Scientific Forecaster Discussion
fxus66 kotx 280008
Area forecast discussion
National Weather Service Spokane Washington
508 PM PDT Sat may 27 2017
high pressure will continue over the inland northwest this
weekend. There is a small chance of thunderstorms in the higher
elevations between Sunday and Tuesday. Otherwise expect dry and
warm weather into early next week, with afternoon highs in the
80s. This mild weather will contribute to rises on rivers in the
Cascades to north Idaho. More seasonal and unsettled weather
returns by mid week with the return of rain and thunderstorm
tonight through tuesday: mostly dry and warmer. A large ridge of
high pressure will remain in place for the period. Temperatures
will warm each day with Tuesday being the warmest day of the week.
Anticipate light winds with an easterly shift through the period.
Nonetheless, there are some subtle differences each day.
On Sunday, the strong ridge flattens slightly and mid level moisture
streams up and over. Most will be arriving in the northwest flow
into Montana brushing through north Idaho, while a little will be
creeping up the Cascades in the southerly flow. Instability will
be on the rise although the ridge should suppress most convection.
Although weak orographic lift may help break the cap and give way
to a few showers and embedded thunderstorms. Will be confining
any activity to the mountains Sunday late afternoon and early
On Monday, mid level moisture increases both along the Cascades over
the north Idaho mountains, along with the mid level instability.
Should see a repeat performance Monday afternoon and early evening
with a few showers with embedded thunderstorms forming over the
mountains, possibly forming by early afternoon. May see the
activity last a little longer in the Cascades based on the
increased moist southerly flow.
On Tuesday, the upper ridge axis shifts east slightly as a Pacific
trough pivots to the coast. This trough looks to be taking a
slightly slower arrival. Deeper southerly flow will move up not
only the Cascades ahead of the trough but parts of the western
basin. Cloud cover will increase. Anticipate a better chance of
afternoon showers and thunderstorms in the Cascades. /Rfox
Hydrology: rivers will be feeling the effects of the warm
temperatures and begin their rises within the next 24 hours. The
Stehekin and Entiat rivers are forecast to reach flood stage late
Sunday into Monday and prompted the issuance of a Flood Watch.
Other area rivers are forecast to rise but stay within banks.
Wednesday through saturday: beyond Tuesday things change as our
ridge finally moves out and begins to be replaces by a trough
that moves into the Washington coast. There still exists a large
degree of uncertainty in the timing of the greatest thunderstorm
potential, but it now looks as if Wednesday will be the best
chance. The 12z run of the ec now shows a much weaker trough
passage with low thunderstorm potential on Wednesday, but it has
been playing catch up for the last several days. The ec had been
holding off on the ridge breakdown until thurs/Fri. Yesterday it
finally decided to go with a Wednesday solution as the GFS and
Canadian had been showing all along. Thus, will treat the ec as
an outlier for now until subsequent runs show some consistency.
Shower and thunderstorm potential will be mainly over the
Cascades Wednesday morning before overspreading the area in the
afternoon. The best chance for thunder will be in the mountains of
the Idaho Panhandle and North Washington during the afternoon, with cape
values >1000 j/kg, lapse rates >8 c/km and Li values below -4.
Storms are possible over the lower elevation as well, though.
Additionally, we'll see gusty winds and showers on Wednesday with
the cold front.
Thursday looks quieter but still unstable under the influence of
the trough. Thunder potential remains in the extreme eastern
zones until Friday when another lobe of the low swings through,
which models are relatively good agreement on. Temperatures
starting on Wednesday will begin to drop closer to seasonal normal
under the cooling influence of the trough. Highs will be in the
70s with lows in the 40s and 50s by Wednesday. /Bw
00z tafs: flat cumulus already beginning to dissipate with skc
overnight and into Sunday morning. Flat cu will develop again
tomorrow aft 19z. Winds will remain light.
Preliminary point temps/pops...
Spokane 54 83 57 86 59 87 / 0 0 0 0 0 0
Coeur D'Alene 53 81 54 85 56 86 / 0 0 0 10 0 0
Pullman 50 80 51 83 53 85 / 0 0 0 0 0 0
Lewiston 54 87 56 89 59 90 / 0 0 0 0 0 0
Colville 51 83 55 87 56 88 / 0 0 0 10 10 0
Sandpoint 47 80 51 81 52 82 / 0 10 10 10 0 0
Kellogg 46 81 50 82 54 84 / 0 10 10 0 0 10
Moses Lake 52 89 54 92 57 93 / 0 0 0 0 0 0
Wenatchee 57 87 60 89 62 90 / 0 0 0 0 10 10
Omak 54 87 55 88 58 89 / 0 0 0 10 0 10