818
FXUS65 KBOU 081041
AFDBOU

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

.KEY MESSAGES...

- Severe storms likely on the northeast plains this afternoon and
  early evening 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.

&&

.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.
CAMs model reflectivity reflects this and also 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 /06Z TAFS through 06Z Sunday/...
Issued at 1221 PM MDT Fri Jun 7 2024

VFR conditions are likely overnight and Saturday. Southerly
drainage expected overnight at APA/DEN at 08-12 kts. Light winds
expected Saturday morning. Confidence decreases with respect to
the wind shift to easterly by the afternoon. It should shift
easterly the 15-18Z timeframe. There could be a period of VRB
or light northerly before it goes east. 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 Saturday night once the storms
exit. Not seeing enough evidence yet to message in the TAF. This
will depend on how much moisture sticks around and the prevailing
wind patterns. Low confidence 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.

&&

$$

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