Severe Thunderstorm Warning 178, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
302 PM MDT Thu Jun 22 2023

.SHORT TERM...(This evening through Friday)
Issued at 302 PM MDT Thu Jun 22 2023

Another active afternoon and evening shaping up with severe
storms and potential flooding with storms from the Front Range and
stretching over the northeast plains. Severe thunderstorm watch
has also already been issued for much of the area as well as
Flood watch. First report of golf ball sized hail already reported
in Evergreen.

Currently, scattered thunderstorms already developing over
the mountains and foothills. In addition, a strong outflow boundary
is moving westward back over the Front Range is ushering in
higher dewpoints into the lower 60s along with easterly winds of
20 to 30 mph. KFTG VAD winds also showing deepening easterly low
level winds up to 700mb. Latest sounding taken from CSU (7 miles N
of Nunn) showing surface based CAPE values of 2700j/kg with
precipitable water values close to .8". Expect pw values over the
plains are close to an inch or a bit higher. Still just a bit of
cin still to overcome around the 700mb layer to overcome over the
Front Range. Mid level drying also indicates from past research
showing possibility for potential for large hail. Main threats
will be large hail but considering the increasing low level
southeast flow won't be surprised to see a few tornadoes as well.
Given latest satellite imagery, best heating and potential
instability over east of Denver and across eastern Adams,
Arapahoe, and Morgan counties.

Storms will decrease from west to east this evening with most of the
activity diminishing close to midnight, but still could still be a
few storms over the far northeast plains.

For Friday, expecting a much drier day at least for the mountains
and adjacent plains as upper trof and low lifts out in northern high
plains by Friday evening. Could still be a few strong to severe storms
over the far northeast plains with continued strong instability. SPC
has a slight chance for severe over the northeast plains and this
looks reasonable.

.LONG TERM...(Friday night through Thursday)
Issued at 302 PM MDT Thu Jun 22 2023

Quieter weather is coming to north central and north east Colorado.
Late Friday evening there could be a few lingering thunderstorms
across the northeast corner of Colorado.  Those storms could be
severe given favorable ingredients in place for rotating storms. The
rest of the area should be in subsident and drying flow.  Any
lingering showers should be gone before sunrise Saturday.  Zonal
flow is the norm Saturday and Sunday with a ridge axis pretty much
overhead.  PW amounts drop dramatically Saturday to 0.2-0.4" area-
wide.  Thus, no convection expected anywhere on Saturday.  On Sunday
a very small increase in PW up to maybe 0.5" across the eastern
quarter of Colorado, less to the west, but it still looks too
dry/stable for any shower activity across our area.  700 mb temps
warm to +12-14 degC, but there is a little cooling on Sunday with
+10-12 degC with the passage of a cool front across the plains.
This will support highs in low to mid 80s across the plains and
I-25 corridor, upper 60s to low 70s in the mountain valleys on
Saturday. With the slight cooling on Sunday, expect highs in the
uppers 70s to around 80 across the plains and I-25 corridor. The
cooling misses the mountains and they should be similar if not a
degree or two warmer than on Saturday. Overall expect excellent
weather for any outdoor activity.

Monday through Wednesday a short wave trough looks to move from
northern California across the northern Rockies and into the
Northern U.S. Plains.  Southwest flow and warm advection will be the
norm for the first half of next week.  700 mb temps warm to +14 to
+16 degC on Monday, then to +16 to +18 degC on Tuesday.  Wednesday's
temps should be similar. PW values look to remain less than we've
seen this week, with 0.5-0.7" across the plains, and 0.3" or so
in the high country. There is a fair amount of instability with
not much CIN across the northeast corner of Colorado each evening.
Only isolated thunderstorms look to be possible across the East
Slopes of the Front Range and adjacent plains. This looks to be a
more typical pattern of diurnal convection for late June. High
temperatures should be in the mid to upper 80s across the lower
elevations, and 70s in the mountain valleys. With the approach of
the short wave trough, southwest winds will increase especially
across the high country and the mountain valleys. In most years
we'd be extremely concerned about fire weather given the hot/dry
conditions and wind 20-25 gusting to 35 mph expected Tuesday and
Wednesday afternoons in the foothills and mountain valleys.
However, fuels are still very green across the area. The one area
that may be close to drier fuels would be South Park given they
haven't had and exceptionally wet June. Something to watch.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1151 AM MDT Thu Jun 22 2023

