Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 240501

Area Forecast Discussion
National Weather Service Riverton WY
1101 PM MDT MON MAY 23 2016

.Short Term...Tonight Through Thursday

Large upper low continues to spin over Southern Saskatchewan with
multiple disturbances rotating around it. Embedded weak wave is
slowly moving ne into Southwest Wyoming attm with some weak
showers/virga. Weak thermal trough and wraparound moisture is also
aiding in some weak showers over the northwest early this
afternoon. Limited instability today and not a lot of moisture to
work with. Tuesday we see a potential stronger shortwave moving up
from the southeast late in the day and then heading towards the
northeastern zones. At the same time, a weak front will drop down
into the northern zones tonight. Some potential jet support may
also come into play late in the afternoon or evening as nose of
srn jet moves into Southeastern Wyoming and right entrance region
of northern jet streak is nearby. How much moisture is able to
move in from the southeast is still in question as is when will it
arrive if it does. It looks like it will be early evening before
any better moisture arrives so we`ll just have to watch how the
shortwave/upper forcing timing is and how our return flow moisture
is to see how strong some of these storms may be in mainly Johnson
County. SPC has ern Johnson in marginal risk and that looks good
for now. Multiple ripples in the southwest flow appear to be in
play Tuesday night and Wednesday to keep a chance of showers and
isold storms across the area, especially in the west and north
where the front may remain. Unsettled weather remains through
Thursday with northern low passing into the ND and a southern
upper low moving across the 4-corners region. Weak frontal
boundary east of the divide may be a focus for afternoon
convection as plenty of mid level moisture will remain with a
little more low level available behind the front.

.Long Term...Thursday Night Through Monday

Interesting extended period as once again we have a Memorial Day
upper low to contend with. This system is currently in the Alaska
region and will drop down into the WA/Nrn ID area on Friday and
then dig into the Inter-mountain west for the remainder of the
Memorial Day weekend as the large scale pattern shows a mean
trough holding over the west through the period. The GFS is
showing the frontal boundary holding across at least the north
half through much of this period with potential overrunning aloft
to increase pcpn chances east of the divide Friday onward. The new
Euro is more progressive with the low swinging it across on
Saturday night already. Not really buying into this idea with mean
trough holding over the west. If that happens, then there will be
likely another low quickly replacing it over the west. Will
continue continuity with an upper low over the west much of the
weekend with cool to cold in YNP, cooler north than south along
with higher pops west and north.



West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

VFR conditions to prevail through the forecast period. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms to most of the west this afternoon and
evening...with periods of brief MVFR conditions in lower cigs in and
near heavier showers and storms. Stronger embedded storms will
produce gusty erratic winds to 35 kts with small hail and brief
heavy rain. Stronger gusts in excess of 45 kts will be possible
across Sweetwater county including KRKS. This activity will decrease
by 04z Wed.

East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

VFR conditions to prevail through the forecast period. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms east of the divide later this afternoon
through the evening...with periods of brief MVFR conditions in lower
cigs in and near heavier showers and storms late this afternoon and
evening. More numerous and stronger thunderstorms are possible in
both Natrona and Johnson counties later this afternoon and evening
with some storms producing winds gusts in excess of 45 kts...hail
from one half inch to one inch...and brief heavy rain with frequent
lightning. This activity will decrease from south to north after 03z



Isolated to widely scattered showers and a few thunderstorms will
be possible into the evening hours. A gusty breeze will continue
across portions of the area, but high winds are not anticipated.
Relative humidity should remain above critical levels. An upper
level disturbance will approach on Tuesday and bring an increased
chance of afternoon showers and thunderstorms. A weak cold front
will move into the north tonight with a northerly wind setting the
stage for lower mixing heights on Tuesday while the south remains
well mixed.


.RIW Watches/Warnings/Advisories...None.



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