Severe Thunderstorm Warning 15, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
321 PM MDT Mon May 6 2019

.SHORT TERM...(Tonight - Wednesday)
Issued at 252 PM MDT Mon May 6 2019

The main near-term concern is the potential for strong to possibly
severe thunderstorms across portions of southeast WY & the western
NE Panhandle. Strong thunderstorms have already been observed over
parts of the CWA, mainly along the I80 corridor from the Summit to
the NE state line, and points north to Chugwater. It was over this
region that the low-lvl stratus cleared very quickly this morning,
which allowed for temperatures to climb into the mid 60s amid very
steep mid-level lapse rates. This is supporting CAPE values around
1500 J/kg in the presence of 40-50 kts of effective bulk shear. As
has already been the case, expect this to continue to support some
organized updrafts/weak mesocyclones capable of producing marginal
hail up to the size of quarters through early evening. Showers are
likely to continue through the night.

It will remain unsettled on Tuesday given large scale troughing in
place. Widespread clouds & precipitation with persistent low-level
upslope, along w/ cooling thermal profiles may prove supportive of
high temperatures up to 15 degrees cooler than today in areas that
saw more sunshine on Monday. By Tuesday night, we may start to see
some accumulating snowfall in the mountains. More details provided
in the long term discussion below.

.LONG TERM...(Wednesday Night - Monday)
Issued at 352 AM MDT Mon May 6 2019

Much colder temperatures expected late Wednesday into Thursday that
will likely result in precipitation type change over from rain to
snow for elevations above 4000ft. Accumulating snow will be likely
for elevations above 6500 ft but this could be lower if temperatures
trend cooler. Some travel/road impacts along I-80 could be possible
late Wednesday night and into Thursday.

Widespread precipitation will likely be ongoing Wednesday afternoon
into the evening as a cold front shifts south of the region as two
intertwined shortwave troughs shift over Wyoming and Nebraska. Rain
will change over to snow through the afternoon and evening for
elevations above 8000ft and then slowly drop lower into Thursday
morning as H7 temperatures fall into the -3C to -7C range. Vertical
temperature profiles suggest a full snow change over for higher
elevations but a rain/snow mix to barely staying all liquid for the
NE Panhandle. For the Wyoming High Plains, there is some indication
of sleet being possible as the snow growth region may be just dry
enough for super-cooled water droplets to freeze before reaching the
ground. Will need to monitor this period for any possible winter
weather headlines.

The base of the upstream shortwave trough remains over much of
Wyoming through Friday but drier air looks to infiltrate a good
portions of the region on the back side and keep overall
precipitation chances lower. Both operational GFS and ECMWF suggest
shortwave ridging from the west over the weekend and allowing for a
warm up as projected H7 temperatures increase above freezing. H7
temperatures could continue to warm even further into early next
week with pleasant spring conditions. Will need to monitor for the
chance of embedded H5 impulses however, and their respective
mesoscale lift on afternoon convection.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1129 AM MDT Mon May 6 2019

Nebraska Panhandle TAFs will be mainly IFR to LIFR through the
period with a persistent stratus deck over the area and possible
intermittent showers and a few thunderstorms. In addition, late
tonight and early tomorrow morning fog will develop due to
residual moisture. Wyoming TAFs will be VFR to MVFR through the
period. Put in some VCTS based on HRRR guidance for storm
development this afternoon. Ceilings will also lower in
association with precipitation and ample moisture today and
overnight tonight.

&&

.FIRE WEATHER...
Issued at 352 AM MDT Mon May 6 2019

Fire weather concerns expected to remain low for at least the next
few days with a trend to cooler and wetter conditions, especially
by midweek.

&&

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

SHORT TERM...CLH
LONG TERM...JSA
AVIATION...CW
FIRE WEATHER...RE

Hazardous Weather Outlook
National Weather Service Cheyenne WY
1106 AM MDT Mon May 6 2019

WYZ116-117-071715-
South Laramie Range-South Laramie Range Foothills-
1106 AM MDT Mon May 6 2019

This hazardous weather outlook is for portions of southeast
Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms are expected across southeast
Wyoming this afternoon and evening. A few storms may become strong
to marginally severe, with hail up to the size of quarters and
wind gusts in excess of 50 MPH.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Showers and thunderstorms are possible again on Tuesday. Cooler
temperatures may allow for snow accumulations at higher elevations
on Wednesday and Thursday.

.Spotter information statement...

Spotter activation will not be needed. However, spotters are
encouraged to report hazardous weather to the National Weather
Service in Cheyenne.

WYZ112-114-071715-
Sierra Madre Range-Snowy Range-
1106 AM MDT Mon May 6 2019

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms are expected across the higher
terrain of southeast Wyoming today and tonight.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Showers and thunderstorms are possible again on Tuesday. Cooler
temperatures may allow for snow accumulations at higher elevations
on Wednesday and Thursday.

.Spotter information statement...

Spotter activation will not be needed.

WYZ106-107-118-071715-
Central Laramie Range and Southwest Platte County-
East Platte County-Central Laramie County-
1106 AM MDT Mon May 6 2019

This hazardous weather outlook is for portions of southeast
Wyoming.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms are expected across southeast
Wyoming this afternoon and evening. A few storms may become strong
to marginally severe, with hail up to the size of quarters and
wind gusts in excess of 50 MPH.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Showers and thunderstorms are possible again on Tuesday.

.Spotter information statement...

Spotter activation will not be needed. However, spotters are
encouraged to report hazardous weather to the National Weather
Service in Cheyenne.

NEZ002-003-019>021-054-055-095-096-WYZ101>105-108>111-113-115-119-
071715-
Dawes-Box Butte-Scotts Bluff-Banner-Morrill-Kimball-Cheyenne-
North Sioux-South Sioux-Converse County Lower Elevations-
Niobrara County-North Laramie Range-
Ferris/Seminoe/Shirley Mountains-Shirley Basin-Goshen County-
Central Carbon County-North Snowy Range Foothills-
Southwest Carbon County-Upper North Platte River Basin-
Laramie Valley-East Laramie County-
1106 AM MDT Mon May 6 2019

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered showers and thunderstorms are expected across southeast
Wyoming and the western Nebraska Panhandle today.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Showers and thunderstorms are possible again on Tuesday.

.Spotter information statement...

Spotter activation will not be needed.

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