Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 222356
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
456 PM PDT Wed Mar 22 2017

Updated AVIATION Section

.SHORT TERM...Tonight through Saturday night...Radar indicates
that there are scattered light showers around the forecast area.
These showers will continue into tonight but dissipate tonight for
our short break before the next system comes in. The next front
is expected to arrive Thursday and will bring a myriad of
different hazards to southern Oregon and northern California. The
first will be strong, gusty winds. Winds could be warning level
near the coast, and are expected to be advisory level in the
Shasta Valley, Summer Lake Valley, and in the Warner mountains
near the Cedar Pass. Although the models have shown somewhat
decent run to run consistency with the inland winds, the coastal
winds have really taken an uptick since yesterday. Have issued a
high wind watch (NPWMFR) for the southern Oregon coast from Cape
Blanco south to Brookings including highway 101.

The next changes made to the forecast regarding hazards is the
rainfall amounts and timing. Have shortened the time frame of this
front to specifically bring the heaviest rain between Thursday
evening and Friday morning. River levels in the Klamath Basin are
still holding steady, and the incoming precipitation is not
likely to create large changes at this point. Although we will
still need to monitor the Klamath River basin, confidence is not
as high for flooding with the next system, and have allowed the
hydrologic outlook to expire.

This system will also bring the possibility for snows in the
higher elevations. Have issued winter weather advisories (WSWMFR)
for elevations above 5000 feet for the Marble mountains near
Sawyers Bar Road, for the Mt. Shasta Ski Park, and for the
northern portion of the Southern Oregon Cascades including Crater
Lake. Snows will be heavy and wet, and will cause travel
difficulties along these areas, including highway 97 near Chemult.
Highway 97 near Chemult will see less snow than the rest of the
Cascades, but is on the low end of advisory criteria. Have decided
to include this area since it has been a bit warmer as of late.

Widespread precipitation will become more showery in the nature
come Saturday as things die down. Another ridge of high pressure
will build in briefly on Saturday afternoon giving another break
before the next system arrives in the long term -Schaaf

.LONG TERM...Sun March 26th through Wed night March 29th... GEFS
Integrated Vapor Transport products and operational runs of the GFS
and ECMWF continue to indicate that the cooler and wetter than
normal pattern is likely to generally persist through this long term
period. Frontal systems and related non-showery precipitation during
this time period are likely to be focused on Sunday, March 26th and
March 29th. Outside of those two days we do expect shower activity
over most of the forecast area.

The frontal system on Sunday will reach the coast and Mount Shasta
area during the morning with snow levels beginning around 5000 feet.
This will keep travel impacts in the higher mountainous areas, but
will be a concern for those traveling to winter recreation areas and
Crater Lake National Park. We`ll probably see another round of gales
in the coastal waters and an upward surge in winds along the coast,
in the Rogue and Shasta Valleys, and across the higher terrain
probably warranting some advisories. The surface low with this
frontal system will swing northeastward toward the Washington coast,
so southwest and south flow favored areas such as the coast and
coastal mountains and western and southern Siskiyou County will see a
healthy round of precipitation. Sunday into Monday those areas are
likely to see an inch or more of water. Showers on Monday ride in on
a west to even a northwest flow and snow levels will likely be near
4000 feet on Monday. Showers look to be more appreciable in the
morning than the afternoon in terms of coverage and intensity.

Models differ on details regarding a weaker shortwave trough on
northwest flow Tuesday. It does appear some showers will occur on
the coast and in the Umpqua, but some of the guidance washes this
impulse out such that Tuesday ends up mostly dry.

For Wednesday both the ECMWF and the GFS dive in a frontal system
under northwest flow. While this system appears as if it will have
some cold air behind it, snow levels surge up to 6000 to 7000 feet
on the front side of it.

There has been a clear trend over the past 3-4 days in both the
operational runs of the GFS and ECMWF as well as the CFSv2 toward
high pressure ridging building into the Pacific Northwest Thursday
into next weekend. Confidence in this solution has grown from low to
moderate. CPC is also leaning this way in their official week two
forecast, so prepare the sunglasses, sunscreen, spring skis, allergy
medication, grill, and lawn mowers, as you deem necessary. BTL

&&

.AVIATION...23/00Z TAF CYCLE...Overall, VFR will prevail this
evening, but in showers, expect brief MVFR ceilings with terrain
partly obscured. Showers diminish by late this evening and with
increasing stability, there is a chance for MVFR/IFR ceilings to
develop in some of the valleys overnight into Thursday morning.
The lower ceilings should dissipate by mid-late morning Thursday
with VFR prevailing thereafter.

Another strong cold front will approach the coast late Thursday
afternoon. South winds will increase along the coast, but since KOTH
will be blocked, expect a period of low level wind shear into the
evening hours. Ceilings gradually lower too, but should remain VFR
through 00z Friday. -Spilde

&&

.MARINE...Updated 300 PM PDT Wednesday 22 March 2017...Steep seas
due to short period fresh swell will continue this evening,
mostly beyond 2 NM from shore. Seas should ease to 6 to 8 feet
overnight into early Thursday morning, but then a strong front
offshore will move toward the coastal waters late Thursday
morning. Widespread gales can be expected late Thursday morning
through Thursday evening, especially beyond 10 NM from shore, but
also closer to shore near Cape Blanco. A few gusts to storm force
are possible. Seas will become steep to very steep during this time
period and persist through Thursday night. Winds and seas will
decrease Friday into Saturday...but seas likely remain quite
steep. Another strong front is due to arrive on Sunday. -Spilde

&&


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 11 PM Thursday to 11 AM PDT Friday
     for ORZ030.
     Wind Advisory from 2 AM to 5 PM PDT Friday for ORZ031.
     High Wind Watch from Thursday afternoon through late Thursday
     night for ORZ021-022.
     Winter Weather Advisory from 11 PM Thursday to 11 AM PDT Friday
     for ORZ027.

CA...Winter Weather Advisory from 11 PM Thursday to 11 AM PDT Friday
     for CAZ082-083.
     Winter Weather Advisory from 11 PM Thursday to 11 AM PDT Friday
     for CAZ080.
     Wind Advisory from 2 AM to 5 PM PDT Friday for CAZ081.
     Wind Advisory from 2 AM to 5 PM PDT Friday for CAZ085.

Pacific Coastal Waters...Small Craft Advisory from 11 AM Thursday to
     5 AM PDT Friday for PZZ350-356.
     Hazardous Seas Warning from 11 PM Thursday to 5 AM PDT Friday
     for PZZ350-356-370-376.
     High Wind Watch from Thursday afternoon through late Thursday
     night for PZZ356.
     Gale Warning from 1 PM to 11 PM PDT Thursday for PZZ350-356.
     Small Craft Advisory for hazardous seas until 11 PM PDT this
     evening for PZZ350-356-370-376.
     Small Craft Advisory from 9 AM Thursday to 5 AM PDT Friday for
     PZZ370.
     Gale Warning from 11 AM to 11 PM PDT Thursday for PZZ370-376.
     Small Craft Advisory from 9 AM to 1 PM PDT Thursday for PZZ376.

$$

BMS/BTL/MAS


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