Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
537 am PDT Tuesday may 5 2015
Aviation...marine...and fire weather discussions
Aviation...for the 05/12z taf cycle...a marine push will bring in
broken to overcast skies west of the Cascades this morning. There is
a chance temporary MVFR ceilings could develop in the Umpqua basin with
higher terrain becoming obscured for an hour or two between 14-16z,
but confidence is low and for now kept it out of the Roseburg taf.
Elsewhere VFR conditions will prevail with higher terrain obscured in
the Rogue Valley between 14-16z. -Petrucelli
Marine...updated 5 am PDT Tuesday, 4 may, 2015...models show
winds increasing enough to reach small craft over the southern
waters late this afternoon into tonight, thus have issued a small
craft for winds. It's possible winds will decrease overnight
tonight, but confidence is low, so ran the headline until 12z
Wednesday. Steep seas will develop across the area this
morning...subsiding tonight over the northern waters, but they are
expected to persist tonight for the southern outer waters due to a
combination of swell and choppy wind driven seas. On Wednesday and
Thursday, moderate north winds and areas of steep seas are
expected as high pressure sets up offshore with low pressure
Fire weather...updated 5 am PDT Tuesday, may 4, 2015...the
threat of thunderstorms is next to zero today. An upper trough
will drop south into the area bringing slight cooling at 500 mb.
However middle level moisture is lacking and lifted indice's are well in the
positive range. So were expecting not much more than some cumulus
build ups in the afternoon east of the Cascades. Any showers today
will be mainly west of the Cascades, but quantitative precipitation forecast amounts will be
light, if anything at all. Also temperatures will be cooler and
min rh's are expected to be higher compared to yesterday. The
upper low will move south over the area Wednesday with cooling
aloft. The models suggest there may be enough instability to
warrant a slight chance of thunderstorms from the Cascades east
Wednesday afternoon and evening. The models suggest the greatest
instability will be along the Cascades Wednesday afternoon and
evening, so it's possible most of the isolated storms will occur
there, but there's als
Previous discussion... /issued 202 am PDT Tuesday may 5 2015/
Discussion...no significant changes were made to the forecast
this morning as the models remain in decent agreement and the
forecast remains on track. An upper low off the British Columbia/Washington coast this
morning will move south across our area over the next couple of
days. This system is not particularly wet or dynamic, but it will
be strong enough to bring some showers to our area along with
cooler weather. Due to a fair amount of low cloudiness ahead of
the system, it will be fairly stable today as the low approaches.
So showers are expected to be confined to north of the Umpqua
Divide, and lightning isn't expected.
However, as we get into tomorrow and the upper cold pool (500 mb
temperatures around -30c) arrives, we could see some lightning. Model
soundings show a middle level cap west of the Cascades, so the best
chance for lightning will be from the Cascade crest east. The low
exits to the south on Thursday with conditions stabilizing in its
wake. There is still a possibility of showers Thursday, but
thunderstorm chances will be confined mainly to Modoc County.
We will dry out and warm up just in time for the weekend as a
ridge builds in over the pacnw. Models are in agreement, so I
have adjusted probability of precipitation down and temperatures up over the weekend.
Another trough may try to break through the ridge and bring
showery, cool weather again early next week. The models do not
agree on much with this system, with the European model (ecmwf) keeping the bulk of
the activity to our north and the GFS digging a trough offshore.
Given these discrepancies, changes were not made. -Wright
Pacific coastal waters...Small Craft Advisory for hazardous seas until 5 am PDT Wednesday
Small Craft Advisory for hazardous seas until 5 PM PDT this
afternoon for pzz350-370.
Small Craft Advisory for winds from 5 PM this afternoon to 5 am
PDT Wednesday for pzz376.