Area forecast discussion
National Weather Service Cheyenne Wyoming
424 am MDT Wednesday Jun 19 2013
Short term...(today through thursday)
issued at 400 am MDT Wednesday Jun 19 2013
The upper level ridge will shift east today ahead of the strong low
moving across the Pacific northwest. A shortwave rounding the base of the low
will move across Nevada and into Idaho today...with upper level
winds increasing over The Rockies as this occurs. In addition...the
Lee side trough will deepen ahead of the wave...and will steadily
move east through this afternoon mimicking a dryline. Strong
moisture advection will occur across the High Plains as southeast
winds strengthen with the developing trough/dryline...with dew points
looking to increase to the middle 50s to low 60s east of the dryline.
As a result...cape readings will increase to as high as 3000 j/kg
in the eastern counties of the Nebraska Panhandle. However...temperatures
aloft will also increase in this pattern with 700mb readings
expected to be 14-16c by the late afternoon. Temperatures at the surface will
peak in the upper 80s to low 90s across the eastern plains in this
warm air advection pattern...but forecast soundings show the
environment ahead of the Lee trough to remain capped through much of
the afternoon. Weakening of the cap in the late afternoon combined
with strong convergence along the dryline and increasing broad scale
lift from the approaching shortwave trough should spark off showers
and thunderstorms over the Nebraska Panhandle. With the energetic
juicy environment ahead of the dryline...could see some storms
become strong and produce moderate to heavy rainfall at times...and
some hail. If the cap can break moreso than what the models are
depicting at this time...could see some storms become severe mainly
east of a Lusk to Sidney line where deep layer shear will increase
to around 40 knots. For now...will keep mention of severe out of the
forecast due to high uncertainty with the cap and marginal shear in
place this afternoon...but again moderate to heavy rain and some
hail should accompany any storms that do form in this area.
Further west...southwesterly 700 mb winds increasing to 30-40 knots
along and west of the Laramie range will bring windy conditions to
this area...and with humidities dropping to the single digits to low
teens...will see increased fire weather threat in this area. Fuels in
this region are still not primed for explosive fire growth so will
just keep strong mention of increase fire weather concerns in the
forecast. Winds within in the Lee trough across the Wyoming plains
will remain less...and so although it will also be quite dry in this
region...the somewhat muted winds should keep fire weather concerns
below critical thresholds.
The shortwave trough will move northeast across the forecast area
through the evening...and with the low level jet increasing after
sunset...should continue to see isolated thunderstorms develop ahead
of the dryline as it pushes eastward. Again...will have to watch for
some of these storms to become strong although elevated as steep lapse
rates will persist above the inversion. The models are not quite
picking up on much activity developing after sunset though so some
uncertainty remains as to exactly what will evolve as the shortwave
moves overhead.
For Thursday...much drier conditions will prevail as the Lee
trough/dryline moves well into Nebraska through the morning...with
yet another shortwave trough rounding the base of the main low and
over Wyoming in the afternoon. This will induce surface winds to return
to the east-southeast through the afternoon and evening...increasing
convergence along the Laramie range. Looks as though more middle and
upper level moisture will be available with this shortwave...so will
maintain at least a slight chance for high based thunderstorms along the
Laramie range in addition to the Snowy Range. Temperatures will be
somewhat cooler on Thursday as the closer proximity of the main
upper low allows upper level temperatures to cool a good 5c or so.
Long term...(thursday night through tuesday)
issued at 300 am MDT Wednesday Jun 19 2013
00z model guidance depicts a more progressive upper level pattern
across the lower 48. The upper ridge from the western Great Lakes
to the southern Great Plains drifts slowly southeast as a trough
over the Pacific northwest lifts east then northeast toward the
northern plains this weekend. Early next week...a broad upper ridge
will extend from the Ohio/Tennessee Valley into the Southern Plains. A
nearly stationary trough will reside offshore the West Coast with
a moist onshore west-southwest flow into the Pacific northwest.
A surface trough/dry line will extend from the Black Hills through
the western Nebraska Panhandle Friday. Marginal instability for
isolated diurnal convection will exist along and east of the dry
line...northeast of a line from Douglas to Sidney. As the low
moves across Montana Saturday...winds will back to southeasterly
advecting low level moisture into the eastern plains. Prognosticated
sbcapes up to 2000 j/kg will result in strong to possibly severe
thunderstorms during the afternoon and evening. Better coverage will be
from the northern Laramie range east through the northern Nebraska
Panhandle closer to large scale forcing.
As the upper low and trough lift northeast from the western Dakotas
toward Hudson Bay Sunday and Monday...it will push the dry line
east into the central Great Plains with warmer and drier air
infiltrating the region. Increasing southwesterly winds aloft will
transport to the surface resulting in gusty surface winds. The
combination of gusty winds...low relative humidities and warm
temperatures will heighten the fire danger as surface fuels dry
out. The warm and dry conditions will continue Tuesday as winds
aloft become more zonal.
700mb temperatures of 13 to 15c will prevail this weekend...rising
to 17c by Tuesday. Daytime high temperatures will warm into the 80s
to middle 90s for early next week.
&&
Issued at 947 PM MDT Tuesday Jun 18 2013
Thunderstorms will affect the far east and far south parts of the
County Warning Area through 08z. Some of storms will produce periods of MVFR
ceilings and visibilities in rain as well as wind gusts as high as
40 knots. Otherwise...VFR conditions will prevail through Friday.
West to southwest surface winds will gust as high as 40 knots...
mainly during the daytime hours along and west of the Laramie
range Wednesday through Friday.
&&
Fire weather...
issued at 400 am MDT Wednesday Jun 19 2013
Elevated to locally critical fire weather conditions are expected
along and west of the Laramie range today through Saturday as dry
conditions combine with increasing west to southwest winds.
Humidities will drop to the the single digits to low teens each
afternoon...with west to southwest winds gusting 25 to 35 miles per hour.
Slightly stronger winds are expected today...with upwards of 40 to
45 miles per hour gusts possible especially in the wind prone areas. At
times...breezy and dry conditions will spill over the Laramie range
into the immediate eastern plains...so will have to watch carefully
for critical conditions to be met in this area as some fuels have
cured. Today should remain just under critical thresholds as winds
look to gust 20 to 25 miles per hour.
&&
Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&
$$
Short term...rjm
long term...maj
aviation...rjm
fire weather...rjm
