294
FXUS65 KBOU 190525
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1125 PM MDT Thu Jul 18 2024

.KEY MESSAGES...

- A few showers and storms should persist into the evening hours.

- Additional showers and storms likely for Friday, with a few
  strong to severe storms possible across far northeastern
  Colorado. Locally heavy rain possible with a limited risk of
  burn area flash flooding.

- A cooler and more moist pattern will exist from Saturday into
  Monday. There will be a limited threat of flash flooding, mainly
  on the burn areas.

&&

.UPDATE...
Issued at 928 PM MDT Thu Jul 18 2024

Isolated convection continues to decrease across the CWA this
evening..with just a couple areas left over the northeast and
southern corners of the CWA.There are some boundaries flying
around but it appears they won`t be doing much anymore this
evening.  Will end all the pops in the grids by 06Z for the
update. Will make a few other minor alterations to the sky, wind
and temperatures grids based on current conditions.

&&

.SHORT TERM /Through Friday/...
Issued at 241 PM MDT Thu Jul 18 2024

Current radar imagery shows a few showers and storms, mainly
across the higher elevations of the Front Range. These storms have
shown poor organization and have struggled once hitting the lower
foothills and adjacent plains. SPC Mesoanalysis suggests that
there is still quite a bit of MLCIN left across the I-25 corridor,
which is supported by recent ACARS data from DEN. Still, guidance
shows this cap eroding over the next couple of hours with a few
showers and storms gradually drifting east across the forecast
area. Any lingering showers/storms should quickly dissipate by the
evening hours.

Tomorrow should feature similar temperatures (near 90F across the
plains), with a bit more coverage in storms. A shortwave trough is
expected to push southward from the Black Hills into far
southwestern Nebraska during the day, with an accompanying surface
front also pushing into the forecast area. Ahead of the front,
sufficient surface heating/moisture (90/50 T/Td) and modest
northwesterly flow aloft (500mb flow near 25-40kt) should provide
a marginally favorable environment for severe weather, mainly east
of the urban corridor. Guidance is not particularly enthused, but
it wouldn`t be surprising to see a couple of strong/severe storms
in far northeastern Colorado. Across the I-25 corridor into the
Front Range, the parameter space is far less favorable for
organized storms... but there should be enough
moisture/instability for a few slow moving storms with small hail
and briefly heavy rainfall.

&&

.LONG TERM /Friday night through Thursday/...
Issued at 333 PM MDT Thu Jul 18 2024

Models indicate that upper ridging will remain west of Colorado
Friday night through Sunday with fairly weak north-northwesterly
flow aloft for our forecast area. Upper troughing will remain
over the eastern half of the U.S. which will keep the hot airmass
to our west at bay. In fact, thickness and temperature grids show
a surge of cooler air to get into the forecast area from the east
Friday night and again later Saturday night into Sunday morning.
High temperatures look to be below seasonal normals both Saturday
and Sunday.

Models show decent moisture over the forecast area Friday night
through Sunday night with precipitable water values in the 1.00 to
1.30 inches over the plains and 0.50 to 0.80 inch in the mountains.
There should be enough synoptic scale energy from the trough to our
east to keep pretty decent pops going over the high county and
immediate plains both late day Saturday and Sunday.  The available
moisture is enough to make for some heavy rain producing
thunderstorms.

For the later days, Monday through Thursday, models continue to keep
the upper ridging west of Colorado with northerly flow aloft and
upper troughing immediately to our east. The cooler, somewhat
moist airmass should stick around two more days. By Wednesday and
Thursday, the upper ridge is progged to move eastward into
Colorado with dry and warming conditions expected.

&&

.AVIATION /06Z TAFS through 06Z Saturday/...
Issued at 1125 PM MDT Thu Jul 18 2024

VFR through Friday and into Saturday. Existing south winds at DEN
and APA 10-14 kts should go light and variable by 14Z. BJC should
be 4-6 kts out of the west until then. North winds should develop
with mixing by 17Z. One change we`ve made with the 06Z TAFs is an
earlier start to the convective impacts. All the CAMs have fairly
robust convection coming off the mountains around 19Z, and it
could impact BJC as early as then. We are going with 20Z at APA
and DEN, but it could be a tad earlier if the current trends in
model timing continue. Gusty outflow winds will almost certainly
occur at the terminals sometime between 19-22Z at BJC, 20-23Z at
DEN/APA, with a much higher chance of those strong outflow winds
occurring closer to 20Z. We have VRB direction in the TEMPO group
for now given the uncertainty, but the best bet on strong outflow
wind direction will be northwest. Once the initial line of storms
passes off to the east and southeast, there will likely be a
period of ENE winds on the backside of the storms within an hour
of 00Z. Showers may move near the terminals late evening through
03Z, but additional impacts are not expected. Drainage winds will
return after 06Z (SSW at DEN and APA of 8-12 kts, W at BJC of 4-7
kts).

&&

.HYDROLOGY...
Issued at 332 PM MDT Thu Jul 18 2024

A passing weak storm system and an accompanying front will provide
the focus for increased storm coverage on Friday. Moisture is
expected to be near or a little above normal. Storm motions should
be quick enough to avoid widespread issues, with mean cloud-layer
flow around 20kt. However, a couple of storms would still be
capable of producing heavy rain...leading to a limited risk of
flash flooding across the East Troublesome/Cameron Peak burn areas

Decent moisture is expected, especially on Saturday and Sunday.
Likely late day shower and thunderstorm coverage is expected both
days over the mountains, foothills and immediate plains. There
will be a limited threat of flash flooding, more so over the
burned areas.

&&

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

&&

$$

UPDATE.......RJK
SHORT TERM...Hiris
LONG TERM....RJK
AVIATION...Schlatter
HYDROLOGY....Hiris/RJK