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Welcome to the weekly weather briefing for Monday April 15, 2013
Generally quiet weather is expected through mid-week over the region. A moderately strong
and wet storm system will bring valley rain and mountain snow to the region from Thursday
night through Friday night. A drying trend will begin Saturday and last through early next
week…although a few weak disturbances will clip the region bringing some mountain
rain and snow showers. Breezy but not unusually strong winds will continue from time to time
through next weekend.
Overall the week will be fairly quiet with a general slow warming trend. The late week
storm will largely skip over the Cascades Lee area including Wenatchee and bring
precipitation to the eastern half of the forecast area.
Including Lewiston.
Beginning Thursday night a warm front will develop over the region concurrent with
increasing moisture. There is high confidence that a 24 hour period of rain and mountain snow
will envelop the region. Steady rain will turn to hit-and-miss showers after the
trailing cold front passes late Friday or Friday evening.
The remarkable aspect of this system will be a deep sub-tropical fetch of moisture
hosing into the region. This deep moisture will be efficiently enhanced into rain
and mountain snow as the warm front moves in Thursday night.
Fortunately…this will be a fairly brief splash from this moisture feed. The plume will
sag south and mainly impact Oregon by mid- day Friday. The northern fringe of this fetch
will fuel continuing showers over Eastern Washington and North Idaho through Friday
afternoon as the trailing cold front sweeps through.
Total precipitation from this storm will run from 1 to 2 inches on the higher terrain of
North Idaho and the Cascade Crest…to a quarter to a half inch in the valleys and eastern
Columbia Basin. The deep basin in the Cascades lee area will be largely shadowed by the
Cascades resulting in much less if any rain. Bear in mind that above 4000 to 5000 feet , most
of this precipitation will fall as snow and thus not be available to runoff into area
rivers. At this time…the model depicted here is a worst case scenario and only roughly
resolves the high terrain of the Cascades and North Idaho.
Because of the relatively brief period of steady precipitation and the high mountain
precipitation falling as snow…runoff into area rivers is not expected to be a problem.
The Coeur D’Alene River at Cataldo for example…which drains much of the area
expected to receive the most precipitation…will show a noticeable rise but should
remain well below flood stage. However…the hydrology aspect is the most uncertain portion of
this week’s forecast and so concerned parties should pay close attention to the
forecasts issued later this week…not just for the Coeur D’ Alene but for all streams and
rivers draining the mountains.
After the wet storm later this week, a progressive northwest flow pattern will set up and
persist through the weekend. No significant storms are expected, but minor
disturbances will maintain a threat of mainly mountain rain and snow showers.
The 8 to 14 day outlook suggest that there is no strong signal indicating higher or lower than
normal precipitation over the area…but the odds strongly favor above normal temperatures
.