Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 280004
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
504 PM PDT Thu Jul 27 2017

Updated AVIATION Section

.DISCUSSION...Climatologically, we are within the hottest time of
year, and the forecast over the next week is expected to reflect
this fact. Upper level ridging and a strengthening thermal trough
will produce a gradual warming trend through the weekend, with
daily highs reaching the triple digits in the Rogue and Illinois
Valleys as well as the valleys of Siskiyou county by Saturday and
Sunday. Highs in the nineties are expected elsewhere. While the
forecast highs are only 10 degrees above normal for this time of
year, it will still be quite hot, even the overnight hours may
not provide much relief, as lows in some areas may not even make
it below 70. Heat advisories may be necessary by the beginning of
next week, especially as these hot temperatures will remain in
the area through the remainder of the forecast term. Day to day
marine layer pushes may produce cooler temperatures along
portions of the coast, but can not be depended on to provide
relief on any given day.

Also worth mentioning, there are a few times during the week in
which the models are hinting at afternoon and evening convection,
mainly Saturday and Monday. However, there is little consistency
between the models, and the latest runs have backed off on the
chances for development. Model soundings also depict a lack
moisture for thunderstorm development, at least until monsoonal
moisture attempts to return to our area late next week. Have
backed off on the thunderstorm forecast and kept chances below
mention until confidence improves. -BPN

&&

.AVIATION...28/00Z TAF CYCLE...VFR prevails over the area this
evening with some fair-weather cumulus over the East Side stretching
back to the Shasta region. VFR will persist overnight into Friday
across all inland areas, with the exception of in the vicinity of
wildfires, where smoke may occasionally restrict visibility to less
than a mile at times. IFR will return to the coast, mainly after 05z
and especially north of Cape Blanco, but also near Brookings. The
marine layer won`t be quite as deep as it was last night, so expect
mainly VFR again at KRBG, though it won`t be far away, so scattered
clouds around 2500 feet are possible for a few hours Friday morning.
-Spilde

&&

.MARINE...Updated 230 PM PDT Thursday 27 July 2017...A thermal
trough in northern California will remain in place into next week
with north winds and steep to very steep seas. Small craft
advisory conditions will persist south of Cape Blanco tonight and
Friday. The thermal trough will strengthen late Friday through the
weekend with gales beyond about 5 NM from shore and south of Gold
Beach. Conditions hazardous to small craft will reach north of
Cape Blanco at times. -Spilde

&&

.FIRE WEATHER...Updated 210 PM Thursday 27 July, 2017...
The transition to drier and hotter conditions has begun. This trend
will begin to erase any temporary dampening effects from rainfall
over the past couple days and promote the growth of sleeper fires in
the area. Additionally, the relatively weak general winds of the
past several days will begin to increase to moderate, more typical
afternoon breezes. With this drying trend, have dropped afternoon
humidities slightly more. With this, very low humidity values near
critical values are expected in Modoc County (California fire zone
285) as well as for the Shasta Valley in 281, and the Southeast
portion of 284. Oregon zones 625 and the southeast portion of 624
will also see the low RH values. Although winds may be slightly
stronger tomorrow than they are today, they are not expected to
reach critical levels. Have cancelled the fire weather watch for
tomorrow for Haines 6 because we do not issue for Haines 6 in
California. Conditions will still support significant fire
growth, however. We will be headlining the Fire Weather Forecast
with both the Haines 6 and the low RH and the Gusty Winds.

Given the thermal trough pattern strengthening along the coast and a
hot air mass overhead, east winds and moderate to poor overnight
humidity recoveries become a concern Friday night and Saturday night
for the Ridges in Siskiyou County and the coastal range. Have
dropped humidity values quite a bit from the previous shift. Latest
data still does not support conditions reaching critical criteria,
so will be headlining in the Fire Weather Forecast for now.

In summary, hotter and drier conditions will increase potential for
fire growth. High temperatures will affect fire crews as afternoon
readings reach about 10 degrees above normal during this hottest
time of the year. Low temperatures during this time period may only
provide temporary relief (if any at all). This pattern is expected
to go from this weekend through next week at least. Long-term
guidance suggests no relief from the hot conditions through next
week. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Gale Watch from Friday morning through Sunday
     evening for PZZ356-376.
     Small Craft Advisory until 11 PM PDT Sunday for PZZ356-376.
     Small Craft Advisory from 11 AM Friday to 11 PM PDT Sunday for
     PZZ350-370.

$$

BPN/BMS/MSC/MAS


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