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Area forecast discussion 
National Weather Service Medford or
933 am PDT Thursday Jul 2 2015

Update...
updates to the forecast were made to adjust sky cover slightly
over the marine waters, to add patchy smoke from the corner creek
fire near Dayville, Oregon over northeastern portions of the area,
and to make some adjustments to waves in the marine forecast.

&&

Discussion...
many record high temperatures were tied or broken yesterday
afternoon. The records that were broken actually had been broken
just last year. Please see the previous discussion, below for
further details.

Highs today look to be almost identical to yesterday's, though
some locations could be a degree or two hotter and some a degree
or two cooler. Records are likely to be tied or broken again at
many locations.

Our focus today will be to attempt to nail down the thunderstorm
risk across the area through early next week. The forecast for
isolated thunderstorms this afternoon and evening, and for Friday
in northern California look on track. While some model guidance
indicates coverage could exceed isolated coverage in western
Siskiyou County Friday afternoon and evening, other guidance
indicates morning cloud cover there on Friday will limit surface
heating and the maximum threat for storms will, instead, end up
further north and east in the Tule Lake basin and across Klamath
County. Thus, with mixed signals, confidence is currently low that
scattered storms will occur over the forecast area on Friday.
We'll continue to work on honing in on this better today. For
Saturday through early next week the thunderstorm threat looks to
drift northwestward, but details on timing and location of
thunderstorm maxima has been changing from model run to model
run. It does stand to reason that, as temperatures gradually
lower and moisture increases, some areas, mainly across northern
California and from the Cascades eastward, will see some locally
significant rain with the storms.

Also on the bright side, it does appear that an upper level
trough edging into the West Coast will likely bring with it a
gradual 7 to 15 degree fahrenheit cool down across the forecast
area from about Tuesday through next weekend. Btl

&&

Aviation...for the 02/12z taf cycle...along the coast...IFR to LIFR
ceilings and visibilities north of Cape Blanco and the South Coast
near Brookings will clear to VFR by late morning...then return again
this evening. Over the remainder of the area...VFR conditions will
prevail...but isolated afternoon and evening thunderstorms are
possible over the Oregon Cascades south of Crater Lake...over
southern Klamath and lake counties...and over Siskiyou and Modoc
counties.

&&

Marine...updated 300 am PDT Thursday 2 July 2015...a thermal trough
near the coast will weaken into Thursday...but persist into
Saturday. Small Craft Advisory level north winds and steep to very
steep seas will persist for the next several days. Winds and waves
will subside this weekend.

&&

Fire weather...updated 300 am PDT Thursday 2 July 2015...hot and
dry weather will persist into this weekend...but the hottest day
will be today. Moisture will increase today and Friday with
isolated afternoon and evening thunderstorms expected over
northern California and over southern Klamath and lake counties.
The main concern in the near term is the possibility of scattered
afternoon and evening thunderstorms over western Siskiyou County
Friday. The uncertainty lies in the timing of a short wave that
will move through that area. The current GFS run is a bit quick
with this feature as far as timing GOES...but it has been varying
from run to run. If subsequent runs put it over the area at maximum
heating...a watch may be needed for that area. Weak offshore flow
will develop along the South Coast range Friday night...making for
poor to moderate relative humidity recoveries on the ridges. Thunderstorm chances
will increase this weekend...mostly from the Cascades east and
Siskiyous south. Lingering showers and thunderstorms are possible
Monday and Tuesday as moisture gradually shifts eastward.

&&

Previous discussion... /issued 250 am PDT Thursday Jul 2 2015/

Discussion...several records have been tied or have been broken
across the County Warning Area over the past 24 hours. We reached 108 degrees at
the Rogue Valley international Airport yesterday afternoon, good
enough to tie the record that was last reached in 1942. Other
record highs that were set/tied Wednesday (previous record in
parentheses): Klamath falls: 98 (97 in 2014), mount shasta: 100
(99 in 2014) and alturas: 101 (101 in 2014).

Today more records will likely be tied or broken...as we're
expecting similar temperatures today compared to yesterday. A heat
advisory continues through Independence day for the
rogue...Illinois...Klamath River...Scott...and Shasta
valleys...found at npwmfr. With all the outdoor activities expected
on a typical 4th of July...folks should really plan accordingly with
the temperatures expected to be 15 to 20 degrees above normal...and
an elevated risk of heat related illnesses.

Today isolated thunderstorms are expected mainly in northern
California...and into southeastern Klamath and Southern Lake
counties...as midlevel moisture and instability increase in that
area. A significant trigger will be lacking as the area will be
under the upper ridge axis...and thus the isolated coverage.

On Friday a trigger arrives in the form of shortwave energy from
the southeast...with the nam12 and gfs40 models agreeing on
general placement and timing. Continued unstable conditions and
increasing precipitable water values will act in concert with the
shortwave to produce higher chances for thunderstorms over western
Siskiyou County. We haven't used scattered wording yet because
run-to-run consistency with shortwave placement hasn't been rock
solid...but if another run of the models shows little convective
inhibition and Li values near -4...this will signal a good chance
for scattered thunderstorms. Otherwise...thunderstorm chances
nudge a bit further north on Friday into Klamath Falls. On
Saturday another area of shortwave energy arrives...and 850mb
computed Li values per the GFS remain negative...so thunderstorm
chances continue...generally higher than the day before due to
generally steeper lapse rates. Finally...on Sunday the instability
pushes north and east...bringing better thunderstorm chances into
southern Oregon...especially from the Cascades east. Steering flow
is not really favorable to bring storms into the Rogue Valley or
any of the west side valleys for that matter. Will continue to
watch as convective inhibition really is minimal from Jackson
County eastward.

The favorable pattern for thunderstorms along and east of the
Cascades continues through next week...as an upper low remains off
the coast of California and pumps in moisture with a long fetch of
southerly flow aloft. This is a rather stagnant pattern and the
latest GFS remarkably shows the upper low off the coast in some form
or fashion through Saturday...whereas the European model (ecmwf) is a little more
progressive by the weekend.

One other important note...temperatures finally decrease to near
normal values late next week. There is no sharp cool down expected
but just a gradual downward trend of temperatures.

&&

Mfr watches/warnings/advisories...
or...heat advisory until 11 PM PDT Friday for orz023.
Heat advisory until 11 PM PDT Saturday for orz024-026.

California...heat advisory until 11 PM PDT Saturday for caz080-081.

Pacific coastal waters...
- Small Craft Advisory for winds until 5 am PDT Saturday for
pzz350-356-370-376.
- Small Craft Advisory for hazardous seas until 5 am PDT Saturday
for pzz350-356-370.
- Small Craft Advisory for hazardous seas until 5 PM PDT Saturday
for pzz376.
- Hazardous seas warning until 5 am PDT Saturday for pzz376.

$$

Btl/nsk/jrs

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