Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 252331
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
531 PM MDT Thu May 25 2017

.SHORT TERM...(This evening through Saturday)
Issued at 244 PM MDT Thu May 25 2017

Weak frontal boundary just to our south and east this afternoon
will wash out early Thursday. This will allow the surface winds to
become more SE`ly on Thursday morning and set up decent moisture
return across the high plains of SE WY and W NE. Aloft, a
shortwave trough will drop south into eastern ID late tonight and
then slowly track eastward into western WY on Thursday. Most
ingredients for strong to severe convection will be present
especially for southern and eastern portions of the CWA tomorrow,
roughly south and east of a Wheatland to Scottsbluff to Alliance
line. Steep lapse rates aloft and strengthening mid level flow
above surface dewpoints in the upper 40s to around 50 will combine
for MLCAPE around 1000 J/KG with effective bulk shear values of
40-45kt. These values would support supercell structures capable
of fairly large hail. LCL`s will be lower than today so can`t rule
out an isolated tornado, but the overall threat will be limited
by weak low level shear and curvature in the lowest 1 km. One
concern with regards to the severe threat will be the amount of
heating prior to convective initiation. Will likely see some cloud
cover around which may limit solar insolation. Capping inversion
seen on most model soundings should hold until later in the
afternoon so may see things fire a bit later than today.

Storms may tend to consolidate into one or more clusters over
western NE Friday evening and persist into the early overnight hours
before exiting to the east.  Saturday will feature the main upper
trough moving overhead so temps will be cooler with brisk northerly
winds east of the Laramie Range.  Cool air aloft and lift from the
upper trough will again allow scattered showers and isolated
thunderstorms to develop but the severe threat should be minimal.

.LONG TERM...(Saturday night through Wednesday)
Issued at 244 PM MDT Thu May 25 2017

Northwesterly flow aloft will dominate the pattern Sunday into
early next week as the upper ridge builds across the Northwest.
The models indicate the ridge axis moving eastward toward Wyoming
by Wednesday/Thursday.  Temps will begin to moderate back toward
normal for late May, and maybe even rise to slightly above normal
by Wednesday. With northerly llvl flow and limited moisture
advection, convection through Tuesday will mostly confined to the
higher terrain along and west of the Laramie Range. The severe
storm risk will be low through early next week with only weak
instability across the region during the aftns. Overall the
weather will be quite nice, especially considering the cool/wet
stretch over the past few weeks.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 527 PM MDT Thu May 25 2017

Wyoming TAFS...VFR, except for IFR at Laramie and Cheyenne from
10Z to 15Z. Isolated showers and thunderstorms through 04Z. Wind
gusting from 25 to 35 knots after 15Z Friday.

Nebraska TAFS...VFR, except for IFR at Sidney from 09Z to 15Z.
Isolated showers and thunderstorms through 04Z. Wind gusting to 24
knots after 15Z Friday.

&&

.FIRE WEATHER...
Issued at 244 PM MDT Thu May 25 2017

Cloudy skies and cooler temps through the weekend with chances
for scattered to numerous convection through Saturday. Conditions
begin to dry out early next week but the recent precipitation and
fuels being in green-up will preclude much of a fire weather
threat.

&&

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

$$

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



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