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Area Forecast Discussion
Issued by NWS Medford, OR
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FXUS66 KMFR 010307
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
707 PM PST Tue Jan 31 2017

.DISCUSSION...An update was sent earlier to increase POPs a bit
for this evening based on radar trends and some surface
observations and web cams indicating light precipitation reaching
the ground. This was occurring mainly from northern Curry/Coos and
Douglas Counties east to the Cascades then over to far northern
Klamath and Lake Counties. These areas are beneath an axis of
deformation that stretches from west to east across the northern
part of the CWA. Just enough lift along this axis with a cold
front nudging southward east of the Cascades is generating some
light QPF with snow levels mainly above 4500 feet. Expect
precipitation chances to decrease overnight. No other changes are
planned this evening. -Spilde

&&

.AVIATION...01/00Z TAF Cycle...Expect VFR to prevail through the
TAF period, with extensive mid-level cloudiness continuing. Fog
chances are low for tonight given the cloud cover, but some moderate
reductions in visibility, only into MVFR, are possible west of the
Cascades by early morning. Decided to remove the fog and low clouds
from the KRBG TAF because it appears that this extensive mid-level
cloud cover will keep the temperature from reaching saturation
overnight into the morning. Otherwise, VFR will continue. BTL/BPN

&&

.MARINE...Updated 300 PM PST Tuesday 31 January 2017...
Breezy northeast winds will persist into Wednesday morning as high
pressure centered well north of the area persists. Northerly seas
are expected to remain below 10 feet through early Wednesday, but
will be steep over a substantial portion of the area. Therefore, a
Small Craft Advisory for Hazardous Seas has been issued for much of
the area beyond 5 nautical miles of the coast, though only a small
portion of the area within 10 nautical miles of the coast is
expected to be affected.

Wednesday through Thursday winds will become southeasterly, waves of
precipitation will begin to move through, and southerly fresh swell
will arrive. This could result in a period of warning level seas in
the 10 to 15 foot range on Thursday. The pattern is then expected to
remain unsettled with several more fronts moving through Friday
into early next week. BTL

&&

.PREV DISCUSSION... /Issued 533 PM PST Tue Jan 31 2017/

SHORT TERM...
Moderate impacting winter weather on the way towards the tail end of
the week from Thursday until Friday for the Mt Shasta region. The
low we have been talking about all week is slowly breaking down the
area of high pressure over us right now. It appears the stationary
front to our north will collide with a weak warm front and bring
widespread precipitation across our region.  The big story for our
area will be snow along I-5 near Mt. Shasta City and the major
summits in that area. We have pretty high confidence that snow will
accumulate on I-5, the major question is simply how much.

Given latest guidance, temperatures still remain cool enough in
the lowest levels of the atmosphere to support snow fall near Mt
Shasta City. In addition, guidance is showing some consistency
with the amount of precipitation Wednesday night into Thursday
morning, so we feel good about this. The major question that is
still up in the air is how warm mid morning to early afternoon
temperatures will become. Cooler temperatures would support higher
snow ratios and higher snow totals in general. For now, a winter
weather advisory seems like the best action at this point.

As for the Cascades, it will snow around 4-6 inches from Wednesday
night until Thursday morning, so there will remain some minor travel
issues at those higher passes on the Cascades.

Eventually this low will weaken and essentially merge with
another closed low around mid day Saturday. The overall wind flow
will shift westerly and we can expect snow starting to really
accumulate along the Cascade range. More on this weekend system
will be discussed below. -Smith

LONG TERM...Saturday through Tuesday Night...As the long term
begins, a large blocking ridge is expected to be n place over
Alaska, with the eastern anchoring low located just offshore of the
Pacific Northwest. This type of pattern is notoriously difficult for
models to reliably resolve, and as a result, the model solutions
vary significantly from run-to-run. Therefore, confidence is low in
any details of the weekend and early next week, but there is some
confidence in the general pattern.

The anchoring low is forecast to remain in place just to our
northwest for the duration of the extended term. Shortwaves orbiting
this low will pass overhead, and each associated front is likely to
produce a round of precipitation and wind. Unfortunately, the timing
and strength of these features remains uncertain. One item of note,
however, is that the latest models have shifted the upper level low
slight further south by early next week, which allows for colder air
and lower snow levels over the forecast area. Overall, expect breezy
and wet weather for much of the extended period, with details
hopefully becoming more clear over the next several forecast cycles.
-BPN

AVIATION...01/00Z TAF Cycle...Expect VFR to prevail through the
TAF period, with extensive mid-level cloudiness continuing. Fog
chances are low for tonight given the cloud cover, but some moderate
reductions in visibility, only into MVFR, are possible west of the
Cascades by early morning. Decided to remove the fog and low clouds
from the KRBG TAF because it appears that this extensive mid-level
cloud cover will keep the temperature from reaching saturation
overnight into the morning. Otherwise, VFR will continue. BTL/BPN

MARINE...Updated 300 PM PST Tuesday 31 January 2017...
Breezy northeast winds will persist into Wednesday morning as high
pressure centered well north of the area persists. Northerly seas
are expected to remain below 10 feet through early Wednesday, but
will be steep over a substantial portion of the area. Therefore, a
Small Craft Advisory for Hazardous Seas has been issued for much of
the area beyond 5 nautical miles of the coast, though only a small
portion of the area within 10 nautical miles of the coast is
expected to be affected.

Wednesday through Thursday winds will become southeasterly, waves of
precipitation will begin to move through, and southerly fresh swell
will arrive. This could result in a period of warning level seas in
the 10 to 15 foot range on Thursday. The pattern is then expected to
remain unsettled with several more fronts moving through Friday into
early next week. BTL

&&

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

CA...Winter Weather Advisory from 10 PM Wednesday to 4 PM PST
     Thursday ABOVE 8000 FEET for for CAZ082.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until
     10 AM PST Wednesday for PZZ350-356.
     Small Craft Advisory for hazardous seas until 4 PM PST Wednesday
     for PZZ370-376.

$$

MAS/CZS/BPN
National Weather Service Regional Headquarters
