Severe Thunderstorm Warning 24, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
259 PM PDT Mon Jun 26 2017

.DISCUSSION...The thunderstorm potential late today and this
evening was the focus of this forecast. Strong thunderstorms have
already occurred well north of our area...mainly north of a line
from Bend to John Day. Across southern Oregon and far northern
California, the area of thunderstorm development later this
afternoon should be across Siskiyou County into the Siskiyous and
Cascades, Klamath County, and northern Lake County. There is
sufficient moisture and instability to support thunderstorm
initiation at higher elevations in this region and the steering
flow will be from the southwest.

There is a distinct difference in the cumulus field at 230 pm
across the Rogue Valley (Yes, we do look outside too). Not much
cumulus development over the Rogue Valley but much more pronounced
building cumulus clouds were over the Siskiyous. The southern end
of the Rogue Valley (Ashland/Talent) has a greater chance of
seeing a thunderstorm later today than points north and west where
the airmass is more stable.

Elsewhere, have taken the isolated thunderstorms out of southern
and eastern Modoc County and far southeast Lake County where
surface dewpoints have dropped considerably with much drier air
above. Also, a thunderstorm has popped up just offshore of the
Douglas-Lane county line. These elevated, not surface-based,
convective storms will move north away from our area. Marine low
stratus will also remain at the coast and into the coastal
valleys.

Not a whole lot to discuss beyond today with more typical benign
summer weather this week. We added a slight chance of
thunderstorms Tuesday late afternoon and evening to the Cascades
and Siskiyous due to instability and the GFS model showing
precipitation developing. For the rest of the forecast period the
temperatures will be near to slightly above normal and probably
dry with a more westerly flow aloft.
Sandler

&&

.AVIATION...26/18Z TAF CYCLE...Along the coast and into the Umpqua
Valley, expect MVFR/IFR cigs throughout the TAF period. The
challenge is the thunderstorm forecast for inland areas... a trough
axis will be located just offshore this afternoon, and scattered
thunderstorms over the western siskiyous northeastward into the
Cascades and East Side are expected this afternoon. Confidence is
lower in thunderstorm coverage in the Rogue Valley...as there
isn't as strong of a trigger as yesterday. Though thunderstorms
can't be ruled out in the Umpqua Valley, did not have the
confidence to put in the TAF. -MSC

&&

.MARINE...Updated 200 PM Monday, 26 June 2017...South to
southwest winds and light seas will persist through tonight. The
thermal trough is expected to develop along the coast Tuesday and
strengthen into Wednesday. This will result in the return of gusty
north winds and steep to very steep wind driven seas. The strongest
winds and seas are forecast from Cape Blanco south, where gales and
very steep and Hazardous seas are possible, but all areas will
experience at least small craft advisory level seas. These
conditions are likely to persist through the remainder of the week.
-BPN/CC

&&

.FIRE WEATHER...Updated 130 PM Monday, 26 June 2017...Unstable
conditions will combine with an upper level disturbance moving in
from the west to generate isolated to scattered storms over much of
the forecast area this afternoon. Lightning amounts should be less
than yesterday as moisture is less and there should be a quick
decrease in storms from west to east as even drier air moves in and
solar heating is lost. Also of concern is the potential for erratic
and gusty winds near storms today. Gusts of 40 to 50 mph are
possible near thunderstorms this afternoon and evening, especially
for storms that develop east of the Cascades. Outside of
thunderstorms, gusty general west winds and continued low humidity
may fan any new fire starts. A Red Flag Warning continues for much
of Modoc County due to expected wind gusts of 30 mph and humidity 15
percent or less.

Red flag warnings remain in effect for the potential of increased
initial attack activity. Tomorrow there is a slight chance for
thunderstorms over Siskiyou County with some lingering instability
and midlevel moisture. The rest of the week should be quieter as
cooler and more stable conditions dominate. -CC/SK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT this evening for ORZ625.
     Red Flag Warning until 11 PM PDT this evening for ORZ621-623.
     Red Flag Warning until 8 PM PDT this evening for ORZ620-622.
     Red Flag Warning until 11 PM PDT this evening for ORZ624.

CA...     Red Flag Warning until 8 PM PDT this evening for CAZ280.
     Red Flag Warning until 8 PM PDT this evening for CAZ281.
     Red Flag Warning until 7 PM PDT this evening for CAZ285.

Pacific Coastal Waters...Small Craft Advisory from 11 AM Tuesday to 11 AM PDT Thursday
     for PZZ356-376.
     Small Craft Advisory for hazardous seas from 11 AM Tuesday to 11
     AM PDT Thursday for PZZ350-356-370-376.
     Hazardous Seas Watch from late Tuesday night through Thursday
     morning for PZZ376.