Special Weather Statement, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
904 AM PDT Wed Aug 9 2017

.SHORT TERM...A low off the Northern California coast will remain
in place today then gradually shift inland Thursday. The main
concern for today is the potential for thunderstorms with a
marginal risk of severe thunderstorms again this afternoon and
evening. Except for more morning clouds, the weather pattern is
very similar to yesterday. With a deformation zone aloft combined
with good moisture and unstable conditions, models show
thunderstorms likely to develop again east of the Cascades in
Klamath and Lake counties this afternoon then move westward into
the Cascades late in the afternoon and into the evening. Storms
are also expected to develop across Siskiyou county in the late
afternoon and evening. Storms may then develop in Modoc county in
the evening, with northern and eastern portions of the county
favored.

There is a marginal risk for severe thunderstorms with large hail
and severe winds this afternoon and evening. This marginal risk
for severe is mainly across eastern Douglas and Jackson counties
and from the Southern Oregon Cascades eastward in Oregon as well
as in Siskiyou and Modoc counties in Northern Calfiornia. With the
easterly flow aloft, thunderstorms may drift westward over Curry
and Josephine county and into western and central Douglas county
today.

Moderate to heavy rain is possible in the core of these
thunderstorms today. Yesterday reports of up to an 1 inch per hour
were reported with the strongest storms. However, fire weather
conditions remain critical since lightning may occur outside the
area of rain with storms and bring the potential for new
wildfires. Strong gusty and erratic winds are likely with storms.
Winds gusting to 40 to 50 mph are possible with stronger storms
and up to 60 mph if severe storms develop. Hail is also possible
with thunderstorms with hail sizes of pea to dime size likely and
up to quarter size hail possible if severe storms develop. Some
lingering weaker nocturnal thunderstorms and showers are possible
tonight into Thursday morning over the area.

As this low gradually moves inland over the region on Thursday,
it will bring southeast moist flow over the area and upper level
forcing. This combined with daytime instability will likely bring
scattered thunderstorms to the area Thursday afternoon and
evening. This upper disturbance will then weaken and shift to the
northeast on Friday while a broad upper trough develops off the
Pacific Northwest coast. As a result, on Friday expect decreasing
chances for thunderstorms.

&&

.AVIATION...09/12Z TAF CYCLE...Along the coast and over the coastal
waters...Areas of MVFR/IFR cigs/vsbys over the waters and along the
coast will continue to spread into the coastal valleys into the
early morning. The low clouds and fog will burn back to the coast by
late Wednesday morning, but are expected to persist along shore
north of Cape Blanco. Inland...VFR will prevail through Wednesday
evening...except for areas of MVFR vsbys in smoke near wildfires. A
few isolated thunderstorms are possible overnight into Wednesday
morning then isolated to scattered slow-moving thunderstorms are
expected over just about the entire inland area again Wednesday
afternoon and evening with a focus over the Cascades. Gusty and
erratic winds and turbulence will likely occur near thunderstorms.
-DW

&&

.MARINE...Updated 111 AM PDT Wednesday 9 August 2017...Persistent
high pressure far offshore and low pressure inland will continue
light to moderate north winds into Saturday. A small area of small
craft advisory seas will persist until this afternoon south of Port
Orford beyond 9 NM from shore. There will be a slight diminishing
trend of wind driven seas into Saturday morning. North winds are
likely to increase Saturday afternoon and trend stronger into next
week. -DW/BS

&&

.PREV DISCUSSION... /Issued 551 AM PDT Wed Aug 9 2017/

Updated fire weather discussion.

DISCUSSION...The closed low off NW California will remain mostly
stationery today. A band of showers with embedded isolated
thunderstorms continued overnight and was well depicted by the
deformation field at 500mb. It is interesting that by early this
afternoon this deformation feature shows up across eastern Lake
County in an arc to the west into the Summer Rim and northern
Klamath County. By early this evening the easterly steering flow
bring instability and thunderstorm chance out of the Cascades and
into the Rogue Valley again. It also appears that Modoc County
will be relatively calm today with thunderstorms not appearing in
that area until late this afternoon into this evening.
Precipitable water is highest from the Cascades west and
thunderstorms that form are likely to produce measurable rain
underneath the core.

