Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
443 PM PDT Wednesday Aug 27 2014

Synopsis...
dry and warm conditions are expected through the workweek. The
next storm system will arrive during the upcoming Holiday weekend.
This will result in breezy to windy conditions along with an
increased chance for showers along with temperatures dropping
below normal.

&&

Discussion...

Tonight through tomorrow..ridge of high pressure continues to
flatten out through this interval and allows a cooling trend most
apparent in maximum temperatures for tomorrow to start. Small and
generally weak disturbances coupled with very limited sources of
moisture to utilize results in a mostly dry forecast with a bit
more cloud cover and increased winds this evening in the gaps of
the Cascades and again tomorrow, with minor mention of showers
noted in close proximity of the British Columbia border. /Pelatti

Thursday night through Sunday...upper level ridge is expected to
depart during this period care of two distinct upper level
disturbances. The first will be a rapid mover on Thursday and
Thursday evening. This system is looking a little more robust than
previous model runs...in that its a little stronger and deeper.
Now most models have it slicing through the southern half of
Washington and onto the Camas Prairie by Thursday evening. Despite
its stronger and deeper trends...it still is not expected to
contain much moisture. In fact...the only area with sufficient
moisture for precipitation will be over extreme NE Washington and
the northern tip of the Idaho Panhandle. Instability per MUCAPES
ranges from 200-500 j/kg in this area...however there is some weak
inhibition to overcome so precipitation is not a sure
bet...especially with the disturbance moving well southeast of
this location. Model soundings could support showers...but the
chances of thunderstorms look quite small. Any threat of
precipitation should taper off rapidly overnight and into early
Friday.

By Friday...the longwave pattern begins to buckle with the ridge
shifting into Alberta and a deep trough setting up off the coast.
This will begin to deepen the moisture over the region ahead of a
well-defined cold front. The front is expected to move into the
Cascades by late afternoon and across the remainder of the inland
northwest overnight. The moisture associated with the front does not
appear impressive, in fact it begins to shear apart as it moves
into Idaho by early Saturday morning. The moisture is expected to
remain most coherent near the Canadian border and this is where we
will leave the best chances of precipitation.

Much drier and cooler air will move into the area on Saturday.
Temperatures should cool anywhere from 8-13 degrees on
Saturday...while winds will pick up into the 10 to 20 mph range
with gusts to 25 mph. The intrusion of drier air will generally
preclude any chance of Post-frontal precipitation with the
exception of along the Cascade crest and near the Canadian border.
Model soundings are backing off on the potential instability and
suggest we might not see enough for thunder. The best threat is
expected to remain north of the international border...however we
will leave in the forecast for now for consistency sake.

On Sunday the core of the upper level trough begins to shift into
Montana with cool northwest flow overtaking most of the region.
The atmosphere will generally remain quite dry. Precipitatable
water values will drop under half an inch...while the chances for
precipitation will remain small. Atmospheric stability will
increase as upper level temperatures (500 mb) climb anywhere from
3-5c outpacing the subtle warming below. If showers were to form,
they would be quite shallow and once again confined to locations
near the Canadian border. Surface temperatures on Saturday and
Sunday will remain cool for this time of year with highs in the
mid 60s and 70s...or roughly whats expected for the third week of
September. Fx

Sunday night through wednesday: the models are in good agreement
for the this period through Tuesday night. A weak ridge pattern
will develop in the region and keep the Columbia Basin free of
precipitation. Some weak instability along the Canadian border
could produce an isolated rain shower in the mountain areas of
northern Washington and the Idaho Panhandle. An occasional
lighting strike with these showers is possible in the Idaho
Panhandle. Tuesday is expected quieter than Monday as the chance
for precipitation continues to diminish across the region. The
models begin to differ on the timing of the trough expected to
impact the region on Wednesday. The European model (ecmwf) is bringing it in late
Wednesday morning and keeping it in the northern mountains of
Washington. The GFS is bringing it through late Wednesday and with
less moisture than the European model (ecmwf). Temperatures for this period are
expected to be around 4 to 5 degrees above the season normals.
/Jdc

&&

Aviation...
00z tafs: weak high pressure will keep VFR conditions over the
aviation area through 00z Friday. A pair of weak disturbances will
result in locally gusty winds this evening...and again Thursday
afternoon. Jw

&&

Preliminary point temps/pops...
Spokane 60 82 58 81 55 72 / 0 0 0 0 0 10
Coeur D'Alene 56 82 55 81 54 71 / 0 0 0 0 0 10
Pullman 54 82 51 82 50 71 / 0 0 0 0 0 10
Lewiston 64 89 61 89 60 77 / 0 0 0 0 0 10
Colville 57 87 53 82 50 73 / 0 0 10 0 10 30
Sandpoint 52 82 52 79 51 70 / 0 0 10 10 10 30
Kellogg 57 80 55 78 52 67 / 0 0 0 0 0 20
Moses Lake 59 89 56 85 52 76 / 0 0 0 0 0 0
Wenatchee 64 87 62 83 58 74 / 0 0 0 0 0 10
Omak 57 86 60 83 56 75 / 0 0 0 0 0 10

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&

$$

National Weather Service Glossary of Abbreviations