529
FXUS66 KMFR 021706
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1006 AM PDT Wed Jul 2 2025

.DISCUSSION...No planned changes to the forecast this morning.
Yesterday`s thunderstorms brought another ~1000 cloud-ground (CG)
strikes across the CWA with the concentration in western Modoc,
Siskiyou and southern Klamath County. We are still expecting
another round of thunderstorms this afternoon and evening, but
they should be a little farther east compared to the last couple
of days as the main axis of moisture and instability shifts to the
east. Isolated to scattered storm coverage will impact areas from
southern Siskiyou County (Trinity/Mt Shasta region) northeast
across Modoc into eastern Klamath and Lake counties. 12z SPC HREF
guidance places the bullseye for lightning probability in these
areas as well enhancing our confidence. Some storms will be still
be dry due to elevated cloud bases (and a very dry sub-cloud
layer). Faster storm motions are also likely today as steering
flow increases to around 10-20kt and this may result in lightning
outside rain cores. Currently, a Red Flag warning is in effect
for these areas this afternoon/evening where numerous new fire
starts are likely due to lightning on dry fuels. In addition to
the new fire starts risk, storms this afternoon will have the
ability to produce strong, gusty outflows of 40-60 mph and hail.
Highest wind/hail threat will be across eastern Lake County.
Storms should push out of the region later this evening (probably
around or just after sunset) and most activity should diminish
anyway due to the loss of instability. -Spilde

&&

.AVIATION...02/18Z TAFs...Marine stratus remains along the Oregon
coast late this morning, mostly affecting areas north of Cape
Blanco, but also the south coast south of Pistol River. Expect
reduced ceilings and visibilities for at least another couple of
hours, but, some improvement to VFR should occur in most areas
this afternoon. Expect marine stratus to re-establish along the
coast tonight and continue into Thursday morning with IFR/LIFR.
Marine layer depth could increase enough to bring some clouds to
the Umpqua Valley near the end of the TAF period, but flight
levels are expected to stay at VFR.

Inland areas look to remain at VFR through the TAF period, though
isolated to scattered thunderstorms east of the Cascades could
briefly lower conditions. Any thunderstorms can produce gusty
outflows of 35-55 kt. All areas are expected to see periods of
gusty winds this afternoon, with those winds decreasing into the
evening. -TAD/Spilde

&&

.MARINE...Updated 800 AM PDT Wednesday, July 2, 2025...Gusty
northerly winds and steep seas continue across area waters.
Conditions will gradually improve through today, with steep seas
continuing south of Cape Blanco through tonight. Relativley calm
conditions are expected Thursday into Friday, then the thermal
trough pattern returns with gusty north winds and sttep seas by
Saturday afternoon. -BPN/DW

&&

.PREV DISCUSSION... /Issued 434 AM PDT Wed Jul 2 2025/

DISCUSSION...This morning`s guidance remains in support of
today`s forecast. An upper level low looks to weaken as it moves
inland over California. PWAT values and upper level instability
both generally decrease from what was present on Tuesday.
Thunderstorm chances remain in the forecast for this afternoon
and evening, but are more limited to areas east of the Cascades.
Most guidance focuses on a band from Modoc County up through
central Lake County as having the highest chances (20-30%) for
thunderstorm activity with lesser chances (10-20%) into eastern
Klamath and Siskiyou counties as well as into eastern Lake County.
Activity looks to decrease quickly into Wednesday night.

Outside of thunderstorm activity, a cooling trend is forecast to
bring temperatures to just below seasonal levels by Friday, with a
trend back towards warm and dry conditions into next week.

Please see the previous discussion for more details on the short-
and long-term forecast. -TAD

AVIATION...02/12Z TAFs...Marine stratus remains along the Oregon
coast early this morning, mostly affecting areas north of Cape
Blanco. IFR ceilings and IFR to LIFR visibilities look to continue
until later in the morning. VFR levels are expected along the coast
by the afternoon, with marine stratus rebuilding along the coast
tonight. Some clouds may form in the Umpqua Valley near the end of
the TAF period, but flight levels are expected to stay at VFR.

Inland areas look to remain at VFR through the TAF period. All areas
are expected to see periods of gusty winds this afternoon, with
those winds decreasing into the evening. -TAD

MARINE...Updated 300 AM PDT Wednesday, July 2, 2025...Gusty
northerly winds continue over area waters this morning, but have
fallen below gale gusts. Steep wind-built seas remain for all
waters until this afternoon, when steep seas will be limited to
waters south of Cape Blanco. Conditions improve to below advisory
levels for all waters by Thursday morning. Unsettled seas could
return during the weekend as a thermal trough rebuilds, bringing
gusty northerly winds back to area waters. -TAD

FIRE WEATHER...Updated 230 PM PDT Tuesday, July 1, 2025...
Thunderstorms continue to be the main concern. After nearly 1000
cloud to ground strikes yesterday, we expect to see another round of
thunderstorms this afternoon and evening, mainly along and east of
the Cascades, followed by more thunderstorms Wednesday afternoon and
evening, again mainly east of the Cascades. A Red Flag Warning
remains in effect for FWZs 280, 281, and 284 today, but areas east
still remain in moderate fire danger, so no warnings have been
issued there for today. However, these areas will be going to high
fire danger at midnight tonight, so a Red Flag Warning has been
issued for FWZs 284, 285, 624, and 625 due to the next round of
lightning Wednesday afternoon and evening.

