Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 300555
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1055 PM PDT FRI JUL 29 2016

.UPDATE...
Updates were made to the fire weather portion of the forecast to
lower relative humidities slightly for Sunday and Monday
afternoons and evenings and increase wind gusts. These updates
bring wind and RHs to critical levels over portions of the East
Side, so Fire Weather Watches have been issued for two fire
weather zones. BTL

&&

.DISCUSSION...
Some build-ups over the Modoc and Siskiyou County resulted in one
briefly healthy thunderstorm between MacDoel and Tennant, east of
Bray, around 5pm PDT. One single cloud to ground lightning strike
was detected.

Meanwhile, there is a wildfire near Bybee Creek, just west of
Crater Lake National Park, that was reported at 48 acres this
afternoon. A smoke plume from this wildfire was evident on
visible satellite imagery this afternoon and evening.

Over the coming days, while the heat will lessen, the dryness
across the area will not. Thus, concerns will continue to revolve
around fire weather, as well as the continuing moderate to strong
winds and steep to very steep seas in the coastal waters. BTL

&&

.AVIATION...30/06Z TAF cycle...IFR marine stratus continues along the
immediate coast south to Cape Blanco. Areas of IFR/LIFR cigs and
MVFR vis will increase along the coast north of Cape Blanco tonight
and continue into Saturday morning. Expect cigs to clear to VFR
around 16z at KOTH, but may see local IFR along the portions of the
immediate coast continue into Saturday afternoon. Moderate to strong
and gusty north winds are expected this evening for most areas along
the coast and offshore. Scattered cumulus buildups are expected over
the higher terrain of northern California into south central Oregon
this evening. Expect that mvfr ceilings will return to the coast late
Saturday afternoon through the evening. BTL

&&

.MARINE...Updated 217 PM PDT Friday 29 Jul 2016...A thermal trough
along the coast and high pressure offshore will continue to produce
moderate to strong north winds and steep to very steep wind driven
seas into early next week.  Hazardous warning level seas and gales e
expected mainly beyond 5 NM from shore today through
Saturday...mainly for locations from Cape Blanco southward. However
an area of hazardous seas warning conditions is expected to next
extend northward to just south of Cape Arago. Winds and seas should
peak on Saturday afternoon and evening. On Sunday, warning seas and
gales are expected from Cape Blanco south with small craft advisory
winds and seas to the north. On Monday, winds may drop below gale
force across most the waters. However, hazardous warning level seas
remain possible from Gold Beach south on Monday. Winds are expected
to rise to gales again by Tuesday evening and continue into Thursday
of next week. -CC

&&

.FIRE WEATHER...Updated 920 PM PDT Friday, 29 July 2016...

With only one lightning strike today and models diminishing
thunderstorm potential for tomorrow, the question overnight will
be whether or not to entirely remove the mention of thunderstorms
from the forecast for Saturday. If we do get any, they will be
dry and very isolated, and more likely over Lake County than
anywhere else. It will probably just be too dry for any, though.

Hot, dry, and, in times and places, windy will be the theme
thereafter, especially for the Modoc. A Fire Weather Watch has
been issued for Sunday and Monday afternoons and evenings for FWZ
285 and southern portions of 624. Model consensus indicates 5-10%
RH over the Modoc Sunday. The question is whether or not winds mix
enough to get gusts above 20 mph for 3 hours. Confidence is
moderate that we will. On Monday RHs may come up slightly and
winds definitely do. Gusts look to be mostly 25 to 35 mph with
RHs in the 5-15% range, so critical conditions are
likely/confidence is high in red flag conditions being met. A
slight cool down and a wind decrease is then expected Tuesday and
Wednesday. BTL

&&

.PREV DISCUSSION... /Issued 242 PM PDT FRI JUL 29 2016/

DISCUSSION...The latest visible image shows cumulus starting to
develop in southeast Modoc County and some in Siksyou County near
the Marble Mountains and Medicine Bow peak. Our main focus will be
the potential for thunderstorms or lack thereof late this afternoon
into this evening and again Saturday afternoon and evening. The last
several runs of the HRRR have been consistent suggesting isolated
storms (if we get anything) will be confined to southeast Modoc
County which is where most of the cumulus is developing at. A look
at the latest mesoscale analysis from SPC shows the highest cape
values in southeast Modoc County, even then it`s nothing that would
suggest any concerns. Therefore we have decided to scale back the
thunderstorms and keep them confined to southeast Modoc County late
this afternoon into early this evening. As the models have been
suggesting the past few days, the instability parameters have been
marginal at best with little or no trigger. Despite this, fire
danger is high fuels are receptive in this area, so it probably
won`t take much (isolated thunderstorms) to get a fire started. Also
models soundings show an inverted "V" which suggest any storms that
develop could be mostly dry and produce gusty outflow winds.

For now were keeping tonight dry. The NAM and GFS show a weak vort
lobe moving east to northeast into northern Cal, but it may not be
enough to trigger convection. The GFS has since backed off on the
convective feedback in the QPF field during the overnight period and
the NAM and HRRR show nothing. The bottom line is we probably won`t
get anything, but this is something that will need to be watched
carefully.

The focus for thunderstorms on Saturday will shift east to northeast
into southern Lake, Klamath, northeast Siskiyou and northwest Modoc
County as the aforementioned vort lobe moves east to northeast as it
gets caught up in the westerly flow as the upper trough in western
B.C. begins to move south. The environment should be similar to
Friday, therefore we`ll keep a slight chance mention. Gusty winds
could be a concern Saturday afternoon and evening east of the
Cascades.

After Saturday the threat for thunderstorms is pretty much over
with. An upper trough will swing north of the area Sunday morning
bringing a dry stable westerly flow over the area with the threat
for storms shifting well east of us. Temperatures will continue to
cool, but will still remain near or above normal. Another upper
trough will swing north on Monday bringing further cooling and
continued dry conditions. Gusty winds are also expected, especially
east of the Cascades Monday afternoon and evening. After Monday,
weak troughiness will remain over the area with dry weather and near
normal temperatures. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Sunday afternoon through Sunday evening
     for ORZ624.
     Fire Weather Watch from Monday afternoon through Monday evening
     for ORZ624.

CA...Fire Weather Watch from Sunday afternoon through Sunday evening
     for CAZ285.
     Fire Weather Watch from Monday afternoon through Monday evening
     for CAZ285.

Pacific Coastal Waters...
- Small Craft Advisory until 5 AM PDT Monday for PZZ350-356-370.
- Gale Warning until 5 AM PDT Sunday for PZZ356.
- Hazardous Seas Warning until 5 AM PDT Monday for PZZ356-376.
- Hazardous Seas Warning until 5 AM PDT Sunday for PZZ350-370.
- Small Craft Advisory from 5 AM Sunday to 5 AM PDT Monday for
  PZZ376.
- Gale Warning until 5 AM PDT Monday for PZZ376.

$$

BTL/MAP/CC



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