Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
800 PM PDT Monday Jul 21 2014
Discussion...22/00z NAM in.
Quite a few lightning strikes over Modoc County this afternoon...
along with a few in Eastern Lake County. Another band developed
late this afternoon and evening...and that round generated a bunch
of lightning strikes over Siskiyou County...arcing northeast into
the Cascades and the east side. Some thunderstorms are still
active at this time...mostly over Lake County...but overall the
activity is winding down.
An active weather pattern...in terms of convection and wind...will
remain over the area through Wednesday. An usually strong trough
will deepen along 130w through Tuesday night...then it will move
east onshore Wednesday night. It will then head out to the east
Initially the primary concern is thunderstorms. There were some
today but tomorrow southerly flow will increase...and this will
bring more monsoonal moisture into the area. The 21/12z GFS
solution shows instability near and east of Interstate 5 but with
the greatest instability in the northern Oregon Cascades.
Thunderstorm coverage will be more widespread...and rainfall
totals will be heavier. Dry lightning will not be a big
issue...but there will be some lightning strikes in areas that get
little or no precipitation. A red flag warning has been issued all
of the County Warning Area but the coast...lower Umpqua and the kalmiopsis/Illinois
The main concern on Wednesday will be winds as the trough moves
inland. Relative humidities will be higher but winds will be quite
strong over the ridges and east of the Cascades. There will be
some showers on the west side...especially along the north coast
and Umpqua basin. It will be more stable that day with the main
thunderstorm threat to the north...but some may get going over
northern Klamath and lake counties. It will dry out quickly
Wednesday night with low level offshore flow developing.
Extended discussion from the Monday afternoon afd...Thursday
through Monday. Temperatures will begin to warm up later in the
week as the upper low moves out and the upper ridge expands
northwest. Hot readings should be felt by this weekend. There
should be a lull in the thunderstorms for our area from Wednesday
into the weekend. Some moisture and instability could work its way
north from the Sierra into the Modoc County area later this
Aviation...based on the 22/00z tafs...showers with isolated
thunderstorms stretch from the Siskiyous and north central
California across the east side Oregon zones this evening. These
will gradually diminish through the evening but will be capable of
producing brief heavy rain with MVFR ceilings/vis, gusty winds, and
lightning. Elsewhere, conditions remain VFR and will through the
night. The exception may be at the coast where stratus with IFR ceilings
is possible toward dawn. -Wright
Marine...updated 1245 PM PDT 21 July 2014...weak high surface
pressure will remain over the waters through Tuesday, then weak low
pressure and an associated weak cold front will move through
Wednesday. This will result in continued light winds and seas
through Wednesday. A thermal trough pattern will redevelop Thursday
and remain in place through next weekend resulting in strong north
winds and steep wind driven seas through the period. -Wright
or...red flag warning until 11 PM PDT this evening for orz624-625.
Red flag warning from 11 am to 11 PM PDT Tuesday for orz625.
Red flag warning from 11 am to 11 PM PDT Tuesday for
Red flag warning from 11 am to 11 PM PDT Tuesday for orz624.
California...red flag warning until 11 PM PDT this evening for
Red flag warning from 11 am to 11 PM PDT Tuesday for caz285.
Red flag warning from 11 am to 11 PM PDT Tuesday for caz280-281.
Red flag warning from 11 am to 11 PM PDT Tuesday for caz284.
Pacific coastal waters...none.