FXUS66 KSEW 220319
Area Forecast Discussion
National Weather Service Seattle WA
820 PM PDT Wed Mar 21 2018
.SYNOPSIS...Moist southwest flow aloft will continue tonight, and
a cold front will move inland early Thursday. A deep upper level
low will make the air mass cool and unstable Thursday through
Saturday. The snow level will fall to around 1000 feet Friday and
Saturday, and isolated thunderstorms are possible Friday. A ridge
will build inland early next week for warmer and drier weather.
.SHORT TERM...Areas of rain have been filling in across the region
this evening. A weather pattern change will bring wetter cooler
weather to the region tonight through the weekend. A deep upper
level low off the B.C. coast will continue to dig offshore
tonight, setting up moist S/SW flow over Western WA. Rain will
increase late tonight into Thursday morning as a cold front moves
inland. Strong onshore flow will develop behind the front. Showers
will continue through Thursday afternoon as an upper level trough
axis swings through. The mountains will see a few inches of snow
with snow levels lowering to around 1500 feet Thursday night.
The broad upper level low will remain over the region on Friday
for more cool and showery weather. We are still under moist,
diffluent flow and there's a slight chance of thunderstorms across
much of Western WA. By this point in time, 500 mb temps will drop
to around -37 C, setting up steep lapse rates and a Lifted Index
near 0. Graupel is possible too.
The deep upper level low will finally weaken and shift inland as
an open trough on Saturday. Snow levels will remain low during the
morning, only a few hundred feet, but showers in the lowlands are
light and spotty. Significant snowfall accumulations are not
expected. Temperatures will continue to trend below normal with
highs mainly in the 40s.
.LONG TERM...An upper level ridge will develop over the NE Pacific
on Sunday for NW flow over Western WA. A weak passing upper level
disturbance may trigger scattered showers. The upper level ridge
will start to drift east and inland on Monday then stall over the
region through early next week. This sets up a drying trend with
temperatures rising a few degrees above normal. The ridge may
flatten toward the end of next week from a passing trough over
.AVIATION...Rain and lowering cigs will be the rule tonight as a
cold front develops over the region. The rain will turn to scattered
showers with some clearing periods later on Thursday as the front
KSEA...Rain a times tonight will give way to scattered showers and
some clearing periods on Thursday as a cold front moves through the
area. Breezy southerly winds should develop during the day Thursday.
.MARINE...A low pressure system and cold front will affect
Western Washington Thursday. Stronger southerly winds will
develop on Thursday as the front moves ashore and then onshore
flow develops behind the front. The low pressure area will linger
just offshore on Friday and then weaken and move ashore over
northern California over the weekend.
.HYDROLOGY...River flooding is not expected in the next 7 days.
PZ...Small Craft Advisory from 5 AM Thursday to 11 AM PDT Friday for
Coastal Waters From Cape Flattery To James Island 10 To 60
Nm-Coastal Waters From James Island To Point Grenville 10
To 60 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater 10 To 60 Nm.
Small Craft Advisory from 11 AM Thursday to 11 AM PDT Friday for
Coastal Waters From Cape Flattery To James Island Out 10 Nm-
Coastal Waters From James Island To Point Grenville Out 10
Nm-Coastal Waters From Point Grenville To Cape Shoalwater
Out 10 Nm.
Small Craft Advisory from 11 AM to 11 PM PDT Thursday for West
Entrance U.S. Waters Strait Of Juan De Fuca.
FXUS66 KOTX 220546
Area Forecast Discussion
National Weather Service Spokane WA
1046 PM PDT Wed Mar 21 2018
A change in the weather is expected as a deep upper level low
digs offshore tonight. This will pool moisture into the region
from the south resulting in an increasing chance of precipitation
beginning this evening and continuing at times through Thursday.
Most of this precipitation will fall as rain however snow will be
possible over the higher mountains. A cold front late Thursday
will bring gusty winds and deliver significantly cooler conditions
from Friday through the weekend with the threat of rain and snow
showers each day.
Evening update to make slight adjustments to overnight low
temperatures tonight had minimal to no impact on the zone
forecasts. Have kept the flood watch in place which addresses the
saturated conditions up over northern locations making soil and
rock susceptable to giving way on steep slopes as mud and rock
slides rather than an issue associated with any mainstem river
06Z TAFs: TAFs are rather lengthy in order to time the various
disturbances that are coming up from the south and southwest and
expected to bring precipitation to the area. Ceilings may go down
to MVFR at times associated with what will be rainfall at TAF
sites. Otherwise there may be some weak pulse thunderstorms
forming between 23Z Thursday and 03Z Friday that may affect
locations east of KMWH including the KGEG, KSFF, KCOE and KPUW
sites. After the clutter of this activity ends/diminishes with a
frontal passage an increase in gusty southwest winds is expected
primarily after 04Z Friday. /Pelatti
.PRELIMINARY POINT TEMPS/POPS...
Spokane 43 52 31 46 30 41 / 50 90 80 30 50 60
Coeur d'Alene 40 51 30 44 29 39 / 50 90 90 40 50 60
Pullman 44 52 32 45 31 42 / 50 90 80 40 60 60
Lewiston 47 59 36 53 36 48 / 30 70 60 30 40 50
Colville 41 53 31 47 28 45 / 70 100 100 50 50 60
Sandpoint 38 47 31 43 29 39 / 50 90 100 40 50 70
Kellogg 37 49 29 42 28 38 / 50 80 100 50 50 70
Moses Lake 43 56 31 53 29 51 / 50 60 10 20 30 30
Wenatchee 39 49 31 48 29 50 / 90 80 0 40 20 20
Omak 41 51 31 48 28 48 / 90 100 20 60 30 40
ID...Flood Watch through Thursday evening for Northern Panhandle.
WA...Flood Watch through Thursday evening for East Slopes Northern
Cascades-Northeast Mountains-Okanogan Highlands-Okanogan