467
FXUS66 KMFR 071746 AAA
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1045 AM PDT Sun Jul 7 2024

Updated Aviation Discussion.

.SHORT TERM...A strong high pressure ridge is centered over the
area. This ridge will remain in place into Tuesday, then the
ridge axis gradually shifts eastward as a weak upper trough moves
into the region from the northwest.

This pattern is bringing continued very hot and very dry
conditions to inland areas and warmer than normal temperatures as
the coast. Near record and record high temperatures along with
unusually warm overnight temperatures are expected through
Tuesday. This is a multi-day heat wave with dangerously hot
conditions. High temperatures today and Monday will be similar or
slightly lower to yesterday. This heat continues on Tuesday with
temperatures trending only slightly less hot (by 1-2 degrees).
Excessive heat warnings remain in place for inland areas west of
the Cascades through Tuesday and heat advisories are in place for
areas east of the Cascades. Please see the NPWMFR and the previous
discussion below for details.

Additionally, today there will be breezy to gusty late day winds
across western and central potions of the area. This combined with
extreme heat and dryness will result in elevated fire weather
conditions. Red flag warnings (RFWMFR) are in place today. Please
see the fire weather discussion below for more details.

On Tuesday, there will also be a weak shortwave that moves up from
the south. Currently, models show little in the way of moisture
with this disturbance to support any thunderstorm development. We
will continue to monitor this period for any potential changes.

On Wednesday, as a shortwave upper level trough moves into the
Pacific northwest north of the area, the ridge will weaken
slightly. This will result in less hot (but still well above
normal) temperatures across inland areas. With the trough nudging
into the PacNW, expect an increase in west to northwest winds in
the afternoon/evening, especially for areas east of the Cascades.



&&

.AVIATION...07/18Z TAFS...Patchy low clouds are expected to remain
off the coast today, then areas of IFR/LIFR are forecast to move
onshore tonight and early Monday morning. These conditions will
mainly affect areas north of Cape Blanco and from Brookings south.
Elsewhere, VFR is expected through the TAF period.
-CC


&&

.MARINE...Updated 800 AM Sunday, July 7, 2024...Gusty northerly
winds continue to build steep seas in waters south of Cape Blanco. A
thermal trough will continue to bring these northerly winds to start
the week, with a Small Craft Advisory remaining for waters south of
Cape Blanco through Monday evening. Steep seas could continue
through Tuesday as well for these southern waters, with current
outcomes right on the edge of Advisory thresholds. The existing
Advisory will not be extended tonight, but future data may bring
more confidence in the expected seas for Tuesday and into Wednesday
morning.


The thermal trough looks to strengthen starting Wednesday afternoon,
bringing chaotic seas that would continue into the weekend under
current guidance. Long-term guidance has good chances (40-70%) for
seas over 12 feet south of Cape Blanco on Thursday and Friday.
Periods of gale gusts are showing up in guidance for this time as
well. Winds start to calm on Saturday, but unsettled seas would
likely persist through the end of the weekend. -TAD


&&

.PREV DISCUSSION... /Issued 515 AM PDT Sun Jul 7 2024/

DISCUSSION...Excessive Heat Warnings remain in effect west of the
Cascades to the Coast Range, with a Heat Advisory East of the
Cascades, both in effect through Tuesday evening.

We have another couple of days, today and Monday, with extremely
hot and extremely dry conditions quite similar to those of
yesterday. For most of our area Tuesday, will also still be quite
similar. Thus, another 3 days of record breaking heat. The extent
of the changes Monday night into Tuesday will be most apparent at
the coast with areas of night and morning low clouds and fog.
Also of note will be a subtle reduction in the heat of a few
degrees west of the Cascades. Lastly, the increase in moisture
aloft on Tuesday has a chance of being just sufficient for a few
cumulus clouds to form over the higher terrain of western Siskiyou
and northern Klamath counties. The aforementioned situation is
being driven by a strong ridge over the west coast. By Tuesday,
the axis of the ridge and peak area of its strength is expected to
shift east...to southern California, Nevada, and eastern Oregon
into Idaho. A weak shortwave trough off the coast will bring the
modest, barely perceptible increase in moisture for Tuesday.
During these next few days, most of the area will have afternoon
and evening northwest to north winds near their normal breezy
strength of around 8 to 15 mph with peak gusts of 15 to 25 mph.

