069
FXUS66 KMFR 312129
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
229 PM PDT Fri May 31 2024

.SHORT TERM...Other than some high clouds, it`s wall to wall
sunshine out there this afternoon beneath high pressure. A few pop
up cumulus could develop in SE sections (Modoc) into this evening,
but that`s about it. Inland areas will end up generally about 10
degrees above normal for highs this afternoon. Offshore flow led
to a nice, warm afternoon in Brookings with the temperature there
peaking at 79 degrees at 1 pm, but the rest of the coast is being
cooled by marine air with temperatures in the low to mid 60s.
Unless something drastically changes from now until midnight (it
won`t), we`ll close out the month of May here in Medford on a
streak of 25 consecutive days without precipitation. Despite that
long dry period, we`ll still end up only a little below normal for
the month due to the wetness during the first week.

For most areas, this evening will be a near perfect evening for
outdoor activities with the waning of the daytime warmth and
any breezes easing to just gentle winds. Overnight lows will be
near to several degrees above normal. This translates to upper
40s/low 50s west of the Cascades and generally in the 40s over the
east side. Marine layer low clouds/fog probably form or push
into Coos and far western Douglas counties.

On Saturday, an upper trough will swing through. While there will
be an uptick in mid/high cloudiness inland, moisture is limited,
so we`re not anticipating any precipitation. Overall, expect 5-10
degrees of cooling compared to today. The trough will serve to
deepen the marine layer, so expect more in the way of low
cloudiness along the coast (10% or less chance of drizzle along
the immediate coast). More marine influence also means it won`t
be as warm in Brookings (low to mid 60s) as it is today. With an
increasing west-east pressure gradient, gusty west-northwest
breezes (25-30 mph) will pick up in the afternoon just about
everywhere, but especially for the inland valleys and over the
east side. Another mostly dry, comfortable night is expected
Saturday night.

Attention shifts to a stronger, moist Pacific front that will
approach the PacNW on Sunday, then move through our area Sunday
night into Monday. By June standards, this front has significant
moisture transport values of 500-750 kg/ms (IVT), which will send
rain onto the coast Sunday. Precipitation will gradually move
south and eastward across the CWA then, but rain will take pretty
much all day to get to Medford/Ashland/Grants Pass. Wetting
rainfall is then likely for most areas from the Cascades westward
Sunday night into early Monday. Amounts will peter out though as
the front loses its punch moving east of the Cascades. Model
Extreme Forecast Index (EFI) of QPF from the ECMWF shows values
approaching 1 in the Cascades to our north, but also healthy
values along our coast and into the Cascades. This is a strong
indication that the front will be considerable for its rain
production for this time of year, but the rain in our area will
largely be beneficial and put the brakes on the start to fire
season (at least over the west side). Storm total rain amounts of
1-2 inches will be common along the coast, perhaps even up to 3
inches in some of the coast ranges. 0.50-1.00 inch of rain is
expected in the rest of Douglas County and into portions of the
Illinois Valley. Here in the Rogue Valley, most likely amounts
will range from 0.20-0.40 of an inch. Over the east side and from
the Shasta Valley eastward, amounts will be mostly 0.10 of an inch
or less with little or nothing in southern Modoc County. -Spilde

.LONG TERM...Monday afternoon (6/03) through Thursday night(6/06)...

Post frontal showers will persist through Monday afternoon, but will
quickly diminish through the evening as strong ridging builds into
the region behind the departing system. The model suites in previous
runs have depicted the ridge well in control of the area, with
steadily warming temperatures and no chances for rain throughout the
extended term.

The recent runs, however, have started to show a more complicated
pattern, with an area of swift zonal flow, mainly lying just to our
north, with ridging to the south and troughing to the north. This
would keep our area mostly dry and hot, just as previously thought,
although maybe not quite as warm. Also, with the zonal flow in the
vicinity, a stray impulse could brush by southern Oregon, producing
some light rain chances along the coast and the upper Umpqua Basin
through Tuesday night. That being said, the most likely scenario
remains dry.

Wednesday and Thursday, the ridge builds north in response to a
deepening trough upstream over the eastern Pacific. Depending on how
far east that trough is, the ridge axis will remain overhead keeping
the area dry and very warm for this time of year (about 10 to 15
degrees above normal), or just to our east, allowing for some
southwesterly flow aloft. This southwesterly flow solution is also
very warm, but typically produces a chance for convection,
particularly over northern California and along and east of the
Cascades in Oregon, so there is a low chance, around 15%, for
afternoon thunderstorms somewhere in the area mid to late next week.
Details on the timing and exact locations will need to wait until
the models better resolve the situation. -BPN


&&

.AVIATION...31/18Z TAFs...VFR conditions will continue across
northern California and southern Oregon through much of the TAF
period under stable atmospheric conditions. Gusty northerly winds
along the Oregon coast will increase this afternoon before calming
this evening. Gusty winds in the valleys west of the Cascades long
the I-5 corridor are also expected. We are not expecting conditions
east of the Cascades to be as gusty as they were yesterday.
-Miles


&&

.MARINE...Updated 140 PM Friday, May 31, 2024...A thermal trough
will continue to bring chances of northerly gale winds to waters
south of Cape Blanco today, with the highest chances within 30 nm of
the coast. A continuing Gale Warning for southern waters and a Small
Craft Advisory for northern waters will remain in place through 11
PM tonight. Some localized areas of steep seas may remain after 11
PM between Brookings and Crescent City, but not with enough
consistency to require any additional hazard products.

A weak upper trough moving over the area will help to break the
thermal trough up early Saturday morning, starting a period of calm
seas. Winds will turn westerly but remain light, and precipitation
chances from this trough are in the single digits for waters north
of Cape Blanco.

A more impactful front will arrive on Sunday morning, bringing
southerly winds and fresh westerly swell. Wide areas of steep seas
are expected to build by Sunday afternoon, but the timing and exact
areas will benefit from additional information. Moderate to heavy
rainfall will be possible Sunday evening into Monday morning,
especially over all waters within 10 nm from shore as well as outer
waters north of Cape Blanco.

Active seas continue behind the front, with current long term
guidance expecting long period westerly swell to enter area waters
on Wednesday morning. Present outcomes suggest seas of 9 to 12 feet
at 10 to 13 seconds will be built through Wednesday and Thursday.
Additionally, a thermal trough may return next Thursday. Confidence
in the trough development is minimal given current uncertainty in
atmospheric conditions so far out, but the chance is worth
mentioning to communicate the expectation of further chaotic seas
through the end of next week. -TAD/Miles


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Gale Warning until 11 PM PDT this evening
     for PZZ356-376.

Small Craft Advisory until 11 PM PDT this evening for PZZ350-370-
     376.

&&

$$

MAS/BPN/MCB