465
FXUS65 KBOU 180920
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
320 AM 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.

&&

.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 /06Z TAFS through 06Z Friday/...
Issued at 1139 PM MDT Wed Jul 17 2024

VFR through Thursday. The rest of tonight, expect normal drainage
wind patters at the terminals (8-12 kt SSW at DEN and APA, 4-8 kts
WSW at BJC). Tomorrow, as typical in the summer, winds should go
light and variable after 15Z. The preferred wind direction by
midday should be ENE 6-12 kts. Scattered convection should move
off the mountains after 21Z, reaching BJC first, then APA and DEN
maybe an hour later around 22Z. Coverage does not substantial,
and for now feel the best way to message convective potential at
the terminals with with VCTS. There will most likely be one or two
wind shifts with gusts maybe up to 25-30 kt because of outflow
after 21Z, with a preferred direction out of the NW but if storms
continue with some intensity well east of DEN, another weaker wind
shift could occur from the east or ESE after 00Z. Given the
convection and potential wind shifts/gusty outflow winds are 15-18
hours away, for now will just broad brush it in the TAFs. In any
case, after 05Z Friday winds will go to typical drainage patterns.

&&

.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.

&&

$$

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