Severe Thunderstorm Warning 121, NWS Denver/Boulder, CO

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

.KEY MESSAGES...

- More thunderstorms today and 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.

&&

.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 /18Z TAFS through 18Z Monday/...
Issued at 1139 AM MDT Sun Jun 9 2024

East to southeast winds are expected to prevail at DEN and
eventually APA this afternoon prior to storm development. North
winds are just west of DEN, but are expected to remain west of the
airport. However, this boundary could help storms form later today.
Main time frame for storms is expected to be 22Z-02Z.

Low clouds are expected to the north of east of Denver Monday
morning, but like this morning should not move into DEN. Will
have a few at 2000 feet for this. More thunderstorms are expected
around or after 21Z Monday. With most models showing a line of
storms, went with a tempo for thunderstorms after 21Z.

&&

.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.

&&

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

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1051 AM MDT Sun Jun 9 2024

COZ030>051-101700-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1051 AM MDT Sun Jun 9 2024

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Showers and thunderstorms are expected to first form over Park
County, the southern foothills, and Palmer Divide early to mid
afternoon. The showers and storms will spread north-northeast
across the Front Range through the late afternoon and evening
hours. Most of the showers and storms are expected over Front
Range Foothills and Urban Corridor with only a few possibly
making it to the nearby eastern plains. Isolated showers and
storms are also expected over the mountains.

The threat of severe storms is lower than yesterday, but there is
potential for a few strong to severe storms. Severe wind and hail
around/just above 1 inch will be possible in the stronger storms.
Heavy rain will be more common today with the storms.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

There will be a drying and warming trend this week. There will
still be a threat of storms that are severe or have heavy rain on
Monday, then the storm activity will be less Tuesday. Wednesday
and Thursday will be hot with few or no thunderstorms. Increased
storms are expected again starting Friday.

The main concern will be heat, with Thursday most likely being the
hottest day. There may need to be heat-related highlights on
Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected today or tonight.

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Preliminary Local Storm Report...Summary
National Weather Service Denver CO
449 PM MDT Sun Jun 9 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0447 PM     Hail             3 W Arapahoe Park       39.63N 104.74W
06/09/2024  E0.75 Inch       Arapahoe           CO   Public

            Report from mPING: Dime (0.75 in.).

0444 PM     Hail             3 NE Foxfield           39.61N 104.76W
06/09/2024  E1.50 Inch       Arapahoe           CO   Public

            Report from mPING: Ping Pong Ball (1.50
            in.).

0440 PM     Hail             2 NE Foxfield           39.61N 104.77W
06/09/2024  E1.25 Inch       Arapahoe           CO   Public

            Report from mPING: Half Dollar (1.25 in.).

0434 PM     Hail             2 S Arapahoe Park       39.60N 104.69W
06/09/2024  E1.50 Inch       Arapahoe           CO   Public

            Report from mPING: Ping Pong Ball (1.50
            in.).

0433 PM     Hail             4 S Arapahoe Park       39.58N 104.68W
06/09/2024  M1.00 Inch       Arapahoe           CO   Public

            Report from mPING: Quarter (1.00 in.).

0337 PM     Hail             1 SE Watkins            39.74N 104.58W
06/09/2024  E0.75 Inch       Adams              CO   Public

            Report from mPING: Dime (0.75 in.).

0309 PM     Hail             3 SE Watkins            39.72N 104.56W
06/09/2024  E1.00 Inch       Arapahoe           CO   Storm Chaser

0232 PM     Hail             2 NW Castlewood Canyon  39.37N 104.80W
06/09/2024  M0.75 Inch       Douglas            CO   Public

&&

Special Weather Statement
National Weather Service Denver CO
456 PM MDT Sun Jun 9 2024

COZ035-092330-
Larimer and Boulder Counties Between 6000 and 9000 Feet CO-
456 PM MDT Sun Jun 9 2024

...A STRONG THUNDERSTORM WILL IMPACT NORTH CENTRAL BOULDER COUNTY
THROUGH 530 PM MDT...

At 456 PM MDT, Doppler radar was tracking a strong thunderstorm over
Meeker Park, or 31 miles southwest of Fort Collins, moving east at 10
mph.

HAZARD...Penny size hail.

SOURCE...Radar indicated.

IMPACT...Minor hail damage to vegetation is possible.

Locations impacted include...
Meeker Park and Allenspark.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4028 10538 4017 10542 4019 10554 4021 10555
      4020 10559 4022 10555 4023 10554 4024 10555
      4028 10554 4025 10549 4027 10548 4029 10549
TIME...MOT...LOC 2256Z 270DEG 7KT 4024 10551

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...<30 MPH

SCHLATTER

Special Weather Statement
National Weather Service Denver CO
505 PM MDT Sun Jun 9 2024

COZ036-041-092345-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
Jefferson and West Douglas Counties Above  6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet CO-
505 PM MDT Sun Jun 9 2024

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL DOUGLAS COUNTY THROUGH
545 PM MDT...

At 505 PM MDT, Doppler radar was tracking a strong thunderstorm near
Sedalia, or 22 miles south of Denver, moving east at 5 mph.

HAZARD...Wind gusts up to 40 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Castle Rock, The Pinery, southern Castle Pines, and Sedalia.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3933 10510 3946 10503 3946 10502 3944 10502
      3944 10501 3941 10497 3941 10495 3943 10494
      3944 10496 3947 10496 3945 10474 3922 10481
TIME...MOT...LOC 2305Z 286DEG 6KT 3941 10499

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

SCHLATTER