280
FXUS66 KMFR 152124
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
224 PM PDT Sun Sep 15 2024

.DISCUSSION...The first of two deep upper level troughs is
affecting the region this afternoon, resulting in late October
like weather. Temperatures are running about 5 to 10 degrees
cooler than this time yesterday for areas west of the Cascades.
Meanwhile, east of the Cascades, temperatures are 10 to as much as
20 degrees cooler than this time yesterday. This cooler weather
will continue through mid-week before temperatures rebound to
values more typical for late September.

The best forcing for showers and thunderstorms today will extend
from NorCal northeastward across SE Klamath and into Lake County,
and this will be the focus area for wetting rainfall. There have
been a handful of lightning strikes already across northern
California and surface observations indicate generally a few
hundreths to a tenth of an inch has fallen out of these showers.
Under the heavier returns, however, upwards of 0.25" has been
recorded. We do expect shower/thunderstorm activity to increase
within the next hour or two, but focus will remain east of the
Cascades today. Meanwhile, as the low continues moving southward
today, there will be an area of subsidence and mid-level drying on
the NW periphery of the low and this will result in a relative
minimum in shower activity, which will be for areas on the west side
of the Cascades. That`s not to say there isn`t a chance of showers
over here (including the Rogue Valley), but they`ll be much more hit-
or-miss than they are over Siskiyou/Modoc up into southern
Klamath/Lake counties and put down much less precipitation compared
to the East Side.

This first trough will progress eastward tonight into Monday, and
wrap around moisture under easterly flow will maintain precipitation
across the far eastern portion of the area in Lake and Modoc
Counties. Widespread wetting rain is likely east of the Cascades
where amounts of 0.10-0.25 of an inch will be common, with up to
0.50 of an inch in the mountains where showers tend to focus. Shower
chances will diminish west of the Cascades, and temperatures will
trend around 5 degrees warmer for the day Monday.

There will be a relative lull in activity Monday night, but the next
trough will move in rather quickly behind the departing one. By
early Tuesday morning, precipitation is expected at the coast, then
will spread inland through the day Tuesday. This low will move into
NorCal Tuesday night and showers will overspread the remainder of
the region, then settle south and eastward Wednesday into Thursday.
We`ll see showers gradually diminish across the area from NW to SE
during this time frame. This system will be a more typical wet
system for this area with the bulk of precipitation expected along
and west of the Cascades. Overall 0.50-0.75 of an inch is likely,
perhaps around an inch in the coast ranges. A tenth to 0.25 of an
inch appear to be the most likely amounts across the remainder of
the area, though with a showery regime, some areas could have more
or less.

Shower activity comes to an end by Wednesday night. There will
likely be some lingering cloud cover, and maybe even some patchy
west side valley fog Thursday morning, but this will give way to
sunny skies for Thursday. A period of ridging is expected for the
latter half of the week and into next weekend, with temperatures
trending warmer, but still remaining a few degrees below normal.
It`s likely to remain dry through the weekend and into early the
following week. However, guidance does show another system moving
over the top to our north during the weekend. Right now, it looks
like mainly a dry trough/frontal passage Saturday or Saturday night.
Rain chances at this time are less than 10%. While this could
change, as of now, it appears this system is much more likely to
cause an increase in afternoon/evening breezes over the east side
than anything else. -Spilde/BR-y

&&

.AVIATION...15/18Z TAFS...Low pressure moves across the area today,
and this will bring scattered showers and occasional MVFR ceilings
to east side locations, while west side locations see just scattered
cumulus and VFR conditions. Showers will gradually diminish and
shift east tonight on the east side. Areas west of the Cascades will
continue to see VFR tonight, but low stratus with IFR ceilings will
be possible along the coast and into the Umpqua Basin. -Wright

&&

.MARINE...Updated 200 PM Sunday, September 15, 2024...North
winds will continue to strengthen tonight into Monday as low
pressure gradually moves inland. North winds and steep to very steep
seas will continue through Monday night, but an incoming front will
turn winds to south and allow seas to diminish Tuesday.

The front will move into the region on Tuesday bringing widespread
precipitation and lowering visibility. Moderate to occasionally
strong north winds and steep seas return late Tuesday into
Wednesday, likely bringing the return of conditions hazardous to
small craft. -Wright

&&

.FIRE WEATHER...Issued 200 PM Sunday September 15, 2024...The upper
trough is digging south with the axis of the upper trough offshore.
Radar image is showing showers starting to develop and moving
northeast in southeast Siskiyou county into southeast Klamath and
central Lake County. So far no lightning has been detected however
some of the returns on radar show higher reflectivity. Instability
will be greatest along and east of the Cascades and eastern Siskiyou
and Modoc county through this evening, thus the best chance for
thunderstorms will be in these areas. However storms will likely
produce rain, some of which could be moderate to heavy at times.

The upper low will dig south of the area overnight Sunday into
Monday, and there`s good agreement we`ll have wraparound moisture
east of the Cascades and northern Cal through the day with wetting
rains likely in these areas. Some of the convective allowing models
(CAMS), paintball, and SPC HREF suggest storms could persist into at
least the first half of the night, and possibly into the overnight
hours. Not as confident we`ll get any storms overnight tonight, but
at the same tine cannot be ruled out. It could be one of those
situations where if storms were to persist into the overnight hours,
it would be the exception and not the norm, and not much more than a
few strikes. Even then they will be rain producers.

Monday, showers will remain persistent in the southeast part of the
area as we get caught up in some wraparound moisture. Meanwhile
showers will tend to be far and few in between west of the Cascades
in Oregon, and it could end up dry for the entire day. Instability
Monday is marginal at best, but there`s some evidence suggesting it
could be enough for at least a few isolated storms Monday afternoon
and early evening in southeast Lake and Modoc County.

Despite the variation of model solutions from run to run, one thing
has been consistent. There will be a brief break in the weather
Monday evening into Tuesday morning before precipitation moves back
in during the day Tuesday as another upper trough drops in from the
northwest, and pretty much remain over the area through Wednesday.
This system will also be wetter, and the chance for wetting rain
will be high for most locations.

The upper trough will evolve into an upper low as it digs south of
the area Wednesday night and we`ll begin to see precipitation
diminish from north to south. Wednesday night.

Dry weather returns Thursday and is likely to last through next
weekend, and possibly into the first half of next week, with warmer
temperatures for the interior. A thermal trough will set up along
the southwest Oregon coast resulting in breezy east to northeast
winds near and at the ridges, but if we get the expected rainfall in
this area today through Wednesday, it won`t pose a concern.
-Petrucelli

&&

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

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

Hazardous Seas Warning until 5 AM PDT Tuesday for PZZ356-376.

&&

$$

MNF/MAP/TRW