772
FXUS66 KMFR 171745
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1045 AM PDT Tue Sep 17 2024

...Updated AVIATION section for 18Z TAFs...

.AVIATION...17/18Z TAFS...Periods of clear and cloudy skies are
expected this morning and afternoon as one low pressure system
leaves to the east while another approaches from the west. Showers
will develop across the area late this afternoon and continue
through Wednesday morning, with more consistent activity west of the
Cascades. There are slight (20-30%) thunderstorm chances over the
Pacific, with lesser (10-15%) chances over west side areas. Showers
can locally lower visibilities and ceilings and obscure elevated
terrain, while thunderstorms can add lightning and erratic gusty
winds.

In addition to the precipitation, the approaching system will bring
a period of gusty winds to the Klamath Falls terminal early this
afternoon that will ease in the early evening. Guidance suggests low
flight levels along the Oregon coast near the very end of the TAF
period, but with little agreement on when and how far levels will
drop. The next round of TAFs should have more clarity on those
conditions. -TAD

&&

.PREV DISCUSSION... /Issued 254 AM PDT Tue Sep 17 2024/

DISCUSSION...A deep upper trough carved out over the western
United States will continue to bring cooler than normal weather to
SW Oregon and northern California today. One upper low is
ejecting to the ENE across Nevada early this morning, while
another trough coming southward from the coast of British Columbia
will form another closed low off the PacNW coast by this evening.
Wrap-around moisture on the back side of the low to the east will
continue to bring some showers to the east side (especially
Warner Mtns eastward) this morning, but a few isolated showers
could be observed as far west as the Cascades. These should end
though later this morning and this afternoon as the upstream
trough boots the low toward western Wyoming. Most of the area will
be dry at least for a few hours today since we`ll be smack dab in
between systems. But, more showers will develop as the offshore
closed low meanders southward along the PacNW coast. Some of these
showers could reach the Oregon coastline around lunchtime, but
are more likely this afternoon. Inland valleys probably remain dry
into the afternoon, but we expect the showers to overspread most
of the west side later this afternoon and evening. Highest
likelihood for measurable rainfall here in the Rogue Valley will
be between 5 and 10 pm this evening. Models have decreased QPF a
bit with this system with the focus for amounts of 0.25-0.50 of an
inch along the immediate coast. Inland valleys west of the
Cascades should receive 0.10-0.25 of an inch while most areas east
of the Cascades will range from nothing to 0.10 of an inch. Hi-
res guidance is showing a small area of increased QPF near Mount
Shasta/Medicine Lake region into NW Modoc near Lava Beds National
Monument beginning late this evening. Amounts there could be
0.10-0.25 of an inch. Model instability does not favor thunder
over inland areas today/tonight, though isolated thunderstorms
are possible nearest the cold core upper low over the nearshore
marine waters. Shower chances will diminish from NW to SE across
the area overnight into Wednesday morning, though could linger in
portions of NorCal Wednesday.

After some low clouds and patchy fog in southern Oregon Wednesday,
many areas will turn out partly sunny with a slightly milder
afternoon, though still a bit below normal for afternoon high
temperatures.

The closed low will shift inland across south-central California
Wednesday night into Thursday and move into southern Nevada/NW
Arizona by Friday. This should be far enough away to keep shower
chances to our south, but we can`t completely rule out a stray
showers in SE Modoc Thursday. Otherwise, we`ll begin a warming/
drying trend for all areas with temperatures getting back closer
to normal (80-85F west side valleys and 75-80F over east side
populated areas). This pattern will persist into the weekend with
mostly flat ridging. Models do show a weak trough moving by to the
north over the weekend (Sat night/Sun AM), but precipitation
chances are low (less than 25%) and only exist north of the Rogue-
Umpqua divide.

There isn`t too much to get excited about in the extended forecast
(Monday and beyond) either with the main storm track still
decidedly to the north. This should favor drier than normal
conditions and temperatures near or maybe even a bit above normal.
-Spilde

MARINE...Updated 245 AM PDT Tuesday, September 17, 2024...

Winds will shift to the south ahead of an incoming front today. This
will allow for winds and seas to remain relatively light
today/tonight. The front will also bring widespread rain
(today/tonight) with a slight chance (15-30 percent) for
thunderstorms (mainly tonight) over the waters. Any thunderstorms
that develop will have the potential for strong, erratic gusty winds
(40-50mph). Moderate to occasionally strong north winds and steep
seas will develop Wednesday as a thermal trough develops, with Small
Craft Advisory conditions expected through the rest of the week.
There is some indication that a Hazardous Seas Warning maybe needed
middle/late this week. There is also some wiggle room in the extent
of the possible Small Craft Advisory later this week. All that said,
will wait on issuance at this time to nail down coverage on possible
warning level conditions that may accompany the Small Craft
Advisory.

-Guerrero

&&

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

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

Hazardous Seas Warning until 5 AM PDT early this morning for
     PZZ356-376.

&&

$$