Area Forecast Discussion
Issued by NWS Cheyenne, WY

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953
FXUS65 KCYS 260620 AAA
AFDCYS

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
1220 AM MDT THU MAY 26 2016

.UPDATE...for the midnight aviation forecast package.

&&

.SHORT TERM...(This evening through Friday Night)
Issued at 300 PM MDT Wed May 25 2016

Unsettled weather to continue through the short term. Challenges
deal with shower coverage and severe thunderstorm possibilities.

Currently...Water vapor imagery showing longwave trough across the
northern Rockies to a closed off low in southern California.
Southeast Wyoming remains in southwest upper flow with pieces of
energy being ejected northeast from the southern California low.
One such piece of energy is moving through the area this afternoon
and it has kicked off scattered showers and thunderstorms. Did
increase pops this afternoon in an earlier update.

Latest SPC Mesoanalyst CAPE showing highest CAPE values over
southwest Nebraska this afternoon...with 2500J/KG over Ogallala.
Further west...CAPEs are on the order of 500J/KG. Convection will
ease by early evening with lack of surface heating.

Process to return Thursday with maybe a little more coverage and
intensity. Both the GFS and ECMWF bring some energy into
southeast Wyoming from the southwest. Looks like the severe threat
should be to our southeast where SPC has an Enhanced area
identified.

Friday shows a closed upper low tracking into southwestern
Nebraska from central Colorado. Should see fairly widespread
shower coverage across our southern zones and especially out west
over the mountains. Fortunately...freezing levels will be quite
low...so most of the precip over the mountains will fall as snow.

.LONG TERM...(Saturday through Wednesday)
Issued at 300 PM MDT Wed May 25 2016

The active pattern persists with daily afternoon/evening shower
and thunderstorm chances continuing thru the period. Low pressure
area centered over western Canada/PacNW over the weekend along
with weak afternoon instability (progged sbcapes of 200-500 j/kg)
will produce isolated showers and thunderstorms Saturday and
Sunday. The upstream system will split as it shifts east on
Memorial Day sending shortwave energy southeast into the
intermountain west. Latest forecast information suggests that
Monday will bring better convective organization and coverage to
the CWA. Otherwise, expect temperatures to slowly warm, but even
so just back to seasonal averages. Models diverge towards the
middle/end of next week as the ECMWF ushers in a drier/warmer
pattern, while the GFS remains seasonally unsettled.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1220 AM MDT Thu May 26 2016

Lingering but weakening shower activity moving northeast out of
northern Colorado will move through the Sidney, NE area through 4
AM...and kept a VCNTY mention for SHRA there for the next few
hours. Otherwise...expecting VFR category to prevail at all
airports across SE Wyoming and the western NE Panhandle through
the forecast period, with scattered showers and thunderstorms
returning with a mention in the mid afternoon through the early
evening hours tomorrow. Fairly similar pattern to what we saw
yesterday.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Wed May 25 2016

Cool and moist conditions will preclude fire weather concerns
through the end of the week. Scattered showers and thunderstorms
will provide wetting rains, with snow showers for elevations above
9000 feet.

&&

.HYDROLOGY...
Issued at 300 PM MDT Wed May 25 2016

Cool temperatures will persist through the end of the week with
morning lows in the upper 20s-lower 30s and afternoon highs in the
mid 40s-lower 50s for the mountains. These cool temperatures will
slow the snowmelt runoff into the streams and tributaries of the
Upper North Platte and Laramie rivers. A low pressure system moving
across Colorado Thursday and Friday will produce a good coverage
of showers and thunderstorms, with precipitation amounts from a
quarter to half inch. Locally higher amounts will be possible with
thunderstorms. The higher peaks of the southeast Wyoming mountains
may receive a couple inches of snow. Will be monitoring the impacts
of rain on snow for area rivers, creeks and streams this weekend.

&&

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

$$

SHORT TERM...GCC
LONG TERM...CAH
AVIATION...JG
FIRE WEATHER...GCC
HYDROLOGY...GCC



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