Severe Thunderstorm Warning 465, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
254 PM MDT Mon Aug 28 2023

.SHORT TERM...(This evening through Tuesday)
Issued at 223 PM MDT Mon Aug 28 2023

Radar shows scattered showers and storms mainly over the
mountains and foothills this afternoon. They are producing brief
heavy rainfall and small hail. The storms that move off the
foothills and onto the plains are struggling to maintain their
strength and most are dissipating quickly. This is likely due to
an inversion around 650 mb that is showing up on the ACARS
soundings. Some additional daytime heating will help to overcome
this inversion but, overall, it will limit the storm coverage
especially east of I-25. These showers and storms will continue
through the early evening and then the lack of instability will
result in them dissipating.

Skies will clear tonight with usual drainage wind patterns. Low
temperatures will be around normal.

Subsident flow will be over Colorado on Tuesday as the axis of a
ridge pushes out a shortwave trough. Sounding show it will be a
very stable airmass with an inversion near 550 mb. Much drier air
will be in place and the vast majority of the forecast area will
be dry tomorrow. The only exception will be the southern foothills
and South Park where a couple weak showers could form. The mostly
sunny conditions will allow temperatures to warm up a couple of
degrees compared to today's temperatures. Highs will still be
below normal as it will be a gorgeous day.

.LONG TERM...(Tuesday night through Monday)
Issued at 223 PM MDT Mon Aug 28 2023

Wednesday, the upper ridge flattens in response to a shortwave
trough moving across the northern portion of the CONUS. As a result,
weak westerly subsident flow aloft works into the region keeping it
mainly dry. Marginal instability develops in the mountains & Palmer
Divide which can support low chances (< 30%) for scattered showers
and thunderstorms in the afternoon. Within the drier airmass,
temperatures increase back into the low 90s across the lower
elevations.

Thursday into Friday, an upper level trough pushes into the west
coast, helping induce southwesterly flow aloft across Colorado.
Ensemble guidance favors another "mainly dry" day with low chances
for scattered showers and storm over the high country. There is an
agreeable signal for increased moisture Friday and through the
weekend as monsoonal moisture re-enters the region. Ensemble
guidance shows a plume of above normal moisture being advected into
Colorado within the southwesterly flow aloft. This will bring
increased chances of showers/storms over the mountains(~40-60%),
foothills, and western Palmer Divide Friday through the weekend.
Adjacent plains will have low chances (< 30%) each day. Temperatures
continue to be above normal across the lower elevations with highs
in the lower 90s through the weekend.

Monday, ensemble guidance shows a general trend of the trough to the
west moving across Colorado. However, there are differences among
solutions regarding positioning and timing of this wave. Depending
on the solution, there could be increased shower/storm chances for
the high country and parts of the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1150 AM MDT Mon Aug 28 2023

Lows clouds have been impacting DEN and APA this morning. These
low clouds may continue to obstruct runways visuals which could
impact arrival rates at DEN through 19Z. The forecast is still on
track for storms to form over the higher terrain and move through
the terminals late this afternoon and evening. The VCTS was moved
up to 19Z at BJC since storms could form earlier than expected
there. The primary impact from these storms will be gusty winds
with gusts up to 35 knots. The atmosphere will be stabilized
later this evening which will put and end to the storms. Normal
drainage winds will develop tonight with light winds and VFR
conditions tomorrow.

&&

.HYDROLOGY...
Issued at 223 PM MDT Mon Aug 28 2023

There is a threat of flash flooding this afternoon as storms
producing brief heavy rain are currently going over the recent
burn areas.

On Tuesday, there is no threat of flash flooding since it will be
dry.

The threat for flash flooding over the burn areas will be little to
none Wednesday. There is a decent chance these drier conditions
prevail Thursday as well resulting in very little risk for flash
flooding over the burn areas. Above normal moisture re-enters the
region by Friday, continuing through the weekend resulting in
increased chances for showers and thunderstorms over mainly the high
country. This may increase the threat for flash flooding over the
burn areas.

&&

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

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

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1109 AM MDT Mon Aug 28 2023

COZ030>051-291715-
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-
1109 AM MDT Mon Aug 28 2023

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

.DAY ONE...This Afternoon and Tonight

Scattered to widespread showers and thunderstorms are expected
for the forecast area this afternoon and evening. The highest
coverage will be over the mountains and foothills. The risk of
flash flooding for the burn areas will be limited. Some storms may
have small hail and gusty winds along with heavy rain.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

A drier and warmer pattern will be in place, from Tuesday through
Thursday, with only a few afternoon thunderstorms over the higher
terrain mainly south of I-70.

Moisture increases Friday, continuing through the weekend
resulting in increased chances of afternoon showers and
thunderstorms, mainly over the high country. This may also bring
an increased risk for flash flooding over the burn areas.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.

Special Weather Statement
National Weather Service Denver CO
308 PM MDT Mon Aug 28 2023

COZ033-035-282145-
Larimer and Boulder Counties Between 6000 and 9000 Feet CO-
South and East Jackson/Larimer/North and Northeast Grand/Northwest
Boulder Counties Above 9000 Feet CO-
308 PM MDT Mon Aug 28 2023

...A strong thunderstorm will impact portions of south central
Larimer County through 345 PM MDT...

At 308 PM MDT, Doppler radar was tracking a strong thunderstorm 4
miles west of Glen Haven, or 26 miles west of Fort Collins, moving
southeast at 20 mph.

HAZARD...Winds in excess of 40 mph and half inch 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...
Estes Park, Glen Haven, and Drake.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4044 10564 4053 10556 4042 10530 4031 10544
      4038 10557
TIME...MOT...LOC 2108Z 304DEG 17KT 4045 10554

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

HEAVENER

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