Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
437 am PDT Tuesday Apr 28 2015
Discussion...the 00z GFS is in very good agreement with the 00z
European model (ecmwf) through Friday, and with its 12z Monday run into early next
Our weather at least into the weekend will by and large be dry and
very warm with breezy/slightly stronger than normal afternoon and
evening winds. The most notable exception will be a slight chance
to chance of light showers today into tonight as a weak cold front
moves east to northeast across the area. The timing of the front
will result in a cooler day for the west side while it is warmer
today on the east side. The probability of measureable showers
will be highest near the coast and into Douglas County.
Additionally, the 00z NAM and GFS indicate weak early evening
instability on the east side with a very shallow saturated layer
based around 12k feet mean sea level. This will likely produce only scattered
to broken cumulus cloud coverage in Lake County. But, a few
lightning strikes cannot be ruled out altogether. So, a slight
chance of thunderstorms has been added. Showers could begin near
North Bend before sunrise and showers will remain near the coast
through the morning. A trailing shortwave trough behind the cold
front and the heating of the day will result in the highest probability of precipitation
during the late afternoon and early evening.
An upper level trough will follow with another couple of embedded
shortwaves on Wednesday. The models have come into closer
agreement that the timing and position of the main shortwave will
result in a slight chance of afternoon and evening thunderstorms
over the Warner Mountains of Eastern Lake and eastern Modoc
counties. The rest of the area will simply have a cooler day with
morning clouds that will diminish later in the day.
Dry and warmer weather will arrive with a low amplitude ridge on
The upper level pattern near the West Coast will become more
complex at the end of the week into early next week. The ridge
looks to retrograde on Friday while a trough moves across British
Columbia and another trough offshore from California moves closer
to the coast. This southern branch of the upper flow could produce
weak instability over the Sierra Nevada and there is a
minimal/around 10% probability of convective showers or a
thunderstorm extending farther north into Modoc County.
The northern branch may resume its influence on our weather during
the weekend with another shortwave trough of uncertain strength. A
5% to 10% chance of far east side showers has been introduced for
Saturday and a slight chance/10-15% of afternoon and evening far east
side showers for Sunday. Most of the area looks to simply have
mostly sunny skies with a few to several degrees of cooling, but
with high temperatures still well above normal.
For Monday into Tuesday, the GFS is much stronger and deeper than
the European model (ecmwf) with another trough approaching from the northwest.
Thus, the probability of showers and thunderstorms is higher than
on the weekend though confidence is low.
Aviation...for the 28/12z taf cycle. At the coast...stratus with
MVFR ceilings will expand with ceilings becoming IFR this morning. Expect
widespread terrain obscuration of the coastal range today.
Stratus will spread into the Umpqua basin bringing ceilings to MVFR and
IFR later this morning...with terrain obscuration of the coastal
range, Cascades, and Umpqua mountains.
Elsewhere...VFR conditions will prevail throughout the day.
Marine...updated 335 am PDT Tuesday 28 Apr 2015...southerly winds
will turn northwesterly behind a cold front moving inland by midday.
Moderate northwesterly swell will move into the waters this
afternoon into Wednesday morning...bringing seas to low end advisory
level. Seas will diminish Wednesday afternoon. A thermal trough will
strengthen inland with high pressure offshore. This pattern will
create strong north winds and the associated steep wind-driven seas
on Thursday and Friday which will likely persist through the
Pacific coastal waters...Small Craft Advisory for hazardous seas from
5 PM this afternoon to 5 am PDT Wednesday for pzz350-356-370-376.