Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
433 PM PDT Friday may 22 2015

Synopsis...
the Memorial Day weekend is expected to be warmer than average,
with afternoon temperatures in the 70s and 80s. Look for scattered
showers and thunderstorms this weekend into next week. Some
thunderstorms will be capable of producing heavy downpours and
frequent lightning.

&&

Discussion...

Tonight: we'll be dealing with short-segment lines of
thunderstorms moving west off the higher terrain of north Idaho and
into Spokane and the Palouse. The other area of concern is the
potential for flash flooding/debris flows on recent 2013-2014
burn scars. So far most of these scars have been missed by the
heaviest rain rates in the Cascades. The devels Elbow complex
south of Republic has, so far, received the most direct hit...but
calls to local authorities have yielded no reports of debris
flows. The cape/shear combo supports heavy downpours and small
hail into this evening with any thunderstorms. We'll be doing
nowcasts, facebook posts and twitter updates when time allows.Bz

Saturday through monday: models are in pretty good agreement of
where to track the upper level low that is moving down British
Columbia and into the inland northwest this weekend. The low now
doesn't push into Washington until Sunday evening/Monday morning.
Until then...northeasterly flow into the northern Idaho Panhandle
and northeast Washington will keep conditions dry with mostly
clear skies. The main concern for showers and thunderstorms will
continue to remain across extreme southeast WA, the central Idaho
Panhandle and along the Cascades. Each afternoon and evening
showers and thunderstorms will develop and then wane with the
setting sun in the evening. Isolated showers is possible through
the overnight and early morning hours for the aforementioned
areas. Given we are expecting less shower activity and clouds
Saturday and early Sunday, have increased Max temps about 1-3
degrees. Sunday night/Monday the upper low will move into
Washington. There are some model differences of where the low GOES
during the day on Monday. Nevertheless the chance of widespread
rain will increase. Monday looks to be the 'crummiest' day of the
Holiday weekend. Have lowered Max temps a few degrees, as we
looked to be the outlier compared to other forecast models.
/Nisbet

Monday night through friday: the inland northwest remains unsettled
with some threat of showers and thunderstorms each day. Most
models keep the region in a weak flow pattern with a mid-level low
bobbling about the northwest United States at least through
Wednesday. Thereafter models diverge, either holding the low near
the northern rockies or showing a transition to a west-southwest
flow with a low migrating down the British Columbia coast. Either way
instability blossoms each afternoon, in the form of expanding
cape. Precisely how much synoptic forcing there is and where it
will lay will come into more focus as models come into better
agreement. But for now look for a threat of showers and
thunderstorms expanding each afternoon, then dissipating but not
entirely ending for the night and morning hours. The threat will
be best throughout the region through Wednesday. Thereafter there
is some suggestion that the threat will retreat away from deeper
Columbia Basin toward Thursday and Friday. Any of these
showers/T-storms may contain the typical brief heavy rain and
perhaps some small hail and lightning, but given the more
convective nature of the system none of this is a definite for any
one location. /J. Cote'



&&

Aviation...
00z tafs: marjority of thunderstorms on the radar this evening are
moving with a general storm track to the southwest at around 20
mph. With loss of peak heating and limited dynamics to support
forced convection the aviation forecasts show majority of
thunderstorm activity gone from most taf sites after 2z and from
just about everywhere at 9z Saturday. MVFR ceilings primarily from
the rain shafts and the small hail from some of the storms. Wind
shifts common through this evening due to all the outflow
boundaries propagating out of all the thunderstorms. Tafs have no
mention of shower or thunderstorm activity Saturday afternoon as
considerably lesser convective activity is expected. /Pelatti

&&

Preliminary point temps/pops...
Spokane 53 82 52 80 53 73 / 10 10 10 20 30 50
Coeur D'Alene 52 80 53 80 52 71 / 20 10 10 20 30 50
Pullman 49 76 46 75 48 71 / 20 10 10 10 20 30
Lewiston 56 82 55 82 55 79 / 30 20 20 20 20 30
Colville 53 86 54 81 51 73 / 20 10 10 30 30 70
Sandpoint 50 81 48 79 49 71 / 10 10 10 20 20 60
Kellogg 50 80 49 80 48 70 / 20 20 10 20 20 50
Moses Lake 56 86 55 83 54 80 / 20 10 10 10 20 20
Wenatchee 59 85 59 81 57 79 / 50 10 10 20 20 10
Omak 53 87 53 83 52 77 / 30 10 10 30 20 40

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Flash Flood Watch until 8 PM PDT this evening for east slopes
northern Cascades.

&&

$$

National Weather Service Glossary of Abbreviations