542
FXUS66 KMFR 050222
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
722 PM PDT Thu Jul 4 2024

.DISCUSSION...Two max temperature records were broken today and
one was tied. The broken records were at Medford and Mt. Shasta
City, and the tied record was at Montague. More records are
expected to occur as the heat wave maxes out this weekend and
continues into next week. No updates were made this evening and
the previous forecast discussion below remains valid.

&&

.AVIATION...05/00Z TAFS...VFR conditions will continue through the
TAF period with gusty north winds north of Cape Blanco, including
North Bend this afternoon into this evening, and breezy afternoon
and early evening winds at Roseburg. There`s some evidence
supporting a very low chance of localized low clouds in portions of
the Coquille Basin late tonight and portions of the coast, including
North Bend late tonight resulting in IFR ceilings, but confidence is
not high enough to include this in the TAF.

Meanwhile, smoke from the Shelly Fire in western Siskiyou county
could result in visibilities dropping below 6 miles this afternoon,
and smoke could settle into the valleys tonight, locally lowering
ceilings and visibility. -Petrucelli/BPN


&&

.MARINE...Updated 800 PM Thursday, July 4, 2024...Winds and seas
will gradually diminish through tonight 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 lingering through this
evening for the outer waters south of Cape Blanco.

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 thresholds.

Conditions improve further over the weekend with sub-advisory
conditions likely for at least the inner waters, and there`s
increasing evidence it will remain below any headlines for the outer
waters as well. Strong high pressure aloft will disrupt the thermal
trough pattern this weekend, 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.

Looking at the start of next week. The thermal trough will likely
develop again over the south Oregon coast, with north winds
increasing on Monday and lasting into at least the middle of next
week. Winds will be strongest south of Cape Blanco during this time.
-Petrucelli

&&

.FIRE WEATHER...Issued 230 pm Thursday July 4th 2024...Heatwave
underway and main concern for this period is weather contribution
to fire danger through the weekend. Initially the combination of
wind and low humidity is a concern for the west side as forecasts
humidities range from the upper single digits to low teens and
winds range from sustained 6-12 mph. Prime area of concern for
Friday afternoon and evening is the low elevation I-5 corridor
from Roseburg to Grants Pass, Medford, and Ashland. More of the
same condition will occur as warmer weather arrives Saturday
except across a broader area. In addition to the abnormally hot
and dry weather being realized in our local forecast grids, the
HDW (Hot Dry Windy) index online is showing the condition as
advertised by the GEFS members to fall within the top 5% of these
events over the 30- year climatology from 1981-2010. In short,
this is very unusual to have the area this hot, dry and (breezy)
for this time of year. So, this occurring across the holiday
weekend was the final consideration. Despite no lightning, there
will be other potential sources of ignition. The heat will
continue into the early part of next week. During that time a
short wave trough is advertised to come up the northern California
coast which is a pattern typically supportive of thunderstorms.
Not seeing the moisture to get us too worried at this point, but
also the solutions are deviating from one another quite a bit so
confidence in strength, track and timing of the low is...low. Keep
an ear out on this development. Stavish

&&

.PREV DISCUSSION... /Issued 234 PM PDT Thu Jul 4 2024/

DISCUSSION...Satellite imagery is showing some smoke associated
with the Shelly Fire now moving toward the northeast, which means
that the thermal trough has indeed relaxed and the winds have
shifted and are not as strong, easterly winds anymore. This is
concurrent with the observations along the coast with Brookings
seeing winds come from the ocean with cooler temperatures. Have
gone ahead and cancelled the heat advisory for the Curry County
coast.

These observations and satellite imagery go far to indicate that
the thermal trough has moved northward leaving us with an area oh
high pressure which will influence our weather for the next
several days. Inland, temperatures are heating up and are already
5 to 10 degrees hotter than they were this time yesterday. This
is going to be part of a long-duration heatwave that begins today
and will likely last through the weekend.

Still, a few of the smaller details have changed somewhat and this
could cause some additional impacts from the weather. The biggest
change to the forecast is that winds are expected to be relatively
calm today, but increase Friday through the weekend as an upper-
level shortwave traverses the ridge. This will not bring any
precipitation nor cloud cover, but it may reduce the potential for
the hottest temperatures slated for Friday and Saturday. For
example there was nearly a 50 percent chance for Medford to tie
it`s all time record high of 115 on Saturday, that went with the
forecast package yesterday, but this has decreased to a 40% chance
today. Still, it is possible, and the weather has already shown to
be difficult to nail the details -- see Brookings which saw a high
temperature of 99 degrees yesterday. Regardless a plethora of
Excessive Heat Warnings and Heat Advisories have been issued (and
have been extended to include southern Siskiyou County).

The other part of this change is less fortunate. It means that
winds will likely be a touch higher. With critical humidities,
this could spell issues for much of the west side as far as fire
weather is concerned. Please see the fire weather discussion for
more details.

This heat wave and associated high pressure will be a long
duration and last through the weekend and likely into early next
week. The ridge of high pressure will shift eastward. This will
bring southwest flow into the area which could increase humidities
over time and gradually decrease temperatures. However, a few of
the ensembles and the deterministic models are showing a low
pressure system traverse up the California coast which, combined
with the southwest flow from before could create thunderstorms for
southern Oregon and northern California. The forecast does not
introduce this quite yet as the NBM is indicating a <5% chance for
thunderstorms late in the week, but this will need to be monitored
as many times these heat waves are broken by a pattern favoring
thunderstorms--which would not be welcome at this point. Keep an
eye to the forecast for updates. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 9 PM PDT Monday for ORZ023>026.

     Red Flag Warning from 4 PM to 8 PM PDT Friday for ORZ616-
     620>623.

     Fire Weather Watch from Saturday afternoon through Sunday
     evening for ORZ616-617-620>624.

     Heat Advisory until 9 PM PDT Monday for ORZ029>031.

CA...Excessive Heat Warning until 9 PM PDT Monday for CAZ080>082.

     Fire Weather Watch from Saturday afternoon through Sunday
     evening for CAZ280-284.

     Heat Advisory until 9 PM PDT Monday for CAZ083>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Friday
     for PZZ350-356-370-376.

     Hazardous Seas Warning until 11 PM PDT this evening for PZZ376.

&&

$$