Heavy Snow in Washington, March 8 to 9, 2018

Area Forecast Discussion
National Weather Service Seattle WA
356 AM PST Thu Mar 8 2018

.SYNOPSIS...A surface low off the Northern Oregon coast will move
northeast and weaken today. The low will move inland late this
afternoon along the Northern Washington coast. The associated
front will reach the coast late this afternoon moving through the
interior tonight. High pressure both at the surface and aloft
will build off the coast Friday then move inland Friday night. The
low level flow will become offshore over the weekend and continue
into Monday. High temperatures will warm back up to above normal
over the weekend. Monday has the potential to be the warmest day
since the day before Thanksgiving.

&&

.SHORT TERM...Satellite imagery shows a surface low about 100
miles west of Newport Oregon at 11z/3 am. Doppler radar has just
some spotty showers over the area with the rain out ahead of the
front associated with the low still off the Oregon coast.
Temperatures under cloudy skies at 3 am were in the mid 30s to mid
40s.

Surface low will weaken today and track towards Forks reaching the
Northern Washington coast late this afternoon. The low will
continue to weaken as it moves inland into Southern British
Columbia this evening. The associated cold front will reach the
coast late this afternoon and move inland tonight. Rain out ahead
of the front will spread from southwest to northeast across the
area this morning with the rain finally beginning up in the
Northwest Interior around midday into the early afternoon hours.
Steady rain will give way to showers quickly behind the front this
evening. The strongest winds for most of the area will be just
ahead and with the front later this afternoon into the evening
hours with gusts in the 30-40 mph range common. The exception to
this will be along the Strait of Juan de Fuca and in the Admiralty
Inlet area where the strong westerly winds in the Strait behind
the front will peak late this evening into the early morning
hours. There is a possibility that a wind advisory will be needed
for the Strait and the Admiralty Inlet area late tonight. A
convergence zone will form quickly this evening behind the front
over Snohomish county then move into the Cascades overnight.

The winter storm watch for the Cascades of Whatcom and Skagit
counties and the Cascades in Pierce and Lewis counties beginning
at noon today has been converted to a winter weather advisory.
Have added the Cascades of Snohomish and King counties to the
advisory with the heaviest snow expected with the convergence zone
this evening in that zone.

Highs today will be near 50 with lows tonight near 40.

Upper level ridge building offshore Friday with the low level
onshore flow weakening. Shower activity decreasing significantly
in the morning with the showers mostly confined to the mountains
by afternoon. Plenty of low level moisture around and with the
onshore flow remaining intact will go with mostly cloudy skies.
High temperatures will remain a little below normal, near 50
again.

Upper level ridge moving inland Friday night and remaining over
the area Saturday. Low level flow turning weakly offshore. This
will help clear out the cloud cover on Saturday. After a chilly
start with lows in the 30s temperatures should rebound nicely with
the sunshine and get into the 50s Saturday afternoon.

.LONG TERM...Extended models in good agreement with a weak
splitting system moving through the area Saturday night. The
models are getting weaker and weaker with this feature. If the
trends continue even the slight chance of rain for the coast will
get taken out of the forecast. Upper level ridge strengthens a
little Sunday afternoon with the warmer locations getting into the
lower 60s.

Monday has the potential to be the warmest day since the day
before Thanksgiving ( the high in Seattle that day was 68 ).
Perfect set up for a warm March day with southerly flow aloft and
a stalling front offshore increasing the low level offshore flow.
Model 850 mb temperatures in the plus 7 to 9C range. Have gone a
few degrees above guidance and put highs in the 60s for most
locations on Monday with mid 60s from about Seattle southward. The
record of 68 degrees ( set in 1998 ) for Seattle on Monday is not
out of reach if the model solution works out.

Extended models remaining in good agreement with the stalled front
moving inland on Tuesday for another round of rain. High
temperatures will drop 10 to 15 degrees from the highs on Monday.
Upper level trough behind the front digging south on Wednesday
which could pull most of the post frontal shower activity down
into Oregon. Felton

&&

.AVIATION...An upper level trough over the offshore waters early
this morning will push into western Washington this afternoon.
Moderate southwest flow aloft will become westerly this evening. Low
level southerly winds will increase midday and remain gusty into the
evening as a weakening surface low lifts northeast across the
region. The air mass will become increasingly moist today with MVFR
ceilings in rain spreading eastward across the area 16Z-20Z. Rain
will turn to showers after the passage of a cold front over Puget
Sound around 06Z.

KSEA...Rain will be increasing by 16Z with MVFR ceilings developing
after around 20Z and persisting into early Friday morning. May see a
period of low MVFR and some reduced visibility during the heaviest
precipitation in the 22Z-04Z time frame. Ahead of the upper
trough...5000 foot winds will be south to southwest near 50 knots
18Z-00Z. Light E-SE surface wind will shift to southerly and become
rather gusty (20-30 knots) early afternoon continuing through the
evening. Winds gradually ease late tonight following the passage of
a cold front. 27

&&

.MARINE...A 999 mb low will move NE to southern Vancouver
Island late this afternoon, with a trailing cold front moving
across Western Washington early this evening. Southeast gales are
possible over the coastal waters in advance of the front this
morning. Following the front, the UIL-BLI gradient should reach
+4.5 mb to +5.0 mb late tonight, bringing westerly gales in the
Strait tonight. Gradients will loosen quickly on Fri morning,
with a surface high pressure ridge directly over the waters on Fri
afternoon. High pressure will move east of the Cascades for
offshore flow this weekend. Haner

&&

.HYDROLOGY...River flooding is not expected the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from noon today to 4 AM PST Friday for
     Cascades of Pierce and Lewis Counties-Cascades of Snohomish
     and King Counties-Cascades of Whatcom and Skagit Counties.

PZ...Gale Warning until noon PST today 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 James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory for rough bar from 9 AM this morning to 9
     AM PST Friday for Grays Harbor Bar.

     Small Craft Advisory until 6 AM PST Friday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Gale Warning from 6 PM this evening to 9 AM PST Friday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 6 PM this evening to 4 AM PST Friday for
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 9 AM this morning to 9 AM PST Friday
     for Admiralty Inlet.

     Small Craft Advisory from 9 AM this morning to 4 AM PST Friday
     for Puget Sound and Hood Canal.

&&

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