On Thursday, upstream long wave trough is forecast to move inside
140W and this will help to eject the closed low eastward. Just
about all of our forecast area except for the immediate coastal
zones will be unstable enough for showers and thunderstorms. Both
the NAM12 and the GFS40 are remarkably similar at painting the
greatest instability in Josephine County north into the Umpqua
Basin and eastern Douglas County, as well as northern Jackson
County toward Crater Lake. Both models also paint an area of
moderate instability from western Lassen County into the southern
half of Modoc County. These areas could see strong storms
although, as stated earlier, just about all of our forecast area
could see thunderstorm activities.

Friday could be somewhat tricky as both the GFS and the ECMWF
bring the upstream long wave trough to the coast. This could be
the start of a marine push into the Umpqua Basin and western part
of the Rogue Valley, but also stronger winds into the higher
terrain and east of the Cascades. In our far eastern part like
Lake and Modoc Counties, the atmosphere could still be warm and
unstable with little change in instability.

By Saturday cooler marine air could filter into the Umpqua Basin
and into the Rogue Valley by Sunday. The ECMWF is a lot more
aggressive at the cool down for Medford on Sunday than the GFS is.
By Monday we should see a shift toward cooler and more stable
airmass across our forecast area. /FB

AVIATION...09/12Z TAF CYCLE...Along the coast and over the
coastal waters...Areas of MVFR/IFR cigs/vsbys over the waters and
along the coast will continue to spread into the coastal valleys
into the early morning. The low clouds and fog will burn back to the
coast by late Wednesday morning, but are expected to persist along
shore north of Cape Blanco. Inland...VFR will prevail through
Wednesday evening...except for areas of MVFR vsbys in smoke near
wildfires. A few isolated thunderstorms are possible overnight into
Wednesday morning then isolated to scattered slow-moving
thunderstorms are expected over just about the entire inland area
again Wednesday afternoon and evening with a focus over the
Cascades. Gusty and erratic winds and turbulence will likely occur
near thunderstorms. -DW

MARINE...Updated 111 AM PDT Wednesday 9 August 2017...Persistent
high pressure far offshore and low pressure inland will continue
light to moderate north winds into Saturday. A small area of small
craft advisory seas will persist until this afternoon south of Port
Orford beyond 9 NM from shore. There will be a slight diminishing
trend of wind driven seas into Saturday morning. North winds are
likely to increase Saturday afternoon and trend stronger into next
week. -DW/BS

FIRE WEATHER...Updated 600 AM Wednesday 9 August, 2017...
Thunder storm threat remains high today and Thursday as the low
low continues to send multiple shortwaves through the area.

A band of showers extend from northern Josephine County westward
to near Agness. This band has been persistent from yesterday evening
and the radar shows an embedded heavier showers which could also be
a precursor to thunderstorm development. The atmosphere continues to
be unstable with the Cascades being the most likely area to see
development this afternoon. With the steering flow being out of the
east, these storms are likely to move down the mountains into the
Rogue Valley again. Elsewhere the atmosphere is quite unstable with
moderate to high shear, so be aware that storms this afternoon could
develop into severe thunderstorms with potential for large hair
and very gusty winds.

Looking further out, model consensus continue to suggest a cooling
trend and a period of more stable conditions from Saturday through
early next week. Sunday could be problematic east of the Cascades,
especially for any new/existing fires, as windy conditions are
possible with low humidity ahead of the approaching trough.
-FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from noon today to 10 PM PDT this evening for
     ORZ624-625.
     Fire Weather Watch from Thursday afternoon through Thursday
     evening for ORZ624-625.
     Red Flag Warning from noon today to 10 PM PDT this evening for
     ORZ616-619.
     Fire Weather Watch from Thursday afternoon through Thursday
     evening for ORZ616-619.
     Red Flag Warning from noon today to 10 PM PDT this evening for
     ORZ617-620>623.
     Fire Weather Watch from Thursday afternoon through Thursday
     evening for ORZ617-620>623.

