208
FXUS66 KMFR 141750
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1050 AM PDT Sat Sep 14 2024

.Updated AVIATION Discussion...

&&

.AVIATION...14/18Z TAFS...VFR conditions prevail across much of
the area this morning. MVFR cigs linger along the coast north of
Cape Blanco with LIFR conditions impacting areas from Brookings
southward. These lower conditions are likely to persist through
the TAF period, though there may be a brief period of VFR
conditions this afternoon. Otherwise, high level cloud cover is
streaming across the region associated with a dry cold front and
this will persist through the evening.

Tonight into Sunday, an upper level trough will move into the
region, bringing increasing lower level cloud cover west of the
Cascades. Low end VFR cigs are expected to develop in West Side
Valleys between 15/03z-15/08z and terrain will likely become
obscured. /BR-y

&&

PREV DISCUSSION... /Issued 256 AM PDT Sat Sep 14 2024/

SYNOPSIS...The evolution of the upper level pattern over the
western United States will begin with the breakdown (or movement
eastward) of an already weak upper ridge. This will allow upper
troughing to become the dominant weather feature Sunday into early
next week with a cooler, showery pattern expected through
Wednesday, followed by drying and milder weather Thursday into
next weekend.

DISCUSSION...The ridge brought a nice day Friday with lots of
sunshine and a warm-up to more seasonable temperatures. An upper
ridge amplifying upstream in the Gulf of Alaska/NE Pacific will
allow an upper trough to dig southward along the coast of British
Columbia today. We are already seeing evidence of this in
satellite imagery this morning with some mid and high level clouds
moving in across the PacNW. We`ll see some of these clouds across
SW Oregon and NorCal today, but aside from a brief sprinkle in
northern Douglas today or tonight, the forecast area should remain
dry. Overall, highs today should be similar to what they were on
Friday, perhaps a couple of degrees lower west of the Cascades and
maybe a couple of degrees higher over the east side/NE Cal.

The upper trough will close off (into a closed low) near Vancouver
Island by Sunday morning, with the closed low traversing the
coastline southward into NW California by Sunday evening. This
will bring another shot of showery, cooler weather to the area
(temps below normal). Isolated showers could develop (15-30%
chance) west of the Cascades Saturday night into early Sunday
morning. But, showers will become more numerous during Sunday. The
focus for shower activity (>60% PoPs) will be in northern
California and from the Cascades eastward Sunday afternoon and
evening, where there is also a slight chance (~15-25%) of
thunderstorms. Shower chances drop off significantly west of the
Cascades during this time, since there will be an area of mid-
level subsidence/drying on the low`s NW periphery. Sunday night
into Monday, the closed low will move across NorCal and into
Nevada with wrap-around moisture continuing to impact areas east
of the Cascades. Highest likelihood of showers (60-80% chance)
will be from Modoc northward into southern Lake County. Shower
chances diminish Monday night into Tuesday morning as the upper
low ejects into eastern Idaho. Overall, rain amounts will be light
west of the Cascades with some areas dodging the showers
altogether, while others pick up a few hundredths to maybe a tenth
of an inch. From the Cascades eastward and in NorCal, though,
amounts will be greater with widespread wetting rainfall of
0.10-0.25". Amounts of 0.25-0.50" can be expected across the
higher terrain, where showers have a tendency to focus and even
some areas from the Warner Mtns eastward could have more than
0.50" of rain.

We`ll basically be between systems Monday night, so showers will
be ending over the east side. However, another upper trough will
slide down the British Columbia coast with precip moving back into
the PacNW on Tuesday. Rain showers should reach coastal areas of
SW Oregon again by Tuesday morning, push inland across much of the
west side Tuesday afternoon, then all areas by Tuesday
evening/night. The trough will evolve into another closed low near
or just off the Oregon coast Tuesday night that will settle into
NorCal on Wednesday. All areas stand a pretty good shot at
showers again, with better chances west of the Cascades this time
around. This will keep us below normal temperature-wise through
Wednesday. Heights rise across the area again Wednesday night into
Thursday, so things should dry out with a milder afternoon
Thursday. Upper ridging is expected to maintain dry, milder
weather late next week with the next upper trough skirting by to
the north. -Spilde

FIRE WEATHER...Dry weather is expected most areas today with
afternoon temperatures very similar to where they ended up
yesterday. We`ll see more in the way of high and mid level clouds
compared to yesterday. Fairly typical W or SW breezes can be
expected this afternoon/evening out over the east side. Afternoon
min RHs will probably be down to around 15% or even a tad lower
out by Hart Mtn Wildlife refuge, but not expecting anything
headline-worthy. We`ll head into a showery, cooler weather pattern
Sunday through Tuesday. There is a slight chance of thunderstorms
Sunday afternoon and night in portions of NorCal and from the
Cascades eastward. Wetting rain is most likely from the Cascades
eastward Sunday into Monday. Another system late Tuesday into
Wednesday could bring wetting rain to west side areas as well. Dry
and milder weather is expected Thursday into next weekend.
-Spilde

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT this
     morning for PZZ350-356-370-376.

Small Craft Advisory from 5 PM Sunday to 11 AM PDT Tuesday for
     PZZ350-356-370-376.

&&

$$