173
FXUS65 KBOU 131648
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1048 AM MDT Tue Aug 13 2024

.KEY MESSAGES...

- Another round of thunderstorms today, with a continued flooding
  threat, and a greater risk of severe weather.

- Gradual drying trend expected from Wednesday through the end of
  the work week with near to slightly above normal temperatures.

&&

.UPDATE...
Issued at 1038 AM MDT Tue Aug 13 2024

A Flood Watch will continue until 11 PM MDT tonight.
Minor updates to wind direction by shifting winds northeast across
the plains and increasing cloud cover this morning. The forecast
package remains on track with afternoon scattered thunderstorms and
showers developing in the higher elevations spreading to the eastern
plains late afternoon through late evening. It is possible storms
could produce heavy rainfall across the region thus increasing the
threat of flash flooding for recent burn areas and plains.

&&

.SHORT TERM /Through Tonight/...
Issued at 436 AM MDT Tue Aug 13 2024

Thunderstorms have finally ended, though there are a few weak
showers exiting the northeast and entering the southwest part of
our area. With increasing cloud cover, we`ll probably keep a lid
on things until noon with only a few mountain showers.

Not much change to today`s forecast; we`ve made adjustments to
better show the convective timing (afternoon/evening mountains and
mostly late afternoon/evening urban corridor with mostly evening
over the eastern part of the plains). Some trends from yesterday:

-- Just as much moisture with precipitable water close to an inch
 over the foothills and up to 1.6 inches on the plains by evening.

-- Storm motions should be faster (10-20 mph) with less risk of
 backbuilding/training.

-- More CAPE (1000-1500 J/kg in the urban corridor and 1500-2500
 J/kg over the eastern plains by 00z.)

-- Some areas will be more flood prone due to the rain of the last
 couple of days, though the overall impact on soil moisture has
 been limited.

So we`ll still have a flood threat though the risk of significant
flash flooding should be lower than yesterday. And the risk of
severe storms is greater. Probably more of a mixed hail/wind
threat, increasing eastward with greater CAPE. There`s probably a
sweet spot in the central part of our plains (ern Weld/Logan
counties south to Limon) again where we`ll have enough heating,
higher CAPE, and a better wind profile in the late afternoon to
early evening and supercell development is possible. And the
potential damage is likely greater than yesterday with the higher
CAPE and shear. It`s not a super tornado environment, but there`s
probably some threat through that zone as I don`t really see any
negative factors.

While there should be some decrease in intensity, we`ll still have
a moist unstable environment into the evening for weaker
showers/storms to continue over the western part of our area. With
a faster storm motion, the strongest storms should be through
before midnight but lesser storms may linger much of the night
over the plains.

&&

.LONG TERM /Wednesday through Monday/...
Issued at 436 AM MDT Tue Aug 13 2024

Drier conditions are expected for Wednesday as a shortwave trough
skirts across the northern Rockies turning flow aloft to a more
zonal regime. This will limit monsoonal moisture transport into the
forecast area compared to the previous few days. There will still be
enough moisture present (PWATs 95-105% of normal), and with the
assistance of the passing shortwave to the north, scattered
afternoon showers and storms will likely develop, with some capable
of producing brief heavy rainfall. Forecast soundings show drier low
levels across the plains with DCAPE values surpassing 1000 J/kg. As
storms move east off the higher terrain, gusty outflows capable of
reaching 40-50 mph may be possible, with a few stronger gusts
possible in the stronger storms. High temperatures are forecast
to be in the 80s across the plains, 70s for the foothills, and 60s
for the mountains. A cool front looks to pass through the area in
the late Wednesday to early Thursday time frame. This is expected
to help keep high temperatures on Thursday a few degrees cooler
than Wednesday`s.

Increased drying is expected for Thursday and Friday as flow aloft
transitions to northwesterly as ridging begins to redevelop over the
Rockies. PWATs drop below normal and instability is expected to be
minimal. Mid-level lapse rates may steepen enough with daytime
heating over the high country to allow for isolated afternoon
showers and storms to develop. With limited moisture in place, any
storms that develop will likely produce light rainfall and gusty
winds. Temperatures will begin a gradual return to the 90s on
Friday as 700 mb temperatures increase by 5-8 degrees and the
ridge continues to amplify.

By Saturday, it looks like we have a shot at tapping back into some
monsoonal moisture as mid-level southwesterly flow may draw it up
around the high centered over Texas and New Mexico. This will
increase chances for isolated afternoon showers and storms, mainly
over the high country.

Increased moisture for Sunday and Monday will increase chances and
coverage of thunderstorms across the CWA. Temperatures are
expected to be above normal through the weekend and into the
beginning of next week.

&&

.AVIATION /12Z TAFS through 12Z Wednesday/...
Issued at 436 AM MDT Tue Aug 13 2024

Low clouds with IFR/MVFR ceilings in the Denver area should
dissipate 14z-15z. After that, VFR conditions are expected.
Thunderstorms are expected to be in the area again 20z-02z with
scattered showers and storms possible after that. Main impact will
be a couple of wind shifts with gusts to 35 knots, but a severe
thunderstorm with heavy rain, 50 knot gusts, and large hail is
possible. The main threat of that is 21z-00z.

&&

.HYDROLOGY...
Issued at 1038 AM MDT Tue Aug 13 2024

Faster storm motions are expected today, but plentiful moisture
will persist. Stronger storms today will produce heavy rainfall of
up to 2 inches in an hour. The likelihood of storms stalling or
training over the same area for longer periods is lower today. The
flood threat will be greatest over the Front Range burn areas
during the afternoon, urban areas in the I-25 corridor in the late
afternoon, and the eastern plains in the evening. A Flood Watch
continues through 11 PM MDT tonight.

Drier air starts to move into the area Wednesday, lowering the flash
flood threat, but keeping a limited threat across our sensitive
burn scars. By Thursday, if any storms are able to form, they are
only expected to produce light rainfall. The drier conditions are
expected to continue into Friday. Moisture begins to increase
Saturday and by Sunday the heavy rainfall/flash flooding threat is
expected to increase once again.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for COZ033-035-036-038-039-
041>044-046-047.

&&

$$

UPDATE...AD
SHORT TERM...Gimmestad
LONG TERM...Bonner
AVIATION...RPK
HYDROLOGY...AD/Gimmestad/Bonner