Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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384 FXUS66 KMFR 081837 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1137 AM PDT Sat Jun 8 2024 .DISCUSSION.../Issued 504 AM PDT Sat Jun 8 2024/ The upper level pattern will begin to transition today. The ridge axis will shift east of the Cascades and a weak trough will approach the region. Ahead of this trough, a shortwave is passing through the area early this morning, bringing a swath of mid and high level clouds. There are some light returns showing up on radar, but we don`t expect these returns to amount to anything. Elevated instability just isn`t there for any thunderstorm development this morning, and while a few areas may see some sprinkles out of these showers, it will be very isolated and limited to areas west of the I-5 corridor and over the marine waters. Ahead of this shortwave, areas of stratus have returned to portions of the coast, with quiet conditions overall expected for the morning hours. With the shift in the upper level pattern, high temperatures today will be around 5 to 10 degrees cooler for locations west of the Cascades compared to Friday`s readings. A few records were broken yesterday: Mt Shasta City recorded 95 degrees, breaking the old record of 92 set in 2015 and Alturas recorded 93 which ties the record set in 1996. Klamath Falls came close, reaching 90 degrees which is just shy of 91 set in 1996. While we expect several degrees of cooling west of the Cascades, temperatures east of the Cascades will only be cooler by a few degrees, reaching into the mid to upper 80s. We don`t anticipate any record challenging temperatures today as high temperatures will be several degrees out of reach of current records. The forecast is on track for a likely broader area with more thunderstorm activity this afternoon and evening. The focus for activity is expected to be in similar areas as the previous two days: in the vicinity of the border of Klamath and Lake counties, extending primarily into the northern portions of those counties, including Chemult and Summer Lake, where coverage of storms (isolated to scattered) will be greater today. A secondary, isolated risk for storms will cover much of Siskiyou and Modoc counties, the remainder of south central Oregon, and the southern Oregon Cascades and Siskiyou Mountains. SPC has delineated a Marginal Risk (10-20%) for isolated severe thunderstorms east of the Cascades, indicating a 5% chance of severe winds (gusts to at least 58 mph) or hail (at least 1 inch diameter). Overall, the atmosphere is fairly similar to the previous two afternoons with similar CAPE and LI values, but there is a modest increase in bulk shear, up to 35 to 40 kts today vs 25 to 35 kts the previous afternoons. We`ve witnessed a few strong to severe storms the previous afternoons as well, and with the increase in bulk shear, storms could persist longer today and increase the chance for severe winds and/or hail. Regardless if thunderstorms reach severe criteria or not, expect strong gusty winds with and near thunderstorms as well as the potential for hail. The previously mentioned weak trough passes through the region late tonight into Sunday, and guidance indicates the potential for showers and isolated thunderstorms to continue across northern Klamath/Lake Counties during this time. The cooling trend continues on Sunday as the weak trough passes through, with the most notable cooling expected east of the Cascades where high temperatures are expected to be about 7 to 10 degrees cooler. West Side will cool further as well, but only by a few degrees. We`ll see yet another day of thunderstorm potential Sunday afternoon, but the focus will shift eastward into Lake and Modoc counties as the trough pushes the moist unstable air farther east as the day progresses. Late Sunday into Monday, energy from this week trough gets cut off from main flow and forms a cut off low off the coast of southern California. The flow will become more zonal over the PacNW through about mid-week, resulting in a stabilizing atmosphere and the loss of daily thunderstorm potential. With zonal flow, we don`t anticipate a big warm up, but temperatures will remain about 10 degrees above normal for the first half of the week. /BR-y && .AVIATION...08/18Z TAFs...An isolated thunderstorm has already popped up this morning ahead of an upper level wave and some modest mid level moisture. Thunderstorm activity will pick up into the late afternoon and early evening as the atmosphere destabilizes. The bulk of the activity will develop east of the Cascades and in northern California. The thunderstorm threat will persist overnight east of the Cascades and in the central Cascades as the upper level wave approaches the Oregon coast. Some models also show a bulk of moisture around 7000 to 9000 feet above sea level, which could aid in initiating convection overnight. Right now the threat of overnight thunderstorms remains low, although these events are sometimes underdone in the models. Overall, be on the lookout for thunderstorms across the forecast area, especially farther to the east through the TAF period. Lower ceilings around 1000 feet are anticipated near the coast overnight as high pressure begins to build. IFR ceilings are most likely, although periods of LIFR ceilings also remain possible. && .MARINE...Updated 800 AM Saturday, June 8, 2024...North winds will be just strong enough to produce an area of steep seas hazardous to small craft south of Ophir today and tonight, generally beyond 2 NM from shore. Then, a moderate west swell moves in tonight through Sunday. During this time, the thermal trough will restrengthen, bringing increasing north winds and steep to very steep seas Sunday into early next week, especially south of Cape Blanco. Conditions will at least remain hazardous to small craft south of Cape Blanco through midweek. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Monday for PZZ356-376. Hazardous Seas Warning from 5 AM Sunday to 11 AM PDT Monday for PZZ356-376. && $$