054
FXUS65 KBOU 100217
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
817 PM MDT Sun Jun 9 2024

.KEY MESSAGES...

- More thunderstorms on Monday with a lower severe threat but a
  risk of heavy rain and localized flooding.

- Minor snowmelt impacts from rising streams, mainly in Grand
  County. Thunderstorms this weekend could further increase stream
  flow.

- Hot and mainly dry weather towards the middle to end of next
  week. There is potential for a day or two to need a Heat
  Advisory, most likely Thursday.

- Cooler conditions will arrive Friday and Saturday with scattered
  showers and storms. Some of these storms could be strong to
  severe with heavy rain.

&&

.UPDATE...
Issued at 809 PM MDT Sun Jun 9 2024

Strong storms late this aftn along portions of the I-25 Corridor
produced very heavy rainfall, flash flooding and large hail in
some areas. Rainfall sensors from varied networks showed 2.5" to
3.5" where the heaviest rainfall occurred. Overall, activity has
pretty much ended in most areas with only widely scattered showers
and a few storms over the higher terrain. Overnight, should see
lingering activity end around midnight.

&&

.SHORT TERM /Through Monday/...
Issued at 214 PM MDT Sun Jun 9 2024

Low clouds over eastern Colorado will continue to slowly burn off
this afternoon. These low clouds wrapped westward into the
foothills of Larimer County. Under the low clouds, temperatures
are only in the 60s. Where it has been sunny most of the day,
temperatures have climbed into the 70s with highs expected to
reach the upper 70s to lower 80s. With temperatures this warm,
MLCAPE reaches 1000-2000 J/kg. There`s a good amount of moisture
in place today with dew points in the mid 50s to lower 60s and
precipitable water values at or slightly above an inch. Weaker
storms are expected today because of the reduced shear, but a few
marginally severe storms will be possible with hail to an inch in
diameter or slightly larger. Storms have started to form over the
higher terrain, of Park County and the southern foothills.
Additional development to the north is expected, and could become
focused over a north/south boundary just east of I- 25. Best
chance for thunderstorms/rain will be across the southern Front
Range where it has been sunny and most unstable. Chances slowly
decrease to the north and east due to less instability and
eventually running into a capped airmass. Storms dissipate mid
evening as the airmass stabilizes. Low clouds are expected to
reform late tonight and Monday morning. However, the extent of the
low clouds should be less than this morning.

On Monday, a short wave trough rounds the ridge that is centered
over the Four Corners. Timing of the best lift looks to be during
the afternoon and coincide with the best heating/instability.
MLCAPE climbs to 600-1200 J/kg and precipitable water values will
be around an inch. Shear will be lacking again, so we will be
looking at another round of thunderstorms with heavy rain and
small hail. Like today can`t rule out a few brief storms just
reaching severe criteria. Hi-Res models show a broken line of
storms forming ahead of the trough along the Front Range. The line
then fills in over the plans as it encounters better moisture and
instability. With fewer low clouds during the morning, expect a
warmer day across the area with highs in the 80s over northeast
Colorado.

&&

.LONG TERM /Monday night through Sunday/...
Issued at 214 PM MDT Sun Jun 9 2024

500 mb heights will increase on Tuesday as the northeast extent of
an upper level ridge will move over Colorado. At the surface, a weak
cold front will move through the area Monday night and southeast
winds will develop during the day on Tuesday behind the front. This
will keep decent moisture in place at the surface with dew points
staying around 50 F in the afternoon. Given there will be warming
aloft, there will be less instability and a stronger cap. Therefore,
the majority of the forecast area will be dry. However, over places
that have more natural orographic forcing like the Palmer Divide and
Cheyenne Ridge, there could be a couple storms that form. These
storms could produce some hail and gusty winds. Otherwise, highs
will be a few degrees (3-5 F) above normal.

On Wednesday, Colorado will be under the right exit region of an
upper level jet which will provide strong subsidence and will
likely keep conditions dry. Temperatures will be warming at 700
mb to around 17 C. Given the strong subsidence and plenty of
sunshine, it will turn into a hot day. Temperatures will climb to
the low to mid 90s across the plains. Denver could reach 95 F
which is only 2 degrees from the record daily high of 97 F set in
1952.

Frequent readers of the AFD are probably sick of me talking about
how hot Thursday is going to be but attention needs to be drawn to
it. A 500 mb ridge will strengthen and move slightly northeastward
on Thursday putting Colorado closer to the axis of the ridge.
There will be a shortwave trough that moves across the upper
Midwest during the day and this will have a surface cold front
associated with it that will eventually move through eastern
Colorado. The timing of when this front moves through the eastern
plains of Colorado will be important. If it moves through
Thursday morning, high temperatures may only reach the low 90s
across the plains (it`s not much of a cold front). However, what
appears more likely is that the front will move through late
enough in the afternoon such that very hot conditions will exist.
The NBM 50th percentile and the ECM ensemble MOS 50th percentile
both have a high of 97 in Denver. Based on the pattern
recognition, this seems well within reason so the forecast high
temperatures in the gridded forecast were kept at those levels.
The "high end" scenario in this case is that the cold front holds
off until later in the evening and the subsidence limits afternoon
cloud cover. In that case, a high of 100 or 101 would be possible
in Denver and the ensembles show that is certainly possible. The
record daily high for the 13th is 99 in Denver and it could be the
earliest 101 in Denver`s climate history. We may not know the
timing of the cold front for a couple days so nailing in the
forecast details may take some time. With that being said, a Heat
Advisory looks like it may be needed as temperatures will spend a
long time above 90 F and it is an early season heat. This is a day
where Denver could hit 90 F by about 9AM. Otherwise, a couple of
very gusty showers could develop given how hot it will be.

There is growing confidence that a shortwave trough will move
over Colorado on Friday with an increase in precipitable water.
There should be scattered coverage of thunderstorms and the
coverage could even reach widespread. Some of these storms could
be strong to severe given moderate instability and decent wind
shear. The cooler weather with scattered storms will continue
during the weekend.

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 519 PM MDT Sun Jun 9 2024

Threat of stronger storms at DIA has diminished, however,
can`t completely rule out a weaker storm thru 01z. After
01z threat of storms should end.  Winds will be mainly
from the south unless an outflow boundary from storms to
the west or northwest moves across.  On Mon, winds will
become light and variable by 15z and then transition to
light east by early aftn. Scattered storms will be possible
in the 21z-24z time period with gusty outflow winds.

&&

.HYDROLOGY...
Issued at 400 AM MDT Sun Jun 9 2024

Elevated flows continue across the upper Colorado River basin and
additional rainfall this weekend could lead to further increase in
the flows. Remain cognizant of the dangers of these cold flows,
and be aware of any Flood Advisories.

Storms will be moving much slower today and Monday. However, they
will likely be weaker than Saturday. The primary threat during
the forecast period will be in Cameron Peak today as a moderate
threat for flash flooding will exist. The threat will be minor
again on Monday. Periods of heavy rain are possible in storms
today, mainly west of I-25 with a marginal risk for localized
flood impacts.

&&

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

&&

$$

UPDATE...RPK
SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...RPK
HYDROLOGY...Gimmestad/Mensch