032
FXUS65 KBOU 140546
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1146 PM MDT Thu Jun 13 2024

.KEY MESSAGES...

- Isolated storms still ongoing this evening. Low severe threat
  yet.

- More numerous thunderstorms and a greater severe storm threat
  Friday afternoon and evening

- A return to hot and dry weather this weekend into early next
  week.

- Snowmelt producing minor impacts from high streams. Gradually
  diminishing flows next week.

&&

.UPDATE...
Issued at 822 PM MDT Thu Jun 13 2024

We`ve had one isolated severe storm move from northern Lincoln
County into southern Washington County with 1 inch hail late this
afternoon, and a couple of microbursts including a 61 mph gust at
Centennial Airport and a 49 mph gust at Northern Colorado
Regional Airport. There`s since been a lull in activity.

The moisture surge was impressive late this afternoon and
evening, with gusty east winds pushing higher dewpoints near 50F
all the way back into the foothills! We haven`t seen too much
convection associated with this push fire off, but that doesn`t
mean we`re totally out of the woods. Latest ACARS soundings
definitely shows the low level stability below 700 mb, but the
airmass is still moistening in the easterly flow as well as
additional mid/upper level moisture now starting to arrive ahead
of tomorrow`s shortwave. To get additional convection, we`d have
to lift the parcel near 700 mb (10,000 ft MSL). This is still
possible this evening due to the upslope component through the
foothills. And, IF it fires off, MLCAPE near 1,000 J/kg would be
available per SPC analysis and ACARS soundings. Thus, we still
can`t rule out a couple strong/severe storms yet. To put a number
on it would be approximately a 30% chance of this happening
between now and midnight. We`ve made slight adjustments for this
to delay the ending of the thunderstorm chances.

Also, one thing to mention about tomorrow is the shortwave
dragging up not just mid and upper level moisture from the south,
but also some thin smoke (HRRR projections) out of Mexico. Could
be just enough for additional haze in the skies. The main focus
for tomorrow will still be the severe weather threat in the
afternoon and early evening.

&&

.SHORT TERM /Through Friday/...
Issued at 249 PM MDT Thu Jun 13 2024

Main concerns are for isolated severe storms this evening, and
more numerous severe storms Friday afternoon.

The "cold" front pushed back into the I-25 Corridor this morning,
but as discussed earlier it didn`t have much impact on
temperatures with highs in the mid 90s! Farther east, at least
there was some cooling with current temps mostly in the upper 80s.
The heating here has eliminated the CIN, with some high based
moderate cumulus. SPC surface analysis shows a ribbon of 1000+
J/kg MLCAPE to the east and northeast of Denver, where post-
frontal moisture depth is larger, with only around 500 J/kg closer
to I-25. Thus, we should get additional convective initiation
closer to the Front Range, and then intensify as it moves into the
more unstable air just to our east. Enough instability and shear
would be present for one or two severe storms with damaging winds
and large hail the primary threats.

Even outside of that area, microbursts will be possible closer to
the I-25 Corridor where DCAPE values are in the 1500-2000 J/kg
range - very impressive values which means isolated damaging gusts
>60 mph will be possible. Also, if deeper moisture is able to push
back (20-30% chance) can`t rule out a more traditional severe
storm bringing a large hail threat.

The bulk of storms should end as we head into the late evening
and overnight hours as the airmass stabilizes. However, with
further moisture/theta-e advection through 700 mb there will still
be a slight chance of storms over the eastern plains overnight.

On Friday, the airmass will destabilize while a shortwave trough
approaches the region from the southwest. This times up well to
produce a greater severe storm threat in the afternoon. MLCAPE
will increase to 1500-2000 J/kg as surface dewpoints hold in the
50s. As southeast flow increases in the afternoon, a Denver
Convergence Vorticity Zone (DCVZ) is expected to develop from the
Palmer Divide/southeast sections of Denver onto the plains. That
will help drive convective initiation (in addition to the elevated
heating source of the mountains), and bring a greater risk of
severe storms including a tornado threat. Large hail, damaging
winds, and heavy rain will all be possible. HREF limited the
amount of updraft helicity, while deep layer shear is a bit
marginal. Nonetheless, the approaching shortwave typically can
make up for that. Therefore, expect at least a few severe storms
on Friday afternoon, continuing into the evening.

