432
FXUS65 KBOU 181813
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1213 PM MDT Thu Jul 18 2024

.KEY MESSAGES...

- Thursday will see a return of the 90s across most of the plains
  and I-25 corridor, with isolated afternoon thunderstorms across
  the area. Main impacts from these storms will be lightning,
  gusty winds, and brief moderate rain.

- A cooler and wet pattern will exist from Friday through Monday.
  There will be a limited threat of flash flooding on the burn
  areas on Friday and Sunday.

&&

.UPDATE...
Issued at 1057 AM MDT Thu Jul 18 2024

Weak convection is gradually bubbling up across the higher
elevations of our forecast area this morning, and scattered
convection is still on track to drift east into the I-25 corridor
later this afternoon. As the previous discussion mentioned, the
severe threat is low, but a couple stronger storms could produce
some hail and briefly gusty winds.

Made several changes to the forecast grids, but most of these were
minor. The main update was to add in a bit more PoP into the
evening hours as many of the HREF members maintain at least some
weak storms across the plains through around 03z or so.

&&

.SHORT TERM /Through Friday/...
Issued at 320 AM MDT Thu Jul 18 2024

The center of the 500 mb ridge will be over northeast Arizona now into
Friday, with weak north-northwest flow aloft. The PW values drop
a little from Wednesday, generally between 0.8-1.0" across the
plains, and 0.5-0.6" across the West Slope, which is near to
slightly above normal for mid-July. However, temperatures aloft
will warm vs. Wednesday, with 700 mb temps rising 2-4 degC and
500 mb temps warming 1-2 degC. The result is less instability
overall, with MLCAPE values ranging from 400-800 J/kg across the
eastern foothills and I-25 corridor, perhaps as high as 1500 J/kg
across the far eastern plains where there is deeper low-level
moisture. With weaker winds aloft (25-30 kts at 500 mb and
above), the severe threat is low but still non-zero given the
instability present across the plains. Overall storm coverage
looks to be pretty low, but the storms that form will be capable
of gusty winds and small hail, along with a few tenths of rain in
a short amount of time. Flash flooding on the burn scars or
anywhere else is not expected.

The slight warming aloft will result in a return to the 90s for
most of the plains and all of the urban corridor. The far eastern
plains might have a little more cloud cover, and be slower to
warm with Tds in the low 60s, so they`ll probably stay in the
upper 80s. The mountain valleys and foothills should be in the
upper 70s to low 80s.

Showers and storms should move northwest to southeast across the
plains east of the Continental Divide, starting in the mountains
around noon and moving eastward throughout the afternoon into
early evening. The far eastern plains may not see any storms
until after 5 pm. Showers and storms should clear the area before
midnight, and skies should clear overnight, resulting in good
radiational cooling and a nice night across the area. Temperatures
should make it into the 50s to lower 60s across the plains and
urban corridor, with 40s in the mountain valleys.

&&

.LONG TERM /Friday night through Wednesday/...
Issued at 320 AM MDT Thu Jul 18 2024

On Friday, the 500 MB high will be centered over the Great Basin
with a weak to moderate northwesterly flow aloft over Colorado. An
upper level shortwave is expected to move across Northeastern
Colorado during the afternoon with a trailing cold front traversing
across the plains by evening. This pattern should result in
scattered to numerous afternoon and evening showers and storms
across the forecast area. With PW`s ranging between 0.60" in the
high country to 1.15" on the plains locally heavy rainfall will be
possible with a limited flash flood threat across the burn scars.
In addition, there should be enough instability and shear to
produce a few severe storms across the plains, most likely east of
the Front Range Urban Corridor, where wind gusts to 60 mph will
be the main threat.

The upper high is progged to amplify over the Intermountain West
this weekend with a due northerly flow aloft over Colorado. This
pattern will allow a couple of upper level disturbances and cold
fronts to move across Northeastern Colorado resulting in cooler
unsettled weather across the region. Upslope flow is expected to
develop east of the divide with the best forcing south and west of
Metro Denver. Therefore, showers and storms should be most
numerous from the Continental Divide eastward across the Southern
Foothills into the Palmer Divide, where locally heavy rainfall
will be possible. Lesser activity is expected from the northern
sections of the Front Range Urban Corridor eastward across the
plains due to more stability. Temperatures are expected to drop to
below normal values both days with Sunday being the coolest day
of the period with max temperatures on the plains only reaching
the upper 70s and lower 80s.

For Monday through Wednesday, a similar upper air pattern is
expected to continue with some drier air spreading into the forecast
area from the north. As a result, should see a gradual decrease in showers
and thunderstorms each day with the activity mainly confined to
the higher terrain along and south of I-70. Temperatures are also
expected to warm through this period with max temperatures
expected to reach or exceed the 90 degree mark by Wednesday.

&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1057 AM MDT Thu Jul 18 2024

VFR through the period. This morning`s weak cyclone has continued
to weaken and northeast winds now prevail across most of the
metro. Convection is developing across the higher elevations and
should slowly drift towards the terminals beyond 21z. Figure there
will be just enough coverage for a TEMPO, mainly for briefly gusty
outflow winds. Any lingering TS should be out of the terminals by
03z.

Drainage winds should prevail tonight. A similar wind pattern is
expected through tomorrow. Additional storms are forecast for
Friday afternoon, but those wouldn`t make it into the metro until
after 18z.

&&

.HYDROLOGY...
Issued at 320 AM MDT Thu Jul 18 2024

Low level moisture trends downward for Thursday, resulting in
lower coverage of showers and thunderstorms with no threat for
flash flooding over the burn areas Thursday.

Friday and Sunday will have the best coverage of storms. Some of
these storms could produce heavy rainfall with the potential for
training storms. The Cameron Peak will have an limited threat of
flash flooding each day, with Saturday the least likely for storms
to produce heavy rain but upslope flow will be strongest on
Saturday. Flash flooding in the Grand County burn scars Saturday
and Sunday is not expected.

&&

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

&&

$$

UPDATE...Hiris
SHORT TERM...Schlatter
LONG TERM...JK
AVIATION...Hiris
HYDROLOGY...JK