Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250536 AAA
AFDCYS

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
1136 PM MDT Fri May 24 2019

.SHORT TERM...(This evening through Saturday)
Issued at 152 PM MDT Fri May 24 2019

Lots to worry about the next few days. Forecast concerns deal with
strong winds today...followed by severe storms Sunday and then
heavy rainfall Monday and Tuesday.

Currently...Surface analysis showing trough moving through
southeast WYoming this afternoon. This trough has caused winds to
increase in the wind prone areas earlier this morning and
afternoon. Weather sensors are showing a decrease in winds at
2PM...so feel we can allow the High Wind Warnings to expire on
time at 3PM. Will continue to monitor though the next 15-20
minutes though to make sure winds are coming down.

Getting some showers out over the Snowy and Sierra Madre Ranges
this afternoon. Will keep chance PoPs going through sunset for
Carbon County.

A pretty nice day Saturday is expected as a transitory high
pressure system moves through the area. 700mb temperatures climb
to +8C over southern Wyoming...so afternoon highs should climb
into the 60s and low 70s.

.LONG TERM...(Saturday night through Friday)
Issued at 152 PM MDT Fri May 24 2019

Next shortwave moves through Sunday. Going to have southeast low
level winds across the Panhandle. GFS/NAM guidance showing
afternoon CAPE near 2000 to 2500 J/KG Sunday afternoon into the
evening across the Panhandle. South to southwest 250mb jet
overhead at 80-90kts for substantial shear over the eastern
Wyoming plains and Nebraska panhandle. There is a risk for
tornadoes across the southern Panhandle with helicity values near
160m2/s2. Would not rule out a couple tornadoes from Scottsbluff
to Sidney to Pine Bluffs Sunday afternoon and evening. Would
expect SPC to expand their Slight Risk area further west into the
Wyoming Plains on later updates.

Upper low moves into western Colorado Monday and slowly tracks
across the state through Tuesday. Guidance going pretty high on
QPFs through that timeframe. GFS soundings Monday and Tuesday
showing forecast storm motions of 10kts or less...so storms that
do form will produce very heavy rainfall. Right now...it looks
like the northern Panhandle into Niobrara County will be in the
bullseye of this heavy rainfall. Being a holiday weekend...decided
to issue a Flood Watch for these zones to cover the storms Sunday
afternoon through Tuesday afternoon. May need to expand watch
further south as the event shows more of its true track. Could
still be a few severe thunderstorms across the southern Panhandle
Monday afternoon with GFS soundings showing elevated CAPE near
Sidney around 2000 J/KG.

Finally see a break in the active weather Wednesday as upper low
moves east and conditions dry. Going to be an active beginning to
the week though. Stay tuned.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1136 PM MDT Fri May 24 2019

VFR category expected across SE Wyoming and western Nebraska for
the next 24 hours, with stratus coming in late tomorrow night
ahead of the next approaching upper trough. Right now any low
ceilings under upslope are on the far end of the 24 hr forecast
and lower confidence to add to the forecast.

&&

.FIRE WEATHER...
Issued at 330 AM MDT Fri May 24 2019

Fire weather concerns will remain low through the period with the
recent precipitation and a period of unsettled weather with almost
daily chances of afternoon showers and thunderstorms. Saturday and
Sunday will have the lowest forecasted Min RHs from the upper teens in
Carbon County to the mid 20s across the WY High Plains. Wind gusts
over the weekend will generally be in the upper teens to low 20s.

&&

.HYDROLOGY...
Issued at 330 AM MDT Fri May 24 2019

With the recent wet, heavy snowfall across the area, initial reports
have area streams and creeks on the rise with portions of the White
River out its banks at Hwy 385. The White River sensor at the NE/SD
border been slowly declining after rising back close to 17 feet
Thursday. Continued wet pattern and snowmelt will likely not ease
the flood risk or water levels for the next several days. A Flood
Advisory remains in effect but considering the ongoing impacts
and little expected relief given an active wet pattern in the
forecast may likely need to be extended. Biggest concern going
forward with the active pattern will be the possibility of rain on
snow from the mountain ranges to the Pine Ridge in NE. Depending
on rates and intensity further flooding concerns remain for rapid
rises in area rivers and streams besides the White River.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flood Watch from Sunday evening through Tuesday morning for
     WYZ102.

NE...Flood Watch from Sunday evening through Tuesday morning for
     NEZ002-003-095-096.

&&

$$

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


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