textproduct: Medford

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.