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Area Forecast Discussion (AFD)

Issued by Cheyenne, WY (CYS)

                            
000
FXUS65 KCYS 191729
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1125 AM MDT Thu Sep 19 2019

.SHORT TERM...(Today and tonight)
Issued at 243 AM MDT Thu Sep 19 2019

Quite a breezy and blustery day across much of the forecast area
today as an upper level trough approaches the region.
Southwesterly winds will be gusting into the 30 to even the 40 mph
range especially across portions of Carbon, Albany and Converse
counties in WY. While the main trough remains over the western
Rocky Mountains, pockets of vorticity will advect ahead providing
lift today to initiate convection this afternoon.

Strong to severe storms will remain fairly isolated in spatial
coverage extending from the Laramie Range eastward into the
northwest corner of the NE Panhandle. Main threats will be large
hail and strong winds. Better convective ingredients will be east
of the Laramie Range over the high plains with around 1500 J/kg of
CAPE and some mid-level speed shear that should provide for some
longer lived storms before they diminish with the loss of
sunlight. 

Decent WAA today with the southwesterly winds will allow for quite
a warm up above seasonal norms with low to mid 80s over the high
plains and mid 70s over the western forecast area. 

.LONG TERM...(Friday through Wednesday)
Issued at 243 AM MDT Thu Sep 19 2019

Upper level trough with associated cold front will slowly move
through the forecast area on Friday with vorticity advection
coupled with the seasonably warm winds will aid in the development
of strong to severe scattered thunderstorms in the afternoon.
Trended POP and QPF grids to reflect this threat and maintain
spatial continuity with the Day 2 Slight Risk issued by the SPC. 

While the main low moves into the western Great Lakes region, a
quick embedded shortwave will pass through Saturday night
providing another chance of light precipitation as a ridge of high
pressure moves into the region clearing things up for Sunday. 

Long-range models covering the extended forecast period still
tracking with the active pattern as another Pacific Low moves
onshore Sunday afternoon. Main 00z solutions still suggest the
stalling of this low as it becomes closed off in southern CA and
AZ. Drier, warmer air from the American Southwest will keep
temperatures above seasonal norms along with another dry spell
with not much precipitation being suggested for Tuesday and
Wednesday. Continued monitoring of model runs on the closed low 
and when it moves back into the atmospheric flow will determine 
how long the warm spell lingers and when we can see additional 
precipitation. 

&&

.AVIATION...(For the 18Z TAFS through Friday morning)
Issued at 1125 AM MDT Thu Sep 19 2019

VFR conditions expected today and tonight across the area. There is 
a 10 to 20 percent chance for showers and a few thunderstorms late 
this afternoon and through this evening, but will keep VCTS or VCSH 
out of the TAFs due to limited coverage.  Gusty west to southwest 
winds are expected this afternoon for mainly KRWL and KLAR with 
gusts up to 35 knots possible.  Further east, a strong low level jet 
will develop ahead of a Pacific storm system which will impact the 
region on Friday. Gusty south winds are forecast for KCDR, KAIA, and 
possibly KSNY after sunset with gusts as high as 35 knots possible 
at times mainly between 03z to 10z Friday. 

&&

.FIRE WEATHER...
Issued at 242 AM MDT Thu Sep 19 2019

Main concerns for Thursday and Friday fire weather wise will be
the increased winds across the western and eastern portions of the
forecast area and increased precipitation chances by strong to
severe thunderstorms. Winds across Carbon, Albany, and western 
Converse counties will see wind gusts in excess of 35 mph today. 
Min RH values today will be from the upper teens into the low 20s
with Friday seeing mid to upper 20s as the lowest RH values ahead
of an approaching cold front Friday. Widespread wetting rains
chances fairly low given the dry air in association with the
frontal boundary as best precipitation chances will be with the
isolated to scattered thunderstorms. 

&&

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

$$

SHORT TERM...WM
LONG TERM...WM
AVIATION...TJT 
FIRE WEATHER...WM