Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
930 am MST Friday Feb 27 2015
Discussion...snow has accumulated at least a couple inches near
Burns/or and the advisory is working out. Latest NAM/met guidance
shows a break this afternoon and tonight...then more snow late
tonight and Saturday...enough for another advisory. Total combined
snowfall may exceed heavy snow criteria for the 24 hours...but
the break between snowfalls along with several hours of above-
freezing temperatures suggest two separate advisories may be better than
a single Heavy Snow Warning. Satellite imagery at 8 am PST shows
maximum clouds and snow right over Harney County. The new 12z
NAM shows precipitation decreasing in eastern Harney County this afternoon.
Weak instability...enough for a slight chance of thunderstorms...
continues this afternoon and evening in southeastern Oregon and near
the Idaho/Nevada border. No forecast changes on that.
Aviation...today and tonight expect areas of MVFR/IFR conditions in
snow across southeast Oregon and southwest Idaho south of the Snake
River Valley...and scattered MVFR/local IFR snow showers in the
central Idaho mountains. The Snake River Valley will continue VFR
except for local MVFR ceilings in rain showers. Surface winds...
variable 5-10 kts. Winds aloft...east 10-20 kts up through 10k feet
mean sea level.
Weekend outlook...scattered to numerous snow showers will continue
through Saturday morning...then decrease to isolated mainly over the
mountains by Saturday evening. Sunday will be VFR with mostly clear
short term...today through Saturday...near vertically stacked
upper low over northwest Washington was already spreading snow near Harney-
Deschutes County border per tripcheck webcams. Moderate snow is
expected across Harney County /except near the Nevada border/ today.
Snow levels will rise to around 4500 feet. More snow there is
possible after temperatures cool off this evening as the low pivots
across southeast Oregon tonight. On the south and east flank of the low
instability looks to be maximized under coldest air aloft and
warmest highs so kept a low chance of thunderstorms from northwest of
Burns to S of Twin Falls 18z-06z tonight. On Saturday rain and
snow is expected generally south of a Burns-Emmett-Idaho City line
as the low expands over Nevada. May need to extend the Harney County
Snow Advisory past this afternoon if temperatures look cool enough and
the low track is maintained across southeast Oregon.
Long term...Saturday night through Friday...upper low is expected to
exit the area quickly Saturday night through Sunday morning and give
way to clear and drier conditions through early Monday. Another
trough is expected to move through the region Monday afternoon...
bringing another chance of rain and mountain snow. Current guidance
is mostly in agreement...although the European model (ecmwf) is more moist and slower
with this feature. Precipitation could last through Tuesday afternoon near
the Idaho/NV/UT borders. Temperatures are expected to drop to below
normal during this time as well. For Wednesday and beyond...guidance
is suggesting a ridge setting up once again over the western US...
which will bring temperatures back to near or above normal and keep
Idaho...Winter Weather Advisory from noon today to 11 am MST Saturday
Or...Winter Weather Advisory until 2 PM PST this afternoon orz061.
previous short term...vm
previous long term....ep