937
FXUS66 KMFR 080442
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
942 PM PDT Mon Jul 7 2025

.DISCUSSION...Made a quick update this evening to extend
thunderstorm chances farther west into Curry and Josephine
Counties through this evening. Strong storms, with a few severe in
the mix, moved through the area this evening. Storms first
started in southeast Siskiyou County, then an outflow boundary
from the first severe storm just east of Montague, CA kicked off
a line of storms that moved northward into Jackson/Josephine
Counties. The Montague Airport recorded a peak wind of 47 mph
with the initial gust front that kicked off those additional
storms. Here at the Medford airport a peak gust of 49 mph was
recorded when a thunderstorm passed right over the office along
with a 0.25" of rain with this storm.

The coverage of showers/thunderstorms has greatly diminished over
the last hour or so, but activity continues over portions of
Josephine and Curry County as well as northern Klamath County north
of Chiloquin. For the most part, this activity should continue to
dwindle into the overnight hours. However, there is a low pressure
offshore of California that is responsible for this thunderstorm
activity, and as it remains in the vicinity, nocturnal thunderstorms
aren`t entirely out of the question tonight. Chances are generally
less than 15%, and with how the atmosphere was just turned over with
today`s activity, confidence is fairly low in any nocturnal activity
tonight. Thunderstorm chances do return Tuesday afternoon, mainly
across northern Klamath/Lake Counties, and more details can be found
on this in the previous discussion below. /BR-y

&&

.AVIATION...08/00Z TAFs...Cumulus clouds are developing over the
southeast portion of the coverage area. As of this discussion,
lightning has been limited to the Siskiyou/Modoc border. Slight
thunderstorm chances (10-15%) are present over Siskiyou, Jackson,
and Klamath counties as well as western Modoc and Lake Counties.
Activity is generally expected to be isolated and dry. Lightning
strikes and gusty, erratic winds may be present near developed
cells. Thunderstorms could return to western Siskiyou and east side
areas on Tuesday afternoon and evening.

Marine stratus has developed along the Oregon coast but has not yet
settled over North Bend or Brookings. This layer is expected to
affect those terminals this evening, bringing IFR or LIFR ceilings
and visibilities. While visibilities look to clear late Tuesday
morning, low ceilings could stay in place through the TAF period.

Other inland areas are expected to remain at VFR levels through the
TAF period, with normal diurnal winds. -TAD

&&

.MARINE...Updated 945 PM PDT Monday, July 7, 2025...A weakening
thermal trough will maintain conditions hazardous to small craft
through late tonight. Then conditions improve for all areas for
Tuesday and Wednesday. The thermal trough returns for the latter
half of the week, bringing the return of gusty north winds and
associated steep to very steep wind driven seas.

&&

.PREV DISCUSSION... /Issued 433 PM PDT Mon Jul 7 2025/

DISCUSSION...Temperatures will be warm this afternoon with
temperatures already in the 90s in west side valleys. More
locations in west side valleys will reach the triple digits this
afternoon.

This afternoon`s thunderstorm chances were expanded last night and
now include more portions of Douglas, Josephine and Jackson
counties. Sunnier skies are still present west of the Cascades with
cumulus building east, especially in Modoc County. The
shower/thunderstorm chances will come later this afternoon and into
the evening, mainly between 4-9 PM. Cloud-to-ground lightning, gusty
winds nearing 50 mph and small hail will be possible.

Also wanted to note some models are indicating a few returns at the
coast tonight that track north. There is a less than 10% chance of
thunder for areas near the coast and slightly inland (into western
Josephine and western Douglas counties), but wanted to bring this
possible outcome to light.

Tomorrow morning will be warmer with more west side locations seeing
lows in the 60s. Tomorrow afternoon will not be as warm as today. An
upper low near San Francisco will be moving towards Southern Oregon
later tomorrow into Wednesday, and this will bring breezier
conditions in the afternoons. Another thunderstorm chance comes
tomorrow afternoon. This will be focused on northern Klamath and
Lake counties at a 25-35% chance while a line of 15-25% chances
extends to the southwest into Siskiyou County.

The last thunderstorm chance of this string comes Wednesday and
is concentrated in central Lake County and eastern Klamath County.
Forecast CAPE values in this region will be near 250-350 J/kg.
Surrounding areas have CAPE up to 200 J/kg, so will look at this
as the CAMs come in to see if the coverage needs to be extended.

In the long term ridging will start to build into the weekend, and
this will bring a return of heat the area. There is currently a 40-
60% probability to see 100 degrees in Medford from Friday through
early next week. For now, dry conditions are forecast during that
time frame. -Hermansen

FIRE WEATHER...Updated 200 PM PDT Monday, July 7, 2025...Upper
ridging over the area this afternoon is bringing hot weather over
the interior with some triple digit readings expected in the west
side valleys and temperatures in the 90s for most locations east
of the Cascades. This is resulting in low RH values over the East
Side with some already in the 10-15% range. For late this
afternoon/evening, with low pressure off the NorCal coast, expect
cumulus to build over the higher terrain, first across NorCal and
up along Winter Rim, but then over the Siskiyous and the Cascades.
Since we`re still under the influence of the upper ridge, forcing
for thunderstorm development and moisture is fairly weak. Even
so, model guidance is showing isolated thunderstorms popping up
this afternoon and evening with storm motions generally off toward
the NW. 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
(10-12k ft or so) that does develop might not produce any
rainfall. For this reason, we`ve indicated "dry" thunderstorms in
the official forecast. Mid-level steering flow appears strong
enough (~15-20 kt) that should cells get going across the southern
Cascades/Siskiyou Mtns, they may be able to drift off the terrain
and over portions of the Rogue and/or Illinois valleys or even
into eastern Douglas County (probably S&E of Roseburg) this
evening. Gusty outflow winds are possible in the stronger cells.
Elevated instability persists tonight across portions of NW Cal
and even SW Oregon. While probabilities are low (generally less
than 15%), we have seen in the past, nocturnal activity that
migrates toward or even off the coast in these situations. Would
not be be surprised if a stray thunderstorm develops in those
areas tonight.

Isolated to widely scattered thunderstorms (15 to 35%) continue
Tuesday afternoon/evening as the low edges closer to the coast.
East Side areas north of the Sprague River Valley and NW of Abert
Rim (northern sections of FWZs 624/625) have the highest
probabilities of thunderstorms (25-35%), so we have upgraded the
Fire Weather Watch to a Red Flag Warning (2-11 pm PDT) there, but
isolated activity could extend back to the SW across the Cascades to
northern and western Siskiyou County. 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. This will maintain a slight chance to
chance of thunderstorms across SE portions of the forecast area,
but especially from Modoc County northeastward into southern Lake
County. We have added a Fire Weather Watch to the SE portion of FWZ
624 and southern part of FWZ 625 (2-8 pm PDT) for abundant
lightning on dry fuels. The trough axis pushes east of the area
fairly quickly Wednesday evening, so felt confident enough that
convection would be ending earlier in the evening.

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...Red Flag Warning from 2 PM to 11 PM PDT Tuesday for ORZ624-625.

     Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for ORZ624-625.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Tuesday
     for PZZ350-356-370-376.

&&

$$