NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 15, 8:57 PM PST, 3 hours 3 minutes earlier.
Area forecast discussion, Aug 15, 8:57 PM PST, 3 hours 3 minutes before
Area Forecast Discussion
National Weather Service Medford OR
957 PM PDT Tue Aug 15 2023
.UPDATE...Updated the aviation section.
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.AVIATION...16/06Z TAFs...Smoke and haze, mainly originating from
the Bedrock Fire in eastern Lane County, will persist. Conditions
will mainly remain VFR, but it could reduce visibility at terminals,
especially at Klamath Falls late tonight into Wednesday morning.
The other main potential impact is the thunderstorm potential. An
increase in activity is anticipated for Wednesday afternoon,
especially across Siskiyou, Klamath, Lake, Modoc, and Jackson
counties. This includes Klamath Falls and Medford. Though activity
will decrease after sunset, there is a continued slight chance of
thunderstorms through Wednesday night.
Lastly, the IFR marine layer is thicker and more extensive tonight,
and will be most widespread in coverage north of Cape Blanco. But,
it is still expected to make relatively little progress inland, up
to several miles into the Coquille Valley (including North Bend).
The stratus is forecast to dissipate after sunrise Wednesday morning.
-DW
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.PREV DISCUSSION... /Issued 840 PM PDT Tue Aug 15 2023/
DISCUSSION...259 cloud to ground lightning strikes have been
recorded in the past 24 hours with most occuring in Siskiyou and
Klamath County; and still counting. There were no record
temperatures set today. However, temperatures were within a few
degrees, and mostly by chance, the records for tomorrow are a
little lower for a few of our sites, with afternoon tempratures
almost the same, so there is still a chance for more records from
this heat. Accourdingly, the excessive heat warnings and heat
advisories remain in place across the region.
As well as the heat, lightning from thunderstorms is expected
again. A red flag warning is out as the new lightning can, and in
a few places has already, produce new wildfires on the landscape.
Chances are maximized at 30-35% in a triangle roughly from Crater
Lake, to the Scott Valley, to Medicine Lake. Coverage of
thunderstorms in this area will probably be scattered in nature,
with more isolated coverage elshwere. Like today, even modestly
strong cells are expected to be well electrified, but look to the
strongest cells for the most cloud to ground strikes.
Speaking of strong thunderstorms, two cells today were just under
severe margins for hail. the environment Wednesday looks equally
condusive to a strong storm or two, along the Cascades and west of
I-5 in Siskiyou County. The envirnment for severe storms grows on
Thursday, with the probability of a thunderstorm increasing to
40-50% across NorCal, and about a 10% chance of on of these storms
becoming severe over any area in NorCal or from the Cascade Crest
east in Oregon.
-Miles
MARINE...Updated 800 PM PDT Tuesday, August 15, 2023...Steep seas
will continue through tonight. Moderate to advisory strength north
winds are expected to return tonight. The end result is a Small
Craft Advisory for all of the waters through at least Friday. Winds
will increase Friday, but some uncertainty remains to exactly how
strong those winds speeds will be Friday afternoon/evening. Either
way, this will produce steep to very steep seas across all of the
waters, but an area of gales south of Cape Blanco may develop.
Winds are currently forecast on Saturday to be near the peak values
from Friday, and seas may remain steep to very steep through the
weekend. For perspective, areas south and southwest of Cape Blanco
will have a probability of 25% for *sustained* winds to exceed 34
knots, and a probability of 75% for *gusts* to exceed 41 knots.
Furthermore, there is a 35% probability of exceeding 48 knots for
gusts. Current forecast shows sustained winds around 30 knots and
gusts around 40 knots for Friday afternoon/evening. In other words,
we are likely going to see Small Craft Advisory conditions now
through the weekend, but we may need to strongly consider Gale force
winds and very steep seas on Friday given the probability of gusts
being 40 knots or greater.
-Guerrero/DW
FIRE WEATHER...Updated 200 PM PDT Tuesday, August 14, 2023...The
two big weather concerns for the forecast period will be the extreme
heat expected through late this week and the thunderstorm potential
also continuing through the week.
