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Area forecast discussion 
National Weather Service Medford or
1029 am PDT Wednesday Jul 30 2014

Update...
an update has been made to the forecast and the fire weather
forecast has also been updated. This update expands the coverage
of thunderstorms westward further into Josephine and Douglas
counties as compared to the previous forecast.

&&

Discussion...
blm lightning indicates about 1200 cloud to ground strikes occurred
yesterday with about 420 of those in southeastern Jackson County.
While significant rain was observed with some of the storms this
abundant lightning with dry vegetation likely resulted in many
fire starts. Some have already been confirmed this morning.

For today a shortwave trough currently along the Mendocino coast
will track northward across the west side this afternoon and
evening. Looking at model performance for yesterday's weak shortwave
and comparing it to today's forecast, the western periphery of
thunderstorms is most likely to be in Josephine County today and
into the eastern half of Douglas County. There is a slim
possibility that storms could form as far west as the Coast Range
per the track of the shortwave trough, but a plethora of indices,
steering flow, and both short and longer term model guidance
indicate they will likely remain to the east.

It should be noted that storm intensity today is expected to be
similar to yesterday to possibly a bit stronger. Indications from
the models are that borderline severe storms will occur along and
near the Cascades to include Jackson, eastern Douglas, and Klamath
counties. The main threat will be similar to yesterday in that
isolated hail in the 1/2 to 1 inch range and gusty winds in the
30 to 50 miles per hour range are expected mainly late this afternoon into
this evening.

For Thursday models indicate a bit less instability and a bit less
available moisture, and some warming aloft. We will be
investigating today what this means for convection across the
area, but the general sense is that it will mean less activity
tomorrow as compared today, especially west of the Cascades. More
on this in the afternoon. Btl

&&

Aviation...based on the 30/12z tafs...

Areas of LIFR conditions are being observed all along the coast and
inland into the Coquille Valley. The low ceilings and fog will burn
back to the coastline around noon. Thunderstorms will form this
afternoon...and will affect most of the forecast area except for the
coast...Coast Range...and Umpqua basin. Gusty outflow winds are
expected with these storms. Storms diminish tonight and stratus will
return to coastal terminals...reaching into the Coquille Valley late
tonight.

&&

Marine...updated 300 am PDT 30 July 2014...

The current pattern...with some slight day-to-day variation...will
persist through the weekend. Offshore high pressure and a thermal
trough over northern California will combine to maintain steep wind
wave dominated seas and areas of Small Craft Advisory winds into the
weekend...with the strongest winds and steepest seas from Cape
Blanco south in the afternoons and evenings. Winds may increase to
gales with very steep seas by Friday afternoon for areas south of
Cape Blanco. Confidence is moderate on the gale and very steep seas
potential...as models have been generally consistent in showing
high-end small craft conditions Friday afternoon...with a few runs
pointing towards low-end gale conditions.

&&

Previous discussion... /issued 229 am PDT Wednesday Jul 30 2014/

Discussion...the next couple of days will be potentially high
impact days for fire weather and severe weather, and thus all of the
focus this morning has been on the forecast for the next 48 hours.

On Tuesday, thunderstorms formed in roughly the expected locations
and approximately right on time. Storms became most intense and the
most lightning was observed in the early evening from near Montana.
Ashland up through the Cascades. Storms actually approached severe
levels at times with at least one middle level mesocyclone observed on
radar (along Highway 97 near chemult) and a couple of overshooting
tops seen in satellite data. Most of our area was very unstable, but
the west side was largely capped at around 700 mb. The previous
shift made the astute observation that storms formed within the area
of concentrated middle level moisture, that is where 700-500mb
humidities exceeded 60%. The west side was capped below much of this
moisture, and not surprisingly, storms made little progress off the
mountains as a result.

That is not expected to be the case today. We should have every bit
as much instability today, but the models show a westward surge in
middle level moisture with the edge of the deep moisture moving as far
west as Grants Pass. In addition, both the GFS and NAM show a decent
shortwave moving through this afternoon, and steering flow backs a
bit more toward the south. There is a short wave just off the coast
now, which shouldn't do much at this time of day, but more energy is
noted moving north through central California. In fact, there were
just a few lightning strikes inland from the Bay area associated
with some of that energy, which seems to be what the models are
picking up on. All of this means that we should see at least as much
activity today as yesterday, and we probably will see storms even on
the west side. Probability of precipitation were adjusted to this thinking and the red flag
warning will be nudged west to include the Rogue Valley today.

As to whether thunderstorms will be severe today...there is little
reason to believe we can't get a severe storm or two given what we
saw on Tuesday. Don't expect widespread severe storms, but in
addition to heavy rain, isolated large hail and damaging wind
gusts can't be ruled out. The most likely location for that will
be Klamath County again.

It remains plenty unstable on Thursday as well. While there will be
a little less moisture, there is still a decent trigger in the form
of a 500 mb shortwave. Thus, coverage and location of storms on
Thursday looks roughly the same as Wednesday, and probability of precipitation were adjusted
up and further west Thursday as well. We will also be expanding the
Fire Weather Watch for Thursday to include similar areas to what the
red flag warning covers today.

Things remain unstable on Friday, but there is a noticeable shift
inland with activity, and thus thunderstorms ought to be confined to
east side areas on Friday. No changes were made to the forecast
beyond Friday. -Wright

&&

Mfr watches/warnings/advisories...
or...red flag warning from 2 PM this afternoon to 11 PM PDT this
evening for orz617-621>625.
Fire Weather Watch from Thursday afternoon through Thursday
evening for orz617-621>625.

California...red flag warning from 2 PM this afternoon to 11 PM PDT this
evening for caz280-281-284-285.
Fire Weather Watch from Thursday afternoon through Thursday
evening for caz280-281-284-285.

Pacific coastal waters...
- Small Craft Advisory for winds until 11 PM PDT Friday for
pzz356-376.
- Small Craft Advisory for hazardous seas until 11 PM PDT Friday
for pzz350-356-370-376.
- Small Craft Advisory for winds from 5 PM Thursday to 11 PM PDT
Friday for pzz350-370.
- Gale watch from Thursday afternoon through Friday evening for
pzz376.
- Hazardous seas watch from Thursday afternoon through Friday
evening for pzz376.

$$

Btl/trw/nsk

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