Area Forecast Discussion
Issued by NWS Missoula, MT
FXUS65 KMSO 291035
Area Forecast Discussion
National Weather Service Missoula MT
435 AM MDT Wed Mar 29 2017
.DISCUSSION...Latest radar and satellite is showing a stream of
moisture moving through Washington and is currently starting to
move into central Idaho and parts of northwest Montana. By this
afternoon, precipitation will spread across western Montana with
periods of light to moderate rain expected for valleys. Areas of
most concern for today and tonight will be over in Idaho and
Clearwater county where 0.50 to 1.50 inches of moisture will be
possible over the next 24 hours. Snow levels during this time will
be around 6000 - 7000 feet thus most areas should see steady
moderate rain with periods of heavy rain this afternoon and
evening. Due to the increasing threat for rock slides and
mudslides across steep highway corridors, a Hydrologic Outlook was
issued for these areas.
Starting Wednesday night, snow levels will begin to lower and will
allow mountain passes such as Lost Trail pass to begin
accumulating snow. On Thursday, as the trough further deepens, a
cut off low will develop. Models are struggling on the placement
of this cut off low and the precipitation amounts on Thursday.
Although there still some uncertainty, confidence is high for
Lemhi county and Lost trail pass to see significant precipitation
on Thursday. Mountains above 6000 feet could see anywhere from 6
to 12 inches of snow by Friday morning. For southwest Montana,
confidence is high for valleys above 5500 feet to see some snow
Thursday evening into Thursday night but, snow amounts still
remains a question. If the cut off low tracks further south, then
only light amounts are expected. If it takes a northerly track, we
could see periods of moderate snow for Homestake pass, and higher
elevation valleys near Georgetown Lake. Stay tuned for more
updates later today as we get a better handle on this system.
Some showers may linger over the southwest Montana, Lemhi County,
and along the Continental Divide through Friday, however the rest
of the Northern Rockies will become mostly dry through Saturday.
Another storm system will impact the Northern Rockies Sunday and
Monday, with mainly valley rain showers and mountain snow. Snow
levels are anticipated to be high enough for any snow covered
roadways to be confined to mountain passes Sunday overnight.
Outside of overnight hours, most snow will likely melt on contact
with the pavement.
Tuesday and Wednesday next week appear to be mostly dry days
across the Northern Rockies, however models continue to depict a
significant moisture surge sometime late next week. This depiction
does represent a notable large scale pattern change, however
details and timing appear a bit delayed compared to the past
several model runs. More discussion of this surge is likely.
.AVIATION...Rain showers will spread across Northern Rockies
terminals from the west throughout much of the next 24 hours. KGPI
will experience the most significant lowering of
ceilings/visibility after 29/1800Z with rain present. Snow will
remain mainly over terrain during the next 24 hours, with
obscurations steadily increasing in coverage.