Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Boise Idaho
305 PM MST Tue Feb 21 2017
Short term...tonight through Thursday...continued showers and
gusty winds this afternoon across the region as a shortwave trough
continues its journey eastward. Have had one lightning strike over
the Boise Mountains this afternoon and will see the convective
threat continue through the early evening. Showers will tapper
off by Wednesday morning and the winds will diminish before
midnight. The Wind Advisory for southeast Oregon and portions of
southeast Idaho will continue through 8pm MST tonight. See
product for more details.
As the upper level flow turns westerly this evening under the
influence of a longwave trough, the moisture plume currently
sitting south of the region will shift it's focus north. This will
bring a good chance of precipitation Wednesday morning and afternoon
to areas along the Nevada border and in the west central
mountains. Precipitation will fall as snow as snow levels are
expected to drop behind today's cold frontal passage.
Temperatures will fall accordingly to the lower 40s along the
Snake River Plain and low 30s in the mountain valleys. Threat of
snow showers Thursday, generally over the higher elevations, as
the upper level flow turns north and the trough pushes out of the
Continued threat of localized flooding at sites where significant
amounts of snow remain under a mild airmass. River flood warnings
still in affect for the Weiser river at Weiser and the Malheur
River at Vale. See hydrology section below.
Long term...Thursday night through Monday...a brief reprieve from
moisture is expected Thursday night with a building northwesterly
flow. Weak moisture returns to the area Friday afternoon, especially
across the higher elevations as an area of low pressure begins to
drop south along the Pacific coast. As the low drops further south,
it looks to become slightly more organized, though it also wobbles
slightly west to keep scattered activity across the forecast area.
The low pressure loses its organization by Saturday afternoon,
becoming an open wave and begins to move inland. However, another
area of low pressure is right on its heels, which is expected to
send a strong surge of moisture across California and into
northwestern Nevada by Sunday morning. This system will dig slightly
to perhaps introduce some cooling temperatures across the area to
bring some precipitation over the area as snow. As this system loses
its organization on Sunday afternoon, yet another area of low
pressure looks to be off the coast of Washington/Oregon. This system
adopts the moisture from the previous low pressure and pushes it
over eastern Oregon and southwestern Idaho by Sunday afternoon.
Models are in fair agreement that increased precipitation coverage
will occur Sunday into Monday, but disagree on the organization
leading to the precipitation initially. By the mid-morning hours of
Monday, all numerical guidance points towards a developing trough
with its axis approaching the western border of the forecast area.
This axis will slide east through the day, with precipitation
anticipated to taper off in its wake.
Aviation...periods of MVFR in scattered showers. Breezy wind to
continue with the strongest wind expected through 00z this evening.
Winds to decrease significantly after 12z Wednesday, though gusty
wind will attempt to return after 18z Wednesday. Surface winds: west-
southwest 15-30 kts with stronger gusts through 00z, then decreasing
to 10-20 kts and becoming more west-northwest. Winds aloft at 10k ft
msl: west-northwest at 20-40 kts, weakening to 10 to 30 kts after
Hydrology...the Weiser river near Weiser is currently above
flood stage at 11.3 ft and is expected to crest near 12.2 feet
around midnight tonight. The Malheur River near Vale is still
below flood stage at this time, but is expected to rise rapidly
today and reach flood stage (19.5 feet) around midnight Tuesday
night. It is expected to crest around 21 feet tomorrow morning and
slowly decrease coming below flood stage Thursday afternoon. Both
rivers are under a Flood Warning. The Weiser river at Cambridge
will continue to rise, with heights rising to bank-full. Expected
to crest around midnight tonight still below flood stage.
Otherwise, rainfall today, combined with snowmelt from the mild
temperatures, will result in rises on nearly all streams and
rivers. Low-lying areas, especially with remaining snow on the
ground, will be the most prone to ponding of water and slow
Idaho...Wind Advisory until 8 PM MST this evening idz029-030.
Or...Wind Advisory until 8 PM MST /7 PM PST/ this evening orz061-063.