Severe Thunderstorm Warning 261, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
352 PM MDT Mon Aug 19 2024

.KEY MESSAGES...

- Scattered to numerous thunderstorms to track eastward producing
  heavy rain and gusty outflow winds through this evening.

- Some storms may be severe over the plains with large hail,
  strong winds, and localized flooding through mid evening.

- Drier Tuesday, with weaker isolated afternoon/evening storms.
  Increasing coverage of storms again Wednesday through at least
  Friday with locally heavy rainfall from stronger storms.

&&

.SHORT TERM /Through Tuesday/...
Issued at 352 PM MDT Mon Aug 19 2024

A short wave trough rounding the upper level ridge off to the
southeast will trigger scattered to numerous showers and
thunderstorms through mid evening. A moist airmass is in place
across a good part of eastern Colorado with dew points in the 60s
and precipitable water values of 150-170% of normal. MLCAPE
reaches 2000 J/kg. This instability and moisture will fuel the
storms today. Add bulk shear of 30-40 knots and few of the storms
will become severe with large hail and damaging winds. Main threat
for severe thunderstorms will be along and east of a boundary
over eastern Elbert/Arapahoe/Adams Counties. Easterly winds
pushing moisture back into Weld County will also help produce
strong/severe storms here. There is slightly drier air over the
Denver Metro area, so storms are expected to be fewer and not
quite as intense. However, heavy rain and wind gusts to 50 mph
will be possible. The showers and storms progress eastward at a
decent speed and should be east of the area by midnight.

For Tuesday, the upper level ridge rebounds over the Central and
Southern Rockies. This will result in warmer temperatures with
highs reaching the lower to mid 90s across northeast Colorado. The
airmass dries with precipitable water values falling to 90-110 of
normal. Instability falls with MLCAPE under 500 J/kg over the
higher terrain and under 200 J/kg for most of the plains. The
limited moisture and instability combined with warming aloft will
make it difficult showers and storms to develop. Expect isolated
high based showers and thunderstorms Tuesday afternoon, mainly
over the higher terrain and south of I-70 where the slightly
higher instability will be found.

&&

.LONG TERM /Tuesday night through Monday/...
Issued at 352 PM MDT Mon Aug 19 2024

Moisture will start to return as the flow aloft goes southwest
Wednesday. We'll have increasing mid level moisture and some low
level moisture on the plains, but there will still be some dry air
in between. If we get full heating with temperatures near 100 on
the plains, we'd have CAPE up to about 1000 J/kg, but there will
probably be enough cloud cover to take the edge off of this.
Precipitable water is up again, but only 0.8 to 1.2 inches and
there will be enough flow aloft for storms to be moving 15-20 mph.
So there will be a little threat of hail, wind, and heavy rain,
but it may mostly become cloudy and showery.

Thursday looks similar, perhaps a bit more moist and a little
cooler. Again it should be a fairly active day but flood/severe
threats may be limited by clouds and the cooler temperatures.

There's a little better agreement on the development and movement
of a trough from the west coast late in the week to the northern
plains by Monday. Winds aloft start to pick up a bit Friday and
Saturday with some drying. There may be some lift as the trough
axis passes Sunday afternoon or evening, but it looks like that's
in a pretty dry environment. Otherwise the drying trend should
bring diminished storm activity each day. There could be fire
weather issues by Sunday or Monday, although right now winds and
humidity look marginal for any highlights and the recent rains
have improved fuel conditions in many places.

&&

.AVIATION /18Z TAFS through 18Z Tuesday/...
Issued at 1124 AM MDT Mon Aug 19 2024

A round of showers and thunderstorms will roll through the Denver
area this afternoon and early evening. Main time frame is expected
to be 21Z to 01Z. Gusty winds to 40 knots and heavy rain is expected
from the stronger storms. Since there will be numerous thunderstorms
through out northeast Colorado, expect a few outflow boundaries to
produce wind shifts. The shower/storm activity shifts east of the
Denver area 01Z to 03Z.

Once the thunderstorm activity is east of the Denver area, expect
VFR to prevail through tonight and Tuesday. Southerly drainage winds
to 15 knots are expected at DEN and APA. Weak winds are then
expected for Tuesday. Expect isolated late day high-based showers
and thunderstorms Tuesday with gusty outflow winds being the main
impact.

&&

.HYDROLOGY...
Issued at 352 PM MDT Mon Aug 19 2024

Heavy rain is expected from thunderstorms today with precipitable
water values running 150-170% of normal. Flood prone areas, such
as burn scars will see the highest threat. Also, any slow moving
storm or a storm anchored to a boundary will be capable of
producing flooding with the best chance for this to occur over the
eastern plains. Threat heavy rainfall/flooding threat will come
to an end this evening as storms weaken of move off to the east.

A limited burn area flood threat will exist on Wednesday and
Thursday as moisture increases again. Instability will be limited
and storms should be moving. The threat will decrease from Friday
into the weekend though there will still be some storms around.

&&

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

&&

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

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1023 AM MDT Mon Aug 19 2024

COZ030>051-201630-
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-
1023 AM MDT Mon Aug 19 2024

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

.DAY ONE...Today and Tonight

Thunderstorms are likely this afternoon and early evening. Some
storms may be severe over the plains with large hail greater than
an inch and strong winds to 60 mph.

