Grants Pass, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

466
FXUS66 KMFR 182143
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
243 PM PDT Thu Jun 18 2026

.DISCUSSION...

Mid level clouds have slowed down surface heating this afternoon
as observed temperatures are roughly 10 degrees cooler than the
hourly temperature forecast in some locations. In addition, some
cumulus build ups are starting to form in southern Siskiyou County
as the atmosphere begins to destabilize. We still have isolated
thunderstorms in the forecast for Siskiyou and Modoc County this
afternoon. Any storms that develop should be weak and fairly brief
given the lack of convective available potential energy(CAPE) and
shear.

Temperatures trend a little cooler tonight into Friday as a upper
level low approaches the California coastline. Models are starting
to initiate thunderstorm development in the morning hours around
Siskiyou and Modoc Counties based on high resolution ensemble
forecast(HREF) data. CAPE profiles are very slim with very
elevated moisture. So we`re thinking the chance of storms is quite
low during the morning hours. In any case, the threat of storms
will increase into the day with surface heating and increasing
mid level moisture. Severe storms are unlikely, although some
shear profiles will be supportive of some stronger and longer
lasting storms.

By Saturday, the axis of the 500 mb trough will be pushing into
the coastline with some embedded energy moving into eastern Oregon
in the afternoon hours. The threat of isolated thunderstorms and
perhaps some showers will still linger for Lake County on Saturday
afternoon. The NBM is also predicting a 15% chance of
precipitation around Mount Shasta City. In any case, thunderstorms
and lightning activity should be limited Saturday afternoon.

The flow pattern becomes more zonal for the start of next week as
temperatures begin to warm. A thermal trough will likely develop
west of the Cascades by Sunday night into Monday and persist into
Tuesday. High temperatures in Medford will approach the 100
degree mark on both Monday and Tuesday. Heat risk becomes
elevated/moderate during these days as low temperatures cool into
the lower 60`s. As a reminder, moderate heat risk affects those
who are sensitive to heat, especially those without cooling.

On a side note, the extreme forecast index(EFI) is showing values
around 0.7-0.85 for maximum temperatures through Thursday west of
the Cascades. These values suggest the ensembles are forecasting
unusually warm temperatures for this time of year, yet by no
means extreme. Conditions will begin to cool down by Thursday and
Friday.

-Smith

&&

.AVIATION...18/18Z TAFs...Clouds moving over northern California and
southern Oregon are staying at VFR levels for inland areas. Stratus
moving along the coast from south to north is bringing LIFR flight
levels to Brookings. This stratus looks to reach North Bend this
evening, bringing IFR to LIFR levels as gusty afternoon winds start
to ease. Once this layer reaches North Bend, it may remain in place
through the rest of the TAF period.

Inland areas are expected to stay at VFR levels through this TAF
period, with thunderstorms possible for northern California counties
as well as east of the Cascades on Friday afternoon and evening.
-TAD

&&

.MARINE...Updated 200 PM PDT Thursday, June 18, 2026...Elevated
northerly winds continue in all waters, but gusts have fallen below
gale levels. Very steep and hazardous seas will continue in all
waters south of Coos Bay through this evening, with steep seas
continuing to the north. By tonight, very steep seas will be limited
to waters south of Coos Bay and beyond 20 nm from shore, while all
other waters remain steep into early Friday morning.

For Friday morning through Saturday morning, normal northerly winds
continue. On Saturday afternoon, a thermal trough pattern starts to
develop, bringing gusty northerly winds south of Cape Blanco.
Through Saturday afternoon, steep seas will remain in waters beyond
10 nm from shore. Steep seas may move into inner waters south of
Cape Blanco on Saturday evening. Very steep and hazardous seas may
be present south of Gold Beach by Sunday afternoon. Long-term
guidance suggests the thermal trough staying in place for much of
next week, with a brief break in winds on Tuesday. -TAD

&&

.FIRE WEATHER...Updated 300 PM PDT Thursday, June 18, 2026...

Thunderstorms are the main fire weather threat through the next 48
hours. We`ll probably see some isolated thunderstorms today in
northern California. Thunderstorms will become scattered on Friday
as some mid level moisture arrives throughout the day. We have
high confidence that the storm mode will be a mix of wet and dry
storms. Based on past experiences, storms could definitely be
drier than what we`ll see on Friday. However, abundant lightning
on dry fuels is exactly what we`ll see and it should be spread out
over northern California and locations east of the Cascades.
Storm motion should be to the north to northeast around 20 mph, so
not super fast storms. precipitable water(PWATS) are also around
0.7 to 0.9 depending on the model you look at, so enough moisture
to get storms going, yet not really wet thunderstorms.

Overall, we issued a red flag warning for our northern California
Zones and Oregon zones east of the Cascades. A few storms could
occur outside of our warning areas, although the majority of
lightning should be within the red flag areas.

Lastly, it will become hot and dry the start of next week. Some
holdovers will likely pop up once a thermal trough settles west of
the Cascades.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 8 AM to 7 PM PDT Friday for ORZ621.

     Red Flag Warning from 1 PM Friday to 1 AM PDT Saturday for
     ORZ624-625.

CA...Red Flag Warning from 8 AM to 7 PM PDT Friday for CAZ280-281-284-
     285.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 8 PM PDT this
     evening for PZZ356-376.

     Small Craft Advisory from 8 PM this evening to 5 AM PDT Friday
     for PZZ350-356-370-376.

     Hazardous Seas Warning until 8 PM PDT this evening for PZZ350.

     Hazardous Seas Warning until 5 AM PDT Friday for PZZ370.

&&

$$