&&

.LONG TERM /Friday night through Thursday/...
Issued at 249 PM MDT Thu Jun 13 2024

A return to well above normal temperatures appears likely by this
weekend as a large ridge builds across the eastern U.S. and
gradually strengthens. Broad west-southwesterly flow will likely
be in place by Saturday behind Friday`s shortwave, with
considerable drying through the day. 700mb temperatures are
projected to reach around 15C during the day with upper 80s to low
90s highs likely across the plains. There may be just enough
lingering moisture for an isolated storm or two across the Front
Range mountains/foothills but anything that does develop would
likely produce more wind than precipitation.

The mid-level thermal ridge is forecast to strengthen
considerably Sunday into Monday. As a trough axis approaches to
our northwest and the ridge out east continues to build, this will
likely result in increasing mid/upper level flow and an added
downslope component. Most deterministic, ensemble, and MOS
guidance favor mid to upper 90s across the plains on Sunday and
Monday as 700mb temperatures warm to near 20C. If we are as
hot/dry as advertised, there would certainly be fire weather
concerns at least one or two days this weekend/early next week.
Heat Advisories may also be necessary if the higher end solutions
pan out.

At some point, guidance does bring a cold front into the region
alleviating the heat for most of the region. The GFS is an
outlier, bringing the front in on Monday, while most other
guidance favors Tuesday. Though the aforementioned trough won`t
bring much precipitation, it does appear that we`ll have a few
days with temperatures near or below normal during the mid/late
week next week. Unfortunately, this appears to be short lived,
with a strong ensemble signal for the heat to return by next
weekend.

&&

.AVIATION /06Z TAFS through 06Z Saturday/...
Issued at 1133 PM MDT Thu Jun 13 2024

Winds should shift back into drainage through Friday morning. By
late Friday morning winds could shift north for a brief period
then shifting east by Friday afternoon. Thunderstorms will develop
as early as 19Z then continuing until 00-02Z for all terminals.
Winds will increase up to 35-40kts gusts. By Friday evening,
showers should push east out of terminals and drainage winds are
expected once more.


&&

.HYDROLOGY...
Issued at 249 PM MDT Thu Jun 13 2024

Thunderstorms Friday afternoon and evening will be capable of
producing locally heavy rainfall. Precipitable Water (PW) values
increase to between 1 and 1.5", with the highest amounts over the
northeast plains. Storms will be more efficient rain producers
than the last several days, as dewpoints on the plains climb into
the 50s, with even some lower 60s over the northeast corner. Storm
motion is expected to be around 20 mph, which isn`t terribly fast
so given the intensity and ingredients above we think stronger
storms will be capable of producing 1-2 inches in 30-45 minutes.
Considering the low level wind fields, we believe the most focused
area of heavy rain would be from the south/east sides of Denver
metro and Palmer Divide in the mid/late afternoon, and then to
the east and northeast across the northeast plains of Colorado
through the evening hours.

Moisture levels across the high country will be lower; however,
there could be localized areas of heavy rainfall which could cause
flooding issues across the burn scars. Cameron Peak would be most
susceptible given somewhat richer atmospheric moisture profiles there.

Elevated flows continue in the mountain streams, with Flood
Advisories remaining in effect for the streams above Granby and
Grand Lake. Remain alert of the dangers of water that is running
high and cold. Flows are expected to gradually decrease over the
weekend and through next week as the peak snowmelt is passing by.

&&

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

&&

$$

UPDATE...Barjenbruch
SHORT TERM...Barjenbruch
LONG TERM...Hiris
AVIATION...AD
HYDROLOGY...Barjenbruch