447
FXUS65 KCYS 141754
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
Issued by National Weather Service Riverton WY
1154 AM MDT Wed May 14 2025

.KEY MESSAGES...

- A Pacific cold front will move southeast across the rest of
  the area early this morning with another round of showers and
  thunderstorms this afternoon through this evening.

- Very windy conditions expected for most of southeast Wyoming
  and portions of western Nebraska on Thursday. Gusts over 50
  mph possible.

- Seasonable temperatures into this weekend with a daily chance
  of showers and thunderstorms.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 227 AM MDT Wed May 14 2025

Current KCYS and KUDX radar mosaic shows the cluster of showers and
thunderstorms, which impacted portions of east central Wyoming and
the northern Nebraska Panhandle, continuing to lift northeast into
the Dakotas early this morning. This activity was in response to
some elevated instability and a surface cold front, which has
pushed southeast across most of eastern Wyoming and is moving across
the central and southern Nebraska Panhandle at this time. Expect
this front to continue sliding southeast across the High Plains,
bringing much cooler temperatures to the area on Wednesday.
Even though high temperatures will be 15 to 25 degrees cooler
compared to earlier this week, it will still be near seasonal
averages for this time of the year.

After a brief lull in the precipitation this morning, models show
the upper level trough axis translating eastward over eastern Wyoming
and western Nebraska/South Dakota during the day. With good mid to
upper level forcing, some low level instability, and midlevel
lapse rates around 7 to 9 C/km, expect rainfall and isolated
thunder to develop in the afternoon and continue through the
late evening hours across the eastern High Plains. Lowered QPF
values since most areas will still have a pretty dry boundary
layer behind the cold front, but a few places could see between
a quarter inch to a quick half inch of rain. Some snowfall above
8000 feet is expected with generally light accumulations in the
mountains through Wednesday night. West to northwest winds are
expected to increase across the area this afternoon and this
evening with gusts as high as 40 mph.

As for Thursday, it looks very windy across southeast Wyoming and
possibly portions of western Nebraska due to surface cyclogenesis
across Nebraska and South Dakota. 700mb winds are expected to
strengthen to around 50 knots over southeast Wyoming, and up to 60
knots across the far northern Nebraska Panhandle. Will have to
keep an eye on the usual wind prone areas and adjacent high plains
zones including most of the I-25 corridor. In addition, guidance
shows the higher ridges and nearby areas of the western Nebraska
Panhandle approaching high wind criteria in favorable northwest
winds. Expect sustained winds of 25 to 40 mph with gusts as
high as 55 mph. Expect another round of showers and isolated
thunderstorms Thursday with most of the activity in southeast
Wyoming into the evening hours. Thursday will likely be the
coolest day of the week with most of southeast Wyoming in the
50s to low 60s, with 60s to around 70 for western Nebraska.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 227 AM MDT Wed May 14 2025

Previous forecast on track through Saturday with models
continuing to show westerly flow aloft and near or slightly
below normal temperatures each day. Should be enough instability
and moisture to initiate widely scattered showers and a few
thunderstorms Thursday evening and on Saturday, especially across
southeast Wyoming. Friday looks like the driest day across the
region as a drier airmass moves into Wyoming and midlevel
subsidence associated with the building upper level ridge
axis increases. Otherwise, expect a slight warming trend just in
time for this weekend with high temperatures returning to the
upper 60s to mid 70s Saturday afternoon.

From late Sunday through early next week, we will be tracking
a potent Pacific disturbance which is forecast to dig southeast
along the West Coast and into the Great Basin region on Sunday.
Will continue to keep an eye on this system as we head into the
weekend, but model consistency has been poor with the new 00Z
GFS showing split flow with the northern branch of the jet the
most dominant into next Monday with no evidence of a Four
Corners low formation, which is completely different from the
00Z GFS solution from last night. Thus, 50th percentile and
ensemble mean QPF from the GEFS is much lower and shows
potential precipitation later in the forecast period compared to
yesterday. However, daytime and evening convection still looks
good in this pattern and can not rule out strong to severe
thunderstorms. 00Z ECMWF has shown better run to run
consistency and remains the most aggressive solution, showing a
well defined closed low lift northeast out of the Four Corners
region, as a series of shortwave disturbances lift northward
ahead of the main low late Sunday through Monday night. Kept PoP
above 50% to 60% for most of the area as this is a favorable
pattern for strong to severe thunderstorms and appreciable
rainfall amounts. Relatively low confidence with temperatures
late in the weekend and early next week as ensemble guidance
interdecile spreads are nearly 25 to 30 degrees.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1154 AM MDT Wed May 14 2025

Rain showers are expected for most locations this afternoon,
with Nebraska panhandle sites seeing a more persistent rain with
embedded thunderstorms that will linger well into the night.
KSNY is the location with the highest chance for stronger
thunderstorms this evening, with hail and strong outflow winds
possible (20% chance). Expect shifting winds this afternoon and
evening, especially in western Nebraska, as the rotating
weather system pivots through the region. VFR conditions are
epxected for a majority of the time; however, brief lowering of
cloud bases and reductions in visibility could happen in the
heavier showers and thunderstorms. Thursday will feature gusty
winds from the west and northwest, starting shortly after
sunrise.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...TJT
AVIATION...WFO-RIW