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000
FXUS66 KMFR 060451
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
951 PM PDT Wed May 5 2021

.UPDATE...
Updates have been made and sent to the forecast for tonight
through Friday morning. Primary updates were to add more fog to
areas along and near the coast and across the coastal waters
tonight into Thursday morning, to increase winds some for Thursday
afternoon and evening, and to adjust precipitation probabilities
based on the latest guidance.

&&

.DISCUSSION...
We reached 90F here at the airport today for the first time this
season. While this is a bit early per the climate record and
nearly 20 degrees above the new 1991-2020 climate normal for the
calendar day, it was still 7 degrees short of the daily record.
Other inland locations reached their warmest values of the
season, thus far, but also were 5-10 degrees short of daily
records.

An abrupt change back to near to even slightly below normal
temperatures is expected to spread across the forecast area from
west to east tonight through Friday. Temperatures along the Curry
County coast are in the mid to upper 40s right now with fog and
drizzle- a sign of things to come. And, while we`re not expecting
much in the way of rainfall, some is likely for most areas from
the Oregon Cascades and Siskiyous westward. We could see up to a
quarter of an inch in the coastal mountains, but most areas that
get precip through Friday morning will see under a tenth of an
inch. Altogether, it will be breezy and notably cooler the next
couple of days.

A word of caution to those getting an early start on summer
gardens- some west side areas are likely to see some frost
Saturday morning. ~BTL

&&

.AVIATION...For the 06/00Z TAF Cycle...Offshore south of Cape Blanco
marine stratus is causing MVFR/IFR. Marine stratus will bringing
another round of IFR to the inland coastal areas tonight. A large
prescribed burn near Chiloquin is producing a smoke plume which is
creating MVFR VSBYs and partial terrain obscuration toward KLMT. All
other inland locations are VFR and will be that way through the TAF
cycle. Smoke will return to KLMT at some point tonight as mixing
decreases.

&&

.MARINE...Updated 830 PM PDT Wednesday 05 May 2021...Winds and seas
will be their lowest this evening. Then, a weak front will move
onshore Thursday, and this will bring small craft winds and seas to
areas north of Cape Blanco beyond 10 nm offshore during the day
Thursday. Winds and seas will decrease behind the front Thursday
night into Friday. Another thermal trough will develop near the
coast Friday afternoon and persist into next week, bringing gusty
north winds and choppy seas to the area, especially south of Cape
Blanco.

&&

.FIRE WEATHER...Updated 200 PM PDT Wed 05 May 2021...The latest
surface analysis shows the thermal trough inland over the west side
valleys. The thermal trough is expected to gradually shift east of
the Cascades later this afternoon.

This afternoon will be marked by dry conditions and very warm
temperatures inland, on the order of 10 to 15 degrees above normal,
and gusty south to southwest winds in the Shasta Valley and east of
the Cascades. Near critical conditions are possible during the
afternoon in portions of Lake, Klamath, and Modoc Counties. However
we don`t think red flag conditions will be met mainly due to winds
not being strong enough. Therefore, we`ll continue to headline.

A cold front will push into the region Thursday, and while light
precipitation is expected from the coast to the Cascades, this will
be a dry cold frontal passage for areas east of the Cascades.
Temperatures will trend cooler across the region Thursday afternoon,
with humidities higher over the West Side. The latest guidance also
suggest higher relative humidities east of the Cascades. The
increase may not be as much as the west side, but it may be just
enough to prevent critical conditions from developing. With that
said, still could not rule out brief critical conditions for the
eastern portions of fire zone 624 Thursday afternoon and early
evening.

Winds across the East Side are expected to be stronger Thursday
afternoon ahead of the front due to a combination of a tighter
pressure gradient and stronger winds aloft (700mb winds between 25
and 35 kts). We did get calls from our partners in fire zones 285,
624 and 625 and they said green up has occurred in fire zones 625
and 285 due to recent precipitation and as a result their fuels are
in the moderate category. However fire zone 624 did not benefit
nearly as much and fuels are still receptive, below 5,000 feet.
Therefore, given the above mentioned reasoning regarding winds and
relative humidities, we`ll continue to headline.

After two days (Today and Thursday) of increased fire weather
concerns, cooler temperatures, higher humidities, and even a few
showers north of the Umpqua Divide and northern Cascades, are
expected Friday as an upper level trough swings through. Breezy
winds are likely east of the Cascades once again Friday afternoon
and evening, but should not be near as strong as those of Thursday,
and relative humidities will also be much higher.

