Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXUS65 KRIW 260815
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
215 AM MDT Wed Jul 26 2017

.SHORT TERM...(Today through Friday night)
Issued at 118 AM MDT Wed Jul 26 2017

Imagery still shows broad upper flat ridging across the CONUS with
bookend trofs/lows over each coast and the high "centered" across
the srn Rockies and over the srn Plains. The strong upper level trof
that has been migrating across srn Canada is now located over/across
Ontario with some re-amplification of the ridge to the west from the
northern PAC NW through BC and Alberta. Monsoonal flow continues to
rotate around the upper high, directed by SFC low pressure over the
Desert SW. The best deep monsoonal moisture stretches from nrn
MX/ern AZ/wrn NM through CO/ern UT and into WY. SFC has general low
pressure across the swrn/wrn CONUS (heat induced over the Desert SW)
with post frontal high pressure over most of WY this morning with a
subtle SFC trof into the ern portion of Sweetwater County but the
main front well to the southeast over the High and Central Plains. A
few showers are exiting the eastern portion of Sweetwater County
with the SFC trof while the heavy areas of precipitation are to the
south spread over parts of CO.

Tuesday, the FA began to feel the first, albeit on the weaker side,
effects of the monsoon. Today the upper ridging pattern continues
flat early but starts to recover heights slowly through the day as
the strong upper low continues to cross into sern Canada and more
amplified ridging over the wrn CONUS rotates back over WY. Dew
points across the CWA are above 50 for most of the lower
elevations...and even near 45 degrees above 9k ft with PWs ranging
from 0.75 to 1.10 inches. A (pseudo) warm front looks to form/return
across WY between building lower pressure west and southwest and
post frontal high pressure to the southeast of the FA. This boundary
and the "return" of flow from the east/southeast will help in
retaining or reinforcing moisture back into the CWA. This boundary
along with the terrain and a weakening upper level disturbance
moving into/over of the area later this afternoon and evening will
help provide the forcing and focusing necessary for day/night
locally heavy rain/showers and thunderstorms. Localized flooding
potential will be heightened once again especially over the
mountains while thunderstorm potential will be better today than on
Tuesday across wrn/swrn WY in the later afternoon/early evening
period. Some breaks in the clouds with sunshine getting through
would certainly help. Storm environment from mid afternoon through
mid evening over wrn WY will be characterized by moderate CAPE/low
shear early...becoming moderate shear as CAPE decreases in the
evening as the weak shortwave moves across. Most storms should
behave except for better chances for some storm organization with
localized heavy rain and flooding possible. Some small hail possible
too.

Thursday, moisture remains across the FA for another day while the
upper ridge continues to translate ewd toward the ern border of WY
while what`s left of the embedded wrn coastal low moves through the
increasingly southwest flow aloft Thursday afternoon and evening,
pushing a weak front through and giving another day of localized
significant rainfall potential (less flooding potential however)
with perhaps even a few more storms on the strong side found across
WY...especially portions of central/eastern WY including Natrona and
Johnson Counties where CAPE and effective shear will be best
over/near a SFC trof/frontal boundary.

Friday, the ridge axis continues to move eastward and the FA dries
out some from the west. Another weak upper lvl disturbance will move
across the nrn FA by late afternoon and evening giving mainly small
isolated chances for showers/storms over nrn and ecntrl WY including
Johnson and Natrona counties.

.LONG TERM...(Saturday through Wednesday)
Issued at 118 AM MDT Wed Jul 26 2017

The driest day in the extended looks to be Saturday as the upper
ridge continues to build into the region with 30 meter rises in
24-hrs. However still can see isolated thunderstorms over the
mountains and adjacent foothills. Monsoonal moisture looks to
surge back into the area Sunday and Monday, and remain across the
area through Wednesday. Steering currents are quite weak so could
see some heavy rain producers. Will go with slight valley/low
chance mountain PoPs through much of early next week with a peak
in the afternoon/evening. Due to the monsoonal nature of the
precip, could see the precip linger well into the night.

Temperatures will be seasonal for the most part as the daily
chances of convection and associated cloud cover will help keep
temps from getting to hot.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 118 AM MDT Wed Jul 26 2017

Showers and thunderstorms will redevelop over the west and south
around 18Z. This activity will develop or spread into the north and
central parts of WY after 21Z. Locally heavy rain will occur with
stronger storms. This will produce local MVFR conditions due to
reduced visibility. Mountains will be obscured at times. Showers and
storms will be decreasing in coverage by 06Z with lingering showers
over the north through 12Z Thursday.

&&

.FIRE WEATHER...
Issued AT 118 AM MDT Wed Jul 26 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). Today, fire danger low for most mountain
locations...low to moderate for all other lower elevations as
moisture, clouds and cooler weather continue across the forecast
area as monsoonal moisture infiltrates Wyoming from the south. Winds
will continue seasonally light across the forecast area today with
the day`s gustiest winds found near stronger showers or
thunderstorms (25 to 35 mph). Today there will be increasing chances
for isolated to widely scattered showers/storms across the lower
elevations...and scattered chances over the mountains. Expect
periods of of localized heavy rain today and again Thursday. Drier
weather to return Friday.

&&

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

&&

$$

SHORT TERM...Braun
LONG TERM...Murrell
AVIATION...Ross
FIRE WEATHER...Braun



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.