Severe Thunderstorm Warning 86, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
932 PM MDT Sun Jun 11 2023

.UPDATE...
Issued at 927 PM MDT Sun Jun 11 2023

Shower and thunderstorms coverage is ongoing across the forecast
area this evening. The Denver Metro area is finally getting some
rain showers, light, as well as a bit of lightning. The strongest
cells are over Weld, Douglas, Lincoln and Elbert Counties as this
time. There have been some areas of accumulating hail over
Elbert County and southern Park Counties. Will leave the Flood
Watch going through 09Z with heavy rain expected to continue in
some areas. Will amend some of the sky, temperature and pop GFE
grids based on current conditions.

&&

.SHORT TERM...(This evening through Monday)
Issued at 254 PM MDT Sun Jun 11 2023

Scattered convection has developed across the southern Foothills
and Palmer Divide over the past hour or two, and this is gradually
expected to organize and drift eastward this afternoon and
evening. Temperatures in the mid 60s have allowed for modest
instability to build south of I-70, with roughly 30-40kt shear in
the region as well. Again, not much has changed since our mid-
morning update. Severe potential will likely be confined to the
southern metro/Palmer Divide. Heavy rain is also a concern this
evening... as noted in the hydro section further below.

Tonight's forecast is largely uncertain as well. The environment
largely supports additional thunderstorm development through the
evening and overnight, as a broad cutoff low spins to our west. As
a previous Mesoscale Precipitation Discussion from WPC notes...
most of northeast Colorado will be under a broad area of
QG/isentropic ascent, while in the diffluent left exit region of
a cyclonically curved 110kt jet streak. Low-level upslope should
reinforce our surface moisture through the night, and assuming
this current batch of convection doesn't completely wash out the
instability in the region... scattered to widespread showers and
storms should continue to redevelop and track slowly across the
area overnight.

The upper low should continue to drift eastward and weaken
tomorrow, with low/mid-level south-southeasterly flow increasing.
With widespread moisture in the region... it shouldn't take much
for additional redevelopment of showers and storms tomorrow,
despite surface temperatures remaining in the 60s. It appears the
best axis of moisture/instability/lift will be displaced further
to the north and east... roughly a Cheyenne-Fort Morgan-Limon
line. A few strong storms are possible across the Palmer divide
and plains, but low cloud cover/cool temperatures should limit the
overall threat. We may also need additional hydro products if
some of the higher end guidance has the right idea, but have
punted that to the midnight shift for now.

.LONG TERM...(Monday night through Sunday)
Issued at 340 PM MDT Sun Jun 11 2023

Models show a weak upper closed low over Colorado Monday night
and Tuesday. Wednesday morning through Wednesday night, an upper
trough moves into and across the CWA. The blocking upper high and
upper ridge still stick around to the north and northeast of
Colorado through the period. The synoptic scale energy is neutral
to light upward Monday night through Wednesday night. In the lower
levels the winds are pretty weak through the periods with some
form of upslope especially Monday night and Tuesday.

Fairly decent moisture is expected to continue in place Monday night
through Wednesday night, with precipitable water values just over an
inch east to a half inch for the western CWA. This has been the
case for many days now. There is some CAPE around, and again the
high values are over the mountains, foothills and Palmer Ridge
Monday evening and both late day Tuesday and Wednesday. The QPF
fields show measurable rainfall all night Monday for much of the
CWA and for Tuesday & Tuesday evening for mainly the mountains,
foothills and adjacent plains. Most of the QPF on Wednesday is
over the alpine areas with a bit in the adjacent plains. Again,
flash flooding will continue to be an issue over the burned areas.
Temperatures continue to stay cool-ish Tuesday, with Wednesday's
high expected to be 4-7 C warmer than Tuesday's highs.

For the later days, Thursday through Sunday, models show that upper
blocking ridge to finally slide eastward into the Great Lakes area
by Friday.  For the forecast area, the flow aloft is expect to
increase a bit later Thursday and continue at moderate speeds from
the west through the weekend.  Moisture is still pretty good on
Thursday and Friday, with Saturday and Sunday to dry out somewhat.
Temperatures should stay a bit below normals Thursday and Friday,
then warm to seasonal averages for the weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 927 PM MDT Sun Jun 11 2023

Models eventually show some drainage winds at DIA by 09Z. Most
models show southeasterly winds at DIA on Monday.  Models keep
Stratus over DIA tonight and Monday. Will go with a range of
BKN-OVC015-030 tonight and Monday for ceilings.  Will need to
keep -SHRA or -TSRA going through about 09Z overnight.

&&

.HYDROLOGY...
Issued at 345 PM MDT Sun Jun 11 2023

Convection has started to develop across the southern Front
Range, South Park, and portions of the Palmer Divide this
afternoon. This is the first of a couple of waves of showers and
thunderstorms for the region. Given relatively slow storm motions,
ample instability, and increasing moisture this evening and
overnight... there are some concerns for heavy rainfall rates and
isolated rainfall totals over 2-3 inches. While most locations
will see less than an inch of rain through tonight, high end
potential and low FFG values justify the current Flood Watch.
There is more uncertainty further north, including the Cameron
Peak burn area, where guidance continues to show little
consistency in the convective evolution overnight.

