Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 240447
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
847 PM PST Mon Jan 23 2017

.SHORT TERM...A weak low is located about 160 miles off the coast
of Northern California and will continue to shift southward
tonight into Tuesday. As the low shifts south, some isolated to
scattered light showers are expected over portions of the area
tonight, with best chance for shower activity along the coast,
across Northern California and into the mountains. Showers will
likely taper off early Tuesday morning as the low moves south of
the area and becomes positioned off the San Francisco Bay area.
Weak high pressure building into the area late tonight behind
this low will allow bring an inversion with stable conditions.
This will bring conditions favorable for freezing fog to develop
over inland valleys tonight and continue into Tuesday morning. Valley
fog is expected clear by early afternoon on Tuesday. Dry weather
is then expected to continue through Wednesday morning. A
shortwave is forecast to move down the ridge from the north late
Wednesday into Thursday while a weak front moves into the coast.
This may bring light precipitation to the area. Thursday night and
Friday, models continue to show a high pressure ridge
strengthening over the region and remaining in place through
early next week.



&&

.AVIATION...24/00Z TAF Cycle...Expect VFR to prevail across the
area this evening...but areas of IFR cigs/vsbys in fog and freezing
fog will develop again over the valleys late tonight into Tuesday
morning. VFR will return Tuesday afternoon. -Spilde

&&

.MARINE...Updated 825 PM PST Monday 23 January 2017...A weakening
low, located off the Northern California coast, will continue to
moves south tonight into Tuesday morning, with weak high pressure
building into the waters from north to south during this time. Seas
will remain very high and very steep through late this
evening...then steep through Tuesday morning. High pressure will
weaken Wednesday and a weak front will move onshore Wednesday night.
High westerly swell will also move through Wednesday night into
Thursday night. High pressure will return Thursday and persist for
the rest of the week. -Spilde/CC


&&

.PREV DISCUSSION... /Issued Issued by National Weather Service Eureka CA/

SHORT TERM...
(Tonight and Tuesday)

The surface low which has affected our weather the past couple of
days is starting to weaken as it continues it`s southward trek. This
afternoon`s surface analysis showed an area of surface low pressure,
on the order of ~995mb, continuing to churn southward as it`s
positioned about 120 miles west of Gold Beach. As this low continues
it`s southward trek overnight, its affects on our weather will
continue to decrease.

Taking a look at the area Doppler radar imagery, most of the light
shower coverage has been confined to southwestern Siskiyou County
and along the coastal range from Gold Beach South. The latter
resides in a region of weak instability, with the latest SPC
mesoanalysis showing about 100 J/kg of MUCAPE. This combined with
mid-level lapse rates around 8 deg. C/km has been sufficient for a
few lightning strikes and even transient mesocyclone development
across the outer waters west southwest of Crescent City, but these
storms have rapidly weakened as they try to approach the
southwestern Oregon coast due to weaker 0-6km bulk shear.

Still, there remains a non-zero chance for a flash or two of
lightning along the southwestern coast and adjacent waters for a few
more hours. However, given the isolated potential, no thunder
mention was included in the zones for this evening. Farther inland,
low-level moisture is more scant and the area is further displaced
from any disturbances passing through the region, but remains close
enough to keep low-end pops in the forecast for portions of the
region through the early morning hours.

Given the recent rainfall, clearing skies, and forecast light winds,
some valley fog or freezing fog development is likely overnight, and
this was retained in the forecast. As the morning fog burns off,
expect mostly sunny skies to dominate your weather by the afternoon
hours, with seasonal temperatures expected tonight and tomorrow.

LONG TERM...
(Tuesday evening through Sunday)

Much of the remainder of the week will be dry, especially as we
approach the weekend. The latest model guidance continues to show a
weak shortwave trough passing through our neck of the woods during
the day Wednesday/Thursday. Ahead of this feature southerly to
southwesterly winds at the surface and aloft will advect moisture
back into the area, with clouds rapidly increasing late Tuesday
evening and overnight.

As the trough crosses the region, lower elevation/coastal showers
and mountain snow showers will develop, with the Wednesday afternoon
through mid-day Thursday time frame looking to be the best chance of
seeing any precipitation. Overall amounts look to be light, but
given a somewhat convective look in the model precip fields and area
soundings near the coast showing some very weak instability,
isolated thunder potential may need to be considered in later
forecasts.

As the trough exits the region for the end of the work week and
through the weekend, ridging aloft will build across the region with
500mb heights climbing into the 576 to 582dkm range. Strong
subsidence will lead to mainly clear skies, with seasonal
temperatures expected. /PD

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 10 PM PST this evening for ORZ021-022.

CA...None.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 10 AM PST Tuesday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 10 PM PST this evening for
     PZZ350-356-370-376.

$$

CC


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