Flash Flood Watch 2, NWS Medford, OR

145 
WGUS66 KMFR 230541
FFAMFR

Flood Watch
National Weather Service Medford OR
1041 PM PDT Tue Aug 22 2017

CAZ080-084-085-ORZ028-230645-
/O.EXP.KMFR.FF.A.0002.000000T0000Z-170823T0600Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Western Siskiyou County-
Northeast Siskiyou and Northwest Modoc Counties-Modoc County-
Siskiyou Mountains and Southern Oregon Cascades-
Including the city of Etna
1041 PM PDT Tue Aug 22 2017

...FLASH FLOOD WATCH WILL EXPIRE AT 11 PM PDT THIS EVENING...

The Flash Flood Watch for portions of northern California and
south central Oregon will expire at 11 PM PDT this evening. 
Locally heavy rain may still occur overnight, but no major
flooding is expected.

$$

Area Forecast Discussion
National Weather Service Medford OR
326 AM PDT Tue Aug 22 2017

.DISCUSSION...The main focus today will be thunderstorms this
afternoon into this evening and possibly overnight tonight. The
latest water vapor image shows some of that moisture starting to
creep up into our area. The upper low in central California will
send moisture, instability and trigger for thunderstorm development
into our area this afternoon through this evening. Right now, most
of the action should be in northern California and Cascades
eastward. However steering winds could push some of these storms
into portions of the westside valleys, including the Rogue and
Illinois Valley. The models suggest PW values will increase today,
therefore there's a chance for wetting storms. Smoke will certainly
be a factor that could inhibit thunderstorm formation in some areas,
primarily extreme Western Siskiyou County, but potentially into the
Cascades too.

The next concern, not only today, but tomorrow will be areas of
smoke which will continue to impact most of the forecast area.
Sources of the smoke vary, for example smoke in Medford will likely
come from the Siskiyou County fires, fires in Western Jackson and
Josephine Counties, and the Chetco Bar fire in Curry County. Not
knowing how much smoke will be produced from fires in the next
several days, we have maintained smoke in the forecast for many of
the areas that are seeing smoke today. We are maintaining an Air
Quality Alert for most areas along and west of the Cascades...and
the Klamath Falls area.

Also could not rule nocturnal storms Tuesday night east of the
Cascades. The models are in pretty good agreement showing enough
instability, moisture and sufficient trigger for thunderstorms to
persist into Tuesday night. They lay tend to be more isolated as we
lose daytime heating, but the threat still exist.

On Wednesday the focus for thunderstorms will shift east of the
Cascades. A southwest flow will set up as an upper trough approaches
Vancouver Island which should push the focus for storms east. Drier
and stable air mass will push in west of the Cascades and western
Siskiyou County bringing an end to thunderstorm chances. Therefore
have trimmed back the coverage of storms Wednesday. The threat for
storms shifts further east Wednesday evening and should be mainly
confined to Lake County.

A weak upper trough with a stable southwest flow aloft will move
into the area bringing dry and cooler weather on Thursday. This will
probably be the coolest day of the forecast period, then significant
warming is in the cards Friday through the weekend. -Petrucelli

&&

.AVIATION...22/06Z TAF CYCLE...Onshore flow is keeping IFR cigs/vis
at the coast overnight and confidence is low that OTH will see any
improvement to VFR during the next 24 hours. Elsewhere smoke from
wildfire blankets southern Oregon and this is affecting visibility
at most terminals. We are leaning heavily toward smoke/particulate
trajectory forecast and base the lowering of visibility to MVFR/IFR
based on particulate concentration at various hours. This keep IFR
vis at MFR all day with MVFR visibility at RBG. Model shows NW wind
coming off the Cascades Tuesday afternoon bringing smoke from
wildfire there and this should lead to MVFR visibility at LMT. /FB

&&

.MARINE...Updated 200 AM PDT Tuesday, 22 August 2017...Low
pressure will move inland today, and north winds will continue to
decrease through the morning. Low pressure will deepen again on the
southern coast Wednesday with north winds increasing again towards
to the end of the week. -Schaaf/Sven

&&

.FIRE WEATHER...Updated 300 AM PDT Tuesday, 21 August 2017...The
main concern will be thunderstorms from this afternoon through
tonight. Thunderstorm chances look good for this afternoon and
evening mainly in northern California and east of the Cascades.
Steering winds could carry a few of these storms into portions of
the westside, including the Rogue and Illinois Valley, but they
should be more isolated. While wetting rainfall will occur with some
storms, lightning outside the storm cores on dry to very dry fuels
is expected to lead to many new fire starts. Also keep in mind the
potential for gusty and erratic winds near thunderstorms. The
coverage area for the Red Flag Warning looks good and no changes
were made. Also did not make any changes to the coverage area of the
Fire Weather Watch on Wednesday. However, drier air arriving from
the west with the best chance for thunderstorms shifting east of the
Cascades, Wednesday afternoon, then mainly confined to Lake County
Wednesday evening. Therefore it's possible the coverage area will
have to be shrunk down. We'll let later shifts reevaluate this.

Thursday will be the coolest day of the week, but winds aloft will
be stronger, some of which could mix down near the surface,
especially east of the Cascades. A rapid warm up is expected Friday
through the weekend. At the same time a thermal trough will develop
along the coast, so we could be dealing with gusty northeast to east
winds near and at the ridges with moderate to possibly poor
overnight recoveries in Fire zones 618, 619 and western 280. It
remains to be seen if recoveries will be as low as they were this
past weekend, but it's something that will need to be monitored.
-Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
     evening for ORZ621-623>625.
     Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for ORZ623>625.

CA...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
     evening for CAZ280>282-284-285.
     Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for CAZ280-281-284-285.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 5 AM PDT early
     this morning for PZZ350-356-370.
     Small Craft Advisory for hazardous seas until 8 AM PDT this
     morning for PZZ376.