Alert archive / Wyoming / Special Weather Statements in 2017

Special Weather Statement, NWS Riverton, WY

July 20, 2017Sweetwater County, Wyoming

NWS Riverton, WY issued this special weather statement at Jul 20, 2017, 9:31 PM MDT for Sweetwater County, Wyoming. It was in force for 29 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued
Jul 20, 2017, 9:31 PM MDT (03:31 UTC)
Expired
Jul 20, 2017, 10:00 PM MDT
In force
29 min
Issued by
NWS Riverton, WY

County Sweetwater County, WY

The radar

The Riverton/Lander radar (KRIW), 159 km from the middle of the area, began a volume at 03:32 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Salt Lake City I, UT (KSLC), launched 00:00Z, 3.5 hours before the alert went out and 302 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Salt Lake City I, UT at 00:00Z on 2017-07-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 783 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Salt Lake City I, UT at 00:00Z on 2017-07-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 26 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
783 J/kg
Mixed-layer CIN
-21 J/kg
Mixed-layer LCL
2771 m above ground
0-6 km bulk shear
15 kt
0-1 km storm-relative helicity
26 m²/s²
0-3 km storm-relative helicity
107 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

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What forecasters said that day

The local office's own words before this special weather statement went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Riverton, WY wrote its last area forecast discussion before this special weather statement went out at Jul 20, 2:56 PM MDT, 6 hours 35 minutes earlier.

Area forecast discussion, Jul 20, 2:56 PM MDT, 6 hours 35 minutes before
Area Forecast Discussion
National Weather Service Riverton WY
256 PM MDT Thu Jul 20 2017

.SHORT TERM...(This evening through Friday)
Issued at 234 PM MDT Thu Jul 20 2017

This evening is shaping up to be one of the more active windows
of opportunity for active weather this week. A well defined
shortwave will be making landfall onto the Pacific Coast today
along with a lead vorticity lobe tracking east across the area.
With PBS of around n inch stream in from the southwest with the
monsoon moisture and instability in place, it appears we have a
good shot of thunderstorm activity during the next 24 hours. the
timing of this feature will result in the majority of this
activity to fire up after 00z this evening. However, there is
already convective activity with sold lightning just to the west
close to the Idaho/Montana border. This activity will move east
and become rejuvenated from afternoon heating resulting in a
fairly active period for the remainder of this afternoon in our
western zones. then this convection will spread to areas east of
the divide after 00z this evening. As it does, this band of
convection will encounter increasing speed and directional shear
as the storm cells approach Natrona and Johnson Counties where we
have a slight risk of severe for strong winds and large hail. it
appears that johnson county stands the best chance of any severe
activity this evening along with a Urn shear factor of 93 by 03Z
this evening.

Then as high pressure builds in from the west, we can look forward
to a dry weekend, Temperatures will start out relatively cooler,
with the biggest cool down expected in Johnson county Friday. There
should be some lingering shower activity in the Casper area Friday
morning and dissipating just after 12z. Otherwise, the only other
activity expected Friday will be some lingering monsoon moisture and
instability for the southern tier zones to experience some sold
to widely sct convective activity Friday afternoon.

Saturday and Sunday will be dry with a warming trend with highs back
up in the low to mid 90s in the central basins and 80s in the
western valleys.

.LONG TERM...(Friday night through Thursday)
Issued at 234 PM MDT Thu Jul 20 2017

Monday will be the hottest day of the week with high temperatures
flirting with the century mark in the Big Horn basin. Then the
temperatures will slowly cool off during the rest of the week
through Thursday as the "ring of fire" consisting of monsoon
moisture laden wet thunderstorms rides up and over the large
bubble of high pressure over the Western United States Tuesday and
Wednesday, along with increasing clouds and wet thunderstorm
activity, thus cooling the daytime high temps. The models are in
better agreement with the overall trend then they were yesterday
keeping the high over us with weak disturbances rounding the
ridge.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 234 PM MDT Thu Jul 20 2017

Expect mainly VFR conditions to continue through the forecast
period. Kept in the mention of VCTS/SHRA for most locations
through the majority of the forecast period until close to 06Z
Friday. KCPR and KBYG stand the best chance of lowered vsbys and
cigs as well as any small hail from thunderstorms this afternoon.
Another round of isolated to widely scattered thunderstorms is
expected across southern Sweetwater County Friday afternoon. KRKS
may get grazed by these storms.

