Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 230924
Area Forecast Discussion
National Weather Service Riverton WY
324 AM MDT TUE AUG 23 2016
.SHORT TERM...Tuesday through Thursday night
The advertised cold front is now dropping southward into the
northern portion of the state and should settle along the
continental divide. And as advertised, it will be a dry frontal
passage. The main effect will be for temperatures to drop about 10
to 15 degrees cooler than on Monday. This will result a lowering of
fire danger for many of the aforementioned areas. The exceptions will
be the Absarokas and the east slopes of the Wind River Range, where
there will be sufficient wind for Red Flag Conditions. Continuity
had this covered well so we left it as is. There could still be some
elevated fire danger in the afternoon at times though. The risk of
high fire danger will shift to southern areas today where the wind
will be stronger and relative humidity quite low. Again, the
previous Red Flag Warning covers this well. As for the chance of any
convection, the only chance would be in southern Sweetwater County
which will be on the edge of some monsoonal moisture. But even here,
anything would be isolated at best.
And for people sick of the high fire danger, how do you spell
relief? C-O-L-D F-R-O-N-T, a stronger one. This next front with
deeper cool air will pass through later tonight. This one will turn
deeper flow to the northeast and more importantly, increase relative
humidity significantly for many locations. Temperatures will also be
fall like with many areas remaining in the 60s. As for the chance of
precipitation, it should increase, especially East of the Divide as
an upper level disturbance drops southeastward out of Montana. As for
amounts, given the recent dry weather and active fires, we kept
amounts on the light side. If we do get more, most people will be
happy. The only place that may have elevated fire danger would be
far southwestern Wyoming and at this point that is a big if. We will
cross that bridge when we get to it. In addition, there could be
some snow in the higher peaks of the northern mountains later
Wednesday night. However, at this point amounts look insignificant.
The cool weather looks to continue into Thursday as well, as well as
the chance of showers and a couple of thunderstorms across the
northern two thirds of the area. And yes, snow levels will be low
enough for some snow in the higher elevations of the mountains. High
temperatures will continue to average below normal, with the
greatest departures from normal across areas east of the Divide.
.LONG TERM...Friday through Tuesday
Synopsis...Cool and unsettled conditions will linger over the area
Friday with chances of showers and thunderstorms. A warmer and
drier west to southwest flow will return over the weekend into early
next week with a return of elevated fire weather conditions.
Discussion...High-amplitude ridge along the west coast of North
America is expected to to retrograde and weaken through this period.
This will lead to backing flow and building heights after Friday.
Beforehand, a shortwave will swing across northern Wyoming on Friday
bringing chances of showers and thunderstorms across mainly the
northern third of the area. Some monsoonal moisture may also get
pulled into southern Wyoming, with slight chances of thunderstorms
along and south of I-80. Drier air will push in from west to east
Saturday looks have the best potential for elevated to extreme fire
weather conditions across the south, though temperatures will be
seasonably cool, very dry and breezy conditions are expected.
There is not a great deal of confidence in either GFS or ECMWF
depictions of shortwaves in SW flow Sunday and onward. Mean upper
trough is expected to be near the west coast bringing dry conditions
to most of the area, with mainly the NW seeing slight chances of
afternoon and evening thunderstorms. Lee side surface trough will
likely bring a return of warm, dry and breezy conditions across the
south and central early next week along with continued elevated fire
VFR conditions to occur through tonight. Smoke from wildfires
will impact visibility today in parts of northern WY.
Breezy to windy by 19z over much of the far west and south with gusts
around 25 knots expected until 01z...then decreasing wind speeds.
A cold front will move southward across northern and central Wyoming
before settling along the Continental Divide today. South of the
front, a combination of low relative humidity and a gusty wind will
bring another day of critical fire weather. Further north, fire
danger should lessen today with cooler temperatures although
elevated fire danger will be possible for a time in the afternoon.
Smoke dispersal and mixing will be fair to good East of the Divide
and very good to excellent West of the Divide. Fire conditions should
improve considerably Wednesday as a stronger cold front brings
cooler temperatures and higher humidity.
Red Flag Warning from noon today to 9 PM MDT this evening for