832
FXUS66 KMFR 051100
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
400 AM PDT Fri Jul 5 2024

.DISCUSSION...After due consideration, have continued with the
inherited set of hazards. After one more new set of data, expect
the day shift to prominently consider whether to extend the
Excessive Heat Warning and Heat Advisory (now in effect through
Monday evening) for another 24 hours into Tuesday, and whether to
upgrade the Fire Weather Watches currently in effect for Saturday
afternoon through Sunday evening. The higher probability is for
the latter, with a majority of models indicating a slight
strengthening trend for afternoon winds from today through Sunday,
while the peak of the heat wave still looks to occur on Saturday,
then nearly as hot on Sunday.

Three max temperature records were broken Thursday. The broken
records were 105 at Medford, 98 at Mt. Shasta City, and 104 at
Montague. More records are expected to be broken as the heat wave
continues into next week. Though Brookings very likely saw their
peak of the heat a couple of days ago, at 98 on Wednesday, a
weaker northeast flow will continue much above normal high
temperatures through at least Saturday, and possibly through
Monday.

Besides the heat, low humidity, and gusty winds, the natural
concern is to be vigilant for any risk of thunderstorms. At this
time, that risk looks extremely small with weak instability, but
especially due to a lack of mid-level 700-500mb moisture available
in the region, perhaps a modest uptick of moisture on the east
side by Wednesday afternoon. There is also a contingent of
ensemble members indicating some instability and increase of
available moisture on the east side with a shift to a
southwesterly flow aloft late next week around Day 7/Friday and/or
Day 8/Saturday.

&&

.AVIATION...05/06Z 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 and portions of the coast,
including North Bend early Friday morning resulting in IFR
ceilings. But, confidence is not high enough to include this in
the TAF.

Meanwhile, smoke from the Shelly Fire in southwestern Siskiyou
county could result in visibilities dropping below 6 miles in
southwest and south central Siskiyou County. -BPN/DW

&&

.MARINE...Updated 200 AM Friday July 5, 2024...Northerly winds
under a persisting thermal trough continue to bring wind-built
steep seas to all waters. While seas are just at Advisory
thresholds, the wide area and duration of this forecast supports
extending a Small Craft advisory through Saturday evening at 11
PM. Some local areas of Advisory-level seas may continue at 40-60
nm from shore past this time and will continue calming into early
Sunday morning.

The brief period of sub-Advisory seas ends on Monday morning as a
thermal trough rebuilds in waters south of Cape Blanco. The wind-
built waves look to remain at small craft levels with possibly
small areas of very steep and hazardous seas south of Brookings on
Tuesday. Long- term probabalistic guidance currently shows a
50-70% chance for waves over 12 feet by Thursday as well as as a
25% chance for areas of gale force gusts south of Gold Beach on
Thursday evening. The confidence is not nearly approaching high
enough to make a forecast for conditions nearly a week out, but at
the very least active seas do look to return and remain for much
of next week.
-TAD

&&

.FIRE WEATHER...Issued 230 AM Friday July 5, 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 similar condition will then occur with slightly
hotter, slightly drier, and slightly stronger winds expected
Saturday 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. Compared
to Saturday, this includes what looks to be a further very slight
strengthening of afternoon winds on Sunday with conditions almost
as hot and dry. During Monday, a short wave trough is advertised
to come up the northern California coast which is a pattern
often supportive of thunderstorms. But, not seeing the moisture
to get us 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/DW

&&

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

     Red Flag Warning from 4 PM this afternoon to 8 PM PDT this
     evening 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
     Saturday for PZZ350-356-370-376.

&&

$$