Area forecast discussion
National Weather Service Glasgow Montana
402 am MDT Thursday may 23 2013
Short term...for northeast Montana...today through Saturday...
today and tonight...main concern will be the gusty winds across
northeast Montana. Models are in excellent agreement with a low
level southeasterly jet translating through the forecast area
today into tonight. The 00z NAM/GFS both have around 50-55 knots
winds at 850mb for a time this evening...with the 00z European model (ecmwf)
slightly lower. BUFKIT soundings show these low level winds quite
well. Given that the strongest winds do not exit to the east until
near morning on Friday...have gone ahead and extended the lake
Wind Advisory until 10z...or 4am Friday morning. Lapse rates in
the low levels also appear to be between 8-10 degree celsius per km.
Will expect the entire County Warning Area to see sustained winds for a time this
afternoon and evening between 25 and 35 miles per hour. Gusts in the 45-55
miles per hour range are certainly a possibility. These conditions are a bit
shy of high wind criteria...but the day shift will have to take a
very close look at the 12z models and will need to monitor
observations very carefully. Noting some showers entering
Petroleum County early this morning and so increased probability of precipitation a little
for the western zones for today as well.
Friday into Saturday...upper trough with closed low across the
western U.S. Will continue to place northeast Montana situated
within a regime of southwest flow aloft. Shortwave features will
propagate through this flow bringing chances of showers and
thunderstorms. The first potential looks to be during the morning
hours on Friday...lifting north of the border into Saskatchewan by
Friday afternoon and evening. Therefore...for the County Warning Area thunderstorm
potential should be quite limited and so lowered probability of precipitation quite a bit
for Friday evening and Friday night. Saturday could be very busy
across northeast Montana. Low level southeast flow will Pump Gulf of
Mexico moisture into the region. The 850mb temperatures will be
rising and so with a warm moist low level boundary layer in
place...noting a nice Theta-E ridge setting up across the County Warning Area.
BUFKIT soundings clearly indicate middle level dry air across the County Warning Area
as well. There is also good 0-6 km directional wind shear with
about 35 kts of speed shear...especially in the eastern zones.
Cape May range between 1500-2000 j/kg for a time in the eastern
zones as well Saturday evening...with Li approaching -4 to -8 and
total totals rising above 60. Shortwave energy also approaches
this thermodynamic environment at just the right time Saturday
afternoon and evening that the combination should be highly
conducive for convection initiation. There is also excellent
agreement and support for these conditions in the 00z
NAM...GFS...and the European model (ecmwf). With models converging on Saturday being
the best opportunity in the short term for convection...there is
much higher confidence in this forecast. Do expect some of these
storms to become particularly strong...and possibly severe. Gusty
winds and hail seem to be concerns given these conditions. With
the upper level wave tapping into the instability...and decent
diffluent flow aloft in place...vertical ascent and lowering
pressures will be very favored. Future shifts will be able to
assess the cape/shear profile as well as other instability parameters
and better determine the most likely Mode of convection...as well
as precise timing and placement. This is because much of the
precise details of this portion of the forecast will be dependent
upon mesoscale processes which are difficult to determine more
than a couple of days out in the forecast period. Maliawco
Long term...Saturday night through Thursday...
upper trough along the West Coast will continue to dominate the
weather pattern through the extended period...resulting in
unsettled weather and near normal temperatures.
Closed low currently over the Pacific northwest expected to lift
into western Canada during the weekend. With inverted trough/dry
line in place over eastern Montana...with southeast low level flow
spreading Gulf moisture into the northern plains along with
another upper level southwest jet crossing the northern rockies
expect organized convection mainly over the eastern zones Saturday
evening.
Pattern for the remainder of the period is more disorganized with
greater model spread. Overall pattern is for West Coast trough to
dig into the Desert Southwest with some splitting occurring as
another upper low slides from Alaska toward the Pacific northwest.
Some hints in the gefs/Gem of ridge tilting back into the northern
plains around middle week to shut off convection but with model
spread kept probability of precipitation near climatology. Ebert
&&
Aviation...
VFR with middle to high clouds. Showers or thunderstorms could impact
kggw by the end of the taf cycle. Strong and gusty southeast winds
expected across the region again today.
&&
Glasgow watches/warnings/advisories...
lake Wind Advisory until 4 am MDT Friday for Fort Peck Lake for
central and southeast Phillips...central and southern valley...
Garfield...McCone...Petroleum.
&&
$$
Weather.Gov/Glasgow
