Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 181540
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
940 AM MDT MON JUL 18 2016

.UPDATE...

.SHORT TERM...Today through Wednesday night

Imagery shows broad ridge across the intermountain west, southwest
and plains with incoming trof over the PAC NW. Embedded
disturbance currently riding through the ridge across northern WY with
a couple of nocturnal showers/storms still in tow. Surface has
generally weak high pressure across WY with low pressure off to the
southwest over the Great Basin and Desert southwest. A monsoonal
type flow is in the process of setting up.

..Red Flag warning for portions of Natrona and Fremont Counties this
afternoon and early evening...

Through the forecast period: Upper ridge moves a bit further east
into the plains while the ridge center sets up across the
southern/central plains. With heat induced low pressure setting
up across the Great Basin and Desert Southwest, a monsoonal type flow
is setting up across the southern and central Rockies. However,and
unfortunately, the moisture at this time is being directed
through the southern Rockies but then is being shunted eastward into
eastern/southern portions of WY...leaving most of the FA, except for
the south, rain free. Each day, a lee side trof/weak surface low
will try to build over central/eastern WY. With the upper ridge axis
then tilted slightly from southeast to northwest, the upper level
flow over most of the CWA will be from the southwest and quite dry
and capped. Today`s through Wednesday`s convection will then lay
across southern/southeastern WY with only a few isolated
showers/storms over possibly initiating across the higher terrain of
the areas mountains with little to offer but sprinkles. The Uinta
and Medicine Bow mountains will have the best chances for laying
down measurable precip. Fire danger elevated across most lower
elevations, moderate to elevated in the mountains and extreme today
across Natrona county where fuels are critical. Red Flag Warning may
be somewhat tricky to verify by winds/rh as it will likely be dry
with less wind early afternoon with then as winds come up late
afternoon and early evening, rh values will also rise with moist
airmass from the south. However, Haines values look to range in the
5 to 6 range which should be good enough. Expecting fuel status to
change dramatically this week across much of WY as a couple of large
incident fires have just recently taken hold the last day or two due
to lightning starts.

.LONG TERM...Thursday Through Monday

Medium range period shows the mean upper high moving wwd from the
KS/OK/N TX region on Thursday wwd to Ern CA/NV area by Monday.
Limited monsoonal moisture is still around the sern zones on
Thursday before a shortwave passes through the Nrn Rockies Friday
pushing drier air in from the west. We might get a secondary sewd
moving shortwave moving into the Nrn High Plains Saturday which may
serve to push some wwd by Sunday. Will add in some isold storms in
Johnson County for starters and see how the pattern looks again
tonight. Models vary on where that Saturday shortwave will end up
being with the GFS further north in MT and the ECMWF further south
with some impact in Nrn Wyo. The GFS also has a sewd moving
shortwave on Sunday that moves right through the area but with
limited moisture. We always have to watch sewd moving shortwaves in
the nw flow so we`ll just have to see how this pattern evolves over
the next couple days. Right now the end of the period, Monday, looks
warm and dry. Temps start out quite hot and then cool a few degrees
Friday into Saturday (with a front dropping into most areas east
of the divide, even if just for a short period) then rebound
slightly for most areas Sunday into Monday.

.AVIATION.../12Z ISSUANCE/

VFR conditions at all terminals through the forecast period.
South to southwest surface wind of 12-25kts will be the main
concern for Monday. Winds will increase between about 18Z-20Z,
and expect these speeds to be widespread. Lowest confidence
is at KCOD and KWRL. Winds will be diurnally driven and will
taper off between 0030Z and 02Z/Tuesday. Enough mid-level
moisture and lingering boundaries to trigger some isolated
high-based showers Monday afternoon. Best chance should come
across the southwest, but overall pin-pointing of genesis
areas is is difficult. Primary hazard with any convection
would be gusty outflow wind of 35-45kts.

.FIRE WEATHER...

..Red FLag Warning for portions of Natrona and fremont Counties...
fire wx zones 280...283 and 300...this afternoon and early evening...

Fire danger will elevated for all lower elevation zones over the
next several days with moderate to elevated conditions in the
mountains as warm/hot, dry conditions prevail with little chance for
rainfall relief across most of the forecast area (except for perhaps
the far southern zones. Otherwise, extreme fire conditions expected
across portions of Natrona County this afternoon through early
evening as low rh and gusty winds combine with Haines values of 5 or
6 and critically dry fuels. Expecting fuel status to change across
much of the region this week as dry conditions continue for yet
another week and some large fire starts have now taken hold few
locations across western Wyoming.

&&

.RIW Watches/Warnings/Advisories...
Red Flag Warning from 1 PM this afternoon to 8 PM MDT this
evening for WYZ280-283-300.

&&

$$

SHORT TERM...Braun
LONG TERM...Skrbac
AVIATION...CNJ
FIRE WEATHER...C.Baker


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