Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Great Falls Montana
1020 PM MST Thursday Nov 26 2015
Aviation section updated.
Tonight...high pressure aloft will continue to keep the airmass dry.
Low level moisture is available, however, and local fog is possible.
Updated to lower some temperatures across the northern and central zones.
Also freshened winds and weather. Zelzer
High pressure is building aloft and the airmass will remain dry.
Local development of fog is possible towards sunrise in valley
locations, including khln. Elsewhere, VFR conditions will prevail
through the next 24 hours.
/issued 428 PM MST Thursday Nov 26 2015/
this afternoon through Saturday evening...somewhat uncommon "rex
block" pattern (closed high pressure circulation sitting adjacent to
and north of a closed low pressure area) continues to take shape
over western U.S. And Canada. The high pressure ridge, currently
centered along the US/British Columbia coast, will dominate the weather over
central and southwest Montana through this forecast period, producing dry
conditions and slightly below normal temperatures. Meanwhile, upper-
level low pressure will remain mostly stationary along the Nevada/Utah
border next 36 hrs, cutoff from the main jetstream flow further to
its south and east. Forecast models continue to show some change in
the blocking pattern this weekend as the upper low drifts
northeastward into ID/WY. General model consensus is that moisture
wrapping around the low center will stay mostly along and south of
the Montana/Wyoming border, but have left in a slight chance of isolated snow
showers over parts of eastern Madison and Gallatin counties on Sat
afternoon as the moisture skirts that area. Toughest part of the
forecast next few days is the overnight low temperatures as there
will be a lot of local variability based on snow cover, terrain and
winds. For tonight and Friday night, have kept temperatures in the single
digits above zero for much of the hiline and central counties and
single digits to teens below zero over southwest Montana but could easily
see 5-10 degree fluctuations in those values because of local
Sunday through Thursday...the large scale blocking pattern in
place over the northwestern U.S. Continues to break down on
Sunday. Differences remain among model solutions with regard to
the position of the closed upper low as it ejects from the
interior west towards the upper plains by late Monday. The European model (ecmwf)
solution is a bit more progressive and maintains dry conditions
over the region. Ensemble means and most other major model
solutions rotate a band of precipitation counterclockwise through
central and southwest Montana early Sunday. For now...will maintain a
general model blend with slight chances for precipitation early
Sunday...and up to about 2 inches of possible snow. Monday through
Wednesday appear dry with weak ridging over the region and
gradually warming temperatures. The ridge breaks down by the end
of the period as a Pacific weather system brings breezy conditions
with better chances for precipitation Thursday night into Friday
mainly along and west of the Continental Divide.
Preliminary point temps/pops...
gtf 3 28 5 31 / 0 0 0 0
ctb 6 33 7 35 / 0 0 0 0
hln -2 18 1 30 / 0 0 0 10
bzn -11 14 -10 25 / 0 0 0 10
wey -13 14 -8 24 / 0 0 10 10
dln -5 16 -1 23 / 0 0 0 10
hvr -1 28 3 30 / 0 0 0 0
lwt -1 28 5 32 / 0 0 0 0