Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
1014 AM MDT Thu Sep 14 2017

.SYNOPSIS...A series of storm systems will bring cooler and
wetter conditions to Utah and southwest Wyoming through Friday. A
milder southwesterly flow will return for the weekend.

&&

.DISCUSSION...The center of the Pacific low has reached the AZ/NV
border this morning. Out ahead of it, an area of showers and
thunderstorms has developed over southwest Utah, bringing brief
heavy rain and at least a few spots of gusty winds. Additional
shortwave energy ejecting out ahead of the low has caused an area
of storms to develop near the UT/ID border, but these are
weakening somewhat as they track into Idaho.

The current activity over southwest Utah is expected to hold
together as it continues into central and northern Utah later this
morning and into the afternoon. Meanwhile, as the Pacific low
continues east into northern Arizona and southern Utah, additional
convective activity will develop. Given the continued moist
airmass, with PWs in excess of 1.0 inch in some southern Utah
locations, heavy rain will continue to be a threat. Though storm
motion will be relatively quick, training of storms is possible,
leading to an enhanced flash flood threat. Have expanded the going
flash flood watch to include southwest Utah, where the most
organized convection is this morning. Though the threat of storms
will tend to diminish from the west as the low continues east,
feel the threat continues enough into the afternoon hours to
warrant this.

With good jet support with the low, dynamics will also continue to
be favorable for organized convection, with strong gusty winds
being the primarily threat. SPC has put southern Utah in a slight
risk for severe thunderstorms today.

The Pacific low is expected to exit the forecast area tonight, but
a Pacific Northwest system will follow quickly on its heels,
bringing a well defined cold front through much of Utah and
southwest Wyoming tonight and tomorrow. The front should be
accompanied by a good band of precip for northern and central
Utah, and 700 mb temps as low as -1C would support snow at the
higher elevations. Temperatures will also be much cooler on
Friday, with maxes running up to 20F below seasonal normals, a big
change from the rather warm weather the area has been experiencing
lately.

Updated the forecast earlier to adjust POPs and cloud cover with
current trends. No additional updates planned.

&&

.AVIATION...The threat of periodic showers and thunderstorms in the
vicinity of KSLC will persist more or less through the valid TAF
period before steadier precip develops overnight. Gusty southerly
winds should persist throughout the day, with the potential for
gusts over 25 knots during periods of nearby showers.

&&

.FIRE WEATHER...A Pacific low will cross southern Utah today,
bringing a very good chance of wetting rains with locally heavy
rainfall possible. Organized convection is also possible over
southern Utah, with some storms producing strong and gusty winds.
This low will exit the district tonight but a Pacific Northwest
storm system will follow quickly behind it, bringing a strong cold
front through much of Utah tonight through tomorrow. Best
precipitation is expected along and behind the front during the
day tomorrow, and significant cooling will bring a possibility of
snow to the higher elevations. High pressure is expected to
return for the weekend, resulting in a warming and drying trend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch through this evening for UTZ012-013-016-
     019>021-518.

WY...None.
&&

Traphagan/Carr

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
410 AM MDT Thu Sep 14 2017

UTZ001>016-019>021-517-518-WYZ021-151300-
Cache Valley/Utah Portion-Northern Wasatch Front-
Salt Lake and Tooele Valleys-Southern Wasatch Front-
Great Salt Lake Desert and Mountains-Wasatch Mountain Valleys-
Wasatch Mountains I-80 North-Wasatch Mountains South of I-80-
Western Uinta Mountains-Wasatch Plateau/Book Cliffs-
Western Uinta Basin-Castle Country-San Rafael Swell-
Sanpete/Sevier Valleys-West Central Utah-Southwest Utah-
Utahs Dixie and Zion National Park-South Central Utah-
Glen Canyon Recreation Area/Lake Powell-Central Mountains-
Southern Mountains-Southwest Wyoming-
410 AM MDT Thu Sep 14 2017

This Hazardous Weather Outlook is for the western two thirds of
Utah and southwest Wyoming.

