199
FXUS65 KBOU 130248
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
848 PM MDT Wed Jun 12 2024

.KEY MESSAGES...

- Much above normal temperatures will continue on Thursday.
  Isolated high based showers and storms with gusty outflow winds
  in the afternoon and evening hours.

- Snowmelt producing minor impacts from high streams, mainly in
  Grand County.

- Slightly cooler conditions will arrive Friday and Saturday with
  scattered showers and storms. Some of these storms could be
  strong to severe along the plains with heavy rain on Friday.

&&

.UPDATE...
Issued at 848 PM MDT Wed Jun 12 2024

High based convection and gusty outflow winds and microbursts are
diminishing this evening as we`ve now worked over the limited
instability and the boundary layer is cooling. We say "cooling"
in a relative sense since many plains locations are still in the
lower 80s. It`ll be slow to cool off overnight, and expect only
shallow weak inversions given the westerly flow and downslope in
place. In fact, I wouldn`t be surprised to see a few spots in the
thermal belt near the base of the foothills to stay above 70 for a
low, while other plains locations struggle to drop through the
60s.

The weak inversions will lead to a fast warmup and another hot day
on Thursday. There is a weak backdoor "cool" front tomorrow
morning, but most of the "cooling" (highs closer to 90) will be
confined to the northeastern corner. While there is some
amplification of the upper level ridging and thus drying aloft,
there is a slow improvement in the low level moisture from the
Front Range eastward due to the easterly flow behind the cool
front. The net is pretty much a wash from today, so we expect
another round of isolated to scattered high based convection with
gusty outflow winds/microbursts but little rain.

&&

.SHORT TERM /Through Thursday/...
Issued at 251 PM MDT Wed Jun 12 2024

Radars are indicating isolated showers and thunderstorms over the
mountains at this time. Highs have reached the mid 90s over the
plains for the warmest day of 2024 so far. Seems to be a bit more
convection than most of the models indicated earlier. The storms
are pretty high based and downdraft CAPE is pretty high. Outflow
winds will be the main issue with the storms later this afternoon
and evening.

The latest high resolution models are showing limited convection
over a good part of the CWA this evening. With that and reality in
mind, will up pops into 10-30% range for much of the CWA. Models
now are not showing much convection for Thursday afternoon, but
we`ll see how that evolves as well. Temperature and thickness
grids point to it being a tad warmer on Thursday than today for
the western half of plains and high country. The eastern half of
the plains could be a bit cooler behind a cold front that moves
in Thursday morning.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 227 PM MDT Wed Jun 12 2024

Upper level high pressure will remain over the Central and Southern
Rockies Thursday night with mostly dry weather and mild
temperatures across the forecast area. The exception may be across
the northeastern plains east of the Front Range Urban Corridor
where moisture convergence along a weak front could kick off a few
evening showers and storms, some of which could be strong.

Friday and Friday evening, an upper level shortwave will move across
the state bringing cooler temperatures and increased precipitation
chances to the CWA. With plenty of instability (1000 J/KG to 2500
J/KG) and shear (35+KTs), some of the storms could become strong to
severe, especially across the eastern plains. In addition, heavy
rainfall will be possible on the plains where PW`s are expected to
range between 1.00"-1.50".

Warmer and drier weather is expected to return across the area over
the weekend as the upper level shortwave moves into the Central
Plains States and upper level high pressure rebuilds over Colorado.
On Saturday, there could be isolated to scattered (10%-30%)
afternoon and evening showers and storms across the foothills and
Palmer Divide as lingering moisture combines with daytime heating.
Some of the stronger storms could produce brief heavy rain and small
hail. By Sunday, hot weather is expected to make its return with max
temperatures are expected to climb into the mid 90s across the
plains. The hot and dry conditions combined with increasing winds
may lead to elevated fire weather conditions across the portions of
the high country and Palmer Divide on Sunday.

On Monday, upper level high pressure will be centered over the
Eastern U.S. with a moderate southwesterly flow aloft over Colorado.
This pattern will result in continued hot and dry weather across the
region. However, with better low level moisture further east across
the plains, can`t rule out a few late afternoon and evening storms
northeast of Denver, some of which could be strong. The hot and dry
conditions combined with increasing winds may lead to elevated fire
weather conditions across the portions of the high country and
Palmer Divide on Sunday. These conditions are expected to spread
eastward across portions of the plains on Monday.

The hot and dry conditions combined with increasing winds may lead
to elevated fire weather conditions across the portions of the
mountains, foothills and Palmer Divide on Sunday.

On Tuesday, an upper level shortwave moving across the Northern
Rockies will push a cold front across Northeastern Colorado.
Consequently, much cooler temperatures along with isolated to
scattered (10% to 30%) late afternoon showers and storms are
expected Tuesday and Wednesday.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 848 PM MDT Wed Jun 12 2024

One last outflow boundary had pushed through the airports
0130-0230Z, with a northerly wind component winning out. Those
winds will subside and transition to normal south/southwest winds
closer to 06Z.

For Thursday, the main concern once again will be gusty outflow
winds from isolated high based showers/storms. While the upper
levels see some drying, the weak advection of low level moisture
combined with strong diurnal heating and upslope behind a weak
"cool" front, could be just enough for another round of high based
convection and gusty outflow winds. Most likely this would occur
after 21-22Z, but enough threat to have TEMPO VRB gusty winds to
35 kts in the forecast.

&&

.HYDROLOGY...
Issued at 227 PM MDT Wed Jun 12 2024

Elevated flows continue across the upper Colorado River basin in
Grand County, with Flood Advisories in effect for streams above
Granby and Grand Lake. Remain alert of the dangers of water that
is running high and cold. Flows may increase over the next few
days as hot temperatures are expected followed by showers and
storms on Friday. Heavy rainfall will be possible on the plains
where PW`s are expected to range between 1.00"-1.50". However,
the storms are expected to be moving at around 25 KTS which
should limit the flooding potential. Moisture levels across the
high country will be lower; however, there could be localized
areas of heavy rainfall which could cause flooding issues across
the burn scars.

&&

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

&&

$$

UPDATE...Barjenbruch
SHORT TERM...RJK
LONG TERM....JK
AVIATION...Barjenbruch
HYDROLOGY....JK