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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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702 FXUS66 KMFR 201036 AFDMFR Area Forecast Discussion National Weather Service Medford OR 336 AM PDT Mon May 20 2024 .DISCUSSION...The weather pattern this week will be dominated by progressive northwest flow aloft, which will keep the PacNW in a regime of lower than normal heights and generally cooler than normal temperatures. Embedded short wave disturbances could cause showers from time to time, especially across the northern half of the CWA, but there will also be long stretches of dry, pleasant weather. One upper trough is exiting to the east of the area today, moving into Montana/Idaho from eastern Oregon. Satellite imagery is showing patchy clouds lingering behind this trough over the Cascade foothills, the Rogue-Umpqua Divide and near the Siskiyous. These should dissipate by late morning yielding mostly sunny skies and a nice afternoon, though NNW breezes will pick up again. A few cumulus will develop near the Cascades and over the East Side this afternoon. Hi-res CAMs are showing some echoes in their composite reflectivity depictions near the Cascades, but the cloud moist layer depth there is limited. So, while a brief sprinkle cannot be ruled out, most areas will stay dry. Expect 3-6 degrees of warming compared to yesterday for a large part of the area, except for southern Lake, Modoc and southeastern Siskiyou counties, where temperatures will likely be similar or down a degree or two. Tonight, short wave upper ridging will provide dry weather, but with some low clouds along the Coos coast and also perhaps into portions of Douglas County. The next upper trough originating in British Columbia will dive SSE into the PacNW on Tuesday. Aside from the clouds at the Coos coast and in the Umpqua, the day will start off sunny. Then, as this system continues to move in, we expect increasing cloudiness (especially of the high and mid level variety). Models are keeping precipitation largely to the north, though shower PoPs do increase to around 20-30% during the afternoon across northern Douglas County (north of Roseburg). Expect most areas will see another 4-8 degrees of warming compared to today (Monday). This system will swing through the area Tuesday night into Wednesday with the highest probability of showers (40-80%) from the Coos coast across Douglas County to the Cascades. Rain amounts in those areas will be mostly less than 0.10 of an inch, though the foothills and Cascades north of Diamond Lake could get up to 0.25 of an inch. While showers are unlikely in Medford/Ashland/Grants Pass, all have about a 20% chance. Areas south of the OR/CA border largely remain dry, though an isolated shower cannot be ruled out near the Warner Mountains. Gusty winds will develop in many areas Wednesday afternoon, but especially over the East Side, where mid-level flow peaks at 40-45 kt. A well-mixed BL should lead to some gusts there near 40 mph at the surface. Expect a reinforcing shot of cooler air on Wednesday with temperatures down 5-10F compared to Tuesday. The upper trough axis shifts to the east on Thursday with slight warming expected to continue into Friday. We`ll do it all over again Friday night into Saturday as the next upper trough pushes through. This system looks slightly weaker and farther north than the previous one, but could bring some showers across the north along with breezy winds and a cooling trend area wide. After that, it appears the flow becomes more zonal and this should allow upper troughing to focus more in the Gulf of Alaska. This would potentially force an upper ridge somewhere in the West by early next week allowing things to warm up above normal. There are still some uncertianties in position/strength of various features, so confidence out at that range is still on the low side. -Spilde && .AVIATION...20/06Z TAFs...VFR conditions will continue through the TAF period, with gusty north to northwest breezes in the afternoon and early evening hours, but guidance shows should not be as strong as they were earlier this afternoon and early evening. -Petrucelli && .MARINE...Updated 200 AM Monday, May 20, 2024...North gales and very steep, wind-driven seas south of Cape Blanco will continue through this evening. Model guidance continues to suggest periods of off-and-on gales south of Cape Blanco, and a Gale Warning remains in place for the areas where these gales are expected to surface. Conditions will be relatively less severe north of Cape Blanco, but still hazardous to small craft with breezy north winds and steep seas. Winds will briefly diminish at night, then increase again during during the afternoon and evening hours today before winds ease tonight. Low pressure approaching from the north will disrupt the thermal trough on Tuesday with winds diminishing. Moderate winds will likely continue into Wednesday with northwest swell gradually increasing Wednesday afternoon. -Petrucelli/CSP && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Tuesday for PZZ356-376. Small Craft Advisory until 11 PM PDT this evening for PZZ350- 370. Gale Warning until 11 PM PDT this evening for PZZ356-376. && $$ MAS/CSP/MAP