We picked up a few more lighting strikes in Klamath and Lake
counties this morning, but conditions have calmed over the last few
hours, with Radar showing only showers as of this writing. We still
expect thunderstorms to develop in just a few more hours, aligning
with max heating this afternoon and evening. Storms today should
behave much like yesterday, with storms early this afternoon perhaps
not producing much of any precipitation to start, then the chance
for wetting rain could increase mid to late this afternoon and
evening. The main reason for the increase chance in wetting rain is
steering winds will be light and high moisture content throughout
the column of the atmosphere. Thus, storms will be slow movers
providing the bigger window of opportunity for storms to produce
locally moderate to heavy precipitation. However, that does not mean
that all storms will produce wetting rain. Some could also produce
little to no rain, because of the dry sub layer below.

Keep in mind, lightning strikes outside of the precipitation cores
are possible. Due to the prolonged period of dry and warm to hot
weather, lightning efficiency will be high to very high for fire
starts. We also have to be mindful of gusty and erratic outflow
winds near and away from the core of thunderstorms.

A few models suggest that some isolated thunderstorms could continue
into the late evening or overnight hours, but as is typical for
these types of situations, confidence on this is low and it will be
something that we`ll need to monitor as it occurs.

It should be noted that any residual cloud cover from nightime or
morning convection, much like we have seen across some of the area
east of the Cascades today, could easily reduce thunderstorm chances
by blocking solar heat and therefore reducing instability. This is
not easily predictable until it occurs, and would be the primary
reason the forecast may not turn out as expected.

Although the trough responsible for these past several days of
convection will kick off to the east by Wednesday night, the concern
for thunderstorms could carry over into Thursday as an upper trough
approaches the area from the west. The best chance for storms
Thursday would be along and around the Warners in Lake and Modoc
counties. -BPN

PREV DISCUSSION... /Issued 425 PM PDT Tue Jul 1 2025/

DISCUSSION...Low pressure near the SF Bay area continues to send
moist, southerly flow northward into NorCal and SW Oregon.
Instability is increasing this afternoon due to daytime heating
and we`re seeing thunderstorms initiate now. These will increase
in coverage through the afternoon and into this evening. As
mentioned earlier today, steering flow for storms is on the weak
side, so storm motion should be slow (5-15 mph), in a general SE
to NW fashion, but with more of a bending toward the SW in
southern portions of the forecast area (Siskiyou County). Storms
that initiate farther north along the Cascades or in the Highway
97 corridor in Klamath County should propagate more toward the
north. Focus for lightning will be in Siskiyou and western
Modoc/Lake Counties, but also northward into Klamath County and up
the Cascades through about 9 pm or so this evening. Lightning
risk isn`t negligible west of the Cascades, but convective
inhibition of 100-300 J/KG should be a limiting factor as to just
how much can really get going and how far west. As it stands,
there is a low probability (~20% chance) of a thunderstorm nearby
the Rogue Valley late this afternoon/evening, but storms are more
likely to affect eastern portions of Jackson County and remain in
the Cascades/Foothills and closer to Butte Falls/Prospect. Main
storm risks through this evening will be strong, gusty outflow
winds due to dry sub-cloud layer and DCAPE in the 1000-1500 J/KG
range as well as small hail and numerous cloud to ground flashes.
With more lightning expected, expect new fire ignitions. Fire
weather discussion below will cover the specifics.

After sunset this evening, the atmosphere will begin to stabilize
and thunderstorms will transition to showers, gradually ending
overnight into Wednesday morning.

The low that is moving into California will continue to move
slowly inland Wednesday afternoon south of Lake Tahoe. This should
bring more of WSW flow aloft from the Cascades westward to end
the risk of lightning in those locations. It will also result in
some gusty afternoon upvalley NNW breezes (15-25 mph) and a drying
air mass. However, the trough axis to the north of the low will
still move through areas east of the Cascades. As such, we are
expecting another round of showers and scattered thunderstorms
over there, primarily from eastern Klamath/Siskiyou counties to
Lake and Modoc counties (just east of Klamath Falls and also
probably just east of Mt. Shasta, though instability could cause
one or two to pop up back to northern Trinity County). A Red Flag
Warning has been issued and should also be detailed in the Fire
Weather section.

Thursday through the 4th of July, another couple of short wave
troughs will swing through in westerly flow aloft. The first will
push onshore into NorCal late Thursday and Thursday night with the
second moving quickly into Oregon behind it on Friday.
Instability and moisture will remain highest in NE Cal and areas
east of the Cascades. So, we have maintained a chance of showers
and thunderstorms for portions of Klamath/Lake and Modoc counties.
It should remain dry though west of the Cascades. Could be some
marine cloudiness each morning/night near the coast. Overall,
with cooler air aloft, most areas should see high temperatures
those days within a few degrees of normal. This means highs in the
low to mid 80s for the valleys west of the Cascades and in the
upper 70s to low 80s over the East Side.

We should be between systems on Saturday. Temperatures edge back
to slightly above normal levels. However, yet another disturbance
will move toward the area. Moisture and instability are modest at
best with this system, so most guidance is not showing any
precipitation. But, we may need to adjust should future model
runs increase these parameters.

Next week, models show a trough (weak closed low?) hanging around
Monday/Tuesday near/just off the NW California coast, but then
the Four Corners high strengthens and retrogrades mid-late week.
This should bring a return of hotter weather with NBM guidance
showing mean high temps in the upper 90s and lower 100s for the
valleys west of the Cascade. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ624-625.

CA...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ284-285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Thursday
     for PZZ356-376.

     Small Craft Advisory until 11 AM PDT this morning for PZZ350-
     370.

&&

$$

MAS/BPN/TAD