Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
300 PM PST Friday Mar 6 2015
Synopsis...an upper ridge will remain over the Pacific northwest
through Monday night...and western Washington will have more sunny
warm days and mostly clear nights. The ridge will weaken on
Tuesday...and a weak frontal system should bring some rain to the
area Tuesday night through Thursday. An upper ridge will build over
the area again on Friday for more dry weather.
Short term...an upper level ridge remains just off the coast of the
Pacific northwest this afternoon...with weak northerly offshore flow
at the surface. The air mass is dry and warm...with 2 PM
temperatures mostly in the middle 50s to middle 60s. The freezing level is
above 9000 feet.
The upper ridge will continue to build as it shifts westward tonight
and Saturday...with the flow aloft over western Washington veering
to northwest. The upper ridge will weaken slightly and shift toward
the Pacific northwest coast again Saturday night and Sunday. The
movement of the upper ridge will induce weak onshore low level flow.
As a result the coast -- one of the warmest parts of western
Washington today and yesterday -- will be a little cooler over the
weekend. But both days will be mostly sunny and warm...with just
patchy morning fog in the south Puget Sound sound and southwest interior.
The upper ridge will flatten a bit more Sunday night and Monday...
and low level onshore flow will increase slightly too. There will
probably be some high moisture moving across the forecast area...
and some marine stratus could move onto the coast. These will be
minor changes though with another dry and relatively warm day.
Long term...the upper ridge will move slowly inland Tuesday...and
models now agree that there will be no threat of precipitation until
A warm front will move through the area around Wednesday...followed
by a weak cold front on Thursday. Showers should decrease Thursday
night as the upper ridge begins to build over the area again. For
now the uw WRF GFS is forecasting total precipitation amounts for
this brief wet period of up to 0.50 over The Lowlands and up to 1.5
inches in the mountains. The snow level will be high...between 5000
and 7000 feet.
Friday should be another dry day with some sunshine as the upper
ridge moves east of the Cascades. Mcdonnal
Hydrology...flooding is unlikely for the next 7 days.
Aviation...an upper ridge will remain over the Pacific northwest
with west to northwest flow aloft. Air mass is stable with
decreasing high level moisture. At the surface...weak high pressure over
western Washington will shift offshore tonight and Saturday.
Cirrus over the area is expected to decrease tonight. This should
allow for some fog patches in the usual favored southwest valleys
Ksea...high clouds. Northwest wind 3-6 knots becoming light east to
northeast this evening. Schneider
Marine...weak high pressure over the waters will shift offshore
Saturday with a weak trough along the West Coast. The trough will
shift into eastern Washington Sunday and Monday. The offshore high
will shift inland Tuesday as a front approaches from the west. The
front will move through the waters Tuesday night and Wednesday with
Small Craft Advisory winds possible most areas. Schneider
You can see an illustrated version of the forecast discussion at