Slow moving scattered thunderstorms are expected across the area
tomorrow, with heavy rain possible wherever these storms develop.
We'll likely need to see how tonight's convection evolves, but a
heavy rain and flash flooding threat will certainly linger for the
burn areas and most of the plains.

Decent rainfall amounts are possible Monday overnight and late
day Tuesday with the flash flooding threat to remain elevated,
especially for the burned areas.

Wednesday through Friday will be only a bit drier, with scattered
showers and thunderstorms still expected over most of the CWA.
There will still be a limited threat of burned area flash
flooding. Moisture decreases for the weekend, with little
flooding expected at this time.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 3 AM MDT Monday for COZ036-039>041-045>047.

&&

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

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1106 AM MDT Sun Jun 11 2023

COZ030>051-121715-
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-
1106 AM MDT Sun Jun 11 2023

...HEAVY RAIN AND SEVERE WEATHER POSSIBLE ACROSS THE DENVER METRO
AND PALMER DIVIDE THROUGH THE EVENING...

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

.DAY ONE...Today and Tonight

Showers and thunderstorms will develop across the mountains and higher
terrain early this afternoon then spread across the plains during
the late afternoon and evening hours. Expect a few severe storms
across the plains, especially from Denver southward through
Douglas, Elbert and Lincoln counties. The strongest storms could
produce hail up to 2 inches in diameter along with damaging winds
and heavy rain. An isolated tornado is also possible.

The flash flood potential will increase today, especially over
Cameron Peak burn area with increasing moisture and instability.
Additional areas of concern will be over the metro and Palmer
Divide where local rainfall rates up to 1 inch in 30 minutes or
less is possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Widespread showers and thunderstorms are expected late day Monday
with showers and thunderstorms likely late day Tuesday. The main
threat will be heavy rains both days. Some storms could produce
small hail as well.

Scattered late day showers and thunderstorms are expected
Wednesday and Thursday. By Friday and Saturday, scattered showers
and thunderstorms are forecast for the alpines areas only. Out on
the plains, coverage will be isolated.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed today after 2 pm, especially
from Denver southward and including the Palmer Divide region.

Special Weather Statement
National Weather Service Denver CO
408 PM MDT Sun Jun 11 2023

COZ041-046-112300-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County CO-
408 PM MDT Sun Jun 11 2023

...A strong thunderstorm will impact portions of northwestern Elbert
County through 500 PM MDT...

At 408 PM MDT, Doppler radar was tracking a strong thunderstorm near
Ponderosa Park, or 26 miles southeast of Denver, moving east at 20
mph.

HAZARD...Winds in excess of 40 mph and penny size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
Elizabeth, Kiowa and Ponderosa Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
east central Colorado.

&&

LAT...LON 3933 10465 3954 10465 3954 10428 3933 10428
TIME...MOT...LOC 2208Z 270DEG 16KT 3943 10462

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

MEIER

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
530 PM MDT Sun Jun 11 2023

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

0528 PM     Hail             7 N Kiowa               39.45N 104.46W
06/11/2023  M0.88 inch       Elbert             CO   Trained Spotter

            Hail covers road to a depth of 1 inch 6
            miles north of Kiowa.

0444 PM     Hail             2 NE Ponderosa Park     39.42N 104.61W
06/11/2023  E0.75 inch       Elbert             CO   Public

            Report from mPING: Dime (0.75 in.).

0302 PM     Hail             2 SSE Highlands Ranch   39.52N 104.96W
06/11/2023  M1.50 inch       Douglas            CO   Public

            Report from mPING: Ping Pong Ball (1.50 in.)
            and measured by the public.

0117 PM     Hail             2 W Keystone            39.60N 106.01W
06/11/2023  E0.75 inch       Summit             CO   Public

            Report from mPING: Dime (0.75 in.).

&&

Preliminary Local Storm Report
National Weather Service Denver CO
919 PM MDT Sun Jun 11 2023

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

0914 PM     Hail             8 ENE Matheson          39.22N 103.84W
06/11/2023  M1.50 inch       Elbert             CO   Trained Spotter

&&

AD

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
923 PM MDT Sun Jun 11 2023

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

0910 PM     Hail             8 SW Limon              39.18N 103.80W
06/11/2023  M1.00 inch       Elbert             CO   Trained Spotter

            Hail accumlatted 2" deep.

&&

Preliminary Local Storm Report
National Weather Service Denver CO
931 PM MDT Sun Jun 11 2023

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

0930 PM     Hail             8 WSW Limon             39.23N 103.83W
06/11/2023  M1.00 inch       Elbert             CO   Trained Spotter

            Accumulated 3-4 deep on highway 24.

&&

AD