Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
000
FXUS65 KCYS 202340
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
540 PM MDT Thu Jul 20 2017

.SHORT TERM...(This evening through Saturday)
Issued at 326 PM MDT Thu Jul 20 2017

Radar shows a scattered coverage of showers with a few thunderstorms
along and west of the Laramie Range. As expected, lapse rates are
steadily steepening across the area, with a minimum tho still
stretching from Wheatland eastward into the Nebraska Panhandle.
Effective bulk shear has increased to 25 to 30 kts across the WY
plains and southern 2/3rds of the NE Panhandle, so still on track
for a few stronger storms to produce small to maybe marginal severe
size hail. At this point, storms look to be moving at a reasonable
speed which will reduce the threat for flooding. However, hints of
training and development along outflow boundaries is evident as
well, meaning the heavy rain/flooding potential may increase over
the next few hours. This is especially true across the plains where
PW`s range from 1" to 1.4", if storms can maintain long enough off
the mountains. Otherwise, not much else to update on the forecast
through tonight from the earlier update.

The upper high over the southern CONUS will weaken and flatten
Friday through Saturday, putting us into a more west-northwest flow.
The monsoonal plume will push to the south as a result, with
showers/storms expected to be more focused across our high terrain
and southern counties on Friday, and mainly near the Colorado border
on Saturday. As has been the trend lately, the bulk of the activity
expected on Friday will occur late afternoon through the evening and
could produce heavy rain and small hail, with showers persisting
overnight. Much drier air will filter in from the northwest on
Saturday, although residual moisture over areas near the Colorado
border could spark off some showers/storms. Temperatures will still
be quite warm in the 80s and 90s through Saturday as well.

.LONG TERM...(Saturday night through Thursday)
Issued at 326 PM MDT Thu Jul 20 2017

Midlvl ridge will continue to build into Wyoming into Sunday with
drier northwesterly flow aloft moving into the region.  The GFS
shows PW values dropping to 0.5-0.8 inches so chances of storms will
remain rather low, especially with the subsidence aloft.  Kept PoPs
rather low through early next week with rather strong ridging and
drier westerly 700-500 mb flow.  Temps will warm to slightly above
normal by Monday/Tuesday, but nothing too hot for late July.  The
GFS and especially the ECMWF show better storm chances returning to
the area by the middle of next week as the subtropical ridge
flattens.  Will be conservative with PoPs for now since this is
nearly a week away.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 537 PM MDT Thu Jul 20 2017

Currently showers and thunderstorms scattered mainly west of a
line from Lusk to Pine Bluffs. Latest short term forecast models
are showing this activity increasing in coverage and intensity as
it tracks into the NE Panhandle early this evening. Maintained
MVFR visibility and gusty winds with this activity for the
Nebraska terminals through the late evening hours. Otherwise VFR
should prevail with another round of scattered convection
developing mainly over the SE Wyoming terminals eastward to KSNY
tomorrow afternoon.

&&

.FIRE WEATHER...
Issued at 326 PM MDT Thu Jul 20 2017

Showers and thunderstorms will continue to increase in coverage from
west to east this afternoon and evening. Some storms could produce
heavy rain and mainly small hail, along with gusty/erratic surface
winds. Another round of storms  is expected Friday afternoon and
evening, then a general warm and dry pattern will take over through
the weekend. Cannot rule out isolated storms through the weekend,
mainly over the higher terrain.

&&

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

$$

SHORT TERM...RJM
LONG TERM...ZF
AVIATION...DEL
FIRE WEATHER...RJM



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.