Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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258 FXUS66 KMFR 072148 AFDMFR Area Forecast Discussion National Weather Service Medford OR 248 PM PDT Tue May 7 2024 .SHORT TERM...through Wednesday (5/8) night...Ongoing shower activity north of the Umpqua Divide will gradually wind down this evening. Afternoon temperatures are quite similar to recent days, running about 10 to 15 degrees below normal for early May. Upper level ridging will build into the region tonight and a thermal trough will develop at the surface. Cloud cover will linger against the terrain tonight, but where skies clear, temperatures will drop. There are freeze concerns for those areas that clear, and a Freeze Warning has been issued for the valleys of Siskiyou/Josephine/Jackson counties. Lingering cloud cover could limit the extent of freeze concerns tonight, but there is about a 40- 70% chance of low temperatures reaching 32 degrees for the Illinois and Applegate Valleys. Confidence is higher for the Shasta and Scott Valleys in Siskiyou County where skies are already clear and we don`t anticipate additional cloud cover. Chances of freezing temperatures in those locations jump to around 70-90%. After a chilly start Wednesday morning, afternoon temperatures will trend warmer by about 10 degrees across the area. Any lingering cloud cover will give way to sunny skies for all areas for Wednesday afternoon. The thermal trough will strengthen along the coast and induce the Chetco Effect, bringing warm temperatures to the southern Coast. Expect highs in the upper 60s/low 70s for areas west of the Cascades and upper 50s/low 60s for areas east of the Cascades. High pressure will continue to strengthen over the region for the latter half of the week, and this trend in warmer temperatures will continue into the extended period. /BR-y .LONG TERM...Thursday (5/09) through Tuesday(5/14)... High pressure will be the rule for the majority of the extended term, with dry and very warm conditions expected for all of southern Oregon and far northern California, with a few possible exceptions. Upper level ridging will extend north and east into the Pacific Northwest Thursday, with a thermal trough north from California and along the southern Oregon coast, 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, creating east winds aloft that will enhance and align with the east winds at the surface. All of this will result in very warm temperatures through the end of the week and into the first part of the weekend. As a result, a strong Chetco effect is forecast for the southern coast near Brookings. This pattern begins to break down late in the weekend, which may allow a weak trough to enter the area early next week, introducing a slight chance of afternoon thunderstorms. This will, in effect, produce the warmest stretch of days so far this season. The Chetco Effect will 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 and Saturday afternoon. For these areas, high temperatures will be more in line with early July than early May, with highs 10 to 20 degrees above normal for this time of year. We also expect strong inversions and warm ridgelines overnight, which this pattern is known to typically produce. 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 as a weak trough enters the region from the northwest, followed by a weak trough nudging in from the southwest. These features could be enough to tap into afternoon instability, resulting form the warm temperatures and a slight uptick in atmospheric moisture, resulting in a thunderstorm or two across Siskiyou and Modoc counties, and perhaps even into some of far southern Oregon. This is a pattern known to produce convection, and roughly 33 percent of all the model solutions are depicting this solution, including the bulk of the deterministics, so confidence this far out is moderate. The NBM is not impressed, but typically lags the GFS and ECMWF by a day, so suspect it will come more in line with this thinking by next cycle. -BPN && .AVIATION...07/18Z TAFs...VFR conditions are expected throughout this TAF cycle, although local MVFR conditions are possible early this morning, mainly along the coastal area north of Cape Blanco. Skies will start to clear this afternoon and furthermore through the evening hours. Conditions will be breezy during the afternoon as well. -CC && .MARINE...Updated 200 PM Tuesday, May 7, 2024...As a thermal trough strengthens along the coast, north winds and steep seas will develop this afternoon and evening south of Cape Blanco. Winds and seas will increase tonight and Wednesday with the worst conditions Wednesday afternoon and night. Gales and very steep, wind-driven seas are expected from Cape Blanco southward Wednesday afternoon through early Thursday morning with gusty winds and very steep seas north of Cape Blanco. Current models show a high chance (50 to 100%) percent for north gales from Cape Blanco southward, highest (70 to 100%) beyond 5 nm from shore south of Gold Beach. The thermal trough will weaken Thursday, but lingering steep to very steep seas are possible. Lighter winds and seas expected Friday into the weekend. -CC && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Freeze Warning from 2 AM to 10 AM PDT Wednesday for ORZ024-026. CA...Freeze Warning from 2 AM to 10 AM PDT Wednesday for CAZ080-081. PACIFIC COASTAL WATERS...Small Craft Advisory from 11 PM this evening to 2 PM PDT Wednesday for PZZ350-370. Hazardous Seas Warning from 2 PM Wednesday to 5 AM PDT Thursday for PZZ350-370. Small Craft Advisory until 2 PM PDT Wednesday for PZZ356-376. Gale Warning from 11 PM this evening to 5 AM PDT Thursday for PZZ356-376. && $$ MNF/BPN/CC