.DAY ONE...Today and Tonight

The first in a series of storm systems will bring widespread
precipitation to southern and eastern Utah, increasing flash flood
risk while bringing the possibility of hail and strong winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

A strong cold front will bring significantly cooler temps to the
outlook area Friday. Widespread precipitation is expected across
the north and west, coupled with temperatures some 10 to 15
degrees below average. Lowering snow levels will have the
potential to allow light accumulations for elevations over 8000 to
9000 feet across the northern mountains. Hunters, hikers, and
others with outdoor and backcountry plans should be prepared for
raw conditions.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

Rogowski/Merrill

For more information from NOAA/s National Weather Service visit...
http://weather.gov/saltlakecity

For information on potential road travel impacts visit...
http://www.udottraffic.utah.gov/roadweatherforecast.aspx

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Special Weather Statement
National Weather Service Salt Lake City UT
1239 PM MDT THU SEP 14 2017

UTZ020-518-141915-
Southern Utah Mountains UT-South Central Utah UT-
1239 PM MDT THU SEP 14 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL GARFIELD AND NORTH
CENTRAL KANE COUNTIES UNTIL 115 PM MDT...

At 1238 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 7 miles southeast of Henrieville, or 22 miles
southwest of Escalante...moving north at 30 mph.

Penny to nickel size hail and wind gusts of 40 to 55 mph will be
possible.

Locations impacted include...
Escalante and Kodachrome Basin State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3743 11178 3748 11201 3785 11188 3775 11157
TIME...MOT...LOC 1838Z 202DEG 25KT 3752 11187

PW

Special Weather Statement
National Weather Service Salt Lake City UT
1250 PM MDT THU SEP 14 2017

UTZ020-518-141915-
Southern Utah Mountains UT-South Central Utah UT-
1250 PM MDT THU SEP 14 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN GARFIELD AND
NORTHWESTERN KANE COUNTIES UNTIL 115 PM MDT...

At 1249 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 16 miles south of Hatch, or 27 miles north of
Kanab...moving north at 30 mph.

Penny to nickel size hail and wind gusts of 40 to 55 mph will be
possible.

Locations impacted include...
Hatch, Tropic and Alton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3731 11233 3738 11254 3775 11241 3764 11209
TIME...MOT...LOC 1849Z 202DEG 25KT 3742 11240

PW

Special Weather Statement
National Weather Service Salt Lake City UT
118 PM MDT THU SEP 14 2017

UTZ020-518-141945-
Southern Utah Mountains UT-South Central Utah UT-
118 PM MDT THU SEP 14 2017

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL GARFIELD COUNTY UNTIL 145
PM MDT...

At 118 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm over Escalante...moving northeast at 35 mph.

Penny to nickel size hail and wind gusts of 40 to 55 mph will be
possible.

Locations impacted include...
Escalante and Boulder.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3766 11154 3774 11178 3811 11158 3797 11124
TIME...MOT...LOC 1918Z 209DEG 29KT 3776 11164

PW

Special Weather Statement
National Weather Service Salt Lake City UT
155 PM MDT THU SEP 14 2017

UTZ020-021-142030-
Glen Canyon Recreation Area/Lake Powell UT-South Central Utah UT-
155 PM MDT THU SEP 14 2017

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN KANE COUNTY UNTIL 230 PM
MDT...

At 153 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 14 miles northeast of Wahweep, or 19 miles north
of Page...moving northeast at 30 mph.

Penny to nickel size hail and wind gusts of 40 to 55 mph will be
possible.

Locations impacted include...
Rural portions of eastern Kane County west of Lake Powell.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3709 11132 3715 11153 3752 11133 3739 11100
TIME...MOT...LOC 1953Z 209DEG 28KT 3719 11138

PW

Special Weather Statement
National Weather Service Salt Lake City UT
211 PM MDT THU SEP 14 2017

UTZ020-021-142115-
Glen Canyon Recreation Area/Lake Powell UT-South Central Utah UT-
211 PM MDT THU SEP 14 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN SAN JUAN AND EASTERN
KANE COUNTIES INCLUDING LAKE POWELL UNTIL 315 PM MDT...

At 207 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorms over the southern end of Lake Powell...moving
northeast at 30 mph.

These storms will be capable of producing winds of 50 mph or greater
on the southern portions of Lake Powell north to near Bullfrog along
with frequent lightning. This will lead to a sudden increase in
waves and very choppy waters which will result in hazardous boating
conditions. Boaters are urged to seek safe harbor if possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Boaters on Lake Powell can expect gusty winds and choppy waves, and
should seek safe harbor immediately until the winds subside.

&&

LAT...LON 3753 11103 3753 11053 3745 11053 3744 11061
      3738 11063 3738 11069 3731 11069 3730 11065
      3726 11062 3707 11075 3707 11081 3700 11091
      3700 11134
TIME...MOT...LOC 2007Z 209DEG 28KT 3698 11121

PW