Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 251745
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1145 AM MDT WED MAY 25 2016

.UPDATE...
Issued at 1121 AM MDT Wed May 25 2016

Latest radar trends showing isolated showers developing across
southeast Wyoming where we had dry conditions in the forecast.
Went ahead and added 20 percent pops in the forecast for this
late this morning and afternoon. Updates have been sent.|

&&

.SHORT TERM...(Today through Friday)
Issued at 330 AM MDT Wed May 25 2016

Predawn water vapor loop depicted a positively-tilted upper trough
from south central Canada across the northern Rockies to a low off
the central California coast. An active southwest flow aloft was
transporting weak shortwave disturbances northeast across the Four
Corners...central Rockies and plains. A fast 250 mb jet max and
shortwave aided in the development of several convective clusters
over the Great Plains. Converging outflow boundaries from convection
over northeast Colorado generated a narrow line of thunderstorms
over the southern Nebraska Panhandle shortly after midnight. This
activity will soon enter western Nebraska. A quasi-stationary
surface front extended from eastern South Dakota into western
Nebraska then south through the high plains. A moist boundary and
light winds over the Nebraska Panhandle resulted in a growing area
of stratus.

Good run-to-run consistency with the numerical models as the upper
trough to the west slowly translates east across the Rockies and
high plains through Friday. The front draped across the high plains
will also shift east with its moist unstable air mass today. The
next shortwave lifting northeast from the Four Corners combined
with the weak surface trough will aid in the development of widely
scattered afternoon showers and thunderstorms. The HRRR and RAP
models indicate cell motion to the east-southeast. There may be a
few stronger cells producing small hail and gusty winds, especially
east of the Laramie Range. High temperatures today will be near
seasonal normals with 60s to mid 70s valleys and plains, and 40s
and 50s for the high country.

The coverage of showers and thunderstorms will increase Thursday
and Friday as the upper low over southern California tracks east-
northeast across the Four Corners, Colorado and central High Plains.
Model QPF has been consistent showing between a quarter and a half
inch of liquid equivalent precipitation. Locally heavier amounts
will be possible with thunderstorms. Snow levels will drop to
8500 feet Thursday night, with scattered showers producing a few
inches of snow over the higher peaks of the Snowy and Sierra Madre
mountains. The greatest severe potential Thursday and Friday will
be focused over the Great Plains, with a marginal risk for a few
strong to possibly severe thunderstorms south and east of a line
from Chadron to Laramie. High temperatures for the high plains
will cool back into the 60s on Friday, with 40s and 50s for higher
elevations.

.LONG TERM...(Friday night through Tuesday)
Issued at 1124 PM MDT Tue May 24 2016

The main weather story through the long term forecast period will
be near normal temperatures with isolated to scattered showers and
thunderstorms. Generally looking at an upper level trough across
the western conus through early next week. Chances for showers and
thunderstorms will occur nearly each day with the main chances in
the afternoon. Several shortwaves will move across the forecast
area this weekend and into early next week but timing is somewhat
in question. Placement and timing will one of the main drivers as
to how much precipitation falls. Currently the expectation is for
weak upper forcing with any given shortwave and limited moisture
availability. generally not looking for widespread or heavy
precipitation through early next week, of course with thunderstorm
activity a few localized places may see some heavier rains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1142 AM MDT Wed May 25 2016

The main concern to aviation ops this afternoon will be the
isolated shower/thunderstorm activity that is already developing
across southeast WY & west NE. Coverage and intensity will be
limited so sufficient to just include mention of VCTS at most TAF
sites. Will of course monitor these trends and amend if
thunderstorms become more imminent. Thunderstorm activity will
dissipate quickly this evening, giving way to just some passing
mid/high-level clouds overnight.

&&

.FIRE WEATHER...
Issued at 245 AM 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 245 AM 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.
&&

$$

UPDATE...GCC
SHORT TERM...MAJ
LONG TERM...SML
AVIATION...CAH
FIRE WEATHER...MAJ
HYDROLOGY...MAJ



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