Severe Thunderstorm Warning 162, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
542 PM MDT Wed Jul 3 2019

.SHORT TERM...(This evening through Thursday)
Issued at 124 PM MDT Wed Jul 3 2019

A stalled front hanging across the north will combine with a
potent shortwave passing through the High Plains this afternoon
producing a round of severe thunderstorms for much of the region.
Helping to aid in severe potential are dewpoints upwards of 50
deg across the High Plains, strong helicity values in the 0-1 km
layer, CAPE values 2000-3000 J/kg especially across the northern
tier, and a deep instability layer. Widely scattered severe
thunderstorms will be focused mainly east of the northern Laramie
Range and continue to the north and east of a Chugwater-LaGrange-
Scottsbluff-Alliance line this afternoon. With this in mind, a
Severe Thunderstorm Watch has been issued, covering the area just
mentioned. Storms are moving off the Laramie Range already, with
a few borderline severe; they will continue east, ending mainly
before 8 PM MDT. There is a marginal threat of severe
thunderstorms elsewhere over the same time period. Main threats
associated with severe thunderstorms this afternoon will be large
hail up to 2 inches, damaging winds up to 80 mph, areas of heavy
rain, and an isolated tornado or two.

As storms taper off this evening and move to the north and east,
the area will clear out and cool down into the 50s for the
overnight period.

Tomorrow will bring another round of severe weather for most of
the region along and east of the I-25 corridor, falling within a
Slight Risk Convective Outlook per SPC. A similar setup is
forecast as a deep and potent shortwave moves through the region
aloft and a front sets up east to west and slowly drops south
throughout the day. Dewpoints will be quite high, about 55-60
deg, allowing for heightened instability. Convective parameters
will be similar or higher to what we are seeing today with CAPE
upwards of 2-3000 J/kg, strong helicity values in the 0-1 km
layer, and steep lapse rates. The setup tomorrow shows the
potential for supercell storms with its main threats being
damaging winds, large hail, and isolated tornadoes given the
enhanced vorticity along the frontal boundary. Timing for the 4th
looks quite similar to today's beginning shortly after noon and
continuing into the early evening. The potential for another
Severe Thunderstorm Watch is not out of the question.

.LONG TERM...(Friday night through Tuesday)
Issued at 314 AM MDT Wed Jul 3 2019

No changes to previous forecast for the weekend and into early
next week. All models indicate a typical July pattern over the
area as an upper level high develops over the southern plains with
500mb Geopotential heights increasing over 590dm by early next
week. This upper level high isn't all that strong, so Pacific
shortwave energy pushing onshore will continue to push east into
the forecast area, bringing additional chances for afternoon
showers and thunderstorms. At this time, Tuesday looks like the
driest day through the extended as the upper level ridge axis
briefly intensifies northwest of the main high aloft. Scattered
thunderstorms earlier in the weekend will become more isolated as we
head into early next week. However, can not rule out some strong to
severe thunderstorms nearly every day, mainly across far eastern
Wyoming and the northern Nebraska panhandle. Temperatures will be
near normal for this time of the year with high temperatures
generally in the 80s to maybe low 90s across the lower elevations.

Further out, all models and most ensembles show the upper level
high, just east of the four corners region, will retrograde
westward and amplify, allowing a stronger cold front to push south
across the area by mid next week and possibly a return to
unsettled conditions.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 536 PM MDT Wed Jul 3 2019

VFR conditions prevail across the region with southerly winds of
10-15 kts and gusts to 25 knots. TSRA still likely across Goshen
County and to the east across the Nebraska Panhandle. Strong and
erratic winds will be associated with these storms. Localized
turbulence will also be possible. Storms will diminish after
04/02Z.

MVFR to IFR ceilings possible 04/09-15Z for KCYS and points to the
east. Will need to monitor trends. TSRA is likely again after
04/18Z along and east of the I-25 corridor.

&&

.FIRE WEATHER...
Issued at 124 PM MDT Wed Jul 3 2019

With the potential for strong storms and heavy rain over the I-25
corridor and to the east over the next several days, fire weather
concerns remain low. Over the mountains, will see much less storm
activity and lower RH daytime values, through winds will mostly
behave with gusts to 20 mph over the western-most portion of
Carbon County. Still, fuels in that area are remain green.
Potential for dry weather is not within the near-term with active
weather forecasted almost each day.

