104
FXUS65 KBOU 172027
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
227 PM MDT Sat Aug 17 2024

.KEY MESSAGES...

- High based showers and a couple storms in/near the mountains
  will produce strong, gusty outflow winds well into the night.

- Precipitation chances increase tomorrow (Sunday), with
  scattered storms expected through next week.

- There will be a limited or greater threat of flash flooding over
  the burn areas Sunday through the middle of next week.

&&

.SHORT TERM /Through Sunday/...
Issued at 227 PM MDT Sat Aug 17 2024

Satellite shows a well defined shortwave lifting northward through
northern Utah, on the periphery of a dominating ridge centered in
northeast New Mexico. Upper level moisture is starting to
increase across Colorado, while most of the mid level moisture is
just now arriving in southwest Colorado. Meanwhile, isolated
storms were developing over the eastern plains in a narrow
corridor of weaker CIN and higher MLCAPE.

For tonight, mid and upper level moisture will continue to advect
into the forecast area, supporting some of the high based
showers/isolated storms to reach our forecast area. Most of these
will be confined to the mountains, with mostly virga for the
nearby plains. Current data (DCAPE near 1500-1800 J/kg in a deep,
dry adiabatic inverted-v profile) and forecast CAMs continue to
suggest microburst or strong outflow winds of 35-50 mph will be
the primary hazard. Can`t even rule out a severe gusts (58 mph or
more) considering the amount of DCAPE. What`s a little atypical is
that the highest threat appears later in the evening, roughly from
7/8 pm all the way through midnight. The most favored areas for
the stronger winds would be immediately in/adjacent to the
foothills, as moisture farther east of the I-25 Corridor is even
more scant. However, an isolated strong storm would be possible
over the far eastern plains where MLCAPE is closer to 1500-2000
J/kg in the deeper low level moisture still residing there.

We should see a decrease in convection as things stabilize in the
late night hours. For Sunday, the upper level ridge holds nearly
stationary, but the mid level moisture plume as seen in the
700-500 mb specific humidity progs slides a little farther east
and across the forecast area. Thus, scattered thunderstorms are a
good bet in the afternoon, first developing in the mountains by
early afternoon and then east and northeast across the plains
later in the afternoon and evening. We should shave a couple
degrees of today`s scorching heat.

&&

.LONG TERM /Sunday night through Saturday/...
Issued at 227 PM MDT Sat Aug 17 2024

A strong upper level ridge of high pressure will remain centered
over Eastern New Mexico and the Texas Panhandle through Wednesday.
Monsoonal moisture circulating around the western side of the
high is expected to move northeast over Colorado through this
period. This moisture combined with daytime heating and occasional
upper level disturbances should lead to scattered afternoon and
evening showers and storms across the forecast area.

For Sunday night, the showers and storms should be most numerous
across the high country with locally heavy rainfall possible. Across
the adjacent plains, widely scattered to scattered high based
convection is expected with gusty winds being the main threat.
However, a few locations could see some brief moderate to heavy
rainfall. Further east across the plains, the atmosphere appears
to be quite capped which may limit the the thunderstorm potential.
However, can`t rule out one or two strong to marginally severe
storms during the evening.

Monday is looking to be the most active day of the week as moisture
levels increase at the surface and aloft in response of the upper
level ridge flattening. With PW`s progged to range between 0.75"
in the mountains to 1.35" on the plains, there is the potential
for heavy rainfall anywhere across the forecast area, with a
threat for localized flash flooding especially in and near the
burn areas. Due to model differences, there is quite a bit of
uncertainty in the amount of instability and severe threat across
the plains. For example, the Monday 21Z sounding is showing an
MLCAPE of 1139 J/KG and decent shear at DIA, while the GFS has
only 56 J/KG of MLCAPE and poor shear. Wouldn`t be surprised to
see a couple of strong to severe storms somewhere across the
plains or Palmer Divide due to enhanced convergence and lift from
outflow boundaries.

On Tuesday, the upper flow is expected to turn more northwesterly as
the upper ridge amplifies over the Central and Southern Rockies.
This should allow a drier airmass to move into the area resulting in
much lower precipitation chances.

We may see an uptick in shower and thunderstorm activity Wednesday
and Thursday, mainly over the mountains and northern sections of the
Plains, as the center of the upper high shifts eastward over the
Southern Plains States and the plume of monsoonal moisture
reestablishes over the forecast area.

Models are suggesting a drying trend by the end of the work week as
the plume of monsoon moisture is either cutoff or pushed to the
south of our CWA.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1206 PM MDT Sat Aug 17 2024

Main concern is for gusty outflow winds from decaying high based
showers/isolated storms attempting to move off the mountains
02Z-07Z. The highest confidence exists near the foothills
including KBJC, but enough threat farther east in this environment
to include (but weaker TEMPO gusts) at KDEN 03Z-06Z. Peak gusts
closer to the foothills could reach 45 kts in line with CAM
guidance and DCAPE values near 1500-1600 J/kg.

Outside of that, fairly normal diurnal wind patterns 10 kts or
less will prevail. On Sunday, scattered thunderstorms will develop
in the afternoon with a Prob30 warranted at the TAF sites after
21Z. No ceiling impacts expected with clouds at or above 10,000
feet AGL.

&&

.HYDROLOGY...
Issued at 227 PM MDT Sat Aug 17 2024

Given a lack of moisture and instability into this evening,
there`s very little concern for any burn scar issues.

For Sunday, moisture increases through a deeper layer, but storm
bases will still be relatively high even with higher precipitable
water values. Stronger storms would likely be capable of producing
a quick half inch of rain, so there will be a limited threat of
burn area flash flooding starting Sunday afternoon.

For most of next week, moisture on the northwestern edge of an
upper level ridge will lead to scattered thunderstorms most days.
Storm motions should be slow given a lack of strong flow aloft.
Monday appears to be shaping up to be a higher threat day. After
Monday, one or two other days over the next week may have a
greater threat, but it`s difficult to say which day(s) that will
be.

&&

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

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...JK
AVIATION...Barjenbruch
HYDROLOGY...Barjenbruch/JK