Special Weather Statement, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
1158 AM MDT Tue Aug 14 2018

.UPDATE...
Issued at 504 AM MDT Tue Aug 14 2018

Please see latest 12z Aviation Discussion

UPDATE Issued at 343 AM MDT Tue Aug 14 2018

Areas of dense fog formed across portions of the southern NE
Panhandle overnight. Visibility was a quarter mile at Sidney.
Issued a Dense Fog Advisory for Morrill and Cheyenne counties
until 9 AM.

&&

.SHORT TERM...(Today through Wednesday night)
Issued at 330 AM MDT Tue Aug 14 2018

Overnight water vapor loop depicted a upper ridge over the Four
Corners, upper trough axis from MT to OR, and upper low centered
over the Central Plains. Surface front stretched from central MN
to a central SD low, then through southeast WY, northwest CO and
northern UT. A few elevated showers and thunderstorms associated
with a weak shortwave over northeast WY were detected over northern
Converse and Niobrara counties. Patchy fog, locally dense, formed
across portions of the southern NE Panhandle, including Sidney.

Short term forecast concern will be the potential for isolated
strong to severe convection today and Wednesday. Potent shortwave
will track east across MT and northern WY today. A surface low
develops along the stalled front near the Laramie Range mid to
late afternoon, with convective allowing models showing storm
initiation along the Laramie Range after 21Z. Low level moisture
convergence with NAM SBCAPEs progged around 1500 j/kg and effective
bulk shear 40-45 kt may result in isolated supercells capable of
producing large hail and wind gusts in excess of 60 mph. Locally
heavy rain that may cause minor flooding is also a concern.
Convection will decrease in coverage and intensity this evening.

The focus for strong to severe convection shifts east of the I-25
corridor Wednesday afternoon, with SBCAPEs exceeding 2000 j/kg
and bulk shear 40-45 kt across much of the NE Panhandle. Isolated
supercells producing large hail and damaging winds will be the
primary threats. Storms will diminish early Wednesday evening.

.LONG TERM...(Thursday through Monday)
Issued at 315 AM MDT Tue Aug 14 2018

Rocky Mountain upper ridge becomes the dominant feature Thursday
and Friday with northwest flow aloft. Diurnal convection will be
limited to the southeast WY mountains and foothills both days. Near
average temperatures will prevail. The next upper trough to bring
more widespread shower/thunderstorm activity will track east from
the Pacific Northwest across MT/WY Saturday and northern/central
Plains Sunday. The attendant surface low and cold front will pass
through the CWA by late Saturday evening. Preliminary QPF from a
quarter to half inch is forecast, with locally heavier amounts
possible in thunderstorms. There is a small chance for strong to
severe convection. The precipitation ends from west to east Sunday
night. There is a slight chance for afternoon/evening convection
Monday with the passage of a trailing shortwave across southeast
WY. Temperatures will cool to below seasonal normals Sunday and
Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1148 AM MDT Tue Aug 14 2018

VFR conditions primarily prevail across the direct TAF sites but
an area of TSRA is shifting across Niobrara County that extends
southwest into Platte and Albany Counties towards KLAR. Areas of
MVFR to IFR are likely in the heavier showers and thunderstorm
activity as this TSRA band moves from west to east. KCDR will
likely be near or directly impacted by this line over the next
several hours. Will time in TSRA directly as it approaches the
area and confidence increases. Additional SHRA/TSRA is expected to
develop along the southern edge of this band over the Laramie
Mountain Range through the afternoon. This activity will shift
east as well and be near KLAR/KCYS and could also enter Nebraska
near KBFF. Lower confidence exists if storms will be able to make
it to KAIA or KSNY this afternoon. All activity should diminish by
04-05Z.

Winds will generally be east to southeast for the High Plains
sites of WY and NE and 15-20 kt. Winds will decrease to below 10
knots after 04Z.

Isolated to scattered areas of MVFR to IFR low ceilings could be
possible once again Wednesday morning per NAM sounding profiles
near KCYS. Have tilted forecast towards lower ceilings and will
monitor for lower or more overcast possibilities.

