010
FXUS65 KBOU 131748
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1148 AM MDT Thu Jun 13 2024

.KEY MESSAGES...

- Much above normal temperatures will continue today.

- Isolated showers and storms will produce gusty, potentially
  damaging microburst winds late this afternoon and evening.

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

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

&&

.UPDATE...
Issued at 952 AM MDT Thu Jun 13 2024

Weak frontal push is occurring across the plains this morning.
This will result in somewhat cooler (but still above normal)
temperatures on the northeastern plains. However, given the weak
inversions and less frontal impact along the I-25 Corridor it will
still be hot. Highs here will be soaring into the mid 90s, and a
few upper 90s in the immediate Denver metro area.

Regarding potential for severe weather, it`s not a clear cut day.
There is moistening in the low levels with a band of 50+
dewpoints spreading back to the southwest. At the same time, low
level cooling behind the front combined with the very warm air
aloft will be adding to stability over the northeast plains.
However, farther west and closer to the I-25 Corridor we`ll be
warming dry adiabatically (reaching convective temps), while at
the same time trying to add to the low level moisture and
instability. We think the NAM is overaggressive as usual with the
amount of low level moisture, especially if it`s mixing into the
drier airmass along the Front Range. But, nonetheless, there
should be a narrow ribbon of near 1000 J/kg MLCAPE with little CIN
near or just east of the I-25 Corridor/adjacent plains into the
Fort Morgan to Limon Corridor late this afternoon and especially
this evening where a couple stronger storms will be possible.
Damaging winds will be the main threat in this environment, but
a large hail threat as well with sufficient bulk shear for a
couple supercells. Overall, the forecast is still on track so only
minor adjustments in PoPs to refine storm threat a bit.

&&

.SHORT TERM /Through tonight/...
Issued at 355 AM MDT Thu Jun 13 2024

As previously expected, mid level temperatures will be a bit
warmer today. However, there`s mid level moisture which will again
produce clouds and high-based weak showers. It`s likely there`s a
bit more of this than yesterday, which should lead to earlier
cloud development. We also have a weak "cold" front that will pass
through by midday. This will only bring a few degrees of low level cold
advection, but the combination of these two things should offset
the warming aloft and result in temperatures similar to, or
slightly cooler than yesterday.

With better coverage of weak convection this afternoon, we may
have more widespread wind. We had one report of damaging
microburst winds yesterday around Eaton and Ault. While we don`t
expect that to be anywhere close to widespread, there may be more
of that this afternoon.

The situation gets a bit more complicated this evening, as
moisture will be increasing from the east. The environment on the
plains may be more favorable for rain, and if it moistens fast
enough there could even be 1000-1500 J/kg of CAPE and an
environment supportive of slow moving supercells. It probably
won`t moisten up enough to realize the full potential of that, but
there`s a better chance of mid to late evening storms with locally
heavy rain and hail over the eastern part of the plains. They will
still be fighting the warm air aloft though, so it`s hard to tell
how long they will hold on.

For now, the main change to the forecast was to increase cloud
cover, and lower nighttime temperatures in the mountain valleys
where we`ve been a little bit too warm the past several nights.

&&

.LONG TERM /Friday through Wednesday/...
Issued at 355 AM MDT Thu Jun 13 2024

An upper level trough axis begins to replace an upper level high
pressure system Friday morning. Lingering showers crossing from
the northeast plains into Kansas are possible early Friday
morning. Winds aloft shift southwesterly and cross sections
indicate potential low clouds persisting over I-76 until late
morning. This would be a limiting factor to the severe weather
potential Friday afternoon if these clouds limit our daytime
heating. Given PWATs range between 1.00-1.50 inches over the
region and QPF fields significantly increasing amongst guidance,
scattered to numerous showers and storm will occur by Friday
afternoon. There are several favorable factors for storms to
become severe along the eastern plains such as MLCAPE nearly
1000-1500 J/kg and lapse rates between 7-8 C/km. Although CAMs are
in favor of this severe potential, looking at temperatures, they
seem to over estimate how much warming will occur in the
afternoon. With higher forecast confidence of cooler temperatures,
leaning towards the severe threat occurring north of I-76 for a
brief window Friday afternoon. These severe storms could produce
wind gusts up to 60 mph and hail. Nonetheless flooding will be
the main hazard through Friday evening. Expecting storm motion to
move rather slow thus there is a higher flooding threat if storms
are able to stall or train over the same area. Across the Divide,
the Cameron Peak burn area near Miller Fork could reach minor
flooding concerns Friday afternoon.

This weekend, 700mb temperatures increase between 15-18C. This
pattern will lead to another round of 90s for the urban corridor and
plains. Mountains and valleys increase between 67-79. Marginal fire
weather conditions could return Sunday due to warm and dry
conditions but this will depend on fuel status. Mid-level moisture
remains limited leading to isolated chances of a shower or storm
mainly for the high country both Saturday and Sunday afternoon.
Next week, warm and dry conditions are expected through Tuesday
night.

&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1148 AM MDT Thu Jun 13 2024

Main concern will be gusty microburst and outflow winds from
passing high based showers and storms. The greatest risk of these
will be from 23Z-02Z, so we`ll have TEMPO VRB winds 25G35-38kts
for this time frame. There`s a small chance (20%) gusts would
reach 45+ kts. Before that, we expect mainly diurnal easterly
winds to prevail behind this morning`s weakening front. However,
there`s a 20-30% chance we could get early outflow or mixing with
a more west/northwest wind at some point this afternoon...before
convective outflows dominate the wind pattern.

Once convection ends this evening, winds should settle down to
more normal southerly flow most likely after 04Z. While low level
moisture increases, this flow is not conducive to any stratus and
airmass is quite warm - also limiting the stratus threat.

On Friday, there will be a greater chance (>60%) of thunderstorms
in the afternoon hours, so TEMPO TSRA and even visibility
restriction is warranted with the potential for strong to even a
couple severe storms nearby after 21Z.

&&

.HYDROLOGY...
Issued at 355 AM MDT Thu Jun 13 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.

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 slow moving which could increase 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...Gimmestad
LONG TERM...AD
AVIATION...Barjenbruch
HYDROLOGY...AD/Gimmestad