000
FXUS65 KRIW 252122
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
322 PM MDT Sun Jun 25 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 233 PM MDT Sun Jun 25 2017

Once again northwest flow aloft remains over the area with colder air
and north to northeast surface winds and dry conditions holding on one
more night.  The upper level high pressure ridge over the great basin
is still expected to build north into western Wyoming with warming
temperatures spreading from southwest to northeast with time.  Limited
moisture will come up but the biggest change will be the surface warming
destabilizing the lower levels enough for some mountains showers mainly
in the afternoon and evening on Monday. The Ridge aloft will continue to
warm up the area Tuesday with increasing showers and deeper instability
supporting isolated thunderstorms.  A pacific trough will ride over the
top of the ridge bringing increased  shear and decreasing stability for
more showers and thunderstorms on Wednesday.   West to southwest surface
winds will develop and increase especially over the south and west.

.LONG TERM...(Wednesday night through Sunday)
Issued at 233 PM MDT Sun Jun 25 2017

The extended forecast will start fairly active Wednesday night, with
the main troughpa coming through Thursday morning under the left
front quad of the jet. The lingering convection in Johnson County
will be fairly strong Wednesday evening with the low level flow
backing to the southeast drawing in low level moisture and resulting
in a BRN Shear of 50 and sufficiently high cape. With the above
ingredients, we could see borderline large hail, locally heavy
rainfall, frqnt LTG, and strong gusty winds. These showers will
taper off after midnight. In the meantime, the rest of the north
half of the CWA will experience scattered more garden variety
thunderstorms tapering off to showers after midnight. Thursday will
turn out to be the coolest day of the week with the pool of cooler
air asct with the trough directly overhead. H7 temps will drop to 3C
over Northern Wyoming Thursday. With the long wave trough over the
Midwest and the long wave high over the Western United States, this
cool trough/cold front will have the greatest affect on our
northeast zones with BYG likely to be 15 degrees cooler after the
fropa by Thursday.  Highs Thursday will be around 70 at both KBYG
and KJAC. This cold pool aloft will encourage further convection in
Northern Wyoming east of the divide later Thursday where the better
moisture and instability will be. Expect dry breezy weather in
Sweetwater County Thursday with the min RH in the teens. On Friday,
a ridge will build in from the west bringing in drier air along with
warming temps. Over the weekend, the GFS flattens the ridge as it
brings in the next trough tracking east across the Northern Rockies
which is more amplified than what the Euro advertises along with the
Canadian in the middle. For now will keep late day isold convection
across far Northern Wyoming during next weekend. High temps will
range from 75 to 80 in the far west and well up into the 80s east.
The min RH in the teens will creep north to other lower elevations
east of the divide next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 233 PM MDT Sun Jun 25 2017

VFR conditions will occur through 00Z Tuesday. Wind speeds will
be less than 12 knots through the period. Very isolated showers
may occur over the mountains from 23Z through 03Z. High and middle
clouds will increase late in the afternoon Monday ahead of the
next upper level trough. Very isolated mountain showers or
possible thunderstorms can be expected again late Monday.

&&

.FIRE WEATHER...
Issued AT 233 PM MDT Sun Jun 25 2017

Once again northwest flow aloft remains over the area with colder air
and north to northeast surface winds and dry conditions holding on one
more night.  The upper level high pressure ridge over the great basin
is still expected to build north into western Wyoming with warming
temperatures spreading from southwest to northeast with time.  Limited
moisture will come up but the biggest change will be the surface warming
destabilizing the lower levels enough for some mountains showers mainly
in the afternoon and evening on Monday. The Ridge aloft will continue to
warm up the area Tuesday with increasing showers and deeper instability
supporting isolated thunderstorms.  A pacific trough will ride over the
top of the ridge bringing increased  shear and decreasing stability for
more showers and thunderstorms on Wednesday.   West to southwest surface
winds will develop and increase especially over the south and west.
The lower air mass will be unstable enough with sufficient wind for very
good to excellent smoke dispersal from late morning to mid evening each day.

&&

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

$$

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