Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
910 PM PDT sun Mar 9 2014
Discussion...with the back edge of the precipitation shield sitting about
130 nm offshore rain continues...heavy at times through the night.
Current forecast looks on track and will not update this evening.
Short term...plenty of moisture is training along the front
boundary and is moving into northwest California and SW Oregon. Another
1 to 2 inches of rain is possible tonight for Curry County with
around 1 inch for western Siskiyou County and the Illinois Valley.
Between a quarter and half inch of rain is expected for the
remainder of the west side with amounts between a tenth and a
quarter for the Klamath and Goose Lake basins. A wave has formed
on the front which will slow the eastward progression a bit but
eventually the front is expected to push into eastern Oregon
around midnight. Gusty winds continue across eastern Klamath and
Lake County and expect wind speed to pick up again later this
evening as the front moves closer to the area.
The upper level trough will move in behind the surface front on
Monday. Cold air aloft is not as deep as in previous model run
meaning it is confined mainly across Oregon. Have removed
thunderstorm chance for the northern California zones but the
threat still exists for our coastal waters and some of the Oregon
zones from late tonight into Monday.
High pressure moves into the area Tuesday with the air mass
transitions to drier and more stable pattern at night. We could
see some valley low clouds and fog at night. The thermal trough is
forecast to build northward into southern Oregon coast and appears
to be the strongest Tuesday night and Wednesday morning. This
could present a fire weather concern in terms of gusty offshore
winds...although recent rainfall should mitigate the effect of
lower night time humidity at the ridges. /Fb
Thursday, March 13th through Monday morning, March 17th...
Mild and dry weather continues to be expected during most of this
time period with plenty of highs in the 60s and 70s across the
western valleys and lows in the 30s and 40s. Altogether, this puts
temperatures near to about 5 degrees fahrenheit above normal for
lows and 7 to 15 degrees above normal for highs. Toward the end of
the period model guidance is indicating that the high pressure ridge
over US the end of this week is likely to rebuild westward allowing
cooler air to push in from the north. Trends in the guidance appear
to be to delay the arrival of that cooling until after this next
Features of note during this time period are the following: flow
shifts from offshore to onshore on Thursday. The frontal system
pushing in to the north of US Friday into Saturday appears to be
focusing a bit farther north, but still may bring some showers to
the Westside mountains and Coos and Umpqua areas. Saturday into
Sunday models advertise some high clouds, but also very mild 850mb
temperatures, so it's a good bet that highs will surge into the 60s
and 70s to near 80f for most valley locations. Dry air in place
means diurnal ranges will be 30f to 40f for most of the interior.
The gfs40 pushes the front arriving from the north in on Sunday,
while the European model (ecmwf) indicates it will take until Saint patrick's day to
arrive. Due to the north to northeast flow building in behind this
feature, expect precipitation to be very little to none with this
front along with a surge of lower dewpoint air across the region.
Aviation...based on the 09/18z taf cycle...
A cold front will remain draped over the area today...producing
widespread rain and total mountain obscurations for most of the taf
period. MVFR with localized IFR at the coast and much of the west
side is expected to continue through the day...with conditions a bit
better on the Oregon interior west side from 18-22z before the next
surge of more significant moisture arrives from the southwest. East
of the Cascades...light rain and VFR with pockets of MVFR will
persist through the day...along with some gusty southwest
winds...especially over higher terrain. Tonight...between 03z and
09z...the front will push eastward with west-northwest winds behind
it. This wind shift with the front will enhance precipitation on its
front end, improve ceilings and visibilities to VFR immediately
behind it in the more open valleys, and likely lead to a MVFR and
local IFR along and near the coast Monday morning. Btl
Marine...a strong cold front has passed over the coastal waters...
but some gusty winds behind the front will continue through this
morning. Winds are weaker tonight than earlier thought...so have
cancelled the Gale Warning...and will keep Small Craft Advisory for
winds in place until Post frontal winds diminish. Wind driven seas
will transition to swell dominated...the overall effect being that
steep seas will gradually diminish through Monday morning. High
pressure will then produce relatively calm winds for much of the
week. However...offshore flow could produce gusty winds and steep
seas south of Cape Blanco Tuesday and Tuesday night. Also...several
systems passing to the north could result in building
swell Wednesday and Thursday. -Bpn
or...Wind Advisory until 5 am PDT Monday for orz030-031.
California...Wind Advisory until 5 am PDT Monday for caz085.
Pacific coastal waters...Small Craft Advisory for hazardous seas
until 5 am PDT Monday