Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
255 PM PDT Monday Aug 3 2015
Discussion...visible satellite imagery this afternoon is showing
congested cumulus fields developing mainly over the higher
terrain, but especially along the Cascades. A cluster of cells
have developed in the last hour between Diamond Lake and Crescent.
Expect more to develop in these areas through the evening
hours...moving fairly slowly to the north-northeast. A subtle but
real short wave evident in water vapor imagery is moving northward
into northern California at this time and this should help to
ignite additional showers and thunderstorms in the unstable air
mass that extends from Siskiyou County northeastward to Klamath
and lake counties, including near Klamath Falls. Recent Storm Prediction Center
mesoanalysis is showing surface based cape in these areas of about
500-1500 j/kg with the highest values to the southwest across the
Siskiyou/Marble Mountains. Smoke in that region may be somewhat
holding back convection, but still expect some storms to fire
there through the evening hours. If any cells do form over the
Siskiyous, they could drift out over portions of the Rogue Valley,
especially the south end into this evening. Expect activity to
wane later this evening with the loss of instability with mostly
tranquil weather overnight.
Smoke will persist across much of the west side to the north and
east of the main fires over at least the next 24 hours. Many new
starts have been reported with yesterday's lightning to the west
of Medford, so there doesn't appear to be much relief in sight
for the Rogue Valley.
On Tuesday, models are now unanimous in showing another shortwave
moving onshore just north of the Bay area. The nam12 yesterday
was farther north with this feature. The same general areas that
get storms today will be unstable again on Tuesday. However,
since the best trigger (the short wave) will remain to the south
and west during the day, we expect mostly isolated thunderstorm
activity with a slight shift eastward compared to today. The
short wave will move through northeast California Tuesday night
and this may keep showers and isolated thunderstorms going into
the night across southeastern portions of the forecast area
(modoc, southeast Klamath and lake counties).
By Wednesday, the flow aloft becomes westerly as a large scale
upper trough digs southward along the British Columbia coast.
Isolated showers and thunderstorms have been maintained in the
extreme south and east portions of the forecast area along a
trough axis, but these may need to be removed in subsequent shifts
as drier air appears it may win out.
Dry weather should persist for much of the forecast area through
Thursday night. Then, yet another upper level low pressure system
will move into the central California coast near S.F. Bay Friday.
This will bring a chance of thunderstorms, especially to southern
and eastern sections Friday into Saturday. A larger trough may dig
into the Pacific northwest for the second half of next weekend
resulting in cooler weather and possible showers. Spilde
Aviation...for the 03/18z taf cycle...areas of stratus and fog
with IFR/LIFR ceilings/visible at the coast should retreat offshore for a
brief time before returning between 1-2z this evening and lasting
into Tuesday morning. Areas of smoke will persist inland bringing
a reduction in visibility and limited vertical visibilities,
especially for the Rogue Valley, including Medford Airport. For
now the smoke should remain out of Roseburg, but it will be
close. Isolated thunderstorms will develop over the Cascades and
east side this afternoon which will produce MVFR ceilings/visible along
with gusty erratic winds. -Petrucelli
Marine...updated 245 PM PDT Monday 3 August 2015...weak low
pressure over the waters will move inland, and high pressure will
build in from the west. This will result in an increase in north
winds and the development of a light chop this evening. North
winds and seas will build Tuesday and remain moderate into
Thursday morning. Winds will strengthen further Thursday afternoon
into Friday and possibly reach gales over the southern waters.
Fire weather...updated 250 PM PDT Monday 3 August 2015...as
another weak disturbance moves in this afternoon, scattered
showers and thunderstorms are expected to redevelop, mainly over
the mountains and east side Oregon zones. Red flag warnings are in
effect for these areas this afternoon and evening. Elsewhere,
thunderstorms are expected to be isolated today. A more
southwesterly flow develops over the region, decreasing the
instability over the region and thunderstorms will be isolated
from the Siskiyous to the Cascades, and much of the east side.
Northwest flow spreads across the region Wednesday, pushing the
area of instability east of the region. Southerly flow returns
returns the end of the week, with a slight chance of thunderstorms
returning Friday through the weekend. Sven
or...red flag warning until 11 PM PDT this evening for
California...red flag warning until 11 PM PDT this evening for caz284.
Red flag warning until 11 PM PDT this evening for caz280.
Pacific coastal waters...Small Craft Advisory for winds from 11 am
Tuesday to 5 PM PDT Thursday for pzz376.
Small Craft Advisory for hazardous seas from 11 am Tuesday to 5
PM PDT Thursday for pzz376.
Small Craft Advisory for winds from 2 PM Tuesday to 11 PM PDT
Wednesday for pzz356.
Small Craft Advisory for hazardous seas from 2 PM Tuesday to 11
PM PDT Wednesday for pzz356.
Small Craft Advisory for winds from 2 PM to 11 PM PDT Tuesday
Small Craft Advisory for hazardous seas from 2 PM to 11 PM PDT
Tuesday for pzz370.