Area Forecast Discussion
Issued by NWS Riverton, WY

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KRIW 192024
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
224 PM MDT Wed Jul 19 2017

.SHORT TERM...(This evening through Thursday)
Issued at 225 PM MDT Wed Jul 19 2017

Subtropical moisture is edging nwd today and this will accelerate
tonight into Thursday as the ridge expands nwd and a surge of
associated low to mid level moisture lifts nwd from UT and CO.
Current band of enhanced mid level moisture from near EVW to CPR has
kept some storms going all day with an ocnl ltg strike since early
this morning. Back to tonight`s surge: Dew points have risen in the
last 24 hours to the south from a few degrees to as much as 6-8
degrees and this higher pw air (around an inch) is headed nwd.
Another disturbance is forecast to move up from cntrl UT tonight
which will likely fire some nocturnal showers and thunderstorms
across our sern zones (Sweetwater over to Natrona County). Hard to
see this fcst cntrl UT one. It could be causing the cntrl UT mtn
convection but not sure. A more evident shortwave is moving up
through swrn UT and that one will arrive in the sw during the early
morning hours Thursday. The moisture surge tonight will likely set
the stage for more convection on Thursday with many areas seeing the
precipitable water levels rise to around an inch. Some of these
storms will be capable of producing heavy rain and hail. Areas that
get the most sun will have the best chance of breaking the cap and
getting a few stronger storms. Gulf of Alaska shortwave then opens
up and moves across the north on Friday with a cold front moving
across the north especially Thursday night into Friday morning with
a drier wly flow developing. Any convection on Friday will likely be
confined to the srn border. A dry nw flow will prevail on Saturday
with slightly cooler temps in the north but still warm.

.LONG TERM...(Thursday night through Wednesday)
Issued at 225 PM MDT Wed Jul 19 2017

A hot and dry weekend is in store as a high builds in from the west.
Then the GFS swings a shortwave trough across the area asct with a
closed low tracking east across Sask and Alberta. However, the
Canadian and Euro keep the ridge in place over the Western United
States which would support the 5 wave pattern of keeping the long
wave trough axis along the Pacific coastline. For now will just keep
low pops across the CWA Monday through Wednesday with pops
increasing a bit each of the three days as PW values increase from
the southwest. H7 temps in the mid to upper teens will support highs
in the low to mid 90s in the central basins and the 80s in the
western valleys Monday. By Wednesday, behind the trough, high temps
will cool to the 80s and low 90s in the central basins and 70s to
low 80s in the western valleys. Any storms that form across the
eastern zones, namely Natrona/Johnson Counties, should gain strength
as they track southwest as they encounter sfc moisture and increased
shear from low level east and southeast flow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 225 PM MDT Wed Jul 19 2017

Mainly VFR conditions will continue through the forecast period.
Have kept in and adjusted VCTS/VCSH mentions for KCPR, KLND, KPNA,
KRIW and KRKS through 07Z time frame. Thunderstorms have already
formed and are tracking northeast across Eastern Sweetwater County.
Then with the more potent surge of monsoon moisture arriving from
the south coincident with an upper level weather disturbance,
another round of moisture laden thunderstorms are expected south of
a line from KJAC east to the Owl Creek Mountains after 21z Thursday.
IFR conditions are possible in the core of any thunderstorms that
form. Southwest winds will increase over the area Thursday afternoon.

&&

.FIRE WEATHER...
Issued AT 225 PM MDT Wed Jul 19 2017

Isolated to widely scattered thunderstorms can be expected through
the night across mainly the southeast part of the district from
Sweetwater County over to Natrona County as another disturbance
moves up from the south and southwest overnight. A more moist
airmass will develop tonight into Thursday with a better chance of
showers and thunderstorms on Thursday. Some of the storms will
produce heavy rain and some hail.


&&

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

&&

$$

SHORT TERM...Skrbac
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Skrbac


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.