Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
800 PM PDT Tuesday Mar 31 2015
Discussion...01/00z NAM in.
The polar projection shows a 4-5 wave pattern around the northern
hemisphere with no particular deep troughs or strong ridges...
except for a strong high over Siberia. This supports a generally
progressive pattern. The coldest air pockets are currently over
northern Siberia...baffin island...and near Iceland. Closer to
home...there is a long wave trough just off the West Coast and a
ridge over the intermountain states. The Medford County Warning Area is under
southwest flow aloft between the two systems. Typically this is a
wet pattern for the area.
Short waves embedded in the flow along with a cold pool of air
aloft is bringing some strong showers to the Medford County Warning Area...several
earlier today contained hail...but no thunder. It is cold enough
aloft over the coast and Umpqua basin to support thunderstorm
A strong short wave is now exiting the area...and flow aloft will
become nearly zonal behind it. Another strong short wave will
move onshore Wednesday evening. This will bring in more cold air
aloft farther south...so the chance of thunderstorms will spread
south Wednesday afternoon and evening.
Once that short wave moves out Wednesday night...a strong long
wave ridge will build into the West Coast. This will bring the
shower activity to an end. The weather will be dry and warmer
Thursday with inland temperatures warming to normal to 5 degrees
above normal for this time of year.
The ridge will break to the east Thursday night but will remain
strong enough Friday to keep the storm track...and most of the
precipitation...to the north of the area.
The moisture remaining after the showers along with northwest
flow aloft should result in a stratus deck over the west side
butting up to the Siskiyous. This should also result in clearing
over northern California...and even though the air mass will be
warmer...temperatures should drop down again Thursday night in the
Shasta Valley into the middle to upper 20s.
The north coast and Umpqua basin may get some light precipitation
from the southern end of an incoming front Friday.
Long term discussion from the Tuesday afternoon afd...Saturday
through Tuesday night. It has been quite a while since I have had
the opportunity to say this, but if the latest runs of the GFS and
European model (ecmwf) models are any indication, it looks as if though forecast
area will be cool and wet during the extended period, if not
longer. Hemispherical plots suggest a very progressive pattern
over North America, which would send numerous waves, and therefore
multiple systems, across our region.
Uncertainty lies in the timing and strength of each individual
event. With this in mind, have trended the forecast towards a
Mutual blend of the GFS and ECMWF, as there does not appear to be a
more likely scenario, and both solutions are relatively similar.
While cooler temperatures will mean lower snow levels in general,
Sunday and Monday could see much lower snow levels than we have seen
in quite a while: under 3000 feet Sunday and below 2000 feet Monday
morning. This would produce snow over nearly all areas passes, and
could have a significant impact on weekend and early week travel.
Temperatures during the long term will hover at around 5 to 10
degrees below seasonal normals. Thus there will possibly be a need
for freeze/frost headlines, especially given the early agricultural
growth resulting form the warmer than normal season up to this
point. Will need to keep a close eye on the potential for lower
elevation snowfall and cold temperatures over the next several
shifts, and the local area should begin to prepare for what could be
a shot of winter, only arriving a few months too late. -Bpn
Aviation...for the 01/00z taf cycle...showers will continue into
the evening behind a passing cold front. This will result in
periods of valley MVFR conditions within any showers...and terrain
obscuration will be common. Showers should almost completely
dissipate shortly after sunset. Another round of showers and
reduced visibilities is expected along and near the Coast Range
and Umpqua basin area beginning around 06z through 12z. One more
round of showers will extend further inland tomorrow afternoon. A
stray thunderstorm cannot be ruled out west of the Cascades
tomorrow. Mixed periods of VFR and MVFR conditions are expected to
continue throughout the remainder of the taf cycle. -Schaaf/Lutz
Marine...updated 300 PM PDT Tuesday 31 Mar 2015...unsettled
conditions are expected to continue through Wednesday evening
with westerly winds and a steep west swell of 9 feet around 12
seconds. Winds are expected to become northerly tomorrow afternoon
and persist through Thursday evening. The strongest winds are
expected to impact waters south of Gold Beach. Waves heights are
expected to lower below 10 feet briefly on Friday before the next
frontal system comes in and brings more unsettled conditions this
California...freeze warning from 1 am to 9 am PDT Wednesday for caz081-281.
Pacific coastal waters...Small Craft Advisory for winds from 5 PM
to 11 PM PDT Wednesday for pzz356-376.
Small Craft Advisory for hazardous seas until 11 PM PDT
Wednesday for pzz350-356-370-376.