858
FXUS65 KBOU 172155
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
355 PM MDT Wed Jul 17 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms this afternoon into early
  this evening with a few strong to severe storms possible.

- Thursday will be warm with scattered gusty afternoon storms.

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

&&

.SHORT TERM /Through Thursday evening/...
Issued at 319 PM MDT Wed Jul 17 2024

Current radar shows scattered showers and thunderstorms this
afternoon over the mountains, foothills, Palmer Divide, and northern
Weld County. MLCAPE values range in the 500-1500 j/kg range from
west to east. Across the I-25 corridor, shear is on the weaker side
keeping storms weaker and capable of brief gusty winds, small hail,
and locally heavy rain. Over the eastern plains, shear is more
sufficient combined with higher instability (MLCAPE > 1000j/kg) to
support a few strong to severe storms. Into early evening, high
resolution CAMs show scattered showers and storms pushing east
across the plains. A few solutions show a transition into a more
linear mode over the far east plains. Given the more favorable
severe environment is there, we`ll have to watch for a severe
wind,hail threat and if storms slow more, perhaps potential for
minor local flood impacts in those areas. RAP mesoanalysis shows
DCAPE values >1000j/kg over the east plains support the gusty wind
threat. Most activity will have exited to the east by mid-evening.

For Thursday, the 500mb ridge centers to the west of Colorado,
around the Four Corners region with N/NNW flow aloft over Colorado.
Model cross sections/soundings show subtle drying in the low levels
and some in the mid-levels from Wednesday. There will be marginal
instability around with ample daytime heating; however, limited
upper level support for ascent. This will support scattered
afternoon showers and thunderstorms lesser in coverage compared to
Wednesday with the higher chances over the higher terrain. MLCAPE
values 800-1500 j/kg and DCAPE 900-1500 j/kg will support a few
stronger storms, capable of strong gusty outflow winds and small
hail on the plains. Temperatures trend slightly warmer with less
cloud cover and building of the ridge to the west. Highs range in
the upper 80s to low 90s across the plains.

&&

.LONG TERM /After midnight Thursday night through Wednesday/...
Issued at 319 PM MDT Wed Jul 17 2024

The upper level pattern will be stagnant and quite unusual for July
or much of the long term period. A broad upper level trough will
move south out of Canada and park itself over the Midwest. 500 mb
flow may be northerly for a few days over our forecast area. This
will lead to wet and cool weather for the long term period.

Getting into specifics, there will be a small shortwave trough that
will move across northeast Wyoming through northeast Colorado Friday
afternoon. At the surface, there will be a weak cold front that will
move trough northeast Colorado along with lowering pressure. The
forcing from the trough and cold front will combine to create
scattered showers and storms across the area. There will be a
concern for flash flooding over the burn areas since there will be
upslope flow and good moisture in the area. Across the northeast
plains, there will be enough instability for storms to become strong
to severe. Since there is organized forcing with the shortwave,
these storms may quickly congeal into a line and produce wind gusts
up to 60 mph. The primary threat will be east of a line from Fort
Morgan to Deer Trail.

On Saturday, our forecast area will be under slight subsident flow
behind the shortwave that will have moved through the area. The post-
cold frontal airmass will have a bit less moisture and will be
more capped than Friday. Despite the low level upslope
northeasterly flow, the coverage of showers and storms will be
limited. Storms will form primarily over the southern foothills as
that area is favored with low level northeast winds.

On Sunday, there will be another small shortwave trough that will
move towards northeast Colorado. At the surface, low level
northeasterly flow will increase and moisture will increase as
well. There will be widespread showers and thunderstorms over the
higher terrain. Some of these storms may train over the same area
and there will be a flash flood threat as a result. Storms may
also form over the plains but coverage will be lower.

By next work week, temperatures aloft will increase and moisture
will decrease in the low levels. There will be more stable
conditions which will limit coverage of storms. Storms will mostly
stay over the higher terrain. By the end of the week, temperatures
will rise and there will be less of a threat of storms as a ridge
aloft moves overhead.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1209 PM MDT Wed Jul 17 2024

Expect VFR conditions for the TAF period. Light E/SE winds this
afternoon, increasing to 7-11 kts mid to late afternoon. Scattered
showers and thunderstorms develop this afternoon. Coverage/chances
are high enough to include as TEMPO for -TSRA from 20-23Z at
BJC/APA and 21-24Z at DEN. Showers and storms may contain gusty
outflow winds similar to Tuesday, so included this in the TEMPO
for VRB gusts up to 30-40 kts. Winds turn back southerly tonight
at 08-12 kts. Winds become light after 14Z, turning NW Thursday
morning, eventually settling easterly for the afternoon. There is
a low chance (< 25%) for a scattered showers or storm in the
afternoon; therefore, not included in the TAF and messaged as a
VCSH for now.

&&

.HYDROLOGY...
Issued at 319 PM MDT Wed Jul 17 2024

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

Friday and Sunday will have the best coverage of storms. Some of
these storms will produce heavy rainfall and there is potential
for training storms. The Cameron Peak will have an elevated threat
of flash flooding each day while the other recent burn areas will
have a limited threat.

&&

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

&&

$$

SHORT TERM...Mensch
LONG TERM...Danielson
AVIATION...Mensch
HYDROLOGY...Mensch/Danielson