Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171803
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1203 PM MDT Mon Jul 17 2017

.SHORT TERM...(Today through Wednesday)
Issued at 315 AM MDT Mon Jul 17 2017

GOES-16 water vapor loop showed the upper ridge axis extended from
north of Lake Superior southwestward across the central Great Plains
and Southwest CONUS. A cold front reached from northwest ND through
southern MT and ID, and northern NV. A weak pressure gradient over
the CWA generated light and variable winds. Skies were fair to partly
cloudy and temperatures ranged from the upper 50s to lower 70s.

The short range models and ensembles are consistent with the gradual
east-southeast shift of the upper ridge, with its center over the
south central Great Plains by mid-week. For today, a shortwave is
progged to track northeast across the CWA this afternoon and evening.
The front to the northwest weakens as it progresses southeast into
the high plains this afternoon. Moisture convergence and lift from
the shortwave will initiate convection west of I-25 this afternoon,
increasing in coverage east of I-25 through this evening. With CAPEs
near 2000 j/kg and 0-6km shear values of 30 kt late this afternoon
and early evening over the high plains, isolated strong to marginally
severe t-storms will be possible. Main threats would be hail and
strong winds. High temperatures will range from the mid 80s to mid
90s.

A more typical July pattern is shaping up for Tuesday with diurnal
convection confined to the mountains and along a stalled front
from the southern Laramie Range into western NE. Similar high
temperatures are forecast Tuesday.

The upper ridge expands westward into southeast WY and western NE
Wednesday. Warmer temperatures aloft will preclude shower/t-storm
develop, except for the southern mountains aided by moisture and
orographic lift. 700mb temperatures around 20 deg Wednesday afternoon
will push the mercury into the 90s to lower 100s across the high
plains.

.LONG TERM...(Wednesday night through Sunday)
Issued at 300 AM MDT Mon Jul 17 2017

The upper high pressure area over the southern plains will continue
to slip slowly east through Friday allowing for a surge of monsoonal
moisture to advect across the CWA especially from Wednesday night
through Thursday night. This looks to be the period for the most
widespread showers and tstms for the CWA. For Friday through the
weekend, the moisture looks to be shunted more to the south of the
CWA as the upper high flattens and leaves the CWA on the southern
fringe of westerly flow aloft. Quite warm still for Thursday, though
clouds may keep temps down some. Friday through Sunday, temperatures
should be cooler and closer to seasonal averages.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1201 PM MDT Mon Jul 17 2017

Wyoming TAFS...VFR. Isolated thunderstorms near Laramie and
Cheyenne from 22Z to 03Z.

Nebraska TAFS...VFR. Isolated thunderstorms near Alliance,
Scottsbluff and Sidney from 21Z to 03Z.

&&

.FIRE WEATHER...
Issued at 230 AM MDT Mon Jul 17 2017

The upper ridge responsible for the very warm temperatures and dry
conditions will shift to the southeast early this week. A upper level
disturbance and front moving south across the high plains will enhance
shower and thunderstorm development this afternoon and evening. Generally
dry and very warm conditions will return Tuesday and Wednesday. Abundant
monsoonal moisture will result in a higher coverage of showers and
thunderstorms Thursday and Friday, with the potential for locally heavy
rainfall. Winds will be light, except variable and gusty in the vicinity
of thunderstorms.

&&

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

$$

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



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