Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
242 PM MDT Monday Apr 27 2015
Short term...tonight through Wednesday...a Sharp Ridge is building
in from the west this afternoon. The axis will pass by overnight...
keeping US mostly clear with light winds. A surface thermal low
will develop in eastern Oregon tomorrow...helping to push temperatures up
well above normal over the entire area. Southeast winds will develop in
the Snake River Plain...resulting in downsloping and further
adding to the heat. Temperatures will rise to around 80 throughout the
lower and upper Treasure valleys...with 75 to 80 in the western
Magic Valley. A short wave trough will approach from the west Tuesday
night...pushing a cold front into eastern Oregon. This will move
through SW Idaho early Wednesday. The cold air advection behind
the front will take our temperatures back down 5 to 10 degrees
compared to Tuesday...but will still leave US around 5 degrees above
normal. Overnight lows tonight will drop to near normal...with
readings 5 to 10 degrees above normal Tuesday night as wind and an
increase in clouds help inhibit cooling. Northwest winds will become
moderate Wednesday behind the cold front...but will not reach criteria
for a Wind Advisory. Precipitation will be hard to come by with this
system as most of the upper level energy passes by to our north.
However...there is a slight chance for showers mainly in the
higher elevations Tuesday night and Wednesday. Wednesday afternoon the atmosphere
over the southeast third of the County Warning Area will be slightly unstable. A slight
chance of showers exists mainly over the mountains of SW Idaho...but
also in the higher terrain of both Oregon and SW Idaho within
about a hundred miles of the Nevada border. At this time...the threat
of thunderstorms is just too small to mention. However...if more
moisture were available...this would change. Also...the 18z NAM
model shows a trend of increasing instability in southern Twin Falls
County. If this continues...we may add a mention of thunder to the
forecast in later updates.
Long term...Wednesday night through Monday...models in good
agreement with the weather pattern through the extended period.
Upper level trough over the region Wednesday will continue to move
east Wednesday night with zonal flow setting up over the Pacific
northwest Thursday. Slight chance of mountain showers will linger
over the forecast area Wednesday night. Zonal flow will be over
the region Thursday through Friday night and then shift to the
northwest as a weak trough moves into the Pacific northwest on
Saturday. There is some moisture moving through the flow but any
chance of precipitation will remain north of the forecast area.
Models begin to diverge on Sunday with timing on how quickly the
trough will move east. GFS at this time is faster than the European model (ecmwf)
but the European model (ecmwf) seems to be trending towards the GFS solution.
Monday models in better agreement with a weak ridge of high
pressure build along the Washington/Oregon coast. Temperatures
through the extended period will be near normal.
Aviation...VFR. Scattered to broken high level clouds. Surface
winds variable 10 knots or less. Northwesterly winds aloft around
20 knots up through 10k feet mean sea level.
Short term...snow pellets