CA...Red Flag Warning from noon today to 10 PM PDT this evening for
     CAZ280>282-284.
     Fire Weather Watch from Thursday afternoon through Thursday
     evening for CAZ280>282-284.
     Red Flag Warning from noon today to 10 PM PDT this evening for
     CAZ285.
     Fire Weather Watch from Thursday afternoon through Thursday
     evening for CAZ285.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 2 PM PDT this
     afternoon for PZZ356-376.

CC/CC/CC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
755 AM PDT WED AUG 9 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0715 PM     TSTM WND DMG     2 NW RUCH               42.25N 123.06W
08/08/2017                   JACKSON            OR   PUBLIC

            PINE TREE WITH 24 INCH DIAMETER WAS SNAPPED
            IN HALF AND TOOK OUT A BIRCH TREE. TIME
            BASED ON RADAR ESTIMATE.

0649 PM     HAIL             JACKSONVILLE            42.31N 122.97W
08/08/2017  M0.50 INCH       JACKSON            OR   TRAINED SPOTTER

0645 PM     HAIL             5 NE GOLD HILL          42.49N 122.98W
08/08/2017  E0.88 INCH       JACKSON            OR   PUBLIC

            MAX HAIL SIZE ROUGHLY THE SIZE OF A LARGE
            MARBLE. REPORT RELAYED VIA SOCIAL MEDIA.
            GUSTS ALSO TO 34 MPH.

0635 PM     HAIL             CENTRAL POINT           42.38N 122.92W
08/08/2017  M0.25 INCH       JACKSON            OR   TRAINED SPOTTER

0627 PM     HAIL             1 NNW CENTRAL POINT     42.39N 122.92W
08/08/2017  M0.25 INCH       JACKSON            OR   TRAINED SPOTTER

0610 PM     TSTM WND DMG     1 ESE CENTRAL POINT     42.37N 122.89W
08/08/2017                   JACKSON            OR   TRAINED SPOTTER

            5 INCH TREE BRANCH DOWN. SPOTTER REPORTS
            TREE WAS HEALTHY AND ESTIMATES GUSTS
            COULD'VE BEEN UP TO 50 MPH. TIME ESTIMATED
            FROM RADAR.

0603 PM     TSTM WND GST     2 E CENTRAL POINT       42.37N 122.87W
08/08/2017  M44 MPH          JACKSON            OR   ASOS

            OUTFLOW FROM THUNDERSTORMS HITTING 44 MPH.

0555 PM     TSTM WND DMG     7 NW WHITE CITY         42.49N 122.94W
08/08/2017                   JACKSON            OR   TRAINED SPOTTER

            REPORTS OF POWER LINES DOWN NEAR THE
            TABLEROCKS. LOCATION AND TIME ESTIMATED.

0348 PM     HAIL             ALTAMONT                42.20N 121.72W
08/08/2017  M1.00 INCH       KLAMATH            OR   TRAINED SPOTTER

0344 PM     HAIL             1 NW ALTAMONT           42.21N 121.73W
08/08/2017  E0.50 INCH       KLAMATH            OR   PUBLIC

            TIME ESTIMATED FROM RADAR.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
855 AM PDT WED AUG 9 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0600 PM     TSTM WND DMG     4 ESE GOLD HILL         42.42N 122.98W
08/08/2017                   JACKSON            OR   PUBLIC

            ROOF DAMAGE - SHINGLES BLOWN OFF OFF ROOF.

&&

Special Weather Statement
National Weather Service Medford OR
132 PM PDT WED AUG 9 2017

CAZ085-092100-
Modoc County-
132 PM PDT WED AUG 9 2017

...A STRONG THUNDERSTORM WILL AFFECT WEST CENTRAL MODOC COUNTY...

At 131 PM PDT, a strong thunderstorm was located 8 miles north of
Howards Gulch Campground, or 24 miles west of Alturas, moving
northeast at 10 mph.

Wind gusts up to 50 mph and nickel size hail are possible with this
storm.

Locations impacted include...
Howards Gulch Campground.

* This includes... Highway 139 in Modoc County California between
  mile markers 5 and 21.

LAT...LON 4143 12103 4157 12123 4181 12093 4160 12070
TIME...MOT...LOC 2031Z 230DEG 9KT 4160 12099

CZS