Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
257 PM PDT Monday Jul 6 2015

Discussion...visible satellite imagery is showing some congested
cumulus development over the Cascades, the east side and the
higher terrain of northern California early this afternoon. Radar
is showing some cells developing near and north of Crater Lake
..across northern Klamath and lake counties...And also over
southeast Modoc County. Expect isolated to scattered thunderstorms
to continue developing this afternoon and evening as daytime
heating further destabilizes the atmosphere. Forcing for
thunderstorms remains relatively weak, so favored thunderstorm
locations will be where the atmosphere is most unstable and also
has the highest middle-level moisture (from the Cascades east and the
Siskiyous south).

Of note, as of 2 PM PDT, Medford hit 100 degrees...which makes 7
consecutive days at or above 100. This is the 6th longest stretch
of 100+ days in Medford. The longest stretch of 100+ (10 days)
occurred in both August 1967 (ending the 19th) and July 1962
(ending the 30th).

Most of thunderstorm activity will dwindle later this evening and
overnight with the loss of instability.

An upper level low off the California coast will move eastward
Tuesday and then onshore south of the Bay area on Wednesday.
Increasing south-southeast middle-level flow ahead of this system
will bring plenty of moisture northward into southern Oregon and
northern California Tuesday. In addition, stronger short wave
energy will lift northward into the area. With instability already
in place, expect numerous showers and thunderstorms to develop.
Precipitable water values today are in the top 10% of climatology
and will be even higher on Tuesday. So, storms that do develop
will likely produce heavy rainfall. The best activity will once
again be from the Cascades east and Siskiyous south, but middle-level
steering flow should be enough to bring some showers and storms
west of the Cascades, especially south of the Umpqua Divide
Tuesday evening.

By Wednesday, the middle-upper flow will become more east-
northeasterly and storm motions will likely be northeast to
southwest. Another active day is expected in the same general
areas..especially northern California. This should continue to
bring much-needed rainfall to that area...where typically little
rainfall occurs during the month of July.

A deformation axis could set up north of the upper low across the
County Warning Area Wednesday night into Thursday keeping showers/T-storms going.
The GFS is farther north and west with this feature, while the
European model (ecmwf) keeps it farther south. The upper low will gradually fill
and open up as it moves into Nevada by Friday.

The next upstream system over the Pacific will likely carve out
another upper trough/low offshore of the Pacific northwest this
weekend and early next week. It should be noted that we will see
a marked changed in temperatures over the next week. Gone will be
the days of 100+ degree heat...and we'll likely see temperatures
finally down to or even perhaps a bit below normal by this
weekend. Spilde

&&

Aviation...for the 06/18z taf cycle...along the coast...IFR ceilings
along the coast will clear to the coast by late morning but will
persist over the coastal waters. The lower conditions will return
to the coast late this afternoon and evening and remain through middle-
morning Tuesday. Inland...VFR conditions will prevail through
Tuesday morning...but isolated to scattered thunderstorms will
develop again this afternoon and evening from the Cascades
east and Siskiyous south.

&&

Marine...updated 130 PM PDT Monday 6 July 2015...a weak pressure
pattern will persist through the week. Light south winds will slowly
turn north to northwest Tuesday...increasing to 10 to 15 knots on
Wednesday. Low northwesterly swell will continue through the week
with several small long period swells mixed in...resulting in
combined seas 4 to 6 feet. Sk

&&

Fire weather...updated 200 PM PDT Monday 6 July 2015...some areas
were dropped from the red flag warning currently in effect due to
wet fuels. A red flag warning will be issued for scattered
thunderstorms Tuesday afternoon and evening. It will cover most of
the inland areas except for the Umpqua basin and the east side areas
that have wet fuels.

Some of the thunderstorms may be very wet. Even the coastal areas
may see some thunderstorms Tuesday and Wednesday. The activity will
gradually shift to the east side toward the end of the week.

Temperatures will start to cool Tuesday and will approach seasonal
values by Friday.

&&

Mfr watches/warnings/advisories...
or...red flag warning until 11 PM PDT this evening for
orz617-621>624.

California...red flag warning until 11 PM PDT this evening for
caz280-281-284.

Pacific coastal waters...none.

$$

Mas/jrs/sk

National Weather Service Glossary of Abbreviations