Heavy rainfall is possible which could lead to flash flooding,
especially in flood prone alpine burn areas.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Warm weather will continue through the week with highs in the low
to mid 90s most afternoons. Drier weather is expected for
Tuesday with isolated thunderstorms. Moisture increases again for
Wednesday through Friday with at least scattered thunderstorms
expected each afternoon and evening. A drier trend is expected
again for the weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight, but
reports of heavy rain and severe weather will be appreciated.

Meier/Gimmestad

Special Weather Statement
National Weather Service Denver CO
154 PM MDT Mon Aug 19 2024

COZ044-045-049-192030-
Washington County CO-Morgan County CO-
Central and East Adams and Arapahoe Counties CO-
154 PM MDT Mon Aug 19 2024

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN MORGAN...WESTERN
WASHINGTON AND NORTHEASTERN ADAMS COUNTIES THROUGH 230 PM MDT...

At 154 PM MDT, Doppler radar was tracking a strong thunderstorm
capable of producing a landspout tornado 4 miles north of Shamrock,
or 21 miles south of Fort Morgan, moving east at 15 mph.

HAZARD...Landspouts, wind gusts up to 50 mph, and penny size hail.

SOURCE...Radar indicated.

IMPACT...Landspout tornadoes can damage mobile homes, roofs,
         vehicles, and trees. Outdoor objects may be tossed about.
         Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Gary, Twelve-Mile Corner, Shamrock, Woodrow, and Adena.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

If a tornado is spotted seek shelter inside a sturdy building.

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

&&

LAT...LON 3984 10394 4010 10393 4011 10356 3984 10356
TIME...MOT...LOC 1954Z 267DEG 13KT 3995 10384

LANDSPOUT...POSSIBLE
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

RPK

Preliminary Local Storm Report
National Weather Service Denver CO
224 PM MDT Mon Aug 19 2024

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

0204 PM     Tornado          1 W Shamrock            39.89N 103.83W
08/19/2024                   Adams              CO   Storm Chaser

            Landspout. Estimated to be 4-5 miles
            south/southeast of Prospect Rd and CR 152 in
            eastern Adams County.

&&

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
227 PM MDT Mon Aug 19 2024

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

0221 PM     Hail             3 N Matheson            39.22N 103.98W
08/19/2024  M1.50 Inch       Elbert             CO   Trained Spotter

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

0204 PM     Tornado          1 W Shamrock            39.89N 103.83W
08/19/2024                   Adams              CO   Storm Chaser

            Landspout. Estimated to be 4-5 miles
            south/southeast of Prospect Rd and CR 152 in
            eastern Adams County.

&&

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
319 PM MDT Mon Aug 19 2024

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

0303 PM     Tstm Wnd Dmg     9 SSE Shamrock          39.78N 103.74W
08/19/2024                   Adams              CO   Trained Spotter

            Large tree limb, 6 inches in diameter,
            snapped. Marble hail and torrential rain.

0255 PM     Tornado          10 NNE Deer Trail       39.75N 103.99W
08/19/2024                   Adams              CO   Trained Spotter

            Location approximate.

0221 PM     Hail             3 N Matheson            39.22N 103.98W
08/19/2024  M1.50 Inch       Elbert             CO   Trained Spotter

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

0204 PM     Tornado          1 W Shamrock            39.89N 103.83W
08/19/2024                   Adams              CO   Storm Chaser

            Landspout. Estimated to be 4-5 miles
            south/southeast of Prospect Rd and CR 152 in
            eastern Adams County.

&&

Preliminary Local Storm Report
National Weather Service Denver CO
340 PM MDT Mon Aug 19 2024

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

0335 PM     Flash Flood      7 NNW Simla             39.23N 104.12W
08/19/2024                   Elbert             CO   Dept of Highways

            Flash flooding. County Roads department has
            closded CR 117 from Highway 86 south to CR
            90. Reed Springs Creek is over the road.

&&

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
405 PM MDT Mon Aug 19 2024

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

0339 PM     Hail             8 S Matheson            39.06N 103.95W
08/19/2024  M0.75 Inch       Elbert             CO   Public

            Report from mPING: Dime (0.75 in.).

0335 PM     Flash Flood      7 NNW Simla             39.23N 104.12W
08/19/2024                   Elbert             CO   Dept of Highways

            Flash flooding. County Roads department has
            closded CR 117 from Highway 86 south to CR
            90. Reed Springs Creek is over the road.

0303 PM     Tstm Wnd Dmg     9 SSE Shamrock          39.78N 103.74W
08/19/2024                   Adams              CO   Trained Spotter

            Large tree limb, 6 inches in diameter,
            snapped. Marble hail and torrential rain.

0255 PM     Tornado          10 NNE Deer Trail       39.75N 103.99W
08/19/2024                   Adams              CO   Trained Spotter

            Location approximate.

0221 PM     Hail             3 N Matheson            39.22N 103.98W
08/19/2024  M1.50 Inch       Elbert             CO   Trained Spotter

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

0204 PM     Tornado          1 W Shamrock            39.89N 103.83W
08/19/2024                   Adams              CO   Storm Chaser

            Landspout. Estimated to be 4-5 miles
            south/southeast of Prospect Rd and CR 152 in
            eastern Adams County.

&&