671
FXUS66 KMFR 051554
AFDMFR

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

.DISCUSSION...Clear skies continue today, and this will aid the
return of dangerous heat this afternoon along with ridging. West
side valleys are still on track to see triple digit highs this
afternoon. The heat products (Excessive Heat Warnings west of the
Cascades and Heat Advisories east) continue through Monday. The
day will be spent reviewing the heat into early next week as these
products may need to be extended.

A Red Flag Warning will be in effect from 4 PM to 8 PM this
afternoon for strong, gusty winds and low relative humidities. This
will be in effect in the Rogue Valley and southern Umpqua Basin into
Roseburg. Please review the previous forecast discussion for further
forecast information. -Hermansen

&&

.MARINE...Updated 815 AM Friday, July 5, 2024...Northerly winds
under a persisting thermal trough continue to bring wind-driven
steep seas to all waters. While seas are just at Advisory
thresholds, the wide area and duration of the continuing hazard
supports a Small Craft Advisory through Saturday at 11 PM. Some
local areas of Advisory-level seas may continue at 40-60 nm from
shore past this time and will continue to decrease into early Sunday
morning.

The brief period of sub-Advisory seas ends 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 Monday
night. Long-term probabilistic 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/Hermansen


&&

.PREV DISCUSSION... /Issued 446 AM PDT Fri Jul 5 2024/

..Updated AVIATION discussion...

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...05/12Z TAFS...Visibilities along the Oregon coast are
hovering at MVFR this morning, although cloud cover isn`t building
in. These lower visibilities should clear out quickly this morning.
Visibilities are also a concern over western Siskiyou County, where
the Shelly Fire may cause some locally reductions.

Other areas will stay at VFR through the forecast period. -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.

&&

$$