Area forecast discussion
National Weather Service Cheyenne Wyoming
541 am MDT Wednesday may 22 2013
Short term...(this evening through Thursday night)
issued at 545 am MDT Tuesday may 21 2013
Low clouds are spreading across the Nebraska Panhandle early this
morning as low level moisture increases in NE surface winds. The pressure
falls associated with a closed midlevel low over the Pacific
northwest will combine with pressure rises across the northern
plains to keep the east-to-southeast surface winds going over the plains
throughout the day. 40s dewpoints reach the Laramie range by late
this afternoon...so there will be some weak instability along and just
east of the range in southeast Wyoming. Kept the general slight chance
probability of precipitation in the forecast. Low level relative humidity forecasts and soundings over the plains show
widespread stratus development tonight. The saturated layer is
around 4-5 kft deep along the Cheyenne Ridge and southern Laramie
range so cannot rule out some drizzle also.
Main story for Thursday and Thursday night will be the strengthening
southeast surface winds and persistent stratus along and east of the Laramie
range. A shortwave will move northeast from Nevada into western
Montana from Thursday into Thursday night. At the same time...a surface
low will follow the parent upper level feature from western Wyoming into
central Montana. S and southeast winds will strengthen with the increasing
pressure gradient through the late afternoon...with occasional gusts to
30-35 kts. Low clouds will likely be quite persistent over the
plains through at least the late morning/early afternoon. Despite the
high dewpoints...there is a strong capping layer on the soundings
between 700-600mb...so thunderstorm potential (except maybe right along the
Laramie range) is quite limited. The winds will likely begin to
come down by late Thursday night as the surface low pulls
northward...however a low level jet over the Panhandle could keep
the winds going there. The GFS shows 800mb south winds of 45-50 kts
and would be most concerned along the ridgetops for Wind Advisory
potential.
Long term...(friday through Tuesday night)
issued at 545 am MDT Tuesday may 21 2013
Stagnant upper level trough over the West Coast will maintain
southwest flow aloft through the period. A number of shortwave
features will move across the region in this flow pattern with
some variation of timing between the the models. Developing surface
low pressure over the northern rockies will move east through the
day and will drag a surface front through much of the forecast
area. Looks to stall along the Wyoming/NE border in the late afternoon
before retrograding westward through the evening. Some midlevel
moisture will move up with the shortwave and surface dew points will
range from the 30s out west to the 40s and 50s across the eastern
plains. 700mb temperatures will be on the high side...ranging from
roughly 9c to 12c by the late afternoon. Nevertheless...the
combination of upper level and surface forcing with marginal deep
layer moisture will bring a chance for showers and thunderstorms
mainly across the Nebraska Panhandle in the later afternoon and
evening where surface forcing is strongest. Further west...dry air and
a strong capping inversion will keep convection limited over the
high country and adjacent Wyoming plains. Saturday will see a
similar setup with models showing a slight timing difference with
the shortwave embedded in the flow. Overall moisture availability
looks better for the late afternoon though...so even with variability
of shortwave timing should still see a chance for showers and
thunderstorms along and east of the Laramie range Saturday
afternoon.
Models then show some differences with the ejection of stronger
shortwave features on Sunday and Monday. The European model (ecmwf) is about 500 Michigan
quicker than the GFS and Canadian...meaning a better chance for
showers and thunderstorms across the good majority of the County Warning Area. Will
maintain relatively low probability of precipitation across the Eastern Plain for the
variation in forecast solutions for now. Models then begin to
converge once again on a solution that digs stronger energy across
the Desert Southwest with the upper trough moving overhead Tuesday
and Tuesday night. There are some bigger differences with surface low
placement from the GFS and European model (ecmwf) which will have a big difference
as to coverage and intensity of showers and thunderstorms for the
forecast area Tuesday afternoon. Could also see lingering
convection through Tuesday night with the trough axis overhead.
Have higher chance probability of precipitation across the east with less over the high
country.
&&
Aviation...(for the 12z tafs through 12z Wednesday night)
issued at 545 am MDT Wednesday may 22 2013
Models keep IFR/MVFR ceilings through the middle-to-late morning across
portions of the Nebraska Panhandle. The low clouds should then become
more scattered through the rest of the afternoon. Weak instability
along and just east of the Laramie range will promote isolated
afternoon showers. With the moist southeast winds continuing
through the end of the taf period...low clouds should redevelop
between 06-09z over the plains. Low clouds will be more widespread
than this previous night. Southeast wind gusts to 30 kts will be
possible at klar by the early morning Thursday.
&&
Fire weather...
issued at 545 am MDT Tuesday may 21 2013
Fire weather concerns will be minimal over the next few days as east
and southeast surface winds transport good moisture along and east
of the Laramie range. The southeast winds will become quite gusty on
Thursday afternoon and Thursday night. A warm up is in store for the
weekend and this will cause afternoon minimum relative humidities to
drop into the 15-20 percent range across the lower elevations of
southeast Wyoming. In addition...southwest winds will be breezy at
times over the weekend across southeast Wyoming.
&&
Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&
$$
Short term...Finch
long term...rjm
aviation...Finch
fire weather...Finch
