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Area forecast discussion 
National Weather Service Cheyenne Wyoming
414 am MDT Sat Aug 29 2015

Short term...(today through Monday night)
issued at 413 am MDT Sat Aug 29 2015

Quiet conditions prevail tonight with some smoke settling in and
bringing visibilities down between 5-7mi. Maintained smoke in the
forecast through later this morning but strengthening south-
southwest flow near the surface should clear things out through
the day considering the current layer that has settled into the
region seems to be somewhat thin.

Today will remain hot and dry with an upper level ridge overhead
and dry airmass in place. Temperatures will spike into the 80s and 90s
while humidities should drop into the low to middle teens by the
afternoon. Winds aloft within the ridge are prognosticated to remain 15
to 20 kts or less through about 250 mb according to NAM and GFS
forecast soundings...meaning gust potential will be limited. A
modest surface pressure gradient will remain in place through the day
and should promote breezy south to southwest sustained winds
with speeds around 15 miles per hour. The strongest winds should occur in
gap locations of northern Carbon County...and also along the Pine
Ridge in northern portions of the Nebraska Panhandle.
However...with relatively light winds aloft...gusts should remain
below critical fire weather thresholds. Thus will just maintain
the elevated fire weather wording in the forecast.

Another hot day is on tap for Sunday with temperatures once again in the
80s and 90s. Southwest winds over the County Warning Area will increase early
Sunday morning and moreso through the day as a shortwave moves
across the northern rockies. A fetch of subtropical moisture
within this strengthening SW flow pattern will filter into the
County Warning Area and increasing clouds moving into western zones will likely
keep temperatures a few degrees cooler than hottest case scenario. The
eastern plains should remain mostly clear until the later
afternoon so temperatures could approach the century mark. Within this
hot and more moist airmass...along with weak shortwave
energy...expecting a chance for showers a thunderstorms to develop over
the mountains in the early afternoon and shifting east through the
evening. Although winds overall will be stronger than today...with
gusts of 25 to 30 miles per hour possible across the southeast
Wyoming...humidities should remain upper teens to low 20s due to
increased moisture advection. Precipitable waters are prognosticated to be in excess of
0.75 inches by Sunday afternoon so wetting rains are quite
possible with afternoon convection. Gusty winds are also a high
likelihood with thunderstorm activity due to breezy gradient winds already
in place and forecast soundings showing inverted-v profiles to
roughly 550 mb.

The fetch of midlevel moisture will shift east and south for
Monday as the ridge moves to the east ahead of the shortwave
racing across the northern plains through this time. Low level
moisture will remain largely unchanged or perhaps may even
increase behind a cold front that will drop south across the area
Monday morning. Winds will veer from the north behind the front
to the south-southeast by the afternoon and evening...maintaining
low level moisture advection and initiating showers and thunderstorms mainly
along and west of the Laramie range in the afternoon and evening.

Long term...(tuesday through friday)
issued at 413 am MDT Sat Aug 29 2015

Monday's passing shortwave lifts out to the northeast by Tuesday
with just a few residual showers/thunderstorms possible Tuesday
afternoon over the snowy and Sierra Madre ranges. The jetstream
shifts back to the northwest through Friday with lighter
southwesterly upper flow over our area with a fairly dry airmass
aloft hanging around through Thursday...so no mention of probability of precipitation
across the forecast area through Wednesday and Thursday. The GFS
and European model (ecmwf) both depict slightly higher mean layer moisture being
drawn north across eastern Wyoming and the western Nebraska
Panhandle ahead of the next approaching shortwave by late
Friday...so we put in some probability of precipitation for the potential of isolated
showers and thunderstorms Friday afternoon generally along and
east of the Laramie range.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1146 PM MDT Friday Aug 28 2015

VFR/MVFR expected all forecast sites for the next 24 hours as the
northern part of a high amplitude upper ridge traverses eastern
Wyoming and western Nebraska. Smoke filtering in on northwesterly
flow aloft will reduce visibilities at times for some sites to
near 5 miles but still within MVFR ranges.

&&

Fire weather...
issued at 413 am MDT Sat Aug 29 2015

Elevated fire weather conditions are expected today as hot...dry
and breezy conditions take hold of the district. Humidities will
drop into the low to middle teens this afternoon but wind gusts
should remain less than 25 miles per hour. Winds will increase for Sunday but
so will humidities as subtropical moisture advects in from the
southwest. There is a good chance for showers and thunderstorms
over much of the district on Sunday as well...with wetting rains
a high likelihood. Monday will also see a good chance for showers
and thunderstorms mainly over the mountains with cooler conditions
expected behind a cold front dropping south through the area in
the morning.

&&

Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&

$$

Short term...rjm
long term...jg
aviation...sml/jg
fire weather...rjm

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