Expect another round of thunderstorms this afternoon and evening
with best window for storms between 21-01z with large hail,
erratic and strong winds and heavy rain. Passing storms may bring
temporary MVFR conditions to airports. Weak boundary pushing back
west towards airports with winds shifting a bit more east and
northeast. This direction temporary which would then become more
southeast and gusty up to 30kt leading up to thunderstorms.
Improving conditions this evening as main thunderstorm complex
shifts east of terminals.

&&

.HYDROLOGY...
Issued at 302 PM MDT Thu Jun 22 2023

Flood watch has been issued for good chunk of the plains through
midnight with strong to severe storms expected with large hail and
heavy rain. Already much of the area saturated from last night's
storms and won't take much of additional heavy rain to cause more
flash flooding. Creeks and streams also running high over much of
the area.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight MDT tonight for COZ039>041-043>046-
049.

&&

SHORT TERM...Entrekin
LONG TERM...Schlatter
AVIATION...Entrekin
HYDROLOGY...Entrekin

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1036 AM MDT Thu Jun 22 2023

COZ030>051-231645-
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-
1036 AM MDT Thu Jun 22 2023

...SEVERE STORMS AND FLOODING POSSIBLE...

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

.DAY ONE...Today and Tonight

Scattered showers and thunderstorms are expected again this
afternoon and evening with strong to severe storms possible
across the urban corridor and plains. Large hail, damaging wind
gusts, heavy rain, and an isolated tornado are all possible with
these storms. Storms will begin earlier today, generally noon to 3
pm over the mountains and adjacent plains, then spreading eastward
during the late afternoon and evening.

Many areas on the plains are already saturated and thus more
sensitive to additional rainfall, including rivers and creeks. A
flood watch has been issued from noon until midnight tonight for
the Denver metro area, and areas south and east of Denver, across
the Palmer Divide, and other portions of the eastern plains. There
is also a limited threat for flash flooding over the burn areas,
mainly Cameron Peak.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Trending toward drier Friday through mid-week next week. There is
a chance for scattered thunderstorms Friday afternoon with a few
severe storms possible; however, storms will be lesser in
coverage. Weekend remains fairly dry. Fire weather conditions
return to the high country/Park County Friday through the weekend
with low relative humidity and breezy conditions. Elevated fire
weather conditions creep into the adjacent plains Saturday. Recent
rain should likely limit these concerns.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed today and this evening,
generally after 1 pm. Hail, heavy rain, flooding and tornado
reports will be appreciated.

Preliminary Local Storm Report
National Weather Service Denver CO
336 PM MDT Thu Jun 22 2023

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

0325 PM     Tornado          2 WNW Highlands Ranch   39.56N 105.00W
06/22/2023                   Douglas            CO   Trained Spotter

            Corrects previous tornado report from 2 WNW
            Highlands Ranch. Report via twitter video.

&&

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Preliminary Local Storm Report
National Weather Service Denver CO
415 PM MDT Thu Jun 22 2023

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

0333 PM     Hail             1 SW Littleton          39.59N 105.03W
06/22/2023  M1.50 inch       Arapahoe           CO   Trained Spotter

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

&&

Preliminary Local Storm Report
National Weather Service Denver CO
416 PM MDT Thu Jun 22 2023

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

0325 PM     Hail             3 WSW Aurora            39.69N 104.87W
06/22/2023  M1.75 inch       Arapahoe           CO   Trained Spotter

&&