Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 181745
Area Forecast Discussion
National Weather Service Riverton WY
1145 AM MDT MON JUL 18 2016
.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.
Showers and thunderstorms will continue to develop across the
southwestern area today. Current activity is mostly confined to
the SE corner of Sweetwater county, and across Johnson county.
VCTS has been included at the southwestern terminals including
KPNA, KBPI, and KRKS. Gusty wind to 35 kts will be possible with
thunderstorm activity today along with mountain obscurations.
Shower activity will weaken through the evening, with primarily
mountain showers remaining along with some activity persisting
across Sweetwater county including KRKS.Additionally, with
ongoing wildfires, some slight visibility restrictions will be
possible, especially across KJAC with the SW flow aloft.
Otherwise, VFR conditions are expected, with a push of stronger
wind possible between 18z and 03z this evening.
..Red FLag Warning for portions of Natrona and Fremont
Counties... fire wx zones 280...283 and 300...this afternoon and
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.
Red Flag Warning until 8 PM MDT this evening for WYZ280-283-300.