds are expected to transition to S/SW around 05/06Z.

For tomorrow, winds are expected to be light and variable in the
morning hours before transitioning to an easterly component in the
afternoon. Expect similar conditions to today with regards to
timing and strength of convection. Scattered thunderstorms are
expected to develop around 20Z which will create variable and
gusty conditions, and may bring brief reductions to visibility and
ceilings.


&&

.HYDROLOGY...
Issued at 230 PM MDT Thu Jun 20 2024

An increase in atmospheric water content will bring increased
shower and storm coverage and more intense rainfall. Rainfall
efficiency will grow, as warm cloud depths increase to 4,000-5,000
ft, rather impressive for this time of year. NAEFS shows
precipitable water (PW) increasing to 1-2 standardized anomalies, and
greater than that on the western slope (due to this earlier than
climatological arrival of the subtropical moisture plume). Storm
motions should move along at a decent clip of 20-25 mph, although
a Bunkers right mover could be closer to 15 mph. Stronger storms
would be capable of producing 1-1.5 inches of rain in 30-40
minutes. Overall, burn scars would be most susceptible to any
flooding threat, although we couldn`t rule out some minor
urban/street flooding if we got a stronger storm in a metro area,

&&

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

&&

$$

SHORT TERM...Mensch
LONG TERM...Barjenbruch
AVIATION...Bonner
HYDROLOGY...Barjenbruch