Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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995 FXUS66 KMFR 062140 AFDMFR Area Forecast Discussion National Weather Service Medford OR 240 PM PDT Mon May 6 2024 .SHORT TERM...Through Wednesday morning...Scattered showers continue across northern California and southern Oregon this afternoon as an upper trough moves over the area. Currently, most of the activity is over Jackson and eastern Douglas counties. Radar is showing sporadic pixels of 40 dBZ reflectivity over northern Lake County, indicating instability present in the area. Model guidance does have a 15-25% chance for thunderstorms over most of southern Oregon through this afternoon, with lower 5-10% chances over Siskiyou, Modoc, and southern Klamath counties. These thunderstorm chances will dissipate overnight. Post-frontal showers will keep 40-60% shower chances over the Cascades tonight, but amounts will be negligible. Cold nighttime temperatures will continue tonight into Wednesday morning, with low 40s along the Oregon coast, mid to high 30s for west side valleys, and mid to high 20s east of the Cascades. Near freezing temperatures remain in the Shasta and Scott valleys tonight, but a Freeze Warning has not been issued for tonight. That product addresses duration as well as temperature, and the confidence in meeting duration thresholds is not high. Additionally, temperatures may be warmer than expected if cloud cover persists into the night. Localized areas may still experience periods of freezing or below temperatures, so extra caution with plants and animals is encouraged. Tuesday is expected to be calm across the area during a transition from active to stable weather under upper level ridging. Temperatures west of the Cascades are expected to be in the mid 50s to low 60s, while they will stay in the low 50s east of the Cascades. Any lingering showers should clear out by Tuesday afternoon. Gusty winds will develop in eastern Lake County, gusting to 25-30 mph before calming overnight. Colder temperatures will continue Tuesday night as well, with similar expectations of near freezing conditions in the Shasta and Scott valleys into early Wednesday morning. -TAD .Long Term...Wednesday (5/08) through Monday(5/13)... High pressure will be the rule throughout the entire extended term, with dry and very warm conditions expected for all of southern Oregon and far northern California. Upper level ridging will build into the region from the eastern Pacific on Wednesday, with a thermal trough developing over California and far southwestern Oregon. The thermal trough will then strengthen and extend northward along the coast through Thursday night, creating generally east winds through the remainder of the week. Meanwhile, the upper level trough that passed over the area earlier in the week will retrograde, moving back to the west and setting up over the Great Basin, just south of the ridge, which by this time will extend across the Pacific Northwest and into the northern Rockies, creating east winds aloft that will correlate and enhance the east winds at the surface. All of this will result in very warm temperatures through at least the first part of the weekend, with a strong Chetco effect likely along the southern coast near Brookings. This pattern begins to break down over next weekend, which may allow a weak trough to enter the area early next week. With all of this in mind, many changes were made to the forecast to adjust temperatures and winds to fit the expected pattern. The Chetco Effect will begin Wednesday ,then peak on Thursday, with highs in Brookings expected to reach the 80s (and a few models even suggest 90 degrees is possible) Thursday afternoon and perhaps Friday as well. When the thermal moves inland, the south coast will begin to cool as the marine layer regains control, while temperatures for most inland areas will reach their warmest Friday afternoon or Saturday afternoon. For these areas, high temperatures will be more in line with early July than early May. Forecast temperatures were adjusted to fit this thinking, while also considering the strong inversions and warm ridgelines that this pattern typically produces during the overnight and early morning hours. Once the thermal trough moves inland, the prevailing flow will take on a more westerly onshore component, and temperatures will begin to gradually cool Sunday and Monday. Some models suites suggest the possibility of a weak front arriving around this time, but given the warm and dry conditions ahead of it, any frontal passage will most likely remain dry. -BPN && .AVIATION...06/18Z TAFs...MVFR ceilings are affecting the coastal terminals early this morning and these conditions will remain through about 21z before more consistent VFR conditions set in. This front will cause showers over inland areas eastward to the Cascades through late this afternoon/early this evening. Many higher terrain areas will be obscured. Scattered showers over NorCal are also being observed on radar from Mt. Shasta west and will continue through this TAF period. VFR will prevail, though may briefly lower to MVFR in showers. Gusty WSW winds are expected east of the Cascades, including at Klamath Falls this afternoon, where peak gusts of around 30 kt are expected. -Spilde/Miles && .MARINE...Updated 150 PM Monday, May 6, 2024...lingering fresh swell and incoming northwest swell dominate the sea state at the moment. Winds will remain out of the northwest through this evening, becoming more northerly overnight. A thermal trough will strengthen Tuesday afternoon with north winds becoming very gusty and steep wind-driven seas develop, highest south of Cape Blanco. Wind speeds will peak during Wednesday afternoon/evening, but gusty northerly winds will persist into Thursday night. During this stretch (Wed pm- Thu), gale force, especially across the southern waters are very likely (90% or more). As such, we have issued a gale watch for areas from roughly Port Orford southward. As new data comes in, the strength of the thermal trough has been growing. We have added a hazardous seas watch to all remaining areas and are considering expanding the gale watch north of Cape Blanco. The thermal trough will weaken Friday into next weekend resulting in weaker north winds and lower seas. -Spilde/Miles && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 8 PM PDT this evening for ORZ031. CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory from 2 PM Tuesday to 11 AM PDT Wednesday for PZZ356-376. Gale Watch from Wednesday morning through late Wednesday night for PZZ356-376. Hazardous Seas Watch from Wednesday morning through late Wednesday night for PZZ350-370-376. && $$ TAD/BPN/MCB