


Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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699 FXUS66 KMFR 182142 AFDMFR Area Forecast Discussion National Weather Service Medford OR 242 PM PDT Fri Jul 18 2025 .DISCUSSION (Today through Thursday)... Overview: Hot, dry, and breezy conditions continue today. There is also a small chance (10%-20%) for thunderstorms this afternoon across Modoc County and southern Lake County. This weekend we will transition to "cooler" temperatures which will be closer to normal for this time of year. By Monday, areas recently in the triple digits will see temperatures fall under 90 degrees which will be a nice relief for some folks. In general, 70s/80s for highs on Monday across the forecast area for the coolest day in the forecast. Monday also starts a pattern change with precipitation chances possibly increasing through the week, but confidence is low at this time. The upper level disturbance passing that could give us precipitation will also bring increased chances for breezy to gusty wind speeds, especially the eastside next week. Further Details: At 500mb, there is a trough passing over southern parts of British Columbia and Washington. Some models are producing weak PVA across the area today, and this could phase with convective temperatures through peak heating. This has warranted an area of 10-20 percent PoPs for Modoc County and southern parts of Lake County. This is a weak forcing event with very little MUCAPE (<300 J/kg), but we just could not rule out an isolated thunderstorm or two this afternoon/early evening. The last couple afternoons where we had a similar weak forcing situation where the HRRR and Rapid Refresh Forecast System (RRFS) did well. We leaned PoPs away from NBM and towards the HRRR/RRFS for this situation. Not expecting severe weather, but isolated lightning and gusty erratic winds are possible today and early this evening. Smoke and haze is spreading across the region, so this may inhibit thunderstorms further. The smoke and haze could also bring unhealthy conditions to sensitive groups today as we continue to deal with wildfires across the region. The aforementioned trough over southwest Canada/PacNW will expand and become a broader area of cyclonic flow over the PacNW through the weekend. This will usher in cooler air through the weekend and early next week, and there is good agreement between global models. Depending on how far south the trough expands, we could see both wind speeds and precipitation chances increase starting early next week. By Wednesday, models are in agreement with a cut- off low developing over the Pacific (~38N/128W) with this low pushing northeast over our forecast area and through the PacNW middle to late next week. As we transition to this cut-off low, there will be small chances for precip/thunderstorms Monday and Tuesday as well. This time of year (warm summer months), we consistently hit convective temperatures in the afternoons, so it doesn`t take a lot of forcing to get a thunderstorm or two to pop up. However, its extremely difficult to forecast exactly where this may happen. All that said, we have two periods next week with thunderstorm chances. First, is the Mon/Tues timeframe as the shortwave over southwestern Canada starts expanding southward. Then, once we transition to the possible cut-off low Tuesday night, we could see those chances increase again Wed/Thurs. Variables are going to have to phase together, so its a little too early to say with much confidence the finer details, but those chances will be there next week. The Wed/Thurs timeframe has the potential for stronger storms as some models are creating a negatively tilted trough as it passes over the forecast area with MUCAPE values progged to be around 400-900 J/kg with 0-6km shear around 25-40 knots. Stay tuned as we refine the details in the coming days. -Guerrero && .AVIATION (18Z TAFs)... Weaker offshore flow should clean up the lower ceilings along the coast briefly this afternoon. With some stronger onshore flow later tonight, we expect LIFR and IFR ceilings to move back into the coast with a stronger marine push into Saturday. The Board Shanty Fire in eastern Josephine County could produce some smoke impacts near KMFR over the next few days. We did drop visibilities down to 6SM this afternoon, although the KMFR ASOS is still happy with 10SM as of now. There is also a very low chance of more thunderstorms in eastern Lake County today. -Smith && .MARINE...Updated 200 PM PDT Friday, July 18, 2025...Sub-advisory conditions will persist through early this evening. Thereafter, a weak thermal trough develops along the coast overnight and persists through much of the weekend. This will bring the gusty north winds, but considerably weaker than the last event. Low end advisory level conditions are expected south of Cape Blanco beginning this evening and continuing through Sunday morning. Winds weaken Sunday as an upper level trough settles over the region and disrupts the thermal trough pattern. Relatively light winds and seas are expected Monday and through much of next week. && .FIRE WEATHER...Updated 230 PM PDT Friday, July 18, 2025... Fire weather conditions remain elevated today into Saturday as a trough passes to our north. RHs settle into the lower teens with wind gusts around 25 to 30 mph over exposed terrain east of the Cascades. Humidities trend about 8 to 15% higher along the Cascades and farther to the west on Cascades by Saturday. However, look for RHs in the lower teens around Modoc and southern Lake County Conditions begin to improve by Sunday as RHs move about 3 to 5 percent higher on Sunday with some breezy conditions still persisting. By Monday, the upper level trough deepens over northern OR/WA, and this will be the coolest day of the forecast period. Minimum rhs are unusually high east of the Cascades as this "cooler" moist airmass moves in. By Tuesday, the trough elongates over the region, resulting in another day of "cooler" temperatures. Guidance shows energy from this trough forming another low pressure off the coast of California around mid-week. This pattern would result in the return of thunderstorms to the forecast for the remainder of the week. There are differences on the position/location/strength of this low, so stay tuned for updates to the forecast as the time gets closer. -Smith/Firmin && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory from 8 PM this evening to 11 AM PDT Sunday for PZZ356-376. && $$