&&

.HYDROLOGY...
Issued at 124 PM MDT Wed Jul 3 2019

Additional rainfall and snowmelt over the next several days will
bring some rivers and streams back into action stage. Heaviest
rain looks to stay to the east of the mountain ranges, but could
see local flooding issues as the potential for slow moving heavy
rainers set up over low-lying areas.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

SHORT TERM...AB
LONG TERM...TJT
AVIATION...AB
FIRE WEATHER...AB
HYDROLOGY...AB

Hazardous Weather Outlook
National Weather Service Cheyenne WY
236 PM MDT Wed Jul 3 2019

WYZ103>106-109>117-042045-
North Laramie Range-Ferris/Seminoe/Shirley Mountains-
Shirley Basin-Central Laramie Range and Southwest Platte County-
Central Carbon County-North Snowy Range Foothills-
Southwest Carbon County-Sierra Madre Range-
Upper North Platte River Basin-Snowy Range-Laramie Valley-
South Laramie Range-South Laramie Range Foothills-
236 PM MDT Wed Jul 3 2019

This hazardous weather outlook is for portions of south central
Wyoming and southeast Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Widely scattered marginally severe thunderstorms are expected this
afternoon, mainly between noon and 8 PM MDT. Some storms will be
capable of producing strong winds, small hail and heavy rain.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

Chances for afternoon and evening thunderstorms will continue each
day, with strong to severe thunderstorms possible on the Fourth
of July and into the weekend.

.Spotter information statement...

Spotter activation will not be needed.

NEZ002-003-019>021-054-055-095-096-WYZ101-102-107-108-118-119-
042045-
Dawes-Box Butte-Scotts Bluff-Banner-Morrill-Kimball-Cheyenne-
North Sioux-South Sioux-Converse County Lower Elevations-
Niobrara County-East Platte County-Goshen County-
Central Laramie County-East Laramie County-
236 PM MDT Wed Jul 3 2019

This hazardous weather outlook is for portions of western
Nebraska...east central Wyoming and southeast Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Widely scattered severe thunderstorms will be focused mainly
east of the northern Laramie Range and continue to the north and
east of a Chugwater-LaGrange-Scottsbluff-Alliance line this
afternoon. Storms will move off the Laramie Range around noon MDT
and continue east, ending by about 8 PM MDT.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

Severe thunderstorms expected again on the 4th over a similar are,
but extending south to the Colorado border. Timing will be similar
to today's. Chances for afternoon and evening thunderstorms will
continue into the weekend.

.Spotter information statement...

Spotter activation may be needed this afternoon and early evening.

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Special Weather Statement
National Weather Service Cheyenne WY
932 PM MDT Wed Jul 3 2019

NEZ002-003-095-096-040430-
Box Butte NE-Dawes NE-North Sioux NE-South Sioux NE-
932 PM MDT Wed Jul 3 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN BOX BUTTE...
SOUTHWESTERN DAWES AND EAST CENTRAL SIOUX COUNTIES UNTIL 1030 PM
MDT...

At 932 PM MDT, Doppler radar was tracking a strong thunderstorm near
Agate Bed National Monument, or 30 miles northeast of Torrington,
moving northeast at 25 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Crawford, Fort Robinson Campground, Box Butte Campground, Agate Bed
National Monument, Box Butte Dam, Marsland and Fort Robinson.

A Severe Thunderstorm Watch remains in effect until 1000 PM MDT for
the Panhandle of Nebraska.

LAT...LON 4231 10374 4241 10384 4287 10342 4240 10288
TIME...MOT...LOC 0332Z 231DEG 23KT 4236 10375

Lyons

Special Weather Statement
National Weather Service Cheyenne WY
932 PM MDT Wed Jul 3 2019

WYZ101-102-040430-
Converse County Lower Elevations WY-Niobrara County WY-
932 PM MDT Wed Jul 3 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN NIOBRARA AND
NORTHEASTERN CONVERSE COUNTIES UNTIL 1030 PM MDT...

At 932 PM MDT, Doppler radar was tracking a strong thunderstorm 18
miles northwest of Bill, or 21 miles south of Wright, moving east at
25 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Dull Center.

A Severe Thunderstorm Watch remains in effect until 1000 PM MDT for
east central Wyoming.

LAT...LON 4314 10494 4337 10554 4350 10550 4350 10476
TIME...MOT...LOC 0332Z 282DEG 21KT 4345 10542

Lyons