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afdotx

Area forecast discussion
National Weather Service Spokane Washington
1051 am PDT sun Apr 30 2017

Synopsis...
breezy to windy conditions today through the Cascade gaps and
spreading out across the basin. Scattered showers today and Monday
as well and mainly over the mountain. A strong ridge of higher
pressure will build over the region next week. The middle of the week
will be warm with afternoon temperatures in the mid 60s to mid
70s before returning to a cooler and unsettled pattern by the end
of the week.

&&

Discussion...
forecast update this morning to increase cloud cover in the Lee of
the Cascades south of Lake Chelan and south of Highway 2 over the
Basin. A standing Lee Side Mountain wave is expected to produce a
field of cirrus cloud cover through the morning and into the
afternoon. /Svh

&&

Aviation...

..Cascade Lee Side Mountain wave today with 35-45 knots wind gusts
possible at Wenatchee Airport...

18z tafs: a cold front positioned over the Idaho Panhandle will
continue to exit the region by early afternoon. The region can
expect west to east clearing clearing conditions for the rest of
the day with increasing Post frontal winds in the range of 20 miles per hour
with gusts into the mid to upper 30s through mid afternoon.
Another push of upper level clouds expected toward end of the taf
period. /Jdc

&&

Previous discussion... /issued 504 am PDT sun Apr 30 2017/

Winds will increase through this morning into the afternoon. The
strongest winds will be in the Lee of the Cascades. Models
indicate a stable layer right at the top of the Cascade mountains
with a northwest to southeast oriented upper level jet. This
is a favorable pattern for mountain wave activity. Breaking
mountain waves may result in periods of stronger gusts around the
Wenatchee area, on the Waterville Plateau and into the western
portions of the Moses Lake area. Models may not be capturing this
potential very well and I have winds on the stronger side of
guidance. I wouldn't be surprised to see some wind gusts at
Wenatchee and Waterville up to near 45 mph. I don't have great
confidence in what gusts will top out at, but the potential is
there and decided to add a Wind Advisory from this morning into
the early evening.

Monday and Monday night: another shortwave disturbance will move
across the region. Dynamics will be weak and the surface low will
fill rapidly as it approaches the northwest coastline. Best
forcing is expected across the northern mtns and into the Idaho
Panhandle. Not much precip will accompany this weather system and
winds will be considerably lighter compared to today. /Svh

Tuesday through sunday: models has come in slightly slower with
the exit of the upper trough, keeping another weak disturbance
sliding through the northwest flow capable of producing a few
showers on Tuesday. This will mainly affect the Panhandle
mountains, while the majority of the forecast area remains dry. By
Tuesday night the long awaited stabilizing ridge begins to move
inland, drying US out and kicking high temperatures up by 4-8
degrees both Wednesday and Thursday. Thus, the warmest day of the
week (and of the year so far) will be Thursday. With clear skies
during peak heating and 850 mb temps now up to 17 c in some
models, temps have been increased into the mid to upper 70s. This
will be 8-10 degrees above normal for early may.

The abnormally warm temperatures will drop a good deal by Friday
as our next low pressure system approaches the Washington coast
late Thursday. Models are in fairly good agreement that a band of
convective precipitation will form well ahead of the frontal
system Thursday evening and move across eastern Washington
Thursday night into Friday morning. Thunderstorm potential has
been added for the north central Washington as this nocturnal
convection exists in an unusually warm environment with good
instability; MUCAPE values approach 500 j/kg overnight.
Thunderstorm potential decreases in the early morning but by mid
day Friday into the afternoon we'll see a good chance of
thunderstorms over much of northeast Washington and the Panhandle.
Any showers that develop will have ample instability to work
with, as MUCAPE values reach 1,000-1,500 j/kg and low level lapse
rates increase to 7-8 c/km. Beyond Friday rain chances stick
around but the thunder potential moves out of the area. Models are
beginning to latch onto a singular solution, that this incoming
low will dip well to our south on Saturday without crossing our
area. This, being nearly 7 days out though, should be taken with a
grain of salt. Confidence is low on exact placement and timing of
showers, but high for the return to a generally cooler and
unsettled than the middle of the week. /Bw

&&

Preliminary point temps/pops...
Spokane 58 36 54 39 61 42 / 10 10 20 10 0 0
Coeur D'Alene 56 35 53 37 60 38 / 50 20 20 20 10 0
Pullman 56 37 53 39 59 41 / 50 10 10 20 10 0
Lewiston 63 41 59 44 65 45 / 30 10 10 20 10 0
Colville 60 34 56 36 65 39 / 20 10 30 30 0 10
Sandpoint 54 34 52 34 58 37 / 70 20 30 30 20 10
Kellogg 51 34 49 36 56 38 / 100 30 30 30 20 0
Moses Lake 65 39 63 39 67 44 / 0 0 10 0 0 0
Wenatchee 60 41 60 41 66 46 / 0 10 10 10 0 10
Omak 64 39 62 38 66 43 / 0 0 10 10 0 10

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Wind Advisory until 7 PM PDT this evening for Moses Lake area-
Waterville Plateau-Wenatchee area.

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