Sneakerwave in Oregon, April 30, 2023

Area Forecast Discussion
National Weather Service Medford OR
934 AM PDT Sun Apr 30 2023

Updated AVIATION discussion

.DISCUSSION...The main update this morning was to upgrade the
flood watch for the Sprague River at Beatty to a flood warning.
The latest stage as of 8 am was 8.5 feet, which was right at flood
stage. This is due to the warmth of recent days and significant
snowmelt into the river system. With temperatures cooling down to
more typical values for this time of year over the next several
days, and despite some new input from rainfall later this week,
models are showing the river leveling off and then falling early
this week. We'll continue to monitor this and update accordingly.
For more information and the associated hydrograph, please refer
to weather.gov/mfr and select "River and Lakes".

A cold front is pushing inland this morning. This front was able
to squeeze out some moisture along the coast with a few hundredths
to a tenth of an inch at most locations. A few of the higher
elevation RAWS in the coast ranges (Flynn Prairie and Red Mound)
reported a tenth to a quarter of an inch, but that's about it --
areas farther inland remain dry. The front will push east of the
Cascades this afternoon and it will turn breezy with the most
noticeable difference for inland areas being the 10-20 degree drop
in temperatures compared to yesterday. Clouds are thickest this
morning north of the Umpqua Divide and also from the coast to
Josephine County. Some of these will come into the Rogue Valley
later this morning/afternoon. Rain showers the rest of today are
unlikely (less than 30% chance), but if any were to occur, the
best chance would be in the coast ranges and in the Cascades.

The upper low will continue to move south off the northwest
California coast Monday and the upper flow will become
southeasterly. The position of the upper low Monday is one that will
bring showers just about anywhere over the forecast area. Showers
will generally move from southeast to northwest on Monday.
Guidance suggests enough instability exists for at least a slight
chance of thunderstorms for portions of the east side, including
most of Lake, eastern Klamath, and northeast Modoc County late
Monday afternoon and early Monday evening.

For details on the rest of the week, please refer to the previous
discussion below. -Spilde

&&

.AVIATION...30/18Z TAFs...A weak front is starting to move over the
Oregon coast and will progress eastward over the area. The front has
helped to clear out marine fog, lifting ceilings behind the front to
VFR. Postfrontal clouds may cause isolated lower ceilings. Ceilings
ahead of the front are falling to MVFR levels in the Umpqua Valley,
but look to raise back to VFR this afternoon. Inland areas farther
east may see some increased cloudiness but remaining at VFR,
although some gusty winds are expected this afternoon.

Ceilings have a 30-50% chance of lowering back to MVFR early Monday
morning, but are unlikely to reach IFR levels. However,
precipitation chances do start to rise overnight and into Monday
morning, which may locally lower visibility to MVFR or IFR levels
and obscure terrain. -TAD

&&

.MARINE...Updated 915 AM PDT Sunday, April 30, 2023...An incoming
weak front is helping to clear out coastal fog this morning. An
influential northwest swell will reach coastal waters this
afternoon, building steep seas of 10 to 14 feet at 14 seconds. Ocean
conditions will be hazardous for craft and for beachgoers. Related
hazard products have been issued to highlight these conditions.

Steep seas will continue through Monday into Tuesday, supported by
gusty northerly winds of 15 to 25 knots gusting to 30 knots.
While beach conditions are expected to be less hazardous, a Small
Craft Advisory continues through this period.

Seas look to calm Tuesday evening as both swell and wind speeds
diminish, and calm conditions are expected to continue through the
week. -TAD

&&

.PREV DISCUSSION... /Issued 303 AM PDT Sun Apr 30 2023/

DISCUSSION...An upper low is centered near 46N/132W is slowly
moving east. At the same time the upper low is digging with a south
flow aloft. Low clouds with light rain and drizzle are being
observed along g the coast and coastal valley and this will remain
the case into the morning hours. At the surface, a weak cold front
will move into the area and bring light intermittent showers along
the coast, coastal mountains and possibly northern Cascades late
this morning into this afternoon. It will be noticeably cooler
compared to yesterday with more cloud cover.

The upper low will move south and remain off the Oregon coast
tonight into early Monday morning. Ahead of the low will be a
continued south to southeast flow aloft with weak to moderate
disturbances moving through. This will be enough to bring isolated
to scattered showers mainly along and west of the Cascades.

The upper low will continue to move south off the northwest
California coast Monday and the upper flow will become
southeasterly. The position of the upper low Monday is one that will
bring showers just about anywhere overt the forecast area. Showers
will generally move from southeast to northwest on Monday. Guidance
suggest enough instability exist for at least a slight chance of
thunderstorms for portions of the east side, including most of Lake,
eastern Klamath, and northeast Modoc County late Monday afternoon
and early Monday evening.

As the upper low moves south on Monday, there's good agreement among
the operational GFS, ECMWF and individual ensemble members that it
will get cut off from the main flow and basically wobble around in
central California next Tuesday through Thursday, The position of
the upper low is close enough to at least warrent a chance of
showers and a slight chance of thunderstorms, with the best chance
for isolated storms along and east of the Cascades and during the
afternoon and early evening hours as instability will be greatest as
a result in max heating in the afternoon along with a weak trigger
by way of weak shortwaves moving through. Afternoon temperatures
during this time are expected to be near or slightly above normal,
especially Tuesday and Wednesday. Keep in mind, with this type of
pattern the timing and location of showers are typically difficult
to pinpoint this far out, and not everyone will have showers all of
the time.

The upper low will weaken by the end of the week, However, there's
good agreement among the operational and ensembles showing another
upper low dropping down from the Gulf of Alaska bringing a
reinforcing shot of cooler and unsettled weather, with showers
likely to persist through next weekend. -Petrucelli

&&

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

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 PM PDT Tuesday
     for PZZ350-356-370-376.

&&

MAS/TAD/MAP/BPN