&&

.FIRE WEATHER...
Issued AT 234 PM MDT Thu Jul 20 2017

Monsoonal moisture and a passing cold front will move through the
area and bring an increased chance of showers and thunderstorms.
These storms have a better chance of bring wet with a chance of
hail and erratic winds as well. Relative humidity should remain
somewhat higher than recent days as well. For the most part, wind
should remain light to moderate outside of any shower or
thunderstorm. Mixing and smoke dispersal will generally range from
good to very good but fair in some of the Basins. Another round of
isolated to widely scattered thunderstorms is expected across
southern Sweetwater County Friday afternoon. KRKS may get grazed
by these storms.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...Lipson
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Lipson
Hazardous weather outlook, Jul 20, 2:21 AM MDT, 19 hours 10 minutes before
Hazardous Weather Outlook
National Weather Service Riverton WY
221 AM MDT Thu Jul 20 2017

WYZ001>020-022>030-211100-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Big Horn Basin-Southwest Big Horn Basin-
Southeast Big Horn Basin-Owl Creek and Bridger Mountains-
Bighorn Mountains West-Bighorn Mountains Southeast-
Northeast Johnson County-Southeast Johnson County-
Teton and Gros Ventre Mountains-Jackson Hole-
Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
221 AM MDT Thu Jul 20 2017

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight

Isolated to widely scattered afternoon and evening thunderstorms.
Heavy rain, hail and strong gusty wind are possible with any
storm. The best chance of strong storms will be in Natrona and
Johnson Counties.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Friday...Isolated thunderstorms across the south.

Monday through Wednesday...Isolated to scattered afternoon and
evening thunderstorms.

.SPOTTER INFORMATION STATEMENT...

Spotters are urged to report wind gusts over 45 mph, hail and any
flooding. Thank you.

In the hours before

Special weather statement, Jul 20, 5:15 PM MDT, 4 hours 16 minutes before
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Special weather statement, Jul 20, 5:57 PM MDT, 3 hours 34 minutes before
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Special weather statement, Jul 20, 6:47 PM MDT, 2 hours 44 minutes before
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Special weather statement, Jul 20, 7:34 PM MDT, 1 hour 57 minutes before
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Special weather statement, Jul 20, 8:07 PM MDT, 1 hour 24 minutes before
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Special weather statement, Jul 20, 9:31 PM MDT, 0 minutes before
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The office that day

Everything else NWS Riverton, WY issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jul 20, 6:47 PM MDTSpecial Weather StatementRIWNatrona43 min
Jul 20, 7:34 PM MDTSpecial Weather StatementRIWNatrona26 min
Jul 20, 8:07 PM MDTSpecial Weather StatementRIW38 min
Jul 21, 5:21 AM MDTSpecial Weather StatementRIWSublette39 min
Jul 21, 6:30 AM MDTSpecial Weather StatementRIW30 min
Jul 21, 8:03 AM MDTSpecial Weather StatementRIW42 min
Jul 21, 8:13 AM MDTSpecial Weather StatementRIW47 min
Jul 21, 9:01 AM MDTSpecial Weather StatementRIW29 min
Jul 21, 9:37 AM MDTSpecial Weather StatementRIW38 min
Jul 21, 10:20 AM MDTSpecial Weather StatementRIW40 min
Jul 21, 10:57 AM MDTSpecial Weather StatementRIW48 min
Jul 21, 11:36 AM MDTSpecial Weather StatementRIW24 min
Jul 21, 12:04 PM MDTSpecial Weather StatementRIW56 min
Jul 21, 1:00 PM MDTSpecial Weather StatementRIW30 min
Jul 21, 1:28 PM MDTSpecial Weather StatementRIW47 min
Jul 21, 2:23 PM MDTSpecial Weather StatementRIW52 min
Jul 21, 2:40 PM MDTSevere Thunderstorm WarningRIWSweetwater35 min
Jul 21, 3:02 PM MDTSevere Thunderstorm WarningRIWSweetwater16 min

Nearby

Special Weather Statements in Wyoming, 2017Every special weather statement in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.