219
FXUS65 KCYS 141945
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
145 PM MDT Sun Jul 14 2024

.KEY MESSAGES...

- Red Flag Warning for the majority of southeast Wyoming and
  portions of the Nebraska Panhandle today. Dry thunderstorms
  will become scattered to numerous, and possible fire starts
  from lightning strikes may occur.

- Very hot temperatures will continue through Monday. Heat
  Advisories remain in effect for the High Plains along and east
  of I-25.

- Increased precipitation chances and cooler temperatures are
  expected late Monday through Wednesday.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 145 PM MDT Sun Jul 14 2024

High based thunderstorms beginning to develop across parts of
the CWA at 1PM. Seeing lightning strikes across central Laramie
County near Cheyenne...and out in Carbon County from Rawlins to
Arlington. Beginning to see development across Albany County and
southern Platte County as well. Looking at GFS forecast
soundings...18Z PWATS range from 0.6 inches out near Rawlins to
0.7 inches in the Panhandle. There is a surface trough analyzed
along a line from Pine Bluffs to Casper along the east slopes of
the Laramie Range. An upper level vort max moving through the
ridge this afternoon providing some upper level lift which will
set us up for a pretty significant dry lightning event the
remainder of this afternoon into this evening.

Looking at HRRR and RAP simulated radar...convection blossoms
after 22Z along the Laramie Range with high based storms moving
into the Panhandle through 03Z-04Z. Given very dry air in the
lower elevations...storms will be high based and mainly dry.
Given what we are seeing currently...will keep the Red Flag
Warnings going as they are through 10 PM this evening. Local
fire customers will need to be on alert for increased fire
starts with these dry thunderstorms through mid to late evening.

PWATS on the increase for Monday...increasing to an inch across
southeast Wyoming and near 1.2 inches in the Panhandle. Better
chances for wetting rains. ECMWF/SREF/NAM and GFS all showing
fairly widespread QPF across the CWA. Continued high PoPs (50-80
percent) Monday afternoon and evening...that dissipate towards
06Z.

These diurnally driven showers and storms will continue Tuesday
with good chances for afternoon and evening storms. Long/skinny
CAPE profiles suggest storms capable of producing heavy rainfall
with these increased PWATS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Issued at 431 AM MDT Sun Jul 14 2024

For the extended period, weather across SE WY and E NE will be
dominated by a persistent ridge of high pressure over the western
half of the United States. A broad upper trough centered over
Ontario at the beginning of the period will shift east into Quebec
by Thursday, allowing the western ridge to expand north and east
causing height rises and weakening flow aloft through Saturday.
Abundant mid-upper level mositure will continue to round the ridge
over WY and W NE. At the surface, persistent southerly/southeasterly
flow will keep low-mid-50s dew points in W NE through the weekend.
Confidence in the large scale evolution through Saturday is high
given ensemble and deterministic model agreement. By Sunday, models
begin to diverge on the timing of a trough digging into the
northwest US, which may begin to break down the ridge for the end of
the weekend and start of next week.

For Wednesday, showers and thunderstorms look to be most abundant
for this day given the position of the ridge  allowing for better
flow aloft and embedded disturbances to force development. With PW
values ranging from 0.75" to over 1" over much of E WY and W NE,
above normal for this time of year, storms that develop could
produce heavy rainfall. Flash flooding potential will be enhanced by
relatively slow storm movement. Both Instability (adequate moisture
beneath steep ll and ml LRs) and borderline deep layer shear (still
decent flow aloft) should support a strong-severe storm, especially
further east into NE. Temperatures across the region will be the
coolest of the forecast, with highs ranging from the low to mid 80s
for most. Confidence in the general precip+temp forecast for Wed is
moderate-high, with details regarding exact location of storms and
severe potential low-moderate.

Thursday through Saturday, as the ridge expands and heights rise,
flow aloft will weaken, and temperatures will rebound. Although deep
layer shear and instability will be slightly weaker, abundant
moisture aloft and very deep inverted V profiles will support
showers and storms producing gusty winds, along with a dry lightning
potential, especially further into WY. The strongest thunderstorm
potential will be confined to W NE where ll mositure and shear will
be best. High temps each day are expected to rise into the upper 80s
to low 90s for the lower elevation areas. Confidence in the forecast
during this period is moderate, while that in thunderstorm intensity
is low given cross-model and run-run inconsistencies in the degree
of ll moisture return and extent during this period.

Sunday and beyond, the upper trough digging into the US should
dampen the ridge at some point impacting our sensible weather.
However, timing and impact differences yield low confidence in when
and what that impact will be.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1053 AM MDT Sun Jul 14 2024

VFR to MVFR conditions likely through the forecast period for
all terminals. Main concerns over the next 24 hours include
high based thunderstorm potentials and resulting gusty/erratic
winds. Current HiRes model guidance have remained consistent
over the morning hours for convection to begin shortly after 19z
across the Rockies and push to the east/northeast throughout the
afternoon hours. Could see a lightning strike or two associated
with any storms able to develop through the evening hours.
Otherwise, mostly gusty to stronger winds associated with the
higher bases expected.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 10 PM MDT this evening for WYZ417-418-
     425-428>433.
     Heat Advisory until 10 PM MDT this evening for WYZ101-102-107-
     108-118-119.
NE...Heat Advisory until 8 PM MDT Monday for NEZ002-003-019>021-054-
     055-095-096.
     Red Flag Warning until 10 PM MDT this evening for NEZ435>437.

&&

$$

SHORT TERM...GCC
LONG TERM...WFOCYS
AVIATION...MRD