Tuesday night through Friday night separates into its own phase
of weather, still influenced by the ridge (which will be centered
in the Great Basin), but with the added influence of broad but
weak troughing from western Canada to the far northern California
coast. For this most lengthy portion of the week, hot temperatures
and low humidity will not be as extreme as earlier in the week.
But, there will be little day-to-day change with temperatures
about 10 degrees cooler on the west side and 5 degrees cooler on
the east side in comparison to our current heat wave...which will
still be around 10 to 15 degrees above normal. While temperatures
will trend in a favorable direction, afternoon and early evening
winds will trend stronger, especially east of the Cascades, with
10 to 20 mph winds and gusts to 30 mph expected to be the general
condition. More of a northerly rather than uniformly
northeasterly flow at the coast will continue night and morning
low clouds and fog, mainly north of Cape Blanco...with a weaker
but still present Chetco effect keeping Brookings high
temperatures in the mid 70s to mid 80s.

Beyond Friday night, model uncertainty increases regarding the
extent of a further eastward shift of the ridge and also the
extent at which we may see our upper level flow back from
westerly to southerly, with a possible increase in mid-level
700-500 mb moisture. Though not the highest probability scenario,
as early as Saturday afternoon, conditions could become conducive
to the development of thunderstorms. If this cluster of model
solutions were to develop, the most likely scenario would first
result in an unstable airmass from the Sierra Nevada northward
into Modoc and Lake counties. A broader risk could develop as
early as Sunday/Day 8. Obviously, we will be watching closely in
the coming days for reason to introduce any thunderstorm risk into
the forecast.

AVIATION...07/12Z TAFS...Marine stratus is creeping towards North
Bend this morning, with a brief period of MVFR ceilings and
visibilities possible early this morning. Anything that does develop
will clear out before noon. Marine stratus looks to return later
tonight into early Monday morning.

Other areas will remain at VFR levels through the TAF period under
stable conditions. -TAD

MARINE...Updated 200 AM Sunday, July 7, 2024...Gusty northerly
winds continue to build steep seas in waters south of Cape Blanco. A
thermal trough will continue to bring these northerly winds to start
the week, with a Small Craft Advisory remaining for waters south of
Cape Blanco through Monday evening. Steep seas could continue
through Tuesday as well for these southern waters, with current
outcomes right on the edge of Advisory thresholds. The existing
Advisory will not be extended tonight, but future data may bring
more confidence in the expected seas for Tuesday and into Wednesday
morning.

The thermal trough looks to strengthen starting Wednesday afternoon,
bringing chaotic seas that would continue into the weekend under
current guidance. Long-term guidance has good chances (40-70%) for
seas over 12 feet south of Cape Blanco on Thursday and Friday.
Periods of gale gusts are showing up in guidance for this time as
well. Winds start to calm on Saturday, but unsettled seas would
likely persist through the end of the weekend. -TAD

FIRE WEATHER...Issued 430 AM Sunday July 7, 2024...Heatwave
underway and main concern for this period remains heat, winds, low
humidities and unstable conditions contributing to fire danger
early this week. The combination of wind and low humidity is
expected to reach critical conditions for inland areas along and
east of the Interstate 5 corridor again today. Forecast humidities
range from the upper single digits to low teens and winds range
from sustained 6-12 mph with gusts to around 20 mph. A red flag
warning in in place today for portions of zones 616, 617, 620,
621, 622 and 623, 624, and 280 for today.

The main difference from Saturday is that winds are forecast to
be weaker east of the Cascades. Given the on-going holiday weekend,
despite no lightning in the forecast, there will continue to be
conditions favorable for the rapid spread of any new or existing
fires. A Red Flag Warning remains in effect for Sunday for zones
616, 617, 620, 621, 622, 623, and 624 in Oregon and zone 280 in
California. Brief or near critical conditions may also occur in
281 and 282.

Heading into Monday, a slight nudge lower of temperatures by a
couple degrees, and similarly nudge lower of wind speeds is enough
to make additional west side Red Flag conditions more of a
borderline scenario. West side conditions will be mostly borderline
again Tuesday, with similar low-end-breezy afternoon and evening winds
with the exception a more impactful nudge higher in minimum
relative humidity values from the coast across Douglas County. The
same setup bringing the slight cooling and higher coastal moisture
for Tuesday may also bring a few afternoon cumulus buildups for
western Siskiyou and northern Klamath counties.

By midweek, expect the edge to be taken off of the heat. Though
no longer as extreme, expect temperatures to still be well above
normal and accompanied by slightly stronger afternoon/evening
winds. Instability with an accompanying risk of thunderstorms
could develop east of the Cascades as early as Saturday.

-BPN/DW

&&

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

     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ616-617-620>624.

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

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

     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ280.

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 9 PM PDT Monday
     for PZZ356-376.

&&

$$

CC/CC/CC