Severe Thunderstorm Warning 91, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
207 PM MDT Tue Jul 12 2022

.SHORT TERM...(This evening through Wednesday)
Issued at 151 PM MDT Tue Jul 12 2022

The upper level high pressure system begins to weaken and progresses
south. This pattern will allow a shortwave to bring moisture
through a northwesterly flow a loft. 700mb levels will increase to
17-19C now through this evening along the I-25 corridor. Models
keep 700mb winds weak near 10-20kts and low level winds 20-25kts.
This environment is lacking shear and with wind profiles at the
lower levels increasing, storm motion will move much faster than
anticipated. Thunderstorm development will remain for the
northwestern mountains and valleys limited due to less MLCAPE
values near 400-500 J/kg and substantial CIN near 400 J/kg. The
latest run of the HREF and NAMNEST have similar placement on
thunderstorms which seem very plausible given the ML CAPE values
near 800-900 J/kg. This will lead to the eastern plains and urban
corridor main time window 4-7 PM for our CWA. Tonight,
temperatures will drop to the mid 50s to lower 60s for the
foothills, urban corridor, and plains. Mountains and valleys will
drop to the mid 40s to lower 50s.

Tomorrow, thunderstorm develop will be limited as drier area and
weak shear impact the entire region. An isolated thunderstorm
cannot be ruled out mainly for the high country. Cloud cover
increases by Wednesday morning.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 151 PM MDT Tue Jul 12 2022

The upper level ridge continues to inch eastward and build over
Colorado Thursday. In response, the plume of above-normal moisture
begins to extend back into the region raising precipitable water
values. Values increase to 0.9-1" for the plains and 0.6-0.8" over
the mountains. Combined with marginal instability, expect to see an
increase in shower/storm chances with the best chances over the
higher terrain. The I-25 corridor/adjacent plains may see isolated-
scattered shower/storm chances. Temperatures will be above normal
with highs in the upper 90s across the plains/Urban Corridor, around
100 for the northeast plains, and 60s to 80s for the high country.

Aside from differences in timing, most model guidance indicates the
passage of a shortwave trough over the northern portion of the ridge
Friday-Saturday. The ECMWF ensemble signals a distinct increase in
precipitable water values during this time period with values
upwards of 0.9 inches over the mountains. This is expected to
promote increased coverage of showers/thunderstorms over the higher
terrain with lower chances over the adjacent plains. Weaker winds
aloft will support slower storm motions thus increasing the threat
for flash flooding over the burn areas. Increased cloud cover may
potentially tamper highs a bit with highs in the mid 90s for most of
the plains and upper 90s for the northeast corner.

Into the weekend, the upper ridge persists over the region.
Anomalous moisture continues to extend into the region Saturday with
marginal instability to support showers/storms over the higher
terrain with chances for the I-25 corridor. Model and ensemble
guidance hints at drier and more stable air in place for Sunday.
Expect highs a degree or two warmer than Saturday and slightly lower
PoPs and coverage for the high country.

There is a general consensus that ridging aloft will continue into
early next week. There is some variance among ensemble guidance in
the moisture availability with the GFS ens mean drier than the ECMWF
ens. Overall, scattered showers and storms will be possible with
better chances over the high country. Coverage will be more
uncertain. Warm temperatures continue with a good chance for 90s
across the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1130 AM MDT Tue Jul 12 2022

The Denver cyclone seems to dissipate north of KDEN and KBJC by
the afternoon. Thunderstorm chances will increase near all
terminals by 21-23Z with supportive thunderstorm conditions
favoring the areas east of the I-25 corridor which will increase
wind speeds for all sites. By 01-02Z, thunderstorms will exit all
terminal sites where winds will continue from the southeast
through normal drainage tonight into Wednesday morning. Wednesday
afternoon, the thunderstorm chances for all terminals remain low
due to dry air but outflows from these storms may produce gusty
winds through late Wednesday afternoon. VFR conditions will
continue for all sites.

&&

.HYDROLOGY...
Issued at 151 PM MDT Tue Jul 12 2022

Scattered thunderstorms will push eastward through this evening thus
the threat of flash flooding for the burn areas remains low.
Isolated thunderstorms could produce heavy rainfall across the
plains late this evening as PWATs reach 0.80-0.90 but storm motion
favors fast moving thunderstorms through Wednesday morning.

A persistent ridge aloft with a plume of above normal moisture
will be in place Thursday through at least the weekend. Combined
with weaker flow aloft under the ridge and modest instability,
this will support slower moving storms capable of localized heavy
rainfall. This will at least result in a low/limited threat for
flash flooding over the burn areas. There is potential for an
additional bump up in precipitable water values in the Friday-
early Saturday timeframe with values upwards of 0.9 inches for the
mountains. Although confidence isn't high, this scenario may lead
to an elevated threat that day.

&&

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

SHORT TERM...AD
LONG TERM...Mensch
AVIATION...AD
HYDROLOGY...AD/Mensch

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1041 AM MDT Tue Jul 12 2022

COZ030>051-131645-
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-
1041 AM MDT Tue Jul 12 2022

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

.DAY ONE...Today and Tonight

Scattered thunderstorms and showers will develop in the mountains
and valleys this afternoon. Best time window for these storms
begins at 1 PM to 7 PM this evening. These conditions will bring a
limited threat of flash flooding to the burn areas. Thunderstorms
will become more isolated after crossing the I-25 corridor.

Tonight, overnight lows will drop to the mid 50s to lower 60s for
the foothills, urban corridor, and plains. Mountains and valleys
will drop to the mid 40s to lower 50s. Clouds will clear by late
evening.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

It will be very warm with highs in the mid to upper 90s most days
across northeast Colorado. A few places could exceed 100 degrees.
Over the foothills and mountains, daily afternoon and evening
thunderstorms are expected. Heavy rain will be possible with some
of the storms. This could produce flash flooding and debris flows
over burn areas.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to send reports of rain, wind, or hail.

Special Weather Statement
National Weather Service Denver CO
221 PM MDT Tue Jul 12 2022

COZ041-122100-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
221 PM MDT Tue Jul 12 2022

...A strong thunderstorm will impact portions of southeastern Douglas
and west central Elbert Counties through 300 PM MDT...

At 221 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles west of Elbert, or 26 miles north of Colorado Springs, moving
east at 20 mph.

HAZARD...Winds in excess of 40 mph and pea 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...
Elbert.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3913 10478 3933 10478 3936 10449 3913 10437
TIME...MOT...LOC 2021Z 281DEG 18KT 3924 10467

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

RODRIGUEZ

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