084
FXUS66 KMFR 012131
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
231 PM PDT Sat Jun 1 2024

.DISCUSSION...

.Short Term...Tonight through Monday Night...A very weak trough is
pushing some clouds through the area this afternoon, and a stray
light shower is possible along the coast, where moist onshore
flow could produce enough uplift to wring out a few hundredths of
an inch of moisture. Otherwise, the area will remain dry through
Sunday morning, especially with a weak shortwave ridge traversing
overhead tonight.

The next system arrives Sunday afternoon, and is shaping up to be
an impressive event for this time of year. The warm front arrives
at the coast by midday Sunday, with overrunning producing light
precipitation along and west of the Cascades through the
afternoon and into the evening. The main belt of moisture arrives
overnight, ahead of the cold front that will pass through the area
early Monday.

A strong plume of moisture (precipitable water values of 1.5" or
higher and moisture transport values (IVT) of 500-750 kg/ms) is
associated with this system, which is more typical of systems in
the winter. However, this is June, and therefore temperatures
will be much warmer (snow levels of 8000 to 11000 feet), and no
winter impacts are therefore expected, although rainfall amounts
will be impressive for early June.

Light precipitation associated with the warm front will the
transition to heavier rain as the the main belt of precipitation
arrives along the coast and across much of Douglas County Sunday
evening. Rain will then spread across the rest of the area
overnight and into early Monday morning. Moderate to heavy
rainfall is forecast along the coast, across the coastal
mountains, Douglas County, and the Southern Oregon Cascades
(especially Crater Lake north), with the rest of the area seeing
mostly light to potentially moderate rain. Areas that see the
heaviest rain may experience localized ponding of water on
roadways, especially in urban areas or areas of poor drainage.
Otherwise, expect the rain to be largely beneficial.

The front will dissipate as it moves through the region, with
post-frontal showers continuing through Monday afternoon for much
of southern Oregon and far northern California, with most
precipitation coming to an end by Monday night. Along the north
coast, and perhaps within the Umpqua Basin, onshore zonal flow
could keep some light showers ongoing into Monday night.

Also, much like the wet season systems, gusty west winds will be
associated with the frontal passage. The strongest winds are
expected along the immediate coast, over the ridgelines, and
across the Eats Side. Our typical windy valley locations (Shasta
and Rogue) will not be impacted as much due to the mostly
westerly flow, but east of the Cascades, 700mb flows of around 50
kt suggest the potential for wind advisories, mainly along higher
terrain and in the Summer Lake area. Will continue to assess the
need for an advisory over the next shift or two. -BPN

.LONG TERM...Tuesday through Saturday night.

The forecast area will remain under zonal flow with an atmospheric
river continuing to hit the region on Tuesday. Some of the northern
sections of our forecast areas have a low chance of of seeing some
showers with other locations remaining dry. There is a cold front
out over the Pacific, but it doesn`t push into sections of southern
Oregon. After the wet start to the work week, temperatures on
Tuesday are anticipated to trend 10 degrees warmer with highs
slightly warmer than normal for this time of year.

This trend of warming temperatures will continue into Wednesday as
high pressure begins to build over the four corners and some light
east to northeast flow develops over southern Oregon. Models suggest
a trough over the Pacific will be lingering and that could influence
our weather by Thursday.

The latest deterministic models hint at convection and thunderstorms
developing over southern Oregon and northern California as a weak
shortwave begins to ride over the ridge on Thursday. The GFS denotes
some modest instability around 1000J/kg of convective available
potential energy with some modest shear at 35 knots out of the
south. The ECMWF also initiates some convection over northern
California Thursday afternoon and evening. The NBM PoP forecast is
most confident is shower or storm active east of the Cascades,
although we can`t rule out storms west of the Cascades as well. In
any case, Thursday will be a day to watch with regards to
thunderstorms in future model runs.

The summer like temperatures continue towards the end of the week
with highs in the upper 90`s and some warmer lower temperatures as
well. The NWS heat risk algorithm is picking up on some elevated
heat risk due to warm daytime temperatures on Friday and Saturday,
although it appears the overnight lows cool off enough to dismiss
the need for any heat products at this time. Regarding the chance
for 100 degrees in a few of the valley locations, it appears the
chances have lowered a bit compared to a few days ago. The upper
level ridge doesn`t appear as built in and temperatures could trend
lower if the ridge ends up farther to the east. The inverse could
also happen as temperatures could move higher with a more westward
position. In any case, the chance of 100 degrees in Medford and
Montague is roughly 35% on Friday.

Overall, thunderstorms on Thursday and the moderate heat risk on
Friday into Saturday are the big weather features in the extended
forecast.  Weather risk to the population at large is low, although
heat will bring an increased threat to those that are sensitive to
heat in valleys west of the Cascades.

-Smith



&&

.AVIATION...01/18Z TAFs...VFR conditions will prevail through the
TAF period daylight hours today, even at the coast. Expect some
gusty afternoon breezes, especially for inland terminals this
afternoon into early this evening particularly east of the Cascades.
MVFR conditions due to ceilings will develop after 06Z along the
coast as a cold front approaches from the Pacific.  These MVFR
ceilings will slowly progress eastward toward the Cascades after
sunrise. -Sargeant

&&

.MARINE...Updated 200 PM Saturday, June 1, 2024...Calmer conditions
are expected through this evening.

A front will arrive on Sunday morning, bringing gusty south winds
and an increasing west swell. Conditions hazardous to small craft
are expected Sunday morning to areas north of Gold Beach due to
increasing winds and swell. Winds may reach low end gale north of
Cape Blanco late morning through early evening. Additionally, a
period of moderate to heavy rainfall is expected Sunday afternoon
into Monday morning.

The front will move inland Sunday afternoon, but another front is
expected to move into the waters Sunday night which will result in
increasing southwest winds. This front will move inland Monday
morning with winds diminishing. However, westerly swell will
increase during the day resulting in continued Small Craft
conditions.

Hazardous conditions are likely to continue through the week, though
due to varying weather patterns. An upper level trough will remain
to the northwest, and this will send another, heavier, longer period
swell (9 to 12 ft at 12 to 14 seconds) into the waters on Wednesday.
Meanwhile, the thermal trough will likely return, bringing the
return of strong north winds and steep to very steep wind driven
seas for the latter half of next week. -Smith/Sargeant

&&

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

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

&&

$$