337
FXUS65 KBOU 081445
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
845 AM MDT Sat Jun 8 2024

.KEY MESSAGES...

- Severe storms possible along the Urban Corridor and likely on
  the northeast plains this afternoon with large hail and
  damaging winds the main threats.

- 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 845 AM MDT Sat Jun 8 2024

Water vapor satellite imagery showing an upper level trough over
Utah with lift ahead of it over northwest Colorado. A few showers
have formed already over northwest Colorado. As the trough and
lift track eastward, it will encounter an unstable airmass east of
the mountains. Expect scattered to numerous thunderstorms to form
early this afternoon over the Front Range Mountains and
Foothills. Threat for severe storms with large hail and strong
winds will be as far west as the lower foothills. Storms will
increase intensity as they progress eastward and ingest more
unstable air. Storm mode evolves from individual storms/supercells
into a line with severe bowing segments over the eastern plains.
Enhanced severe threat seems on track here with damaging winds a
good possibility somewhere over the eastern plains.

Going forecast for today is in good shape. Fine tuned PoPs to
line up more with the 12Z Hi-Res model runs, which shows the best
chance for thunderstorms across the Urban Corridor early to mid
afternoon.

&&

.SHORT TERM /Through tonight/...
Issued at 415 AM MDT Sat Jun 8 2024

More active weather day expected today, including the threat for
strong to severe thunderstorms across the plains. Moisture and
synoptic forcing are currently upstream of northeast CO early this
morning. Mid-level water vapor imagery shows a defined shortwave
trough in UT, moving east. Weak ascent ahead of this incoming wave
has already spit out some showers in northern Larimer and Weld
Counties early this morning. The incoming moisture is also quite
notable, rounding the flat ridge ahead of the incoming system.

A shortwave trough coupled with a mid-level speed max will provide
sufficient synoptic ascent and favorable shear. An axis of MLCAPE
values > 1000 J/kg orients across the central eastern plains.
Some guidance shows values around 2000 J/kg across east Elbert
Co. and Lincoln Co. Moisture will also be a big player. Anomalous
moisture is expected to shift into the region, about 150-200% of
normal. Upslope flow establishes by the afternoon, which will help
bring in higher dewpoint air westward. A few initial boundaries
will set up across northeast CO and help initiate the first
storms of the day, likely in the 12-2PM timeframe. One boundary
along the north border with the shortwave and another weak boundary
extending off of the Palmer Divide. Daytime heating will be
something to keep watch of, especially more north where there were
showers around this morning. This may inhibit initiation early
this afternoon (poss. failure mode).

Soundings/hodographs support singular/supercell mode initially.
The CAMs model suite reflectivity favors this evolution and
continues to hint at the transition to more linear mode with
upscale growth later on. Large hail upwards of 2" and damaging
winds will be the primary threats with any severe storms on the
plains. Hodographs are a mix of straight to a slight curve in
shape at the lower levels, to support splitting cells and a low
tornado threat on the plains. Around the urban corridor, can`t
rule out a few strong to severe storms with gusty winds being the
more likely threat. Late afternoon/early eve, storms move across
the far east plains. There is a marginal threat for excessive
rainfall, more in the hydro discussion. Temperatures will be
considerably cooler today compared to previous days with highs in
the 80s across the urban corridor and plains.

&&

.LONG TERM /Sunday through Friday/...
Issued at 415 AM MDT Sat Jun 8 2024

There`s been some convergence in model solutions for Sunday and
Monday, though significant questions remain on whether it will be
too cool for much convection and the related severe storm and
flooding threats. The NBM does seem to be a fair consensus solution
with highs from the mid 70s in the northeast corner to around 80
near the mountains on both days. Depending on the dew points, this
may be a little shy of the convective temperature, which would lead
to convection being forced by upslope into the foothills and the
plains ridges, but then probably able to drift east or southeast for
a while after initiation. Warmer solutions would have more storms on
the plains, while the cooler solutions would be pretty well capped
over the plains but likely still have some showers and a few storms
over the foothills.

The lack of shear will limit any severe threat, though there could
still be a weakly capped 1000-1500 J/kg if the warmer end of the
forecast range is realized, enough for some severe hail with
stronger pulses. The main threat though should be heavy rain with
precipitable water around an inch and storm motions under 10 knots.
In this pattern sometimes the initial storms are stationary for an
hour or two, and the greatest threat is for that to happen in a
susceptible area. After that, there should be some storm motion into
the low level winds but a localized storm producing 1 to 3 inches of
rain in a couple of hours would still be possible in areas just east
of the mountains in the late afternoon and evening.

Monday had been looking a little drier and warmer, and possibly more
of a severe threat if it got warm enough. But now it looks like the
winds aloft will still be fairly light and the low level air may not
be much different, with a little drying possibly offsetting any
warming. Threats may be similar to Sunday or less due to the drying.

Not much change to the warming and drying forecast for the rest of
the week. We`ve got low to mid 90s for Wednesday through Friday with
Thursday the warmest day. It could be a few degrees warmer than
that. Still questions about timing of some moistening Friday, but
the current slight cooling and chance of storms is reasonable. It
could be slower to get here.

&&

.AVIATION /12Z TAFS through 12Z Sunday/...
Issued at 543 AM MDT Sat Jun 8 2024

VFR conditions are likely today. Light, variable winds this
morning, gaining more of a light N/NE component through the AM.
Easterly flow likely increases in the 16-18Z timeframe. Main
concern for impacts will be the showers and thunderstorm potential
in the afternoon. Development looks likely after 18z with
scattered thunderstorms around the terminals for the afternoon,
potentially lingering into the early evening. Variable gusts will
likely accompany any nearby or passing storms with gusts up to
30-40 kts. Keeping an eye on potential for low stratus tonight
(after 02Z) once the storms exit, mainly at BJC and DEN. Not
seeing enough evidence/confidence to message strongly in the TAF
yet, but included a SCT020 for now.

&&

.HYDROLOGY...
Issued at 415 AM 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.

Thunderstorms will be likely across the recent burn areas today
through Monday. The strongest storms may occur today, but with
strong winds aloft, they will be moving quickly. Therefore, there
is a minor threat of flash flooding today. The plains are under
marginal risk per the Excessive Rainfall Outlook (WPC) for today.
This threat mainly applies further east. Stronger winds aloft
should favor quicker moving storms to keep this threat limited.

The flow aloft will weaken on Sunday and Monday which will lead
to slower moving storms. Considering strong storms are still
possible on Sunday, there will be a moderate threat for flash
flooding. By Monday, storms will likely be weaker and the threat
will be lower.

&&

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

&&

$$

UPDATE...Meier
SHORT TERM...Mensch
LONG TERM...Gimmestad
AVIATION...Mensch
HYDROLOGY...Gimmestad/Mensch