Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Glasgow Montana
833 PM MDT Friday Aug 22 2014
Short term...for northeast Montana...tonight through Sunday...
current forecast looks fine. No changes for this evening.
Southwest flow is continuing to drag precipitation over the cooler
surface temperatures and generate rain showers across the area. As
a low forms over northern Wyoming and transition north... coverage
for rain showers is expected to increase into the evening and
overnight hours. Gah
Previous short term discussion...
there is an amplified pattern set up across Continental U.S. With a long wave
trough in the west and a long wave ridge in the east. The trough
will dig across the west and Montana through the short term. This
system continues to bring ample Pacific moisture with it. An
inverted surface trough setting up will focus in increasing
amounts precipitation over northeast Montana tonight through
Saturday night...possibly generating heavy rain at times. This
same surface trough will also increase the surface pressure
gradient to produce strong easterly wind tonight through early
Saturday evening. Therefore a lake Wind Advisory remains in effect
for Fort Peck Lake. Models still leave room for enough instability
to produce isolated thunder this evening and again on Saturday
afternoon/evening...but likely not Sunday. On Sunday the low
center and the upper trough will be stacked up and headed
northeast into southern Saskatchewan and Manitoba. Also the
moderate strength wind will begin to back around to the north...
then northwest. Most precipitation will begin to taper off Sunday
Final rain amounts are expected to be impressive...from 2 to 4
inches. Soil moisture conditions are highly varied as some areas
in the southeast counties have had heavy rain recently. Will wait
for now...but there could be the need for flood watches later if
conditions continue to develop.
As the upper low center moves across northeast Montana Saturday
night and Sunday 700mb temperatures fall below 0c and 850mb
temperatures fall as low as 4c. This brings about the possibility
of Sunday maximums nearing the record low maximum...which for ggw was
56f degrees set in 1992. This would be roughly 15f to 20f degrees
below normal for late August. Scattered
Long term...Sunday night through Friday...
didn/T place much emphasis with this period today since the storm
system in the short term Drew more attention. Otherwise...going
forecast in this period looked good. Just made a downward tweak to
the high temperature Monday. Tfj
synoptic set up... long term begins with hot high pressure over
the southern US plains... Four Corners... and California. A large
trough runs down Saskatchewan into Montana and the northern US
plains. Behind the trough and to the west a ridge runs up the
coast of the Pacific northwest and into northern British Columbia.
Sunday night through Monday night... center of the base of the
large trough will eject east over the northern US plains and upper
Mississippi Valley. This will carry the last of the rain showers
out of the area Sunday night but leave behind a cool air in place
at the surface across much of Montana through Monday night.
Tuesday through Thursday... ridge to west will move on shore and
gain strength during these periods. Cold air will be whittled out
and a warming trend will take place with temperatures warming to
near seasonal norms at first but topping out well above normal by
Thursday with a ridge overhead. These periods look to remain dry
through most of the time.
Thursday night Onward... model breakdown behind the ridge settles
in at this point. Models agree to ridge breakdown but are unsure
of the wave following it. Current guess is for zonal flow to a
weak trough to pass through. However... this could quickly change
with new runs. Gah
flight category: MVFR to at times IFR. MVFR clouds will linger
tonight with a rain shield moving in from the southwest. Some of
the rain will be briefly heavy starting after midnight and lasting
6 to 9 hours...longest at kggw. Expect IFR with the heavy rain.
Synopsis: a stacked low pressure system will move over far eastern
Montana through period.
Winds: east winds increase into tonight and continue Saturday.
Speeds could briefly top 30 kts especially at kggw. Tfj/proton
lake Wind Advisory until midnight MDT Saturday night for Fort
Peck Lake for central and southeast Phillips...central and