684
FXUS65 KBOU 192148
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
348 PM MDT Wed Jun 19 2024

.KEY MESSAGES...

- Continued cool into tonight with scattered showers and a few
  storms.

- Scattered thunderstorms Thursday and Friday. A few could be
  strong to severe, and also produce locally heavy rain.

- Hotter and drier this weekend into early next week.

&&

.SHORT TERM /Through Thursday/...
Issued at 121 PM MDT Wed Jun 19 2024

Current GOES-16 visible imagery shows clouds have persisted into the
afternoon as expected. The latest radar scan shows a few storms have
developed over southeastern CO, and showers are forming over the
high country. These showers are expected to continue into the
evening with some hi res models indicating a chance of nocturnal
storms over portions of the plains tonight. With low level flow
coming from the southeast, there is a chance that some patchy fog
develops across the Palmer Divide and spreads northward across the
adjacent plains, as well as areas near the Cheyenne Ridge and
adjacent plains this evening and tonight, and is expected to
diminish by the early morning.


Southwesterly flow aloft continues for tomorrow as upper level
troughing continues over the western CONUS. Temperatures will be
much warmer than what was seen on Wednesday with the potential for
another 90 degree day across portions of the plains. With increasing
low level moisture, synoptic forcings, ample surface heating, and
forecast soundings indicating a veering profile, thunderstorm
development is likely across the forecast area. The environment
looks to have potential for a few thunderstorms to become severe,
especially for locations north of I-76. These locations are where
MLCAPE values are expected to range from 1200 - 1800 J/kg, bulk
shear values ranging from 25-35kts are also portrayed in Buffkit
soundings within this area. The SPC has placed portions of
northern CO in a marginal risk with the biggest threats expected
to be wind and hail. These are expected to persist into the
evening hours. More on this below.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 250 PM MDT Wed Jun 19 2024

Not a lot has changed since 24 hours ago, except that we now
officially have the first named storm of the Atlantic, Tropical
Storm Alberto. That system will have some play in our weather,
bringing a connection of subtropical moisture northward into
Colorado. We`ll likely be on the northern edge of this plume, but
it will still add to the amount of available moisture from
Thursday evening through Friday evening, and likely enhance shower
and thunderstorm coverage and rainfall efficiency. More on that in
the hydro discussion below.

With the increase in moisture and instability for Thursday, we`ll
see those showers and storms continue into the evening, with the
greatest coverage likely shifting just east of the I-25 Corridor
and onto the plains, as per normal diurnal evolution. A couple of
those could still be strong to severe given the parameters
mentioned above. Meanwhile, showers could linger in the mountains
overnight as the mid level plume of subtropical moisture arrives.

For Friday, another repeat of showers and storms can be expected,
although there`s still no strong forcing to increase coverage to
anything more than scattered. It still appears the embedded
shortwave that rides across the Central/Northern Rockies will be
in the late night hours Friday night or early Saturday morning,
and thus not a big contributor for coverage. That said, showers
could linger during the night Friday night with weak forcing in
the moisture plume.

By daytime Saturday, we`ll get into subsidence and a drier airmass
overall. This will allow temperatures to warm into the lower 90s
across the lower elevations, and also confine most convective
coverage to the higher elevations and Palmer Divide.

For Sunday through Wednesday, there is still good agreement that
an upper level ridge will dominate the Central and Southern
Rockies. We`ll be on the northern periphery of this ridge, but the
westerly (downslope) flow will support a return of hot weather.
High temperatures for the plains and I-25 Corridor will likely
push into the mid to upper 90s each day. There does appear to be a
little moisture trapped under the ridge, enough for isolated high
based convection most days.

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1149 AM MDT Wed Jun 19 2024

Ceilings continue to fluctuate this morning at and around the
5000-8000 ft range. This is expected to continue with a pronounced
lifting not anticipated until later tonight. The persistent cloud
coverage has kept temperatures cool across the area and winds
have become increasingly gusty a little ahead of schedule, which
are expected to keep a gusty and southerly component through the
evening at DEN/APA. The latest guidance shows potential for winds
to gust in the low 30kt range at DEN/APA. There is low probability
that a thunderstorm passes near APA this afternoon, however, with
the persistent cloud coverage and low instability, showers are
the most likely scenario, so have left out of the TAF.

With greater instability over the higher terrain this afternoon,
have put VCTS at BJC as a storm may develop over the high country
and move east across the area. There is still a chance this
doesn`t happen with the current cloud cover. Winds at BJC look to
become variable around 4Z tonight and guidance shows this
continuing through the morning. There is a chance a Denver Cyclone
develops and N/NE winds setup. Or southerly winds may be another
option. Either way, winds are expected to stay light for either
scenario.

&&

.HYDROLOGY...
Issued at 250 PM MDT Wed Jun 19 2024

An increase in low level moisture, combined with mid/upper level
moisture spilling northward from Tropical Storm Alberto will
support storms with locally heavy rainfall Thursday and Friday.
Rainfall efficiency will grow, as warm cloud depths increase to
4,000-5,000 ft, rather impressive for this time of year. NAEFS
show 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. Overall, burn scars would be most susceptible to any
flooding threat over the next couple days, but we have seen
vegetation improvement in the last couple years and somewhat
higher flash flood thresholds. So, overall a limited to elevated
threat for burn scars at this point. We couldn`t even rule out
some minor urban flooding if we got a stronger storm in a metro
area.

&&

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

&&

$$

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