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074
FXUS66 KMFR 301049
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
349 AM PDT FRI SEP 30 2016

.DISCUSSION...This morning`s fog/low cloud satellite product is
showing low clouds and patchy fog along the coast with a clear sky
over most inland locations. The main weather feature expected to
impact southwest Oregon and northern California this weekend will
be an upper level low pressure system currently spinning near 47
N and 132 W. We are in a broad, mostly dry southwest flow aloft
ahead of this system. So, we`re not expecting much rainfall today,
except for a chance of showers along the coast and perhaps the
Umpqua Valley this afternoon. Model 700 mb winds are expected to
be in the 30-40 kt range through this afternoon from NorCal
northeastward to areas east of the Cascades. So, we`ll get some
pretty gusty southwest winds again, some up to 40 mph, especially
over the upper slopes and ridges. The Shasta Valley will be windy
again too with gusts to 35 mph, but these values remain below wind
advisory thresholds. It will also be noticeably cooler inland with
most areas 5-15 degrees lower than yesterday.

IR imagery is showing some pretty cold cloud tops and a good
amount of lightning associated with the upper trough this
morning. The upper trough and associated cold pool will move
southeastward and onshore tonight bringing a high likelihood of
showers to the coast. Sufficient instability coincident with the
H5 -25C isotherm will bring a slight chance of thunderstorms to
the coastal waters during this time frame and these may even move
onshore near Coos Bay overnight. Shower chances dwindle rapidly
the farther inland you get and while there is a slight chance of
showers around the Rogue Valley Saturday, measurable rainfall is
unlikely.

We`ll have to wait for another deeper upper low and vigorous
short wave to dive southward on the back side of the upper trough
Saturday night into Sunday. This system will bring a band of
frontal precipitation that could be briefly heavy at the coast
Saturday night. This band will move inland Sunday morning with
wetting rainfall likely across all of the west side. Precipitation
will become more showery and intensity will ease a bit by Sunday
afternoon. H5 temps associated with this upper low/cold pool will
be around -28C, so have introduced a slight chance of
thunderstorms again over the coastal waters behind the frontal
band. The upper low will move onshore into SW Oregon Sunday
afternoon and post-frontal showers will continue through the
evening hours before diminishing or ending Sunday night. Sunday
will be the coolest day with temperatures only in the upper 50s
for highs here in Medford. Snow levels will drop to around 5500
feet, so while Crater Lake Rim and other higher mountain areas
may see a few inches of snow, snow impacts are expected to be
minimal.

We`ll have to keep an eye on Sunday night into Monday morning for
some of the colder valleys, like the Shasta and Illinois. It is a
low probability, but there is some potential for a few hours of
frost if skies clear quickly enough.

Models continue to show another fast-moving system at the nose of
a 125-kt jet developing over the northern Pacific Ocean early
next week. This disturbance and its associated warm front will
move through the Pacific Northwest Monday night into Tuesday with
another shot at some rainfall. Models had been splitting this
system with some energy moving into coastal areas before petering
out, but 00z runs bring a more cohesive front through the area
with another area of precipitation. Have increased POPs during
this time frame, especially along the coast and in Douglas County
where rain is likely. This system will lift northeast of the area
Tuesday night with a flat ridge developing on Wednesday. Late
next week, the EC brings in another deep system Thursday/Friday,
but the GFS is weaker and flatter with the flow, so it is drier.
-Spilde

&&

.AVIATION...29/06Z TAF CYCLE...VFR conditions will continue for most
locations inland from the coast (including KMFR and KLMT) through
the TAF period. At the coast, stratus/fog with IFR cigs/vis is
already filling in and will continue to expand down the coast
through the night. It is also expected to move into the Umpqua Basin
overnight and will probably reach KRBG. It is expected to lift and
erode back to the coast by mid morning. -Wright

Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available between 04Z and 14Z.

&&

.MARINE...Updated 300 AM PDT Friday 30 September 2016...Winds and
seas will diminish further this morning as weak high pressure
moves in. A fairly weak and disorganized cold front will move
through today followed by an area of low pressure through Saturday
morning. Showers are expected today, with rain more steady and
moderate, at times, tonight through Saturday. Stronger south winds
are expected with a more organized cold front Saturday. Sven

&&

.FIRE WEATHER...Updated 300 AM PDT Friday 30 September
2016...The newest model suite shows little change in the forecast
for today. Although most areas will continue to see humidity values
rise, a dry slot is expected to mix down to the surface this
afternoon. This will help keep humidity values slightly lower with
higher winds across the East Side today.

Confidence remains moderate for wetting rains for areas from the
Cascades west on Sunday. A cool and unsettled pattern remains
through the weekend into the early part of next week. A weak upper
ridge builds over the region for the middle of next week with brief
warming and drying before changing back to an upper trough pattern
with cooling and unsettled weather returning. Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 1 PM this afternoon to 7 PM PDT this
     evening for ORZ624.

CA...Red Flag Warning from 1 PM this afternoon to 7 PM PDT this
     evening for CAZ285.

Pacific Coastal Waters...None.

$$

MAS/SBN/TRW