Flood in Oregon, April 29 to 30, 2023

Area Forecast Discussion
National Weather Service Medford OR
913 PM PDT Sat Apr 29 2023

.DISCUSSION...

A cold front sits off the Oregon coastline this evening as some
high and low clouds cover certain sections of the coastline. A
moist boundary layer will bring a light drizzle and some fog to
the coast through the overnight hours. Some of these conditions
are already being observed within Brookings. A few models
anticipate this fog/drizzle to persist into Monday morning along
the coast. Elsewhere to the east, drier conditions are
anticipated overnight as the boundary layer remains fairly dry.
The HREF anticipates these lower ceilings to spread into the
Umpqua Basin and perhaps the Rogue and Illinois valley by sunrise.

Read the previous discussions below for more information beyond
tonight.

&&

.AVIATION...30/00Z TAFs...IFR/LIFR visibilities and ceilings in
marine fog and stratus has pushed inland and latest model runs show
an MVFR deck spilling into the Umpqua basing vcty KRBG. The IFR
ceiling near the coast are expected to burn back offshore
mid to late tomorrow morning, and lift to VFR inland.

Elsewhere, VFR conditions and generally light winds will persist
over inland areas. -Sven

&&

.MARINE...Updated 845 PM PDT Saturday, April 29, 2023...Relatively
calm conditions will persist tonight, with widespread fog and
stratus. On Sunday , a steep west northwest swell will build quickly
into the area, accompanied by a weak front with breezy south winds
and light showers. Gusty north winds will return Monday into
Tuesday, with building steep wind seas on top of the diminishing
swell. Calmer conditions and showers are expected to return for the
latter half of the week. -Sven

&&

.PREV DISCUSSION... /Issued 300 PM PDT Sat Apr 29 2023/

SHORT TERM (Today through Sunday night)...

Overview:
A transition period will be underway as we shift from high
pressure aloft towards our next incoming system. This will likely
lead towards cooler temperatures and more cloud cover, especially
tomorrow when inland temperatures may be about 20 degrees cooler
in some locations compared to today. We will also see a chance for
rainfall with accumulations possible across western portions of
Oregon and coastal areas. The big question of course will be how
far inland the marine layer/stratus pushes inland tonight.
Nevertheless, tomorrow will ultimately see more cloud cover
generally across the area with less sunshine expected to end the
weekend.

Further Details:
An H5 axis of high pressure will slide just east of the Cascades
today/tonight as a strong closed low starts advancing towards the
Pacific Northwest. An Omega blocking pattern appears to set up,
and the aforementioned low is forecast to stall out over the
coastal areas before sliding south along the coast Monday. The
path and evolution of this closed low should lead to at least some
light rainfall across coastal areas and western portions of the
forecast area starting tonight and going into parts of Sunday
morning. In other words, a trace to 0.01" is very much in the
realm of possibilities, but probabilities drop of significantly
once we start talking about higher rainfall amounts. Below are
some probabilities for rainfall.

	* Probability for 0.01" or greater
		- 80% - 100% for coastal areas
	* Probability for 0.10" or greater
		- 20% - 60% for mainly Port Orford to Gold Beach

Since the Port Orford to Gold Beach probabilities are very much
for a small area, it should also be noted that outside of this
small area the probabilities for 0.10" or greater are less than
10% for nearly the entire forecast area.

As the closed low slowly meanders south along the coast we could
see precipitation chances linger into Monday/Monday night as well.
This could impact areas inland, but at this time there is a lot of
uncertainty with the blocking pattern strength and the evolution
of the low along the coast. That said, central to western portions
of the forecast area could see another round of showers Sunday
night. The probabilities for 0.01" or more of rainfall appears to
be on the high end again (similar to tonight/Sunday morning), but
again the evolution of this closed low could be tricky in this
blocking pattern.

Guerrero

LONG TERM...The 500 mb ensemble cluster patterns are in excellent
agreement through Wednesday and mostly similar Thursday through
Saturday. Despite this pattern agreement, the day to day weather
forecast for southern Oregon and far northern California is still
challenging. The combination of showers favored in the mountains
versus the valleys and instability mainly from Siskiyou County to
the Cascades eastward creates variable spring weather.

Low pressure will move south just offshore of the Pacific Northwest
and far northern California on Monday. Southerly flow aloft will
turn to the southeast and east Monday night. This low will move to
the Bay Area by Tuesday and then move very slowly south into
Thursday before coming back to the north Friday into Saturday near
Eastern Oregon. The main theme is that the low's influence will
impact our region but any showers will be intermittent most days
with a fair amount of sunshine. Temperatures will be near normal or
even a little above normal after cooler temperatures on Monday.

Sandler

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from Sunday morning through Sunday
     evening for ORZ021-022.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM Sunday to 5
     PM PDT Tuesday for PZZ350-356-370-376.

&&