456
FXUS66 KMFR 070556
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1056 PM PDT Sun Jul 6 2025

...Updated AVIATION discussion for 06Z TAFs...

.DISCUSSION...

An upper level low is settled right off the central California
coastline this afternoon. It`s not showing up on visible
satellite, although the mid level water vapor shows the low
fairly well. This suggests that it is pretty dry at the moment
with little to no cloud cover except for the lower marine stratus.

The main weather feature tonight will be the typical marine fog
filling into the coast overnight and into the morning. The MOS
bulletins were hinting at some stratus and low fog, so we decided
to put some fog into the weather forecast along the coast.

By Monday, isolated dry thunderstorms are the main concern,
mainly around the northern California and southern Oregon border
based of the latest ensemble guidance. The ECMWF ENS members have
been fairly consistent painting this area with weak convection.
the SPC HREF has now jumped in and shows a 10-20% chance of some
cloud to ground lightning around the California and Oregon state
border. Coverage looks isolated at this time and this forecast
could completely miss with no thunderstorm activity.

Another concern on Monday will be the heat around the Rogue
Valley. Latest forecasts have temperatures around 102 degrees with
lows in the middle 60`s Monday night. The heat risk algorithm says
there are small areas of high heat risk around Medford. However,
considering the region as a whole, the heat risk appears more
moderate. Therefore, we opted out of issuing a heat advisory this
afternoon. The brief nature of the heat was also considered. Cloud
cover from thunderstorms could mix things up and keep
temperatures a few degrees lower.

As for Monday night storms, they`ll have a very low chance(~5%)
of persisting overnight. No data really shows this at this time
and it`s based on some environmental data in forecast soundings.
More specifically, steeper lapse rates between 300mb and 500 mb
with moisture arriving in the 800mb to 900mb layer overnight.
There is still plenty of convective inhibition at this time, but
it could break or simply not be there.

Storm coverage will shift farther north on Tuesday as the low
center moves farther north into north eastern California. Some
storms could still develop in other areas in northern California,
but the probabilities of that occuring are lower.

Finally this low will depart the region mid day Wednesday and has
sped up compared to 24 hours ago. The result should be less
thunderstorm coverage for our area. A few storms could still pop
up east of the Cascades Wednesday afternoon.

Beyond Wednesday, the forecast pattern looks rather unsettled with
deeper north west flow aloft, although flow closer to the surface
looks more north and appears to turn north east at times.
Temperatures do cool down down to normal by Wednesday and
Thursday. However, temperatures are anticipated to warm back up
again around Friday. -Smith

&&

.AVIATION...07/06Z TAFs...Marine stratus has brought LIFR ceilings
to North Bend, with chances of ceilings reaching into Brookings as
well. LIFR visibilities may develop overnight as well. Conditions
along the coast look to clear on Monday afternoon as gusty northerly
winds develop. Those winds ease and marine stratus is forecast to
return early Monday evening.

Inland areas will remain at VFR levels through Monday morning.
Slight chances for isolated thunderstorms (10-15%) will be present
over Siskiyou and Klamath Counties in the afternoon and evening.
Active cells may bring lightning, locally heavy rainfall, and gusty
and erratic winds. Thunderstorm activity looks to decrease into
Monday night. -TAD

&&

.MARINE...Updated 245 PM PDT Sunday, July 6th 2025...Gales will
persist south of Port Orford through the overnight hours. Steep
seas and hazardous conditions will develop beyond shore into the
outer waters. Conditions will still remain hazardous to smaller
crafts through Monday. Conditions briefly improve Tuesday into
Wednesday.


&&

.FIRE WEATHER...Updated 200 PM PDT Sunday, July 6, 2025...An
upper ridge will be in place over the area this afternoon into
Monday, while low pressure aloft settles to near or just off the
coast of Northern California. Expect dry conditions area wide with
temperatures trending higher and humidity lower through late
afternoon. Gusty north winds will affect the coast, while typical
late afternoon/evening winds are expected over the interior. A few
fair-weather cumulus or even a buildup or two out in Modoc County
near the Warners are possible this afternoon, but thunderstorm
probabilities are generally less than 5%. The dry air mass will
bring poor to moderate upper slope/ridge humidity recoveries
tonight. Heat builds further Monday and Tuesday (esp Monday) with
high temperatures in the mid to upper 90s and even some readings in
the West Side/NorCal valleys exceeding 100F.

With the low positioned off the California coast, just west of San
Francisco Bay, this is a similar set up to the pattern that
brought convection to the area for several days last week. One
(fairly large?) difference though is that the deep southerly flow
of moisture available during the last event appears to be less
with this one and, as such, should be a limiting factor for
convection. Even so, we do expect some thunderstorms to develop
and along with that, the potential for cloud to ground lightning
and gusty outflow winds. Latest guidance continues to show
isolated to widely scattered thunderstorms (15 to 35%) beginning
Monday pm/eve and continuing through Tuesday afternoon/evening as
the low edges closer to the coast. Areas from NorCal up the
Cascades and across western Modoc into western Klamath County are
the favored areas for isolated thunderstorms Monday
afternoon/evening. Model PWs with this potential convection
continue to be shown around 0.50-0.75" (esp southern and eastern
areas, where values could be below 0.50"). So, any high-based
convection that does develop might not produce any rainfall. For
this reason, we`ve indicated "dry" thunderstorms in the official
forecast. It isn`t totally out of the question either that a
thunderstorm drifts off the terrain into the southern Rogue Valley
Monday evening (probability around 10%). Elevated instability
persists Monday night across portions of NW Cal and even the
mountains of SW Oregon (coast ranges). While probabilities are low
(generally around 15% or lower), we have seen in the past,
nocturnal activity that migrates toward or even off the coast in
these situations. Don`t be surprised to hear rumbles of thunder
Monday night in those areas.

Then, on Tuesday, Cascades and East Side north of the Sprague River
Valley and NW of Abert Rim have the highest probabilities of
thunderstorms (25-35%). Since the lightning probabilities have
increased up across northern sections of FWZs 624/625, we have
issued a Fire Weather Watch for those locations from 21Z Tuesday to
06Z Wednesday (2-11 pm PDT) for abundant lightning on dry fuels.
Models show the convection beginning in our area, then lifting north
into Deschutes County, so there are some uncertainties in quantity
of lightning prior to the storms exiting to the north.

By Wednesday, an upstream "kicker" trough will cause the low off the
Cal coast to move onshore, and fairly quickly. Some guidance now
pushes the trough axis east of the area by peak heating so that the
atmosphere stabilizes and thunderstorms are no longer a risk.
However, some slower solutions also still exist and, as such, we
have maintained a slight chance of thunderstorms across the far
East Side (Lake County) Wednesday afternoon/evening. We`ve removed
the chance in NorCal.

Following the trough passage, drier westerly flow aloft moves in
Wednesday night and the thunder risk ends. Expect slight cooling
Wed/Thu over inland areas, but northeast winds provide warmer
weather to the south coast. A return of hotter weather is expected
Friday into the weekend with fairly typical late-day summertime
breezes, but also dry afternoon humidity and poor to moderate RH
recovery at night. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ624-625.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 AM PDT Monday
     for PZZ350-356-370-376.

     Gale Warning until 8 AM PDT Monday for PZZ356-376.

&&

$$