Special Weather Statement, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
533 PM MDT Mon Jun 18 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 154 PM MDT Mon Jun 18 2018

Cool and moist weather expected through the next several days in
an upslope regime behind a cold front. High temperatures will be
quite mild through the period, rarely breaking out of the mid
70s.

There is severe potential this afternoon and evening as a
shortwave trough ejects out of the main closed low centered over
the Great Basin. Deep moist upslope flow has been occurring all
day with dewpoints at CYS rising into the middle 50s as of 2 pm
MDT. Low stratus has slowly lifted and broken up through the
afternoon along the Interstate 25 corridor north to Chugwater.
Solar heating has been slowly working to warm temps into the upper
60s and low 70s. With the moisture in place, 1000-1500 j/kg of SB
CAPE should develop by 21-00z. Boundary layer cumulus to the west
of the Laramie Range has shown signs of deepening through the
early afternoon. Isolated storms are expected to form along the
higher terrain west of I-25 by 22z as these initial updrafts
interact with the deep moisture and ascent. Multiple CAMS show
isolated storms within an environment characterized by 0-3 km
helicity near 300 m2/s2 and moderate low level buoyancy. Backed
low level winds and effective bulk wind difference of 40-50 kts
will favor supercell structures with all hazards possible. The
spatial extent of the threat will be limited to the areas getting
sunshine, as the instability will be somewhat limited. The slight
risk looks spot on with latest thinking.

More showers and storms should develop this evening and overnight
as upper level forcing continues to increase. Widespread rainfall
is expected to develop Tuesday overspreading much of Wyoming.
Heavy rainfall rates could lead to some flash flooding over areas
that saw rain from the last few storms. A Flash Flood Watch was
issued to cover the threat of any flash flooding from training
cells. See Hydro section fro a bit more detail...

.LONG TERM...(Tuesday night through Monday)
Issued at 154 PM MDT Mon Jun 18 2018

The Flash Flood Watch will continue until Wednesday evening when
the last push of moisture makes its way off to the northeast. QPF
values over 1.5 inches with locally higher amounts definitely
warranted some sort of preemptive product, as much of the area
highlight has seen significant rainfall. The long term continues
to look somewhat unsettled as northwesterly flow aloft develops. A
clipper will dive down Friday and Saturday bringing a chance for
showers and thunderstorms. A larger upper trough moves in early
next week bringing more active weather. Temperatures will recover
slightly thursday and Friday as mostly clear skies are expected.
however, daytime highs wont be nearly as warm as they have been
for most of june with highs 10 to 15 degrees above normal. beyond
the extended period ridging looks to take shape which should keep
the weather mostly quiet and warm.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 525 PM MDT Mon Jun 18 2018

Wyoming TAFS...VFR at Rawlins until 08Z, with wind gusts to 30
knots through 03Z, then MVFR from 08Z to 14Z, then VFR. Wind gusts
to 23 knots after 19Z. VFR at Rawlins until 05Z with thunderstorms
in the vicinity, then MVFR until 15Z, then VFR. Wind gusts to 25
knots through 01Z, and gusts to 25 knots after 19Z. VFR at
Cheyenne until 03Z with wind gusts to 20 knots and thunderstorms
in the vicinity, then MVFR until 05Z, then IFR until 15Z, then
VFR. Wind gusts to 20 knots after 19Z.

Nebraska TAFS...Occasional IFR at Chadron until 03Z, otherwise
MVFR until 09Z, then IFR until 15Z, then MVFR with possible
thunderstorms from 19Z to 23Z. MVFR at Alliance until 07Z, then
IFR until 15Z, then MVFR with a chance of thunderstorms between
19Z and 23Z. MVFR at Scottsbluff until 06Z, then IFR until 15Z,
then MVFR with a chance of thunderstorms from 19Z to 23Z. MVFR at
Sidney until 08Z, then IFR until 15Z, then MVFR with a chance of
thunderstorms from 19Z to 23Z.

&&

.FIRE WEATHER...
Issued at 154 PM MDT Mon Jun 18 2018

Fire Weather concerns are low through the period as a cool and
moist weather pattern continues. Afternoon RH will be well above
35%. Wetting rain will be possible through Thursday.

&&

.HYDROLOGY...
Issued at 154 PM MDT Mon Jun 18 2018

...Flash Flood Watch from Tuesday morning through Wednesday...

A stalled frontal boundary in combination with a slow moving upper
level low will set the stage for heavy rain across southeastern
Wyoming and northwestern Nebraska. The ground is saturated given
the recent wet pattern with as much as 3 inches falling in
Converse, Niobrara, and Goshen counties. Another 1.5 to 2 inches
of QPF through Thursday morning suggest flash flooding will be a
possibility.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flash Flood Watch from Tuesday morning through Wednesday
     afternoon for WYZ101-102-107-108.

