Flood in Oregon, May 1 to 3, 2023

Area Forecast Discussion
National Weather Service Medford OR
901 PM PDT Sun Apr 30 2023

.DISCUSSION...

A few radar returns are popping up well north of Diamond Lake
this evening. We're watching the mostly dry cold front move
through the forecast area this evening with a lot of mid and high
level clouds cover the Cascades and sections east of the Cascades.
Medford is currently trending 17 degrees cooler compared to
this time yesterday. We'll see pretty typical Spring temperatures
for the region tonight with low temperatures in the upper 40's in
valleys west of the Cascades and lower 40's east of the Cascades.

Lastly, the Sprague river near Beatty remains in minor flood as
snow melt is pouring into local rivers. The latest RFC forecast
does have that river cresting later tonight.

Read the previous discussion below for more information beyond
tonight.

-Smith

&&

.AVIATION...01/00Z TAFs...A weak front is moving eastward over the
coverage area this evening, bringing occasionally gusty winds to
the west side. VFR levels are generally prevalent currently,
although MVFR ceilings are possible along the Oregon coast and in
the Umpqua Valley overnight. Model guidance is also showing a 15%
chance of MVFR visibility in the Rogue Valley Monday morning.

Precipitation chances will increase behind the front, rising over
higher terrain first than over lower areas. But chances will remain
uncertain (25-50%) through the TAF period, and any precipitation
that does fall is expected to be light. These scattered showers
could still locally lower visibility, especially over elevated
terrain. -TAD

&&

.MARINE...Updated 835 PM PDT Sunday, April 30, 2023...The rapid rise
in the northwest swell has subsided on our northern coast, and has
recently occured in northern California, where rises of 4 to 5 feet
in swell has occurred in the past 3 hours. This should subside as
happened in our northern coast soon and align with the current
timing of beach hazard statement for sneaker waves.

Steep seas will continue through Monday into Tuesday, supported by
gusty northerly winds of 15 to 25 knots with gusts up to 30 knots.
While beach conditions are expected to be less hazardous, a Small
Craft Advisory continues through this period for all waters. Some
waters beyond 10 nm and south of Cape Blanco may experience periods
of Hazardous Seas, although the confidence and duration of these
conditions does not currently require a formal product.

Seas look to calm Tuesday evening as both swell and wind speeds
diminish. Calm conditions are expected to continue through the
end of the week. -TAD/Sven

&&

.PREV DISCUSSION... /Issued 219 PM PDT Sun Apr 30 2023/

DISCUSSION...The front that brought the marine push to the coast
and other areas west of the Cascades this morning is weakening as
it heads east of the Cascades. Clouds are most prevalent in a
corridor from Curry/Josephine County NNE to inland Coos, northern
Jackson and Douglas County. There really isn't any precipitation
being detected out there right now and only some high clouds are
showing up on satellite east of the Cascades. The only real
discernible difference that a front moved through -- or is moving
through -- is the drop in temperatures compared to this time
yesterday. 24-hour change in temperatures is 10-20F in many areas,
but a little less over the far east side where the front is just
getting there at the moment. Some gusty WNW breezes are expected
this afternoon in many locations, then will subside around
sunset. The clouds that are out there near the Cascades, over the
Coast Ranges and along the coast south of Bandon are unlikely to
produce precipitation this afternoon and evening (30% chance or
less). Most other areas will also remain dry during this time
period.

Meanwhile, an upper level closed low is spinning just off
Vancouver Island with a short wave at the base of it that will
head into NorCal tonight. With a blocking ridge downstream over
the Intermountain West and another ridge axis centered on 140W,
the closed low will have no choice but to move southward. It will
remain just offshore, moving to a position just off Cape
Mendocino by late Monday afternoon, then near the San Francisco
Bay area by early Tuesday morning. On Monday, the upper flow over
our region will back to southeasterly and this will bring an
uptick in moisture, clouds and showers over our CWA. Showers can
occur just about anywhere over the forecast area, but the highest
probabilities (60-80%) will be over the mountains, particularly
the Cascades and the higher terrain of the East Side. It will be
cooler with high temperatures generally in the 55-65F range (about
10-15 degrees below average west side and about 5 degrees below
average east of the Cascades). Showers will generally move from
southeast to northwest on Monday. Models are showing enough
instability (BLCAPE values in 200-500J/KG range) 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 into Monday night. I should note
that the CAPE values actually increase over there during Monday
evening, so there may be some nocturnal activity as well.

The closed low will basically wobble near the Bay Area through
Tuesday, then head a bit farther south just off the southern
California coast by Wednesday. This will keep shower chances high
here Tuesday with highest probabilities again from the Cascades
eastward. There should be a downward trend in shower coverage
Tuesday night into Wednesday morning as the low wobbles
southward. But since the circulation is so broad, we expect
instability driven showers and a slight chance of thunderstorms to
continue on Wednesday afternoon. Eventually, the closed low will
weaken and eject across southern California and into Nevada around
Thursday. However, models and ensembles remain in good agreement
showing yet another closed low moving southeastward from the Gulf
of Alaska, which would provide another shot of cooler air and
unsettled weather with showers possible next weekend. -Spilde

HYDROLOGY...A river flood warning remains in effect for the Sprague
River at Beatty. The river reached flood stage (8.5 ft) this
morning and slowly rose to 8.6 feet early this afternoon. The
main driver behind the rise has been snowmelt due to the recent
period of warm weather. Today and this week, temperatures won't be
quite so warm with east side high temperatures in the 50s/60s as
opposed to the upper 70s/low 80s that occurred Thu-Sat. And, it
will be much cooler at night, so that should slow the snowmelt a
bit. Despite some new runoff from snowmelt and 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".
-Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement until 11 PM PDT this evening for ORZ021-
     022.

CA...None.

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

&&