National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KCYS 282120
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
320 PM MDT Wed Jun 28 2017

.SHORT TERM...(This evening through Friday)
Issued at 320 PM MDT Wed Jun 28 2017

Scattered showers and thunderstorms have develop across southeast
WY over the past few hours ahead of a shortwave that is
currently located across western WY. The boundary layer is deep
once again today with dewpoint depressions of 35-45F. Current
thinking is that gusty downdrafts/outflows will be the main threat
through the early evening with the SPC showing Downdraft CAPE of
1200-1400 J/kg. Cannot rule out small hail also with a more
organized storm with good westerly flow aloft and bulk shear. Kept
20-30 PoPs going through at least 06Z, with good ascent ahead of
the shortwave. The other story this afternoon is the very dry
conditions to the west of the Laramie Range. The Red Flag Warning
for FWZ 306 is verifying right now with RH values of 15 percent
and gusts to 25-30 mph at Saratoga.

Shortwave will be directly over WY during the day on Thursday with
cooler temps behind a morning fropa.  Despite the cooler temps, min
RH values will drop to 15-20 percent for FWZ 306, so mentioned an
elevated fire weather threat in the FWF.  Highs will be around 10
degrees cooler.  Should see scattered showers and isolated tstms
develop by early aftn, with the best coverage across northern zones.
Dewpoint depressions will not be high owing to the cooler temps,
especially over the plains, so there is generally less threat of
strong downdrafts. A better push of cold air will move across the
CWA on Thursday night with highs on Friday falling another 5-10
degrees. Overall convective activity looks minimal, although with
colder air aloft, weak instability is progged.

.LONG TERM...(Friday night through Wednesday)
Issued at 320 PM MDT Wed Jun 28 2017

A steady warming trend will occur through the extended timeframe as
a broad area of high pressure develops over the western Conus. We`ll
start off in the 70s/80s on Saturday, increasing to the 80s/90s but
Wednesday. Outside of a few showers and isolated storms Sunday and
Monday associated with an upper level disturbance, conditions look
mostly dry. Most of the activity will remain in the mountains, but a
storm or two could affect the plains as well. Winds will generally
be breezy each afternoon across the region. The combination of dry
and breezy conditions may enhance fire weather concerns through
early next week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 320 PM MDT Wed Jun 28 2017

Scattered showers and thunderstorms have developed this afternoon
across the forecast area. Main concern will be gusty and erratic
winds in excess of 40 kts from any shower or storm that moves over
the terminals. As a result of the stronger winds, blowing dust
could reduce visibility in this activity. Showers and storms
should dissipate by 04Z for most locations, but locations near the
terrain may see a few showers continue overnight as an upper level
disturbance approaches from the northwest. Perhaps marginal MVFR
cigs may filter in from the north late tonight across the plains
in the wake of a weak cold front. A stronger cold front will move
north to south Thursday afternoon, bringing yet another round of
showers and storms to the area.

&&

.FIRE WEATHER...
Issued at 320 PM MDT Wed Jun 28 2017

Critical fire weather conditions will continue through the afternoon
for Fire Weather Zone 306 as relative humidity values have fallen to
around 15 percent and west winds will gust to 25-30 mph.  Isolated
to widely scattered showers and thunderstorms will be possible
across region through the evening.  These storms will contain little
rain, with gusty outflow winds being the main threat.  Cooler
temperatures on Thursday will cause an increase in humidity values,
especially along and east of the Laramie Range.  An elevated fire
weather threat is expected across zone 306, as west winds will still
be gusty and afternoon humidity drops to 15-20 percent.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 6 PM MDT this evening for WYZ306.

NE...None.
&&

$$

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