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449
FXUS65 KCYS 252331
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 PM MDT Wed Sep 25 2024

.KEY MESSAGES...

- Elevated to critical fire weather conditions are expected
  Thursday. A Red Flag Warning has been issued for parts of
  southeast Wyoming.

- Above average temperatures and dry conditions expected for the
  forseeable future.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 155 PM MDT Wed Sep 25 2024


There is not a cloud in the sky across the forecast area this
afternoon as we remain under the axis of an unseasonably strong
upper level ridge. 700-mb temperatures approaching or exceeding the
99th percentile of climatology are already in place this afternoon
and will hold for most of the next 24 hours or so. However, the next
shortwave trough is already visible on satellite imagery starting to
push into the Pacific northwest. This feature will race inland
tonight into tomorrow, with the southwest flow supporting lee
cyclogenesis over the Montana/Canada border tonight. Falling surface
pressure to the north and northwest while modest high pressure
remain in place over the plains will increase the surface pressure
gradient across the area tonight. The resultant low level jet should
keep a southerly breeze over the elevated areas along the High
Plains tonight. Thursday morning, the trailing pressure trough to
the south of the surface cyclone well to our north will pull east of
the mountains, bringing an end to the southerly winds but increasing
the westerly winds. Downslope flow in addition to the extremely warm
temperatures at the top of the boundary layer will lead to Thursday
being the warmest day of the period. Afternoon highs will challenge
daily records as well as the latest readings of certain temperature
thresholds. Look for temperatures to surge into the low to mid 90s
for most of the Nebraska panhandle and low spots of Wyoming. With
very low humidity in place, the westerly breeze may be enough to
reach critical fire weather conditions in a few spots. See the Fire
Weather section below for more details.

A weak surface cold front will drift southward through the area by
Friday morning, but 700-mb temperatures around +11 to +13C will
still be near the 90th percentile of climatology. Despite dropping
perhaps 5-10F below Thursday`s highs, Friday`s highs will still be
close to 10F above average for this time of year. Fortunately, winds
will be a little weaker and humidity a little higher on Friday,
which should reduce fire weather concerns.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Issued at 155 PM MDT Wed Sep 25 2024

Upper-level ridging is expected to dominate through the long term
period. On Saturday an upper-level ridge will remain firmly in place
across the Intermountain West. Strong subsidence will be present
under the ridge leading to mostly clear skies and warm temperatures.
700mb temperatures will be between 13 and 15C, which is around the
90th percentile across the area. This will promote above-average
temperatures for this time of year, with highs in the low-80s to low-
90s. This pattern will continue through the weekend before an upper-
level Canadian trough traverses off to the north of the CWA on
Monday. This trough passage is expected to be dry, but cooler
temperatures will return in its wake. 700mb temperatures drop into
the 1 to 10C range, with the warmest temperatures across
southwestern portions of the CWA where the trough does not impact
nearly as much. Due to the low moisture available, this passage
should remain mostly dry. Ridging builds in once more behind the
departing upper-level trough. Expecting temperatures to increase as
700mb temperatures warm back into the 10 to 12C range Wednesday
onward.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
-- Changed Discussion --
Issued at 530 PM MDT Wed Sep 25 2024

A strong upper level high pressure for late September will push east
into the Great Plains tonight and Thursday. This will result in a
continuation of quiet weather.

HAZARDS/WEATHER TRENDS: VFR conditions will continue over the next
24 hours. Breezy conditions for KCDR with gusts up to 30 knots
possible between 04z and 11z Friday.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Issued at 155 PM MDT Wed Sep 25 2024

Warm and dry conditions continue for the forseeable future. Poor RH
recoveries are possible tonight in a few areas, mainly in the wind
belts where breeziness will keep temperatures warm tonight. This
includes the Laramie range, Pine Ridge, Snowy and Sierra Madre
foothills, and northern Carbon County. The southerly winds over the
High Plains will weaken Thursday morning but westerlies will then
increase across much of the area through the afternoon. Critical
fire weather conditions are now expected across much of southeast
Wyoming north of the I-80 corridor. Confidence is high in RH
reaching critical, but there is some uncertainty if winds will reach
25 MPH. However, the probability is high enough to warrant a Red
Flag Warning.

Slightly cooler temperatures and lighter winds will improve
conditions for Friday and Saturday, but winds may start to pick up
again Sunday into early next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

-- Changed Discussion --
WY...Red Flag Warning from 11 AM to 8 PM MDT Thursday for
     WYZ417>422-427-432.

NE...None.
-- End Changed Discussion --

&&

$$

SHORT TERM...MN
LONG TERM...AM
AVIATION...TJT
FIRE WEATHER...MN