FXUS66 KSEW 191111

Area Forecast Discussion
National Weather Service Seattle WA
311 AM PST Tue Jan 19 2021

.SYNOPSIS...High pressure aloft builds over the region and
remains in place much of the first half of the week, though a weak
front will clip the area late Tuesday. Another disturbance
arrives Thursday. A stronger front likely arrives this weekend
with cooler temperatures and lower snow levels.


.SHORT TERM /TODAY THROUGH THURSDAY/...High pressure and offshore
flow will lead to dry conditions across western WA today. Expect
patchy low clouds and fog in the interior this morning with skies
becoming partly sunny this afternoon. Highs will be close to
normal in the mid to upper 40s. The ridge will flatten over WA
tonight while a weak trough cuts through B.C. This trough will
clip western WA for a chance of light showers, mainly in the north
interior and north Cascades. Weak high pressure then rebuilds on
Wednesday for another dry day.

We`ll see another round of showers on Thursday while a cool upper
low tracks south down the coast. Precipitations amounts look
light with just a few hundredths of an inch over the lowlands.
However, snow levels will be low, around 1500-2000 ft, and could
see a light rain/snow mix in areas near the Cascades (mainly
Thursday night). 33

.LONG TERM /FRIDAY THROUGH MONDAY/...Cool (but dry) northerly
flow will prevail Friday and Saturday with temperatures trending
below normal - highs in the lower to mid 40s and lows in the 20s
to lower 30s.

The following system on Saturday night or Sunday shows some
potential for lowland snow due to low snow levels (around
500-1000ft). Around half of the ECMWF and GFS ensemble members
show snow but amounts look spotty and light. NBM at Sea-Tac has a
60% chance of snow with accumulations less than 1". The
percentages are a little higher at Bellingham where snow levels
will be lower due to N/NE flow. The coast will likely just see a
rain/snow mix with no accumulations. So we`ll see how this
continues to unfold as we get closer to the event. As always, snow
amounts will depend on timing of snow levels, temperatures and
moisture. The threat for more lowland snow continues into early
next week as snow levels will remain low, with more systems headed
our way. 33


.AVIATION...West northwesterly flow aloft with front dissipating
just to the north of the area tonight. Light flow in the lower

Mid and high level clouds over the area today. Areas of ceilings
below 500 feet and visibility below a mile, tops 500-1000 feet,
until 20z.

KSEA...Ceilings below 200 feet and visibility below 1/2 of a mile
until 18z. Mid and high level clouds after 18z. Light northerly
winds becoming southerly by 20z. Felton


.MARINE...High pressure will remain over the waters through
Wednesday. A front will dissipate just north of the area tonight.
A weak system will arrive Thursday with high pressure rebuilding
again Friday. Another system will approach the waters late
Saturday. Outside of the possibility of some small craft
northerly winds over the Northern Inland waters Friday no
advisories are forecast through the end of the week. Felton


.HYDROLOGY...No river flooding is expected through the next seven





NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather