FXUS65 KRIW 250827
Area Forecast Discussion
National Weather Service Riverton WY
227 AM MDT Sun Aug 25 2019
.SHORT TERM...Sunday through Tuesday night
Once again, the main concern for today will be fire concerns. And
this looks like the highest danger of the days this week. A cold
front will drop out of Montana and move into northern Wyoming later
this morning. Ahead of the front, with the tightening pressure
gradient and much of central and southern Wyoming moving into the
right front quadrant of the jet, breezy to windy conditions will
develop. As for high winds, 700 millibar winds do not look strong
enough. However, combined with humidity that could drop to around 10
percent in some areas, Red Flag Conditions look likely for many
areas. Given strong winds, we did add the Wind River Mountains to
the warning as well. As for the chance of precipitation, a weak
disturbance is riding across Montana early this morning. I can't
rule out a stray shower over northern Johnson County early but this
would be it until about early afternoon. The chance of showers and
thunderstorms will increase this afternoon and especially this
evening across the north as the front passes through. Most of the
upper level support should remain east of the area. The Storm
Prediction Center does have a marginal risk into eastern Johnson
County but this may be overdone. We do have showers there and
isolated thunder, and this may last into later Sunday night before
the upper level support shifts eastward.
Monday at this point looks quieter. With cooler air moving into the
area, fire conditions should improve somewhat East of the Divide and
in northwestern Wyoming. Winds will also decrease somewhat. Relative
humidity will remain very low though. However, across the south
critical fire conditions remain a good possibility. I could see the
Red Flag Warning continued for Monday, but this would only be in
southern Wyoming. Otherwise, expect a cooler day, especially East of
the Divide where it will actually feel sort of autumn like. A couple
of models have some splotches of QPF over the northern mountains,
but amounts are only 0.01 and with a dry air mass in place we
On Tuesday, a bubble of high pressure will build over the area. This
will finally shut the wind off for all areas so no fire highlights
for anyone despite humidity remaining low. This also looks to be the
coolest day of the three with even the lower elevations east of the
Divide possibly remaining in the lower 70s for highs and possibly
the 60s in a few locations.
.LONG TERM...Wednesday through Sunday
A dry northwest flow will occur Wednesday ahead of a ridge over the
West Coast. After a relatively cool start to the work week,
temperatures will rebound to seasonal to above average temps on
Wednesday. A ridge over the West Coast is progged to flatten by
Thursday with weak waves pulling across the northern Rockies
Thursday and Friday. At the same time, a cold front is expected to
push south, east of the Divide late Thursday into Thursday night.
This front looks to remain quasi-stationary along the Divide Friday
before washing out Saturday. There will be chances of convection
mainly along and east of the Divide Thursday and Friday. An upper-
level jet couplet pulling across the area Thursday night and Friday
could enhance this area of precipitation.
Global models are now showing a ridge developing next weekend with
the Labor Day weekend being dry and warm.
On the fire weather aspect, elevated to critical conditions look to
continue at times mainly over the southwest through the extended.
VFR conditions will continue across the forecast area through the
forecast period. SKC conditions are expected for most of the day
today. Scattered to broken clouds will enter northern portions
along the MT border between 22Z and 00Z Monday, as a cold front
proceeds southward over portions east of the Divide. Windy
conditions will impact most, if not all, terminals today. The
strongest winds will occur at terminals west of the Divide, with
gusts of 25 to 30kt also occurring at KLND, KRIW and KCPR. Winds
will gradually decrease across the area by 06Z Monday.
...Red Flag Warning in effect for much of central and southern
A cold front will drop southward across Wyoming today. A combination
of low humidity and a gusty west to southwest wind will bring
critical fire weather to much of central and southern Wyoming today.
As the front moves in isolated showers and thunderstorms will be
possible in northeastern areas, especially in Johnson County.
Humidity will fall to around 10 percent at times in portions of
central and southern Wyoming. Mixing and smoke dispersal will range
from good in the north to excellent in western, central and southern
Wyoming. There should be some improvement in conditions on Monday.
Red Flag Warning from 10 AM this morning to 8 PM MDT this
evening for WYZ277>280-283-288-289-300-414>416.
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