Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 271618
Area Forecast Discussion
National Weather Service Medford OR
918 AM PDT THU OCT 27 2016
A broad stream of subtropical moisture emanating from the Eastern
Pacific Ocean west of Mexico continues to push into the forecast
area today. 24 hour rain amounts have been 3-6 inches across
Curry County, and greater than an inch for most areas west of
Roseburg and Grants Pass. Several embedded moderate to locally
heavy bursts of rain this morning are likely associated with
pulses of higher precipitable water values in the 1.5 to 2 inch
range. Rainfall this morning will focus from the Coast Range to
just east of the Cascades and then will shift slowly eastward to
areas along, near and east of the Cascades this afternoon. Rain
will diminish with time from north to south this afternoon and
evening. For the Mount Shasta area, rainfall amounts will be
greatest late this morning through early this afternoon. Snow
levels are currently at or above the highest points of the Crater
Lake Rim and the 8kft Grey Butte station on Mount Shasta. Rainfall
will mostly wind down tonight with Friday precipitation free for
most locations. BTL
.AVIATION...28/12Z TAF cycle...A cold front will slowly move inland
today with light to moderate precipitation, mixed MVFR/VFR ceilings
and terrain obscured. Ceilings may temporarily lower to IFR in
heavier rain this morning from the Cascades west. Gusty
south to southwest winds ahead of the front are still expected for
areas east of the Cascades with light to moderate turbulence in the
vicinity of terrain. The front will push east of the Cascades this
evening with some clearing expected behind it. This may result in
some MVFR or IFR ceilings/visibility in fog or low clouds toward
sunrise Friday. -Spilde
Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available generally between the
hours of 04Z and 14Z.
.MARINE...Updated 300 AM PDT Thursday, October 27, 2016...
Seas will continue to lower today and tonight, but will remain steep
and hazardous to small craft. Conditions should improve briefly
behind a cold front Friday, but a long period west swell will arrive
Friday night and persist through Saturday. A broad area of low
pressure will move through the waters Saturday night into Sunday.
Model guidance has come better in line with respect to next week.
Another closed low pressure system will likely move south of the
waters and into California Monday into Tuesday with the next strong
front arriving Tuesday night into Wednesday. This front will have
the potential to bring gales and very steep hazardous seas, but
given the active pattern, confidence in this scenario is low at this
.PREV DISCUSSION... /Issued 458 AM PDT THU OCT 27 2016/
DISCUSSION...27/00Z NAM/GFS/EC IN.
The northern hemispheric pattern shows a wave number of five
around the globe. This is normally a progressive pattern, but with
a deep nearly cutoff trough off the west coast, progress will be
That trough will remain in roughly the same location through at
least the rest of this week, as short waves diving down the back
side of it will force it to maintain its position. As long as it
remains out there, the Pacific Northwest will remain under
southwest flow aloft, and short waves ejecting from the trough
will push fronts onshore through the period. It will remain
relatively wet, with high temperatures near normal for the most
part over Oregon, and several degrees below normal over northern
A front that was stalled along the coast is now slowly making its
way inland as a short wave moving in from the west is pushing it
eastward. The coast and Coast Range have gotten a lot of rain
during the past few days. The front will move into eastern Oregon
and far northeast California today, where it will stall once
again. Precipitation will move inland as well, but by that time
there won`t be a lot of it, and it will end over most areas late
Thursday night through Friday.
A split flow regime will affect the area beginning Friday. One
short wave will move up from the southwest into the east side
Friday, and another one coming in from the west will move onshore
Friday night. The first short wave will induce wave development
on the stalled surface front, which will retrograde over the CWA
Friday into Friday night and then weaken. The front associated
with the offshore wave will move onshore with the wave Friday
night, effectively merging with the other front.
More waves will follow Saturday into Sunday as the pattern remains
wet and occasionally windy. Snow levels will remain well above
Long term discussion from the Wednesday afternoon AFD...Sunday
through Wednesday night. There is still general model agreement on
an active weather pattern for next week with a series of frontal
systems to move into the west coast. However, as was the case
yesterday, the model differences in the timing, track, and
strength of these systems quickly increase and increase with time.
The forecast utilizes a model blend while incorporating typical
climatology and topographic influences associated with a west to
southwest flow aloft. The GFS solution remains generally faster
and stronger/colder/wetter with these disturbances than the ECMWF
The long term begins on Sunday with better though still not great
model agreement that the southern branch of a split flow aloft will
send an occluded front into southern Oregon and northern California
with the highest probability of precipitation into Curry, Josephine,
and Siskiyou Counties with a snow level around 6000 feet. The ECMWF
is still slower than the GFS but has sped up a bit. Both of the
models bring a broad closed low into our area by Sunday evening with
a transition to showers and a modest decrease in snow levels to
around 5500 feet.
Another colder trough is expected to follow from the west on Monday.
The GFS remains notably stronger and faster with this system. The
earlier in the day and the farther to the east that one goes, the
higher the possibility that the weather will be dry/between systems
for Halloween activities. There is a decrease in forecast confidence
beyond the day-time on Monday as model differences increase
regarding the evolution of the upper low and associated front.
By Wednesday, the next broad cold trough is expected to move into
the Gulf of Alaska. A new series of disturbances moving through the
base of the trough into the Pacific Northwest are expected to be our
dominant weather producers during the second half of the week. -DW
OR...Wind Advisory until 8 PM PDT this evening for ORZ029>031.
CA...Wind Advisory until 8 PM PDT this evening for CAZ083-085.
Pacific Coastal Waters...
- Small Craft Advisory for hazardous seas until 8 PM PDT this
evening for PZZ350-356-370-376.
- Small Craft Advisory until 5 AM PDT Friday for PZZ370.