Area Forecast Discussion
Issued by NWS Riverton, WY

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764
FXUS65 KRIW 151145
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
545 AM MDT Tue Oct 15 2019

.SHORT TERM...Today through Thursday night

The cold front has now passed through the area, and dry as expected.
The main effects from the front will be somewhat cooler temperatures
East of the Divide, especially the further east you go. But nothing
unusual for the middle of October. It will still be a bit breezy
across southern Wyoming, but certainly much less windy than
yesterday. The only concern would be for fire weather, but it looks
borderline. We may issue a statement to cover for conditions, but
this would only be in Sweetwater County.

Temperatures look to take an upward trend for Wednesday as flow
turns to the southwest. Some lower elevations will likely see
temperatures climb back into the 70s at times. With no precipitation
expected the only concern would again be fire conditions. Across the
south where fuels are still critical, humidity will certainly be low
enough. However, wind at this point looks borderline at best, even
less than today. Areas around Casper may have a bit of wind, but
fuels are not critical in that vicinity. As for any potential fire
weather watches, we will punt to the day shift to make the final
determination.

Things look to become more active on Thursday. A trough will
approach from the west and bring our next chance of rain or snow.
The models have trended a bit slower with it`s progression. The NAM
only has high elevation precipitaion but this is usually wrong,
especially this far out. The European is completely dry. The GFS
does have some but it is late and is notoriously too fast with
Pacific systems more than 48 hours out. We will maintain some POPs
in the west but keep them in the slight category. The best chance
would be at night but with the system splitting amounts look fairly
light. Meanwhile, expect a breezy to windy and mild day East of the
Divide. Again, the main concern is for fire conditions in the south.
This time, the wind will be there. However, guidance does show dew
points rising through the day. The models do tend to be too bullish
on this sometimes though. Still time to watch it though. As for any
showers jumping the Divide, there could be a few but not a lot. For
now, we kept POPs mainly in the slight category with many areas
remaining dry.

.LONG TERM...Friday through Tuesday.

Friday looks to start off on the cooler and wetter side with a
cold front having moved from west to east through the state
overnight. An initial shortwave trough in the 500mb flow will keep
a chance of precipitation over the northern half of the state,
particularly over the northwest and the higher terrain. High
temperatures will cool by at least 10 degrees compared to the
previous couple of days, to more seasonable values. Saturday looks
to be a cool in-between day with less of a chance of
precipitation and slightly more southwesterly flow. The primary
wave with the trough over the PacNW and Northern Rockies then is
expected to move through the forecast area Saturday night into
Sunday. Uncertain at this time to the extent of the precipitation
since the GFS, ECMWF, and Canadian all show slightly different
paths and timing for the 500mb low. Temperatures will certainly
cool more on Sunday and chances of precipitation will increase.
700mb temperatures less than -6C suggest mostly snow, with a mix
of rain/snow for the lower elevations east of the divide. Moist
cool northwest flow will continue on Monday behind the main
trough. Warming with some clearing is expected then on Tuesday as
high pressure builds back over the western US, though some light
showers could continue of the far northwest mountains. Overall,
Friday through late Sunday looks to be an active weather pattern
for Wyoming with cooler temperatures and a good chance of
precipitation.

&&

.AVIATION...(For the 12Z TAFs through 12Z Wednesday morning)

VFR conditions are again expected to prevail during the next 24
hours at all TAF sites.  A weak cold front has pushed down east of
the continental divide late Monday, with a few mid-level ceilings
between KBYG and KCPR.  This cloudiness will move eastward from 15z-
18z/Tue.  High pressure builds from the southwest over western WY
today into Wednesday.  Southwest WY will see lighter breezy
conditions after 18Z/Tue with gusts from 15-25 kts, which is lighter
than Monday afternoon.  Other TAF sites will generally be under 10
kts.  Wednesday should see more breezy conditions from the southwest.

&&

.FIRE WEATHER...

Expect dry conditions today with less wind than yesterday. Locally
breezy conditions will still be possible in the south. However, with
somewhat higher humidity and less wind, fire conditions look
marginal for any highlights. Humidity will remain above critical
levels elsewhere. Temperatures will be slight cooler East of the
Divide when compared to yesterday. Mixing and smoke dispersal will
range from poor in most of the north to fair to good in the south.
&&

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

&&

$$

SHORT TERM...Hattings
LONG TERM...McDonald
AVIATION...McDonald
FIRE WEATHER...Hattings



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