254
FXUS66 KMFR 171528
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
828 AM PDT Sat May 17 2025

.DISCUSSION...An upper trough will bring cloudy skies and
scattered showers through the day today. The highest forecast
rainfall totals remain over the Cascades and west side foothills,
the Warner Mountains, and southern Lake County. These areas could
get between 0.25 and 0.50 inches of rainfall through Sunday
morning. Other areas will get a few hundreths of an inch at most.
Nocturnal thunderstorms left the system earlier this morning, but
slight thunderstorm chances remain in the forecast for this
afternoon and into the early evening hours. 10-15% chances for
thunderstorms will be present over Oregon counties west of the
Cascades, and southern Lake County and areas around the Warner
Mountains will have 15-30% chances for thunderstorms. Any
thunderstorms that do develop are likely to be isolated and only
locally impactful. Showers decrease overnight and skies clear
through the day Sunday.

Please see the previous discussion for more details on the short-
and long-term forecasts. -TAD

&&

AVIATION...17/12Z TAFs...A front is moving inland early this morning
bringing rain, mountain obscurations and MVFR and areas of IFR
conditions. Expect showers and a mix of MVFR and VFR conditions
through the morning, with some localized areas of IFR.

Isolated to scattered thunderstorms embedded with rain showers have
developed this morning across Klamath, Lake, and Modoc counties,
including at Lakeview and Alturas. This risk will continue through
the afternoon. Chances for thunderstorms (15-20%) are also expected
tonight into Saturday across Douglas County and for the Southern
Oregon Cascades.

Ceilings will gradually lift to VFR this afternoon, but expect areas
of MVFR and showers to linger into the evening. Showers should taper
off into tonight, with VFR prevailing by the end of the TAF period.
-BPN

&&

MARINE....Updated 800 AM Saturday, May 17, 2025...Rain showers
with light to moderate winds and increasing west seas are expected
through Sunday morning. Another frontal system will move into the
area on Monday with winds veering from south to northwest.
Northerly winds will increase on Tuesday from the brief
development of a thermal trough near shore. Meantime, building
seas on Tuesday may possibly becoming high and steep with the
combination of the higher wind waves and a building west-northwest
swell at 13 seconds. Conditions are likely to improve slightly on
Wednesday. -BPN


&&

.PREV DISCUSSION... /Issued 355 AM PDT Sat May 17 2025/

DISCUSSION...A fairly vigorous upper trough offshore supported by
a 150-kt jet will sharpen as upper level energy dives ESE into
northern California this morning. Showers have already broken out
along the coast, along the Cascades, and across the East Side.
The best forcing is over the East Side where showers and
thunderstorms have formed in the last few hours. This is a bit
unique to have a sharpening upper trough to swing through in the
middle of the night and also to have enough instability present
east of the Cascades (about 300-500 J/KG) to support convection.
As such, we expect isolated to scattered thunderstorms to continue
through the morning (mainly east of Klamath Falls), with
thunderstorms most likely to form in Modoc and Lake counties. We
don`t expect severe weather, but some of the stronger cells could
contain gusty winds, small hail, and, of course, cloud to ground
lightning.

The main axis of instability shifts to the east later this
morning, but the cold pool aloft will move in, so we`ll maintain
scattered showers, most numerous near and north of the Rogue/Umqpua
Divide, over the Cascades, and from around Winter Rim eastward
over the East Side. There is also a risk of thunder in portions of
Douglas County Saturday in any of the heavier showers, but
isolated (15-20% chance) at best. For the Rogue Valley, showers
will be more hit-or-miss. Some areas may have brief downpours,
while others miss out all together. Locally breezy conditions
develop today as well, especially east of the Cascades in the
afternoon where non-thunderstorm wind gusts could be 30-40 mph.
Overall, expect a cooler than normal day with highs generally in
the 60-65F range for the west side and 55-60F east of the
Cascades. Shower coverage diminishes this afternoon/evening as
warmer air aloft moves in, though some may linger into Sunday
morning near the Cascades due to moist onshore flow.

Seasonal temperatures under zonal flow aloft is then expected to
continue through the week. A couple of weak disturbances passing
just to our north may briefly affect conditions for certain
locations. On Monday, a weak front could bring some clouds to Coos
and eastern Douglas counties. Light showers are possible over
these areas on Monday morning and afternoon, but amounts will be
one or two hundreths at most. On Wednesday or Thursday, a weak
disturbance could bring gusty winds and isolated showers to the
northernmost border of the CWA. Deterministic guidance for both
the ECMWF and the GFS show some upper instability passing over the
area, with some variation in timing and structure. Individual
ensemble members for both the GFS and ECMWF are split on showing
the disturbance or not, and those that show it do so with some
variation in timing and location.

Zonal flow continues on Friday, with some uncertainty for the
weekend. While both models show some amount of upper level ridging,
the strength and position of the ridge vary. The general expectation
seems to be additional warming on Saturday and Sunday, but little
overall consensus on how warm next weekend will be. NBM
probabilistic guidance echos this uncertainty, with daytime highs
ranging between seasonal temperatures to 10 degrees above normal.

-Spilde/TAD/BPN

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$