&&

.FIRE WEATHER...
Issued at 315 AM MDT Tue Aug 14 2018

A stalled surface boundary near the Laramie Range combined with
increasing monsoonal moisture and instability wil result in scattered
showers and thunderstorms. A few strong to severe storms will be
possible this afternoon, with the threat for locally heavy rainfall.
Drier conditions will prevail over portions of Carbon and Albany
counties through Thursday. Lowest humidities will range from 10 to
15 percent. Wind speeds will be non-critical through the period,
except variable and gusty near thunderstorms.

&&

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

UPDATE...WM
SHORT TERM...MAJ
LONG TERM...MAJ
AVIATION...JSA
FIRE WEATHER...MAJ

Hazardous Weather Outlook
National Weather Service Cheyenne WY
436 AM MDT Tue Aug 14 2018

NEZ002-003-019-020-054-095-096-WYZ101>103-105>108-115>119-151045-
Dawes-Box Butte-Scotts Bluff-Banner-Kimball-North Sioux-
South Sioux-Converse County Lower Elevations-Niobrara County-
North Laramie Range-Shirley Basin-
Central Laramie Range and Southwest Platte County-
East Platte County-Goshen County-Laramie Valley-
South Laramie Range-South Laramie Range Foothills-
Central Laramie County-East Laramie County-
436 AM MDT Tue Aug 14 2018

This hazardous weather outlook is for the western Nebraska
Panhandle...east central Wyoming...south central Wyoming and
southeast Wyoming.

.DAY ONE...TODAY AND TONIGHT

Patchy fog will develop over far southeast Wyoming early this
morning, mainly along the Interstate 80 corridor. Visibilities
will be reduced to a half mile at times.

Isolated to scattered thunderstorms will develop this afternoon
and evening. A few strong to severe storms with large hail
and wind gusts in excess of 60 mph are possible over much of
east central and southeast Wyoming into the extreme western
Nebraska Panhandle.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Isolated to scattered afternoon and evening thunderstorms will
develop Friday through Sunday. Severe weather is not expected at
this time.

.Spotter information statement...

Spotter activation will not be required.

WYZ104-109>114-151045-
Ferris/Seminoe/Shirley Mountains-Central Carbon County-
North Snowy Range Foothills-Southwest Carbon County-
Sierra Madre Range-Upper North Platte River Basin-Snowy Range-
436 AM MDT Tue Aug 14 2018

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

.DAY ONE...TODAY AND TONIGHT

Isolated afternoon and early evening thunderstorms will develop.
Gusty winds and occasional lightning will be the primary hazards.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Isolated afternoon and evening thunderstorms Friday will become
scattered this weekend. Severe weather is not expected at this
time.

.Spotter information statement...

Spotter activation will not be required.

NEZ021-055-151045-
Morrill-Cheyenne-
436 AM MDT Tue Aug 14 2018

This hazardous weather outlook is for portions of the western
Nebraska Panhandle.

.DAY ONE...TODAY AND TONIGHT

Areas of dense fog will persist through early this morning.
Visibilities will be reduced to a quarter mile or less. A
Dense Fog Advisory is in effect until 9 AM.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Isolated to scattered afternoon and evening thunderstorms will
develop Wednesday and this weekend. A few strong to severe storms
with large hail and damaging winds will be possible Wednesday.

.Spotter information statement...

Spotter activation will not be required.

Special Weather Statement
National Weather Service Cheyenne WY
1215 PM MDT TUE AUG 14 2018

WYZ106-115-116-141900-
South Laramie Range WY-
Central Laramie Range and Southwest Platte County WY-
Laramie Valley WY-
1215 PM MDT TUE AUG 14 2018

...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL ALBANY COUNTY UNTIL
100 PM MDT...

At 1214 PM MDT, Doppler radar was tracking a strong thunderstorm near
Bosler, or 24 miles north of Laramie, moving east at 15 mph.

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

This storm will remain over mainly rural areas of east central Albany
County and just north of Bosler.

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 4161 10578 4174 10578 4182 10534 4152 10535
TIME...MOT...LOC 1814Z 264DEG 13KT 4166 10568

Allen