Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
849 PM MST Monday Dec 9 2013
Discussion...temperatures not dropping off like the last couple
of nights thanks to increasing middle and high clouds. This will be
the case much of the night though models are showing potential
clearing from northwest to southeast towards sunrise Tuesday morning. Given
uncertainy will keep with current forecast low temperatures in the
single digits around zero for most areas. Also for the Snake River
Valley surface winds will stay up enough to stir up the air.
Updated to lower the probability of precipitation for this evening and increase sky cover.
Aviation...VFR conditions expected most locations through sunrise
before stratus deck moves into the area...except MVFR with light
snow and mountain obscuration through the west central mountains
including McCall through the early morning hours. Light surface
winds. Winds aloft at 10k feet mean sea level...west to northwest 15-20kt.
short term...tonight through Wednesday...northwest flow had enough
moisture due to upslope component to result in 1-2 inches of snow
across the west central mountains...most of which fell this morning.
Latest webcams showed that the snow was ending for most areas.
Models maintain the similar flow and even with meager moisture and
due to the cold air mass...light snow showers will continue across
the northern areas through Tuesday. Clouds will be increasing across
the remainder of SW Idaho and southeast Oregon. The flow aloft will weaken
Tuesday night and Wednesday as an upper ridge starts to build into
the Pacific northwest...thus ending the snow showers. Temperatures
will gradually moderate but the amount of warming will depend on
cloud cover and strength of the inversion...which are difficult to
forecast in this pattern.
Long term...Wednesday night through Monday...upper ridge will shift
east of the area Wednesday night/Thursday in response to upper level
trough for Friday. Pressure gradient tightens Wednesday night
through Friday ahead of the upper trough which will bring increased
south-southeasterly surface winds /5 to 10 miles per hour/ which should erode
and also push the cold air into the lower Treasure valley. The cold
air could mix out of the Lower Valley on Friday with passage of the
trough...though that is less certain at this time. Thus...have
increase temperatures to above freezing on Thursday and Friday for
most areas except the lower Treasure valley. Models differ in the
timing of the trough for Friday with the latest model runs showing
the passage on Friday. Went with an earlier timing around 12z at
kboi but confidence remains low at the moment. Precipitation amounts
with this system are light and should be focused on the higher
terrain. Beginning Saturday upper ridge builds along the West Coast
which weakens significantly by Monday as a deep trough forms over
eastern North America. This will return the region to mostly dry
northwesterly flow and keep temperatures around normal.
previous short term...bw
previous long term....jds