Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191139
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
539 AM MDT THU MAY 19 2016

.SHORT TERM...(Today through Saturday)
Issued at 330 AM MDT Thu May 19 2016

Predawn water vapor imagery depicted a potent shortwave trough
moving into the Pacific Northwest...with some active convection
developing from idaho into western Montana. A downstream ridge
dominated the Great Basin northeast across the central Rockies. A
surface trough extended from central Montana through central
Wyoming and western Colorado. South to southwest winds 5 to 15 kt
and temperatures from the upper 30s to lower 50s prevailed.

The 00Z short range model guidance progs the upper ridge to slowly
translate east toward the Great Plains through Friday as the
closed low and associated trough dig south along the Pacific coast.
Warmer temperatures and modest lapse rates over the higher terrain
of southeast Wyoming will result in widely scattered shower/thunderstorm
development this afternoon over the higher terrain...spreading east
onto the high plains mid to late afternoon. High temperatures this
afternoon will be 5 to 10 degrees warmer compared to yesterday.

Upper diffluence and southwest flow aloft will increase Friday
and Saturday. South to southeast low level winds will advect higher
dew points /45 to 55 degrees/ into the high plains both afternoons.
Surface-based CAPE is forecast to peak between 500 and 1000 j/kg.
Convection Friday will primarily be focused over and just downstream
from the Laramie Range...with a few strong thunderstorms with brief
heavy rain and small hail possible. High temperatures Friday will
warm into the 70s to lower 80s. The best chance for marginally
severe thunderstorms will be Saturday afternoon over the eastern
plains of Wyoming...mainly east of I-25 as CAPE values exceed 1000
j/kg with 0 to 6 km shear values near 30 kt. The main threats would
be strong winds...locally heavy rain and hail. High temperatures
Saturday will be nearly identical to Friday.

.LONG TERM...(saturday night through Wednesday)
Issued at 330 AM MDT Thu May 19 2016

Saturday night...We may experience a few strong to severe thunderstorms
in the evening along and east of I-25...and mainly north of a Wheatland
to Alliance line in the evening along a surface trough/dryline based
on projected shear and instability. Thunderstorms weaken after midnight.

Sunday...Focus for afternoon and evening thunderstorms will shift to
our southeast counties from Cheyenne to Alliance where a low level
convergence boundary is progged. Isolated late day thunderstorms
elsewhere.

Monday...Low and mid levels dry out considerably with southwest flow
at low and mid levels, thus only isolated late day thunderstorms on
tap.

Tuesday...Perhaps a slight increase in low and mid level moisture
suggests a slight increase in afternoon and evening thunderstorm
coverage, mainly over and near the mountains.

Wednesday...Models prog another shortwave across our counties in the
afternoon with a low level convergence axis setting up. With an
increase in low and mid level moisture, expect an increase in late
day thunderstorm coverage, especially along and east of I-25.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 538 AM MDT Thu May 19 2016

VFR prevails. Isolated thunderstorms at Laramie and Cheyenne
this afternoon. Wind gusts from 20 to 30 knots from late this
morning through this afternoon.

&&

.FIRE WEATHER...
Issued at 230 AM MDT Thu May 19 2016

No fire weather concerns anticipated with green fuels and recent
moisture. A more typical late springtime pattern with warmer
temperatures and daily chances for isolated to scattered mainly
afternoon and evening thunderstorms will prevail through Saturday.
Minimum humidities will remain above critical thresholds. Wind
gusts will generally remain below 25 mph...except near thunderstorms.
It will turn cooler following the passage of a cold front Sunday...
with mainly isolated showers and thunderstorms.

&&

.HYDROLOGY...
Issued at 245 AM MDT Thu May 19 2016

For the North Platte River, the latest forecast for Mitchell, Nebraska
indicates a crest near 9.2 feet today and remaining near that level
through the weekend. Minor to moderate flooding will continue near
Henry and Minatare, Nebraska for the next several days. Moderate
flooding will also continue at Fort Laramie, with the river steady
near 8.2 feet. Finally, the Laramie River at Laramie is forecast to
rise to near 9 feet today, fall to 8.5 feet Saturday and rise once
again to near 9 feet Monday. Minor flooding is forecast for Saratoga
and Sinclair, Wyoming late this weekend.

Will be monitoring snowmelt runoff through the weekend as mountain
daytime temperatures warm into the 50s with nighttime lows in the
mid-upper 30s...along with gusty southwest winds. Additional rises
in streams and river levels are likely. High water levels will
continue for the Little Snake River near Dixon and Baggs, Wyoming.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

SHORT TERM...Jamski
LONG TERM...Rubin
AVIATION...RUBIN
FIRE WEATHER...Jamski
HYDROLOGY...Jamski



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