Dry but cooler weather is expected Saturday, then a warming and
continuing drying trend is expect early next week as upper level
ridging and the coastal thermal trough return. -BPN/Petrucelli

&&

.PREV DISCUSSION... /Issued 458 PM PDT Wed May 5 2021/

UPDATE...Updated aviation discussion for the 06z TAFs.

SHORT TERM...After the very warm temperatures today, expect
cooler conditions and some areas of showers as a front and upper
trough move into the region Thursday and Friday. Gusty winds east
of the Cascades are expected this afternoon and moreso, Thursday
afternoon along with dry humidities resulting in elevated fire
weather concerns. On Saturday, the upper trough will be east of
the area and expect cold morning temperatures with some areas of
frost in valleys west of the Cascades.

Today will be the warmest day over the area with a
strong high pressure ridge in place. High temperatures this
afternoon are on track to reach the mid 80s to around 90 for
inland valleys west of the Cascades and the upper 70s to 80 east
of the Cascades. Should Medford reach 90 degrees today, it will
be the first high of 90 or above since October 2nd of last year.
Along with these very warm temperatures, breezy to gusty winds and
dry humidities will occur this afternoon into early this evening,
especially for areas east of the Cascades and within the Shasta
Valley, where fire weather concerns will be elevated.

Models are on track showing a weak front moving into the coast
Thursday morning then weakening further as it moves inland
Thursday afternoon and night. This front is followed by an upper
trough moving across the area Friday. This pattern will result in
cooler temperatures Thursday and moreso, Friday as well as areas
of light rain, mainly at the coast, in the Umpqua Basin and over
the Southern Oregon Cascades. There is slight chance for some
rain showers south of the Umpqua Divide into Josephine and Jackson
Counties late Thursday into Friday, however any amounts would be
very light. Ahead of the front, areas east of the Cascades will
see windy conditions with continued dry humidities Thursday
afternoon and early evening. West winds may briefly reach advisory
levels with gusts to 45 mph but only for isolated locations over
the higher terrain east of the Cascades, primarily near Summer
Lake. Overall, models support winds just below advisory levels
for most of the area with west winds 15 to 20 mph and gusts 35 to
40 mph east of the Cascades. The combination of gusty winds and
dry humidities though, will result in elevated fire weather
concerns. Please see the fire weather discussion below for
additional details.

Friday will be the coolest day for inland areas this week with
highs around 5 to 10 degrees below normal. Daytime high
temperatures are forecast in the lower to mid 60s for most valleys
west of the Cascades and in the mid 50s to near 60 for valleys
east of the Cascades. This is followed by cool temperatures
Friday night and Saturday morning. Low temperatures are expected
to lower into the 30s for western valleys and in the 20s for
valleys east of the Cascades. Areas of frost are possible in some
valleys west of the Cascades with these lower temperatures,
clearing skies and mainly light winds.

Saturday is expected to be dry with northwest flow over the region
as the upper trough remains to the east and ridge remains
offshore. Expect mild daytime temperatures with highs near or
slightly below normal for this time of year, except at the coast
where normal to slightly above normal temperatures are possible
under offshore, northeast flow (especially for areas south of Cape
Blanco).

LONG TERM...(Sunday through Wednesday)...Not much has
changed in the extended. It`s likely to remain dry through the
forecast period. Even the individual ensemble members of the ECE and
GFS show no measurable precipitation. Afternoon temperatures Sunday
will be near normal for this time of the year. It will be cool to
cold at night with the coldest temperatures in the Klamath Basin in
northern Klamath County.

Upper ridging will build just west of the area Monday into Tuesday.
At the same time a thermal trough will set up along the coast with
increasing offshore flow. Afternoon temperatures will be higher for
most inland locations, but even milder temperatures are possible for
the south coast near Brookings.

The ridge will flatten out some Wednesday resulting in slight
cooling and increased onshore flow west of the Cascades, but
remaining dry. Of Note, the GFs shows a weak upper trough moving
through Wednesday evening and night, but the trajectory and strength
is one that normally does not result in precipitation. -Petrucelli

&&

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

CA...None.

Pacific Coastal Waters...
- Small Craft Advisory from 5 AM to 2 PM PDT Thursday for PZZ370.


$$

BTL/CC/MB