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Office: CYS

FXUS65 KCYS 171120
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
355 AM MDT Wed Aug 17 2022

.SHORT TERM...(Today and tomorrow)
Issued at 355 AM MDT Wed Aug 17 2022

Key Impact Messages:

1) No impact messages needed do to quiet weather.

Weather Details: We are tracking an area of low clouds across the
NE Panhandle this morning. This area of low clouds is beginning to
approach the NE/WY border and may move close to Cheyenne. Road
cameras are not showing and significantly reduced visibilities
and or fog. Expect this area of low stratus to dissipate soon
after sunrise.

Short term forecast remains under the influence of an area of high
pressure building across much of the Intermountain West. This area
of high pressure has shutoff the moisture tap and brought in some
dry air into the region. This system will slowly move east today
through Thursday. Mostly clear skies and light winds are expected
with warm temperature. Models are beginning to trend toward this
area of high pressure remaining the main weather feature as latest
model runs want to stall out the high pressure system keeping the
better moisture well south of our area.

.LONG TERM...(Friday through Tuesday)
Issued at 355 AM MDT Wed Aug 17 2022

Precipitation chances Friday through Sunday are trending lower with
the latest ensemble runs bringing very little to no precipitation to
southeast Wyoming and the Nebraska panhandle. The best chance is in
the Snowy and Sierra Madre mountain ranges, and maybe the south
Laramie Range. However, with precipitation chances trending lower,
temperatures have also trended lower this weekend with a backdoor
cold front dropping across the Nebraska panhandle into eastern
Wyoming! Saturday morning looks to be the coolest morning with lows
across southeast Wyoming being 41 to 55 degrees (53 deg F in
Cheyenne) and 53 to 56 degrees across the Nebraska panhandle.

The main uncertainty will be in how far southwest the front drops.
Right now, the GFS has the cold front stalling along a line from
Sidney, Nebraska to near Casper, Wyoming Friday afternoon, then
backing up as a warm front through the day Saturday.

Tuesday another backdoor cool front moves into the Nebraska
panhandle and southeast Wyoming. This front looks to be stronger and
advect both monsoonal and Gulf moisture, greatly increasing the
precipitation chances as it combines with the instability from the
front. Stay tuned for more details as we get closer to mid-next
week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 520 AM MDT Wed Aug 17 2022

A low stratus deck is bringing IFR with intermittent LIFR CIGS
across the NE terminals this morning. This area of low clouds may
expand toward the KCYS terminal over the next hour. This low status
deck will begin to dissipate between 14-15z, with rapid improvement
to VFR conditions. Expect VFR conditions to prevail through the rest
of the TAF period. Winds will continue to be light across all
terminals at less than 10 knots, become light and variable at times.

&&

.FIRE WEATHER...
Issued at 355 AM MDT Wed Aug 17 2022

Conditions will continue to warm and become drier
today and into Thursday. Minimum relative humidity values may
approach critical conditions for areas west of the Laramie Range
today, then spreading across the rest of the region on Thursday.
The limiting factor that will help keep fire weather concerns low
will be the continued light winds today and Thursday. Moisture
looks to return Carbon and Albany counties by the weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...AW
LONG TERM...LK
AVIATION...AW
FIRE WEATHER...AW



Office: RIW FXUS65 KRIW 171037 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 437 AM MDT Wed Aug 17 2022 .SHORT TERM...(Today through Thursday) Issued at 332 AM MDT Wed Aug 17 2022 Any remaining showers taper off by early Wednesday morning. Lows overnight range from the mid 50s to low/mid 40s. Winds will be light and variable with skies remaining mostly clear at sunrise. Wednesday is dry for many with mostly sunny skies and highs slightly above average. By the late afternoon/early evening a weak shortwave maked its way through northeastern WY. The disturbance taps into moisture and provides favorable lift, leading to convective showers and thunderstorms mainly over the Bighorn Mountains, which subsequently drift over Johnson County. Other than Johnson County, the high terrain has the best chance for getting a brief shower. Skies will again clear out by Wednesday evening into early morning Thursday. Most stay dry overnight as the upper level high to the west shifts further east, shifting flow aloft to a more north- northwest direction. Thursday will be mostly sunny with highs still slightly above average. Johnson county may have cooler highs in the wake of the shortwave that moved through Wednesday. Even with isolated showers and thunderstorms developing over the high terrain of western WY by the afternoon, most of the state will remain dry. Precipitation clears out by late Thurs evening, with high clouds moving into the western portion of the state. .LONG TERM...(Thursday night through Tuesday) Issued at 332 AM MDT Wed Aug 17 2022 Pattern remains relatively unchanged through the extended. A ridge stays entrenched across the western US until the middle of next week. A few week disturbances will try to undercut the ridge and provide some lift to WY. Thursday night monsoonal moisture begins moving into southwest WY as the first disturbance makes its way eastward. Slow movement of this disturbance is likely as it struggles to move east with the ridge acting as a blocking feature. This will result in isolated to scattered thunderstorms across southwest WY Friday and Saturday afternoon. By Sunday isolated thunderstorms are possible in central basins and the Bighorn Mountains as the disturbance shifts east. PWATs decrease on Monday, still remaining above normal, as monsoonal flow gets shut off. At the same time a shortwave passes to the northwest of the area, providing sufficient lift for showers and storms, especially across western WY. Wind aloft will consistently be light resulting in very weak wind shear. This combined with above normal PWATs will continue the trend of thunderstorms capable of producing localized flash flooding over the next seven days. The shortwave is still expected to influence weather on Tuesday with a shift in the location of convection to eastern portions of the CWA. This will be where the better moisture and lift exist. Another weak shortwave passes through on Wednesday with very little jet support. As of right now this appears to be the day with the most widespread showers and thunderstorms, especially for northern and eastern portions of the CWA. For the first half of the long term period, temps will be moderated in western WY thanks to rain chances and cloud cover. East of the divide, where skies will remain mostly clear, highs are not expected to be record-breaking, but seasonable highs in the upper 80s F and low 90s F are likely. This should change as cloud cover increases ahead of the shortwave and a cold front drops down over the north on Wednesday. Wind will be light through the long term period as this type of pattern keeps the pressure gradient lax. && .AVIATION...(For the 12Z TAFS through 12Z Thursday morning) Issued at 436 AM MDT Wed Aug 17 2022 VFR prevails at all terminals through the TAF period. Very isolated showers and thunderstorms are possible this afternoon, mainly impacting KCPR and possibly KPNA. Late this afternoon strong northerly outflow wind is likely at KCPR with gusts above 30 knots possible. Other terminals will have wind below 12 knots over the next 24 hours. Skies will be mostly clear across the area today through tonight. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued AT 332 AM MDT Wed Aug 17 2022 Today is likely to be the warmest and lowest humidity day of the week. Temperatures increase by a couple degrees compared to yesterday (Tuesday), and RHs will drop into the mid to upper teens during the afternoon hours. Winds will be light, and generally under 15 mph, except in the immediate vicinity of any isolated showers or thunderstorms. Most of the limited convective activity is forecast to remain over the high terrain, but Johnson county could see an isolated cell drift eastward off the Bighorn Mountains during the afternoon. Temperatures cool and and RHs will be a few percentage points higher on Thursday, as a trough edges in from the east. Light north and east winds are expected Thursday, with gusts 20 to 25 mph during the afternoon. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...VandenBoogart/Dziewaltowski LONG TERM...Rowe AVIATION...Rowe FIRE WEATHER...VandenBoogart/Dziewaltowski