A very hot air mass will be over the region this week and several
days of 100+ degrees is anticipated west of the Cascades with mid to
upper 90s east of the Cascades. Although high temperatures will
trend "slightly" less hot compared to yesterday, still expect very
hot temperatures today. These unusually hot temperatures will
continue through Thursday. Although conditions may get close for a
brief time, we aren't expecting critical RH/wind conditions today as
minimum RHs trend slightly higher, temperatures trend slightly lower
and monsoonal/tropical moisture increases in the region...which
leads us to the thunderstorm concerns...
This afternoon and evening expect isolated to scattered
thunderstorms, mainly from the Cascades east and Siskiyous south.
Isolated thunderstorms are also possible in southeast Jackson County
today. The favored area for scattered thunderstorms today continues
to be from the Fremont-Winema National Forest and westward into the
Cascades. A Red Flag Warning for abundant lightning on dry fuels
remains in effect for FWZ 617/623/624 for this afternoon and
evening.
Scattered thunderstorms are possible over a broader area on
Wednesday, and a Red Flag Warning has been issued to cover this
threat in zones 624/623/621/280/281/284/285. West of the Southern
Oregon Cascades, a slight chance for thunderstorms is also expected
on Wednesday, including in FWZs 617, 620 and 622.
Storms will begin as a mix of west and dry, then transition wetter
late today and Wednesday. Thursday into the weekend, the chance for
isolated to scattered thunderstorms continues. Despite storms
transitioning to wet, strikes outside of storm cores remain a
concern. Gusty outflow winds are also a concern, especially for
today as storms may start out on the dry side, then become wetter
late in the day. Gusts of 30-40 mph will be possible with any
outflow winds. -CC/BPN
PREV DISCUSSION... /Issued 635 PM PDT Tue Aug 15 2023/
DISCUSSION...An upper level ridge remains over northern California
and southern Oregon, bringing generally stable conditions through
the rest of the week. Temperatures will remain significantly above
average today and Wednesday, with the Oregon coast looking to be in
the mid 70s to low 80s. West side valleys will be in the mid-100s,
and east side areas will see temperatures in the mid 90s.
Overnight temperatures will not offer much relief for west side
valleys, with nighttime lows reaching the low 70s while usual lows
are in the mid 50s. This is important to consider because the
temperature at any point in the day will be about 10 degrees warmer
than usual. Outdoor activity that might be pleasant on a normal
evening might still be hazardous tonight and Wednesday night.
There are possibilities of convective activity this evening from
eastern Douglas county to northwestern Lake County. CAPE values of
300-500 J/kg and about 1 inch of precipitable water could provide
enough uplift and moisture for some isolated showers and
thunderstorms. The forecast for tonight has 25% chances for activity
in the Douglas-Klamath-Lake area and 15% chances across Siskiyou and
Modoc counties. There will be similar chances tomorrow, with a
slight (15%) chance extending into parts of Jackson and Josephine
counties as well.
A Pacific low pressure system will help to lower temperatures
starting Thursday afternoon, with a cooling trend expected to
continue through the weekend. Southerly flow from the system will
bring extra moisture over the area, bringing moderate chances (25-
40%) of precipitation across northern California and areas east of
the Cascades.
In the long term, an upper level trough looks to drop down from the
north and pass over the area late in the weekend. How this trough
and the existing low pressure system interact will determine if and
where any further precipitation happens. Beyond the trough's
passage, high pressure is expected to develop over the central
United States and rebuild an upper level ridge. The exact
development of that ridge is uncertain, but National Blend of Models
outcomes only has a 20% chance of temperatures later next week. So
warming is expected, but triple digits are currently unlikely.
-TAD
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM to 11 PM PDT Wednesday for ORZ621-623-
624.
Excessive Heat Warning until 11 PM PDT Thursday for ORZ021>024-
026-028.
Excessive Heat Warning until 11 PM PDT Thursday for ORZ025-027.
Heat Advisory until 11 PM PDT Wednesday for ORZ027-030-031.
Red Flag Warning until 11 PM PDT this evening for ORZ617-623-
624.
Heat Advisory until 11 PM PDT Thursday for ORZ028-029.
CA...Excessive Heat Warning until 11 PM PDT Thursday for CAZ080>082.
Red Flag Warning from 2 PM to 11 PM PDT Wednesday for CAZ280>282-
284-285.
Heat Advisory until 11 PM PDT Thursday for CAZ084-085.
PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Friday
for PZZ350-356-370-376.
&&