Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 270926
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
326 AM MDT Tue Jul 27 2021

.SHORT TERM...(Today through Wednesday night)
Issued at 325 AM MDT Tue Jul 27 2021

A strong ridge of high pressure aloft dominated the majority of
the Rockies and Plains. The 595 dm center was analyzed over WY.
Considerable dry air aloft and subsidence will promote very warm
to hot temperatures today and Wednesday as the ridge remains
nearly stationary. Areas of smoke from western CONUS wildfires
will continue to affect northern and western parts of the CWA
today. However, it will have little affect on high temperatures
today. 700 mb temperatures between 18 and 20 degrees Celsius
will yield afternoon temperatures between 90 and 105 degrees,
with 70s and 80s for the higher terrain. MOS guidance, which
underforecast Monday/s high temperatures by 3-5 degrees, is
within 1-2 degrees of today/s expected highs. A Heat Advisory
remains in effect for portions of east/southeast WY and the
northern half of the NE Panhandle for afternoon heat indices
around 100 degrees combined with low temperatures at or above 70
degrees. The 06Z high-res convective-allowing models (CAM) keep
convection confined to western WY through southern CO this
afternoon.

Subtle changes occur Wednesday as the monsoonal moisture plume
shifts east into central WY/CO. Daytime heating and orographic
lift will yield isolated to scattered diurnal convection over
Carbon and most of Albany counties per the latest CAMs. This
activity will lower high temperatures into the 80s and lower 90s.
Over the remainder of the CWA, it will be another hot afternoon
with highs in the mid 90s to mid 100s.

.LONG TERM...(Thursday through Monday)
Issued at 325 AM MDT Tue Jul 27 2021

Elongated upper ridge from the Central Rockies to the Lower/Mid
MS Valley will drift slowly south through the weekend. Subtropical
moisture will spread northward into the CWA. Precipitable water
values will rise above an inch Friday, and peak between 1" and 1.4"
Sunday and Monday. A backdoor front will move west across southeast
WY Thursday, with moderate easterly low level flow. Increasing
moisture at the surface and aloft combined with orographic lift
and upper level shortwaves will enhance shower and thunderstorm
activity, with the greatest coverage during the afternoon and
evening hours. Steering flow between 500 and 700 mb will be less
than 20 kt with weak effective shear. The primary hazard will be
locally heavy rain (greater than 0.25"/15 min), which will increase
the risk for burn scar flash flooding and debris flows. There is
a Marginal Risk of excessive rainfall for areas north and west of
a line from Cheyenne WY to Bridgeport NE. High temperatures in the
80s and lower 90s Thursday and Friday will cool into the 70s to
mid 80s this weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1123 PM MDT Mon Jul 26 2021

VFR. Wind gusts to 25 knots at Chadron until 10Z, and to 30 knots at
all terminals after 17Z.

&&

.FIRE WEATHER...
Issued at 325 AM MDT Tue Jul 27 2021

A strong ridge of high pressure in the upper levels of the atmosphere
will hold nearly stationary through Wednesday. This ridge will produce
hot daytime temperatures. Heat indices will rise to around 100 degrees
over the plains. Lowest humidities will range from 10 to 15 percent,
however wind speeds will remain less than 25 mph. Precipitation is
not expected today, with isolated to scattered showers and thunderstorms
west of the Laramie Range Wednesday as monsoonal moisture begins to
spread northward. Gradually cooler temperatures with increasing chances
for showers and thunderstorms is expected Thursday through the
weekend.

&&

.CLIMATE...
Issued at 325 AM MDT Tue Jul 27 2021

A record high temperature of 105 was set at Chadron NE Sunday. Forecast
high temperatures for Tuesday and Wednesday may tie or break records.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Heat Advisory from noon today to midnight MDT Wednesday night
     for WYZ102-108.

NE...Heat Advisory from noon today to midnight MDT Wednesday night
     for NEZ002-003-019-095-096.

&&

$$

SHORT TERM...MAJ
LONG TERM...MAJ
AVIATION...RUBIN
FIRE WEATHER...MAJ
CLIMATE...MAJ


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