666
FXUS66 KMFR 032341
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
441 PM PDT Wed Jul 3 2024

.Updated Aviation Discussion.

.SYNOPSIS...

An extreme heat event will impact the area on Friday and Saturday
with high temperatures testing all time highs. Temperatures will
cool relatively the start of next week as high pressure moves
eastwards.

&&

.DISCUSSION...

Latest satellite imagery shows a wildfire growing within the
Marble Mountains southwest of Shelly Lake near the PCT in south
west Siskiyou County. Siskiyou County Emergency management is
requesting hikers along the PCT to be aware of and avoid this
fire. Otherwise, clear skies dominate the rest of the satellite
picture as plenty of dry air is spread out over the forecast area.

Dry northeast flow along the coast and over southwest Siskiyou
County will continue into tonight. Temperatures in Brookings only
fell to 75 this morning, so the Chetco effect and downsloping
winds should keep things warm there for another 24 hours. The flow
pattern will change a bit as high pressure really begins to build
in by Friday and Saturday. Some deterministic guidance shows 500
mb geopotential heights approaching 600 dam in Siskiyou County,
which is pretty extreme based on Medford Sounding climatology.
We`ve only hit 600 dam once at MFR and reaching 598 would put us
in the top 10 500 mb height recordings.

Given how strong this high is and the time of year, we`re getting
plenty of heat this weekend. Friday and Saturday are the most
concerning as this is when high temperatures will be at their
peak during this heat wave. In addition, we`ll be testing the all
time high temperature record for Medford of 115 degrees. As of
now we`re forecasting a high of 113 on Saturday, which will still
easily beat the existing high temperature record of 104 set in
1922. Lows will also be on the warm side, although not
exceptionally warm like the 2021 heat wave. Ashland looks like it
might not drop below 70, although almost all other valley
location should drop below 70. In any case, the NWS HeatRisk
algorithm is rightfully predicting extreme risk. This type of heat
will be problematic to anyone without access to cooling
facilities. For more temperature record information, check out the
weather story on our home page.

The coast seems like the best place to escape the heat with high
temperatures only hitting the upper 80`s. Brookings should improve
as well as the northeast flow will weaken and we should get some
onshore flow starting around Sunday. The area of high pressure
will weaken and track farther east around the start of next week.
It will still remain hot, although the NWS HeatRisk drops into
the moderate category when considering the region at large.

Depending on the model solution one looks at, an upper level wave
will approach the California coastline sometime between Tuesday
and Thursday. We don`t have thunderstorms in the forecast right
now, although the probability of thunder is closer to 10% on
Thursday. The air will be awfully dry ahead of this wave, so
perhaps that 10 percent is still too optimistic.

-Smith

&&

.AVIATION...04/00Z TAFS...VFR will prevail through the TAF period.
Gusty north winds at North Bend will diminish later this evening,
then increase again between 19-20z tomorrow. Gusty breezes at
Roseburg will also diminish early this evening. -Petrucelli

&&

.MARINE...Updated 220 PM Wednesday, July 3, 2024...A strong thermal
trough will remain with strong north winds, gales south of Port
Orford, and steep to very steep and hazardous seas for all areas
through early Thursday. Winds will be strongest and seas will be
steepest this afternoon and evening. Conditions gradually improve
Thursday morning as the thermal trough pushes inland and expands
northward. North to northeast winds will ease some at this time, but
seas and winds will remain hazardous to small craft with hazardous
warning level seas likely lingering through Thursday night.

North winds will continue their downward trend Friday with the
strongest winds over the northern outer waters, but they are
expected to remain below small craft.

Conditions improve further over the weekend with sub-advisory
conditions likely for at least the inner waters. Strong high
pressure aloft will disrupt the thermal trough pattern, keeping
winds in the 10 to 15 knot range. Also the swell is expected to be
low with combined seas expected to remain below any advisory
levels. -Petrucelli

&&

.FIRE WEATHER...Updated 200 PM Wednesday, July 3, 2024...

...Near critical fire weather possible today through the next week
for much of southern Oregon and northern California...

...RED FLAG WARNING REMAINS IN EFFECT FROM 11 PM THIS EVENING TO 8
AM PDT THURSDAY FOR EAST WIND WITH POOR OVERNIGHT RH RECOVERY FOR
FIRE WEATHER ZONES 619 AND 620...

Fire weather concerns will remain elevated through the week due to
two different patterns. First, a strong thermal trough along the
coast will persist through tonight. This will bring moderate to
locally poor overnight RH recoveries to upper slopes and ridges
again overnight tonight, along with gusty northeast winds of 15-25
mph with gusts to 30 to 35mph. Although the thermal trough will
shift northward and winds are expected to relax tomorrow, there will
be enough overlap for critical fire weather conditions and a Red
Flag Warning remains in effect for 11 PM tonight through 8 AM
Thursday for portions of Oregon FWZ 619/620.

In the meantime, this pattern will also lead to near critical
conditions for portions of the area this afternoon. Minimum
humidities of 10-15% are expected in western and central Siskiyou
County with north winds of 10 to 15 mph and gusts to 25 mph
(strongest in the Shasta Valley near Montague). Similarly, northeast
winds also be near critical thresholds in the Illinois Valley at 10-
15 mph with gusts to 20 mph, and with minimum humidities of 10-15%.
However, Intel on fuels remains that the live fuels are not quite
there while dead fuels are. Therefore, will continue to headline the
near-critical conditions this week. As an example of what this
means, a wildfire has recently ignited near the Pacific Crest Trail
in California Zone 280 where emergency services has issued a fire
warning for hikers. This just demonstrates the nature and just how
near-critical the conditions are for the next several days.

Strong high pressure aloft moves over the region for the latter half
of the week and through the weekend. The thermal trough will expand
northward, with weaker winds expected along the coast beginning
Thursday. Very hot temperatures (100-110 degrees) and very low (low
teens/single digit) humidities are expected during this time away
from the immediate coast. While afternoon breezes won`t be quite as
strong as today, the extreme heat, and long duration of the heat
will allow even typically breezy afternoon conditions to result in
dangerous weather that is favorable for rapid spread of fire.

It is worth noting that we are paying attention to an upper level
disturbance forecast to move northward into our area from
California. While the atmosphere will be too dry for thunderstorms,
this may cause winds to uptick a little bit, especially west of the
Cascades. Will continue with the headline for now, but it is worth
noting the increase of winds could bring critical conditions to
portions of Oregon fire zones 620 and 622 over the weekend.
Confidence is low for this scenario, but it is starting to increase.
We will continue to collaborate with partnering agencies regarding
this situation. -Schaaf/BR-y

&&


.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 8 AM Thursday to 9 PM PDT Monday for
     ORZ023>026.

     Heat Advisory from 8 AM Thursday to 9 PM PDT Monday for
     ORZ029>031.

     Red Flag Warning from 11 PM this evening to 8 AM PDT Thursday
     for ORZ619-620.

CA...Excessive Heat Warning from 8 AM Thursday to 9 PM PDT Monday for
     CAZ080-081.

     Heat Advisory from 8 AM Thursday to 9 PM PDT Monday for CAZ084-
     085.

PACIFIC COASTAL WATERS...Gale Warning until 8 AM PDT Thursday for
     PZZ356-376.

     Small Craft Advisory from 8 AM to 8 PM PDT Thursday for PZZ350-
     356-370.

     Hazardous Seas Warning from 8 AM to 8 PM PDT Thursday for PZZ356-
     370-376.

&&

$$