Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 242152

Area Forecast Discussion
National Weather Service Medford OR
252 PM PDT Wed May 24 2017

.DISCUSSION...The latest visible image shows clear skies over most
of the forecast area. Cumulus buildups are showing up just east of
Mount Shasta along Medicine Bow Peak and portions of Modoc County.
This is where most of the instability is at, but it`s not going to
be enough for thunderstorms. The models show the greatest
instability and thus the best chance for thunderstorm development
remaining south and east of our forecast area. Therefore we will
keep thunderstorms out of the forecast.

Gusty winds are expected east of the Cascades and westside valleys,
especially near and at Roseburg and Rogue Valley, including Medford
into this evening, but they won`t reach advisory criteria.

The latest water vapor image shows the upper low moving east along
southern Canada and a weak upper trough dropping south in central
Washington. This trough will continue to push south later this
afternoon through tonight and bring a dry cool northerly flow.

This type of pattern will typically yield dry weather with the best
chance for precipitation staying north and east of us. Therefore
expect continued dry weather tonight through Thursday with afternoon
temperatures almost the same as today. Skies will be mostly clear
with some cumulus buildups in eastern Klamath and Lake county
Thursday afternoon and early evening.

On Friday we`ll be sandwiched between the upper ridge offshore (near
130w) and upper trough in central-eastern Oregon. Dry weather will
continue with warmer afternoon temperatures for most inland
locations. Skies will remain clear to mostly clear for most inland
locations. At the coast, the thermal trough will weaken Thursday
night and a wind reversal is expected to take place allowing marine
stratus to push northward through Brookings Friday morning. The
models suggest the marine stratus could push further north all the
way up the coast Friday night.

The upper ridge will build over our area Saturday through Saturday
night. The models differ slightly with the position of the ridge
axis, but it will still be dry and warmer. I took a look at the
thunderstorm potential on Saturday afternoon and evening and decided
to remove them for the following reasons. Lack of a trigger
(shortwave), very marginal instability and insufficient moisture at
the mid levels. We`ll get cumulus build ups along the Cascades,
Siskiyous and portions of the eastside in the afternoon and early
evening, but it`s not looking favorable for these to develop into
thunderstorms. However, we`ll have to keep a close watch on this.

.Long Term...Sunday through Wednesday...The ridge will continue to
build into the Pac NW. Highs in the Rogue Valley are expected to be
in the lower 90s into Tuesday. Models indicate that mid level
moisture will also be spreading into southern Oregon from the south
and we could see increasing cumulus clouds. At this point there is
enough instability for isolate showers and possibly a few lightning
strikes over the Cascades and Siskiyous. Both the GFS and the ECMWF
begin to shift the ridge axis eastward toward Idaho in response to
upstream trough. If this scenario verifies, it could lead to some
cooling but MOS guidance still calls for above normal high
temperatures. Of note is the increase in mid level moisture in the
700-500mb layer on Tuesday and Wednesday. We could see isolated
thunderstorms across our forecast area. /FB


.AVIATION...24/18Z TAF CYCLE...VFR cigs will continue into early
this evening for all terminals. The main concern will be gusty winds
along the coast, especially north of Cape Blanco and inland TAF
locations through this evening with increased turbulence. Marine
stratus is expected to move back along the coast, north of Cape
Blanco around 6z. CIGS should remain VFR, but could not rule out
brief MVFR Cigs. Also, confidence is low to medium on the timing of
the marine stratus.

Over the Umpqua and Coquille Basins...areas of MVFR cigs with higher
terrain obscured is expected around 12z. Elsewhere VFR will
continue through the TAF period. -Petrucelli


.MARINE...Updated 230 PM Wednesday 24 May 2017...A strong
thermal trough is in place today...which is resulting in strong
north winds and choppy and very steep seas across the coastal
waters. Seas will be very steep across much of the waters through
tonight with wind driven seas around 10 to 17 feet, with the highest
seas from Cape Blanco south North gales will continue into tonight
from Cape Blanco south with gusty small craft advisory winds north
of the cape. Winds will decrease on Thursday but there will still be
some gale force winds from Brookings south and very steep hazardous
seas from Cape Blanco southward. North of Cape Blanco on Thursday,
expect small craft advisory conditions.

Winds will subside further Thursday night, but steep  fresh swell
will persist into Friday morning for the waters Cape Blanco
southward and into the waters beyond 10 nm from shore north of Cape
Blanco. Also on Friday expect a southerly surge of winds to develop
along the Curry coast and expand northward along the Coos and
Douglas coast Friday evening and night. This will bring low stratus
and fog to the waters.


OR...Hazardous Seas Warning until 5 AM PDT Thursday for ORZ022.


Pacific Coastal Waters...Hazardous Seas Warning until 5 AM PDT Thursday for PZZ350-370.
     Small Craft Advisory until 5 AM PDT Friday for PZZ350-356-370.
     Gale Warning until 5 AM PDT Thursday for PZZ356-370.
     Hazardous Seas Warning until 5 AM PDT Friday for PZZ356-376.
     Small Craft Advisory from 5 AM Thursday to 5 AM PDT Friday for
     Gale Warning until 5 AM PDT Friday for PZZ376.

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