Special Weather Statement, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
605 PM MDT Sun Aug 4 2019

.SHORT TERM...(This evening through Tuesday)
Issued at 200 PM MDT Sun Aug 4 2019

Forecast concerns deal with thunderstorm chances today and Monday.
Severe storms possible.

Currently...Water vapor imagery showing Four Corners high firmly
in place with quite a flow of monsoonal moisture moving across
Colorado and Wyoming this afternoon. 12Z Grand Junction sounding
this morning at 1.04 inches...Riverton at 0.69 inch...both show
increases over the past 12 hours. Appears to be an upper level
shortwave working through the periphery of the ridge in southwest
Wyoming at 1PM that could help provide increased coverage of
storms this afternoon and evening. At the surface...southeast
winds in the Panhandle with 1PM dewpoints in the mid 50s. A
surface front is being analyzed over northeast Wyoming back into
southwest Montana this afternoon.

Looking at better coverage of storms this afternoon and evening
over Saturday. Still looking at two waves of showers. First
developing on short term guidance (HRRR and HiRes) after 21Z that
persists until maybe 00/01Z. Second later this evening as the
surface front approaches form northwest to southeast. Latest SPC
mesoanalysis showing a pretty much uncapped environment across
CWA with surface based CAPE in the Panhandle 2500 to 3000 J/KG.
Thinking the storms that form east of Laramie Range will move east
into the Panhandle into this better instability after 22Z. Pretty
warm column with 700mb temperatures of +15 to +16C...so hail may
be a challenge this afternoon. High based storms with inverted V
soundings indicating more of a wind threat today.

By this evening...looking at the front approaching from the north
and northeast with winds behind the front shifting northeast.
Looks to be quite a bit of shower activity. Looks like these
storms may last til at least midnight...if not longer.

CWA is going to be in northwest flow Monday with another upper
shortwave moving through this flow and interacting with the
surface boundary Monday afternoon. Upper jet finger of 70 to 75kts
Monday afternoon could result in better shear for more organized
severe convection. Colder 700mb temperatures Monday afternoon
should result in steeper mid level lapse rates.

Repeat of storms on Tuesday...though maybe not as much coverage
as surface front begins to move east in central Nebraska.

.LONG TERM...(Tuesday night through Sunday)
Issued at 200 PM MDT Sun Aug 4 2019

Wednesday...Weak to moderate west northwest flow aloft prevails.
Looks like adequate low and mid level moisture, combined with a low
level convergence axis to initiate scattered showers and
thunderstorms, most likely from Laramie and Cheyenne northward to
Lusk.

Thursday...As the ridge axis aloft moves over western Nebraska,
increasing low and mid level moisture moves over our counties,
producing an uptick in the coverage of late day showers and
thunderstorms.

Friday...A bit less coverage of late day showers and thunderstorms
as some drier air advects into our counties, though still enough
moisture for isolated to scattered afternoon and evening
thunderstorms mainly over far southeast Wyoming.

Saturday...Slightly drier in the low and mid levels, thus expect
less coverage of showers and thunderstorms, with the best coverage
over and near our southern mountains.

Sunday...Low levels dry out somewhat due to west winds, and with 700
mb temperatures rising to near 18 Celsius, thunderstorms will have
trouble initiating, thus only isolated thunderstorms possible near
the higher terrain.

&&

.AVIATION...(For the 00Z TAFS through Monday afternoon)
Issued at 605 PM MDT Sun Aug 4 2019

Expect VFR conditions tonight across the western Nebraska terminals
with daytime thunderstorms moving east of the area and no fog
expected through early Monday morning. Further west, tracking an
area of showers and thunderstorms between KRWL and KLAR this
evening. These storms will likely impact KLAR in the next few hours,
and possibly KCYS between 01z-04z if they hold together.  Brief MVFR
conditions are expected with occasional lightning.

&&

.FIRE WEATHER...
Issued at 200 PM MDT Sun Aug 4 2019

Minimal fire weather concerns across southeast Wyoming and
Nebraska Panhandle with monsoonal moisture in place. Looks like
just about every area should see chances for wetting rains this
afternoon through Monday with the moisture in place. Afternoon
humidity expected to stay well above critical levels for every
area with good to excellent overnight recoveries. Unsettled
weather through the upcoming week with daily chances for showers
and thunderstorms. Begin to dry out the end of next week...so we
could start to see increasing fire weather concerns by Friday.

&&

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

SHORT TERM...GCC
LONG TERM...RUBIN
AVIATION...TJT
FIRE WEATHER...GCC

Hazardous Weather Outlook
National Weather Service Cheyenne WY
339 AM MDT Sun Aug 4 2019

WYZ103>107-109>118-050945-
North Laramie Range-Ferris/Seminoe/Shirley Mountains-
Shirley Basin-Central Laramie Range and Southwest Platte County-
East 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-
Central Laramie County-
339 AM MDT Sun Aug 4 2019

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

.DAY ONE...TODAY AND TONIGHT

General, non-severe thunderstorms possible this afternoon into the
early evening. Small hail and brief gusty winds be main concern.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

General thunderstorm to marginal risk of severe weather possible
over the next couple days with hail, winds, and heavy rainfall
biggest concerns.

.Spotter information statement...

Spotters are encouraged to report their precipitation, wind
damage, and/or hail to the National Weather Service Office in
Cheyenne, Wyoming.

NEZ002-003-019>021-054-055-095-096-WYZ101-102-108-119-050945-
Dawes-Box Butte-Scotts Bluff-Banner-Morrill-Kimball-Cheyenne-
North Sioux-South Sioux-Converse County Lower Elevations-
Niobrara County-Goshen County-East Laramie County-
339 AM MDT Sun Aug 4 2019

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

.DAY ONE...TODAY AND TONIGHT

Strong to severe thunderstorms possible late afternoon into the
evening. Strong, damaging winds, large hail and locally heavy rain
are the main threats.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

General thunderstorm to marginal risk of severe weather possible
over the next couple days with hail, winds, and heavy rainfall
biggest concerns.

.Spotter information statement...

Spotters are encouraged to report their precipitation, wind
damage, and/or hail to the National Weather Service Office in
Cheyenne, Wyoming.

Special Weather Statement
National Weather Service Cheyenne WY
812 PM MDT Sun Aug 4 2019

WYZ101-102-050300-
Converse County Lower Elevations WY-Niobrara County WY-
812 PM MDT Sun Aug 4 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN NIOBRARA AND
NORTHEASTERN CONVERSE COUNTIES UNTIL 900 PM MDT...

At 811 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 7 miles northwest of Dull Center to 11 miles
west of Manning Ranch. Movement was southeast at 35 mph.

Wind gusts of 50 to 55 mph will be possible with these storms.

Locations impacted include...
Dull Center, Lance Creek and Manning Ranch.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4285 10454 4300 10519 4350 10513 4350 10439
TIME...MOT...LOC 0211Z 294DEG 30KT 4348 10507 4301 10514

Lyons

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