Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
341 PM MDT Thursday Jul 24 2014
Short term...tonight and Friday
Subtropical plume which brought weak morning convection with gusty
wind to 40 miles per hour is now bringing isolated thunderstorms to the mix for
our southeastern third. Airmass has actually juiced up in the far south so
red flag warning is actually struggling to verify due to the higher
dew points and cooler temperatures. Otherwise...hot and dusty with
plenty of sunshine further north. One other item of note today is
some mountain wave action going on in central Wyo with strong SW
winds mixing down at times between 40 and 50 miles per hour. Beefed up winds
some more to cover this. One area to watch over the next several
hours will be our northestern zones where surface low is sitting with very
moist airmass just to the north and east. Frontal boundary aided by
approaching upper low will likely push south into the area so
potential for a few stronger storms exist for a couple hours into
the evening up there in Johnson County. Flow turns more westerly on
Friday so monsoonal plume should be pushed south to the northern Colorado
border with only far southeastern Sweetwater seeing the potential for isolated
thunderstorms. Frontal boundary which sags south into central Wyo tonight
will wash our on Friday across all but potentially the northestern zones
leading to another hot day with low rh's and gusty west wind.
Long term...Friday night through Thursday
An area of low pressure over the Canadian and Montana border will
cause the ridge of high pressure to flatten Friday evening. The
resultant zonal flow will remain dry...though the influence of the
low will bring cooler temperatures across the forecast area on
Saturday. The ridge of high pressure will work to amplify again
Saturday afternoon and evening. As the system amplifies...it may
permit some moisture to move int southern Wyoming Saturday with some
additional cloud cover possible.
The ridge will continue to amplify and move east through Sunday. The
axis of the ridge will be over western Wyoming by Sunday evening.
The axis will struggle to move fully into the state as a series of
disturbances in the flow impact the forecast area. Disturbances will
bring repeating periods of showers and thunderstorms during the
afternoon and evening hours. An upslope component is possible during
these showers...which increases the chances for activity across
favored locations. Temperatures across the area are not expected to
fluctuate significantly each day. The combination of cloud
cover...showers...and high pressure will permit temperatures to
remain fairly persistent each afternoon.
Isolated high based showers and thunderstorms with outflow winds of
40 to 50 miles per hour will be possible through the evening hours in the
southeast parts of the area including krks and kcpr. Isolated
stronger storms are possible in Johnson County until 03z. A cold
front will push south into northern Wyoming around 01z Friday and
then move south into central Wyoming between 06z and 08z Friday.
The cold front will be pushed east on Friday by a dry...hot...
westerly flow with dry conditions for all but the southeastern
corner of Sweetwater County where isolated thunderstorms are
.Red flag warnings to continue through 03z Saturday for fire zones
275...276...279...280...281...282...283...285...287 and 300...
Updated to include red flag warnings for 275...281 and 282 until
9 PM this evening for wind and low relative humidity.
The combination of hot temperatures...low rh's...Haines index of 5
to 6 and gusty west wind will continue the threat of critical fire
conditions through Friday evening. Moisture levels have come up some
in 279 today but it will dry out more again on Friday. Otherwise...
expect more critical fire conditions to continue through Friday.
There is a cool front that will drop south into the central zones
tonight but it is expected to weaken and be pushed east of the area
Friday afternoon but a dry...hot westerly wind. Many areas will see
west winds of 15 to 25 miles per hour during the afternoon and evening with
gusts varying from 30 to 35 miles per hour. Isolated gusty showers and
thunderstorms will continue for 279...280...289 and 300 through this
evening. The rest of the area will continue warm to hot with gusty
wind at times with min rh's between 10 and 20 percent. Critical fire
conditions may continue in 279 through Saturday.
red flag warning until 9 PM MDT Friday
Red flag warning until 9 PM MDT this evening wyz275-281-282.