Area forecast discussion
National Weather Service Medford or
930 PM PDT Monday may 20 2013
Discussion...see marine section below for an update to the marine
forecast overnight into Tuesday morning. A strong low pressure
system near 44 north and 130 west will move quickly toward the south
Oregon coast tonight, reaching the coast Tuesday morning. A cold
front accompanying the storm will move through the west side in
the morning, then shift quickly to the east side by the afternoon.
This will result in a dramatic change across the area. Highs today
were in the middle 80s in Medford, but will only be in the upper 50s
to lower 60s Tuesday. Some rain will accompany this system, but
the vast majority of the precipitation will occur along and west
of the Cascades. The main weather impact east of the Cascades will
be gusty southwest winds shifting to the northwest in the
afternoon. Right now, it doesn't look quite strong enough for
advisory headlines, but suffice it to say, it will be windy in
many areas Tuesday afternoon. It will also be one of the windier
afternoons here in Medford with a strong west-east pressure
gradient and good mixing. Expect some gusts of 30-35 miles per hour. Snow
levels will also plunge rapidly behind this front down to as low
as 2500 feet by Wednesday morning. For more specifics, please see
spsmfr. A freeze watch is out for late Tuesday night/early Wednesday am for
the Shasta Valley at npwmfr. This will be highly dependent on
cloud cover, but any clearing will allow temperatures to fall to
or below freezing. Forecast from midweek on is pretty much on
track, so have made no changes there. Spilde
&&
Aviation...based on the 21/00z taf cycle.
Initially clear skies will prevail over the Medford County Warning Area.
However...clouds will move onshore late this evening...spreading
inland to the Cascades by morning. Ceilings will be mostly VFR but there
will be some local MVFR ceilings...and higher terrain will become
obscured. Rain will develop along the coast after midnight...
spreading inland to the Cascades Tuesday morning. Areas of MVFR
ceilings/visibilities will develop along the coast after a cold front moves
onshore around middle-morning Tuesday. These lower ceilings will spread
into the Umpqua basin by afternoon. Some showers will develop east
of the Cascades Tuesday afternoon...but conditions will remain
VFR. Stockton
&&
Marine...vigorous low pressure near 44n and 130w this evening
will track right over our coastal waters Tuesday morning. Latest
guidance is indicating boundary layer winds approaching 50kt on
the west and southwest flank of this system as it approaches our
outer waters. As a result, have opted to hoist a Gale Warning
for a brief period of strong winds for our outer zones mainly from
6 am to around noon PDT. The strongest winds will be over the
southern half of pzz370 and all of pzz376. Winds will be
not be quite as strong as they approach the inner waters so will
maintain the Small Craft Advisory for winds there. Either way
though, seas will be quite steep and hazardous as this feature
moves through...and also with a building swell behind it. Spilde
Previous discussion... /issued 232 PM PDT Monday may 20 2013/
Discussion...models continue on track with the approaching cold
air mass approaching the region with the upcoming system. The
system moves into the area Tuesday with models still indicating
850 temperatures in the -4c range and 500 mb temperatures a little warmer than
yesterdays runs were showing. 500 mb temperatures are in the -18 to -27 c
range compared to the -25 to -35c range they showed yesterday.
With this in mind have cut back the area of thunderstorms to the
cooler pool areas along the northern coast. Snow levels continue
to indicate around 2500 feet and with strong low level lapse rates
this could drop to around 2000 feet briefly. However...with
seasonably warm surface temperatures am not expecting this to last
long on the ground. Onshore flow continues showers with the cold
air mass through Thursday. As the upper low slowly moves east
increased southwesterly flow on Thursday brings warmer low level
temperatures to the far east side and thunderstorms are possible in this
location. The upper level trough remains roughly in place with
another closed low moving into the region towards the
weekend....but the air mass accompanying it will not be nearly as
cold resulting in a showery but near normal temperatures Holiday
weekend.
&&
Mfr watches/warnings/advisories...
or...none.
California...freeze watch from late Tuesday night through Wednesday morning
for caz081.
Pacific coastal waters...Small Craft Advisory for winds from 11 am to
8 PM PDT Tuesday for pzz350-356.
Hazardous seas warning from 11 am Tuesday to 8 PM PDT Wednesday
for pzz350-356.
Gale Warning from 6 am to noon PDT Tuesday for pzz370-376.
Hazardous seas warning from 6 am Tuesday to 8 PM PDT Wednesday
for pzz370-376.
$$
Mas/sbn/jrs
