Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 250430
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1030 PM MDT Mon Jul 24 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 153 PM MDT Mon Jul 24 2017

Today will be the last day we can call hot and dry as several
upper level disturbances/vort maxes are poised for our area to the
south and west of us. One area of interest have been the ongoing
light rain showers/virga showers that have been lurking over
Sweetwater County since this morning and will be replaced by a
fresh round of isold convection later this afternoon/evening as a
result of an area of weak vorticity in that area. Then a more
pronounced vort over central Idaho will be scooting eastward to
give our northwest zones some weak nocturnal convection tonight.
Two other areas of interest, a vort max that has been producing an
area of thunderstorms over Arizona, which the NAM seems to handle
the best, and another one over the Nevada/Oregon border, which
the GFS handles the best, will be arriving and converging over our
CWA Tuesday for much more significant rainers out of Tuesdays
convection as higher dew points in the 50s spread north, replacing
dew points in the 30s along with PW values well over an inch.
Lifted indices will decrease to near minus 4 across the southeast
CWA Tue. The added moisture will increase our cape values,
especially over the southern CWA. Tuesday afternoon and evening
will be very active as scattered to numerous thunderstorms develop
from these multiple vort maxes and increasing monsoon moisture.
Locally heavy rainfall and frequent lightning as well as some
gusty winds should be the dominant feature with these storms.
These storms should persist well into Tuesday night as these
weather features track across the CWA, a common phenomenon that
occurs with us deep into monsoon season. Localized flooding is
certainly a possibility across portions of the cwa. Wednesday
should be a repeat of Tuesday as another shortwave tracks
northeast across the area with another round of wet thunderstorms.
These storms should persist into Wednesday evening before drier
air begins to filter into the areas late Wednesday night from the
west as the ridge over the far west begins to amplify. Thursday
will feature another round of late day convection, but the
distribution of any convective cells will be a bit less across the
south and southwest but still more numerous in the north half
with PW values ranging from 1.3 in Northeast Johnson County to 0.5
across the western CWA. Temperatures will be 10 to 15 degrees
cooler Tuesday and Wednesday from the significant increase in
clouds and precip with highs in the 80s east of the divide and
upper 60s to 70s west of the divide. Thursday will be warmer once
again after the bulk of the clouds/precip move off to the
northeast. Beginning Thursday, more of the monsoon moisture supply
will start to be shunted off to the south and east.

.LONG TERM...(Tuesday night through Monday)
Issued at 153 PM MDT Mon Jul 24 2017

Medium range period will likely see little change with varying
amounts of monsoonal moisture streaming n and ne across the area
each day. The mean large scale ridge looks like it will stay near
or just east of the 4-corners. The GEM and Euro want to take the
upper high nwwd bringing a drier nw flow to the area by Friday
into the weekend but I lean towards the upper high staying off to
the south with our area being susceptible to disturbances and
moisture from the s/sw each day. Temperatures will remain
seasonable warm with daily variations due to cloud cover and
showers (some of which could be in the morning at times depending
on shortwave location each day). Generally mid 80s and mid 90s
east with 70s and 80s west. High country generally 60s and
70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday)
Issued at 1030 PM MDT Mon Jul 24 2017

VFR conditions will continue through 18Z Tue. Isolated showers will
occur in southwest WY overnight through 15Z. After 15Z, showers and
thunderstorms will be developing over south and southwest WY. This
activity will spread northeast through Tuesday afternoon into Tue
night. Locally heavy rain will occur which will create local MVFR
conditions due to reduced visibility. Some wind gusts to 30 knots
will occur near storms. Showers and storms will decrease toward 06Z
Wed.

&&

.FIRE WEATHER...
Issued AT 153 PM MDT Mon Jul 24 2017

Fuels are now at critical levels for most forecast zones east of the
Divide (Please see the Fire Weather Forecast product for more
information). Fire danger is moderate for most mountain
locations...elevated for all other lower elevations due to very
warm to hot daytime temperatures and low humidity levels. Tuesday
will begin to see a stronger influx of monsoonal moisture into the
forecast area and fire danger levels should decrease. Winds will
continue seasonally light through this evening across the entire
forecast area with typical diurnal slightly gusty afternoon winds
found around the region as the atmosphere mixes out. Slightly
stronger frontal/post frontal winds out of the north expected on
Tuesday before winds settle down once again Wednesday. Some
exceptions will occur, of course, near any stronger shower/storm
when winds could briefly gust 25 to 45 mph...especially through
this evening over the northern mountains and adjacent foothills.
A slightly better isolated to widely scattered chances for
showers/storms will occur over the northwest mountains and
adjacent foothills tonight before much better chances for wetting
rainfall, even possible periods of of localized heavy rain, on
Tuesday and Wednesday.

&&

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

&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...AR
FIRE WEATHER...Lipson


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