Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 231735

Area Forecast Discussion
National Weather Service Cheyenne WY
1135 AM MDT Tue May 23 2017

.SHORT TERM...(Today - Thursday)
Issued at 406 AM MDT Tue May 23 2017

Rain showers have decreased considerably in coverage and intensity
over the last few hours, but recent radar imagery still shows some
lingering activity over mainly southeast Wyoming. We will continue
to be under the influence of cyclonic flow aloft today, as another
piece of upper-level jet energy translates across southeast WY and
western NE. The HRRR suggests scattered instability showers mainly
between 15z-21z, decreasing from NW-SE as the H25 jet continues to
advance. Temperatures are expected to be a bit cooler today in the
post-frontal air mass, but still expect widespread 50s or possibly
low 60s. Breezy today along and east of the Laramie Range with the
passage of the aforementioned wave. Warm and dry for Wed as upper-
level ridging rapidly builds into the region and H7 temps climb to
+10 to +12 deg C. Low-level gradients become fairly strong on Weds
as a vigorous disturbance/clipper system over WA/ID/MT contributes
to cyclogenesis and a sub 990-mb sfc low tracking across northeast
WY on Wed afternoon. Wind gusts to 40+ MPH are possible, mainly in
areas along/W of the Laramie Range. The models suggest down-stream
blocking will slow the progression of the low/associated shortwave
along the Canadian border, forcing another cold front into the CWA
on Thursday along with increasing chances for showers/storms.

.LONG TERM...(Thursday night through next Monday night)
Issued at 445 AM MDT Tue May 23 2017

Medium and Long Range models continue to show an unsettled weather
pattern across southeast Wyoming and western Nebraska with nearly
daily chances of showers and thunder through the weekend.
Northwest flow aloft will continue across the northern and central
Rockies and will likely bring cool temperatures through the
Memorial Day weekend. An upper level low in southern Canada will
move very little through the weekend, keeping the forecast area on
the western flank of this low as it drifts south into the northern
plains/Great Lakes region. Upper level disturbances and jet energy
will dig southward out of Canada resulting in periods of rain
showers, widely scattered thunderstorms, and high elevations
rain/snow across the mountains. Friday and Saturday look to be the
most unsettled days with high temperatures struggling to reach
the mid 50`s along and west of I-25, with highs around 60 further
east. Kept POP between 40 to 60 percent across the region for
scattered to numerous showers and widely scattered thunderstorms.
Pretty good chance for a tenth to three tenths liquid each day
along the I-80 corridor. So will have to continue to watch streams
and creeks across the area. Models shows a lower coverage of
showers and thunderstorms by Sunday and Monday as the upper level
low begins moving northeast across the Great Lakes area. High
temperatures should increase into the 60`s to low 70`s across the
area on Monday although models show convection developing in the
mountains and pushing east across the valleys and high plains.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1131 AM MDT Tue May 23 2017

Cyclonic flow combined with the low level moisture will continue
to trigger scattered showers mainly east of the Laramie Range this
afternoon. These showers will be diurnally driven, and should
mostly dissipate after sunset. Gusty north winds will also prevail
this afternoon, but these wind speeds should also diminish after
sunset along with clearing skies.


Issued at 406 AM MDT Tue May 23 2017

No fire weather concerns due to recent, widespread heavy rain/snow
and resultant moist fuels. Wednesday is expected to be the warmest
day this week, with widespread highs in the 70s and perhaps around
80 in the Platte River Valley. This will result in RH values of 25
percent or less in many areas, along w/ gusty winds along and west
of I-25. Again, fuel conditions should preclude the threat for any
significant fire growth.


Issued at 230 PM MDT Mon May 22 2017

Concerns through the middle of this week will focus on runoff from
the recent heavy precipitation into area creeks and streams east of
the Laramie Range. Although flooding is not anticipated, many of the
creeks and streams may reach bankfull by the middle of the week.
High temperatures Wednesday in the 50s and 60s above 8000 feet will
result in snow melt and runoff. Cooler temperatures over higher
elevations after mid-week should slow the snow melt and resultant
runoff into the mainstem rivers. Routine monitoring of water levels
will continue over the next few weeks.




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