NE...Flash Flood Watch from Tuesday morning through Wednesday
     afternoon for NEZ002-003-019-095-096.

&&

SHORT TERM...LYONS
LONG TERM...LYONS
AVIATION...RUBIN
FIRE WEATHER...LYONS
HYDROLOGY...LYONS

Hazardous Weather Outlook
National Weather Service Cheyenne WY
533 AM MDT Mon Jun 18 2018

NEZ002-003-019>021-054-055-095-096-WYZ101>103-106>108-116>119-
191145-
Dawes-Box Butte-Scotts Bluff-Banner-Morrill-Kimball-Cheyenne-
North Sioux-South Sioux-Converse County Lower Elevations-
Niobrara County-North Laramie Range-
Central Laramie Range and Southwest Platte County-
East Platte County-Goshen County-South Laramie Range-
South Laramie Range Foothills-Central Laramie County-
East Laramie County-
533 AM MDT Mon Jun 18 2018

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

.DAY ONE...TODAY AND TONIGHT

A few thunderstorms are possible late this afternoon and early
evening across the high plains of southeast Wyoming and the
western Nebraska Panhandle. Some storms could become strong to
severe, with large hail and damaging winds. A tornado or two is
also possible.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

A few strong to severe thunderstorms are possible again on
Tuesday.

.Spotter information statement...

Spotter activation is possible between 3 PM and 10 PM MDT today.

WYZ104-105-109>115-191145-
Ferris/Seminoe/Shirley Mountains-Shirley Basin-
Central Carbon County-North Snowy Range Foothills-
Southwest Carbon County-Sierra Madre Range-
Upper North Platte River Basin-Snowy Range-Laramie Valley-
533 AM MDT Mon Jun 18 2018

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

.DAY ONE...TODAY AND TONIGHT

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

The probability for widespread hazardous weather is low.

.Spotter information statement...

Spotter activation will not be needed.

Special Weather Statement
National Weather Service Cheyenne WY
409 PM MDT MON JUN 18 2018

WYZ106>108-182300-
East Platte County WY-
Central Laramie Range and Southwest Platte County WY-
Goshen County WY-
409 PM MDT MON JUN 18 2018

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL GOSHEN AND
SOUTHEASTERN PLATTE COUNTIES UNTIL 500 PM MDT...

At 408 PM MDT, Doppler radar was tracking a strong thunderstorm 11
miles southwest of Bordeaux, or 17 miles south of Wheatland, moving
northeast at 30 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Slater, Chugcreek, Bordeaux and Y-O Ranch.

This includes Interstate 25 in Wyoming between mile markers 59 and
76.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Cheyenne.

&&

LAT...LON 4173 10506 4180 10512 4208 10491 4191 10441
TIME...MOT...LOC 2208Z 228DEG 25KT 4180 10504

Claycomb

Special Weather Statement
National Weather Service Cheyenne WY
514 PM MDT MON JUN 18 2018

WYZ106>108-190000-
East Platte County WY-
Central Laramie Range and Southwest Platte County WY-
Goshen County WY-
514 PM MDT MON JUN 18 2018

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL GOSHEN AND
SOUTHEASTERN PLATTE COUNTIES UNTIL 600 PM MDT...

At 514 PM MDT, Doppler radar was tracking a strong thunderstorm near
Slater, or 16 miles southeast of Wheatland, moving northeast at 30
mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

Locations impacted include...
Yoder, Slater and Veteran.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4179 10479 4193 10486 4218 10449 4191 10426
      4184 10449
TIME...MOT...LOC 2314Z 241DEG 21KT 4189 10473

Allen

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
543 PM MDT MON JUN 18 2018

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

0515 PM     HAIL             7 NNE CHUGWATER         41.84N 104.75W
06/18/2018  M0.88 INCH       PLATTE             WY   STORM CHASER

            THE DURATION OF THE HAIL EVENT WAS 10
            MINUTES.

&&

WM

Special Weather Statement
National Weather Service Cheyenne WY
633 PM MDT MON JUN 18 2018

NEZ019-WYZ108-190115-
Scotts Bluff NE-Goshen County WY-
633 PM MDT MON JUN 18 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN SCOTTS BLUFF AND
SOUTHEASTERN GOSHEN COUNTIES UNTIL 715 PM MDT...

At 632 PM MDT, Doppler radar was tracking a strong thunderstorm over
Hawk Springs, or 22 miles south of Torrington, moving east at 25 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
La Grange, Hawk Springs Recreation Area, Hawk Springs Campground and
Hawk Springs.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 4182 10436 4180 10405 4160 10406 4172 10439
TIME...MOT...LOC 0032Z 289DEG 20KT 4175 10427

Claycomb