Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Glasgow Montana
1052 am MST sun Feb 1 2015
Updated aviation discussion below...
Short term...for northeast Montana...today through Tuesday...
Sent an update this morning to indicate more clear skies than
previously depicted and to adjust high temperatures today a bit
colder given the colder start to the day than previously expected.
Previous short term discussion...one system with snowfall through
the region this morning...two more to come over the next few days.
Skies clearing and Arctic air filtering south from Canada this
morning. Temperatures dropping below zero as the clouds depart
over several inches of fresh snowfall. Upper ridge to the west
begins to push a little east today with warmer middle-level air moving
off the mountains. With fresh snow across the central part of the
County Warning Area temperatures may be slow to recover even with sunshine today.
Weak shortwave brings moisture across the Arctic boundary late
tonight into Monday morning...for some light snow mainly from the
northwest to southeast across the County Warning Area. Surge of cold air behind
the wave will push the boundary slightly southwest on Monday. A
stronger wave then slides along the boundary Monday night into
Tuesday with a better potential for measurable snow...with several
inches possible by Tuesday afternoon. Ebert
Long term...Tuesday night through Sunday...
A Pacific Ridge and broad eastern Continental U.S. Trough will maintain
northwest flow aloft across the northern High Plains as the
extended period begins Tuesday night. An upper level shortwave
will be exiting northeast Montana and pushing into the Dakotas.
The timing and track of this feature will be critical for
temperature forecasts overnight. If the system pushes out more
progressively...sky conditions could abruptly clear. Given 850mb
temperatures in the -15c to -20c range and abundant new snow
cover...efficient radiational cooling could result. The result
would be lows well below zero across the region. However...should
the system exit more slowly the result would be lingering cloud
cover and temperatures somewhat less cold. Will have a middle of
the Road approach for now...slightly colder than the 00z model
guidance...especially considering that guidance likely does not
factor in all the new snow cover out there.
Models exhibit fairly good agreement having the Pacific Ridge
translate eastward during the middle and latter half of the
week...leading to gradually warming temperatures and dry
conditions. At some point a shortwave trough upstream may flatten
the ridge and bring about renewed precipitation chances to the
County Warning Area. Will carry a slight chance pop for Friday and Saturday as
current model guidance shows a fair amount of variance on specific
handling of shortwaves. Precipitation type may also prove to be a
challenge. Ensemble 500mb heights show increasing spread this far
out into the extended period...lending to further uncertainty.
Future shifts will be able to make refinements as guidance arrives
at consensus. Maliawco
Thanks to a short-wave high pressure ridge...VFR conditions in
clear and sunny skies are expected for most of the day. On its
heels...a short-wave disturbance will ride up and over the
northern rockies later tonight which will increase cloudiness
from the west overnight and eventually bring some MVFR/IFR
conditions in light snow showers to the taf sites toward the end
of this taf cycle. Bmickelson