Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
313 PM PDT sun Jul 5 2015

Discussion...satellite imagery today shows the Medford County Warning Area in between two
regimes...with a cutoff low offshore from California and a weak boundary to
the north. Good atmospheric stretching is occurring with east winds
aloft on the west half of the forecast area and west winds aloft on
the east side of the forecast area. This deformation zone is a
favorable area for thunderstorms...potentially strong to
severe...and east of the Cascades is where the deepest moisture
is to support scattered thunderstorms. A red flag warning at
rfwmfr continues through this evening for parts of northern
California...and portions of Klamath and lake counties. A mass of
clouds present earlier today is beginning to clear from south to
north and is resulting in increased sunshine and enhanced

Tonight...storms should diminish as moisture in the atmosphere
becomes limited and diurnal overnight stability takes hold. On
Monday there is some lingering moisture...both surface moisture from
recent rains and middle level moisture...but the middle level moisture
will be less than today. Perhaps the most challenging aspect of
the thunderstorm forecast tomorrow is the fact that the models
are not showing a good trigger for Monday afternoon.
Typically...its difficult to get scattered thunderstorms with weak
triggers. Therefore...we are maintaining a Fire Weather Watch for
tomorrow at rfwmfr and will let the midshift take one more look at
things before deciding on products. We have focused the best
potential for scattered thunderstorms over the Cascades north of
Crater Lake...and just to the east...where middle level moisture
values of 50- 60% align with instability.

On Monday night and Tuesday the weather pattern becomes even more
active...with solid east southeast flow aloft...and very high
precipitable waters of 1 inch+ along and west of the Cascades. These
are anomalously high values...and with models now on the second day
of showing this scenario...we have increased probability of precipitation and quantitative precipitation forecast for
much of the southern two-thirds of the forecast area. Wednesday
shows a similar pattern...but with focus of instability and
moisture a bit further south. There is certainly a good chance for
much of the forecast area...from the Umpqua Divide see
a thunderstorm sometime between Tuesday and Wednesday. In
fact...we have thunderstorm chances all the way to the coast from
Monday night into Tuesday. On Thursday the upper low finally
slowly pushes inland...which the models have been fairly
consistent in showing the past few days...but this maintains
favorable dynamics and instability over the area through Friday
before west winds aloft begin to stabilize and dry things out on
Saturday from west to east. The weekend may signal a break from
the steady chances of thunderstorms...but southerly flow rebounds
on Sunday based on the latest GFS run.


Aviation...for the 05/18z taf cycle...along the coast...IFR ceilings
along the coast and offshore will move back onshore Sunday
evening...then burn back to the coast by late morning Monday.
Over the remainder of the area...VFR conditions will prevail
through Monday...but isolated to scattered thunderstorms will
persist into this evening from the Cascades east and Siskiyous


Marine...updated 310 am PDT Sunday 4 July 2015...seas and winds
will remain relatively low through the middle of next week at
least. In the near-term...stratus and fog will affect the coastal
waters through Sunday. Winds will switch from southerly to north
to northwesterly by Tuesday. Winds and seas will stay below
advisory criteria through the week. /Sven


Fire weather...updated 300 PM PDT Sunday 5 July 2015...afternoon
and evening thunderstorms are likely every day during the coming
week. Activity will be slightly less widespread Monday...but will
increase Tuesday and Wednesday. The favored area this afternoon and
evening is over northern California...where clearing is allowing
surface heating. On Monday activity will be mostly over the higher
terrain from the Cascades east and Siskiyous south. Tuesday and
Wednesday will see greater coverage. Even the coastal area may see
some thunderstorms in that time frame. The activity will gradually
shift to the east side toward the end of the week.

Temperatures will remain hot Monday...but will start to cool
Tuesday. Temperatures will approach seasonal values toward the end
of the week.


Mfr watches/warnings/advisories... flag warning until 11 PM PDT this evening for orz623>625.
Fire Weather Watch from Monday afternoon through Monday evening
for orz623>625. flag warning until 11 PM PDT this evening for
Fire Weather Watch from Monday afternoon through Monday evening
for caz285.

Pacific coastal waters...none.



National Weather Service Glossary of Abbreviations