Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 241158
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
458 AM PDT Mon Apr 24 2017

.DISCUSSION...The forecast is focused upon two frontal systems.
The first now through this evening and the second Tuesday
afternoon into Wednesday afternoon. Southwest to west Winds may
end up slightly stronger with the second system, but snow levels
will be much lower with the first. The systems will be similar in
that precipitation will be favored on and near west facing
slopes...including the coast, coastal range, and the Oregon
Cascades.

24 hour rainfall totals in the Curry County mountains have
already measured around 1 to 2 inches with more than an inch yet
to come. Amounts will be heaviest through around 8 AM PDT this
morning but intensity will likely be moderate at times thereafter
through this evening. Southwest winds have recently gusted to 46
MPH at Flynn Prairie in the coastal range, and that is likely to
be at or near the peak strength. Gusts of 25 to 35 MPH will be
more common over the higher terrain with some blowing and drifting
of snow possible. A Winter Storm Warning and Winter Weather
Advisory remain in effect for portions of the Southern Oregon
Cascades and Siskiyou Mountains. Crater Lake will very likely
receive the heaviest snow with 12 to 18 inches expected through
this evening while 6 to 12 inch amounts will be common above 5500
fet. Lesser/sub-advisory amounts are expected at elevations
between 4000 and 5500 feet with lowest snow levels early this
morning. Some of the major passes including Siskiyou Summit, Lake
of the Woods, and Diamond Lake will likely receive light snow or
a rain/snow mix from now through the morning commute. A minor
impact of up to 3 inches of snow is also likely for elevations
above 4500 feet in Siskiyou, Lake, Modoc, and the remainder of
Klamath County...mainly for the higher terrain of western Siskiyou
County and near Highway 97 in northern Klamath County.

Precipitation will taper off late this evening then there will be
a brief shortwave ridge late tonight into Tuesday morning before
the next developing system sends a warm front into western Oregon
on Tuesday. Winds will be strongest and precipitation rates at
their highest with the cold frontal portion of the system late
Tuesday night and passage of the associated upper level trough
axis on Wednesday morning. The 00Z NAM indicates that Flynn
Prairie peak gusts early Wednesday would be around 50-55
MPH...just a bit stronger than early this morning, and perhaps
strong enough to reach wind advisory criteria in Lake County.

Model confidence has increased in a solution of a dirty ridge
Wednesday night into Friday with a few shortwaves in a northwest
to north flow bringing slightly below normal temperatures, variable
amounts of cloud cover, and perhaps wringing out a few very light
showers...mainly in western Oregon.

Model uncertainty increases quickly beyond Friday. Having
experienced a frequently wet winter and spring, I would hesitate
to latch on to the warmer and drier 00Z GFS solution for Friday
into next week. Many of the other GFS ensemble members and the
ECMWF show less influence from ridging offshore of California and
more influence into our area from systems tracking through the
Gulf of Alaska into the Pacific Northwest.


&&

.AVIATION...24/06Z TAF CYCLE...Over the coastal waters...along the
coast...and in the Umpqua Basin...Areas of MVFR cigs/vsbys and local
IFR cigs in rain and rain showers with higher terrain obscured will
persist through Monday evening. Low level wind shear will affect
KOTH and KRBG late tonight into early Monday morning with turbulence
possible on approaches and takeoffs elsewhere. Over the remainder of
the area...VFR with local MVFR cigs and areas of higher terrain
obscured in rain/snow will persist through Monday evening. Freezing
levels will be 4500-5000 feet. Gusty winds to 35 kt are possible at
KLMT for a few hours Monday afternoon. -Spilde

&&

.MARINE...Updated 300 AM PDT Monday, 24 April 2017...
A strong frontal system will cause winds to peak along the coast
before sunrise this morning. A brief period of gales is possible
north of Cape Blanco between 5 and 25 nautical miles of the coast.
Seas will also peak this morning as the front moves through, but
remain steep through Tuesday morning. Another frontal system will
then move through Tuesday into Wednesday with showers lingering in
northwest flow Thursday. High pressure is likely to build in from
the southwest Friday into Saturday bringing northerly winds. The
ECMWF model is suggesting weak fronts will again be possible early
next week in northerly flow, and the GFS model also indicates one
such weak front moving through on Sunday. -BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 11 PM PDT this evening for
     ORZ027-028.
     Winter Storm Warning until 11 PM PDT this evening for ORZ027.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Tuesday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 11 AM PDT this morning for
     PZZ350-356-370-376.

$$

DW/BTL


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