Area forecast discussion
National Weather Service Riverton Wyoming
300 am MDT Wednesday Jun 19 2013
Short term...today through Friday night
Southwest flow increases ahead a pacnw trough as it moves further
inland. Very hot dry air will overspread the region with frequent
gusts over 25 miles per hour expected...with gusts around 40 miles per hour in favored
areas. There will be very little chance of a thunderstorm in air
this dry...with the exception of Yellowstone and The Tetons...where
there could be enough middle level moisture for a few thunderstorms
with the front and upper level support from an approaching jet
streak around the base of the upper low.
Vegetation across eastern portions of the County Warning Area is beginning to cure
and become more receptive to fire...therefore a red flag warning has
been issued for hot...dry...windy and unstable conditions this
afternoon. A cold front associated with the upper low finally moves
into the west late tonight...cooling the airmass and providing good
relative humidity recovery in the western mountains...relative humidity recovery east of The
Divide will likely be very poor ahead of the front and the frontal
passage will produce a sudden wind shift and no precipitation.
The first day of Summer will actually be a bit cooler than the last
day of Spring as the cooler air associated with the upper low moves
into the region. However...dry southwest flow will maintain a sunny
sky and near normal temperatures in spite of the cold front. Gusty
southwest winds could again raise fire weather concern across the
southeastern portions of the County Warning Area...however the event looks to be
very marginal as winds meeting criteria will be very localized.
By Friday the upper level low continues to move a bit further east
to be located over western Idaho by the evening hours. The cooling
aloft will make it easier for the atmosphere to destabilize...again
moisture will be lacking across the south but there could be a few
showers in the northern Big Horn basin and across the northwest with
a shortwave brushing by. Breezy southwest winds again return to
Sweetwater and Natrona counties along with low humidity...like
Thursday it will probably be too marginal for a red flag warning.
Long term...Saturday through Wednesday
Medium-range global models show more detail with upper low currently
along the northwest coast as it wobbles across the northern rockies into
the northern plains over the weekend. Vorticity lobe on the south side
of the upper low moving into northwest Nevada early this morning will do a full
orbit around the main upper low and lift across northwest Wyoming on
Saturday. Forecast continues trend of higher probability of precipitation across the north
on Saturday. Upper low lifts across the northern plains on Sunday
leaving dry airmass over most of the area...the exception along and
east of the Bighorn range where isolated showers and storms may
linger in northwest flow. Most temperatures on Sunday will be near normal
before a more Summer-like hot and dry pattern begins to take shape.
Upper high over the Southern Plains is forecast to retrograde into
the southern/central rockies by Wednesday and looks like it will
find a home there for quite some time. We will see a warming trend
Monday through Wednesday with highs soaring into the 90s across
across most central basins by Wednesday. A few late day storms may
develop across the northwest mountains during this period further out on
the periphery of the ridge. However...locations across central and
southern Wyoming...many of which have only received little or no
precipitation so far in June...
Big Piney...trace
Lander...trace
Riverton...0.01
Rock Springs...trace
..do not look like they will receive much more over the next 6 to
10 days. Lander has had two junes on its 123 years of record
(1891-2013) with a trace or less of precipitation...1956 and 1971.
&&
Aviation.../12z issuance/
Dry conditions expected to start off the forecast period. This period
of VFR conditions may be short lived...as another round of showers
and thunderstorms may develop over the western mountains. Activity
should generally remain confined to the mountains...though will
impact arrivals and departures into nearby airports such as kjac.
Though shower activity will be sparse...wind is expected to increase
across much of the area...especially after 18z. The southeastern
portion of the state including krks and kcpr will see the strongest
increase in wind. These strong gusty winds will linger into the late
afternoon hours...and relax through the overnight hours...with a
significant decrease anticipated after 07z Thursday.
&&
Fire weather...
..red flag warning for Casper dispatch today...
An upper low approaches from the west today...increasing southwest
flow ahead of it...raising concern for areas with critical fuels. A
red flag warning has been issued for the Casper dispatch zones.
These conditions will also be present across Rawlins and Cody
dispatch where fuels are a little less critical...no highlights for
these areas but the widespread hot...dry...windy and unstable
conditions will still raise some concern. In addition...a dry cold
front will approach the west late tonight...it will move east
through early Thursday. Continued dry and breezy conditions expected
on Thursday and Friday...but more marginal. There could be a few
mixed wet and dry thunderstorms across Yellowstone and zone 415 this
afternoon as the front approaches...with another chance on Friday.
&&
Riw watches/warnings/advisories...
red flag warning from 11 am this morning to 10 PM MDT this
evening wyz280-281-285-300.
&&
$$
Short term...Allen
long term...aem
aviation...branham
fire weather...Allen
