Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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632 FXUS66 KMFR 280357 AFDMFR Area Forecast Discussion National Weather Service Medford OR 857 PM PDT Mon May 27 2024 .DISCUSSION...Isolated showers and even a couple of thunderstorms popped up in southern Siskiyou, Modoc and Lake counties this afternoon and this evening ahead of an upper trough offshore. Only about 5-10 cloud to ground flashes occurred, according to various lightning detection networks. Most were in NE Lake County, but there were also a couple in southern portions of the Modoc. These are dissipating this evening as the sun sets and instability wanes. Overnight, expect a clear to partly cloudy sky for most, though low clouds and patchy fog will return the coast north of Cape Blanco and also down around Brookings. A bit deeper marine push (compared to last night) is possible Tuesday morning. The upper trough will move onshore on Tuesday with more in the way of clouds, but also some sunny intervals. For many areas, including here in the Rogue Valley, this trough will move through dry and only result in some cooling and an uptick in afternoon WNW breezes. These winds could become gusty at times (peak gusts of 20-25 mph west side), but especially over the east side where peak gusts of 25-35 mph are likely. In terms of precipitation, shower chances will be highest (20-40%) across NW sections in northern Coos and Douglas counties. Instability will peak again Tuesday afternoon and evening from eastern Siskiyou to Modoc and southern Lake counties. Similar to today, these areas stand the best chance at showers/isolated thunderstorms. The upper trough axis will shift east of the Cascades Tuesday night, but onshore flow west of the Cascades will cause some cloud cover along the coast and also to bank up against the mountains. Inland, these clouds should dissipate Wednesday morning yielding a nice, sunny afternoon, though some will likely remain along the coast. Warmer weather is expected Thursday and Friday. -Spilde && .AVIATION...28/00Z TAFs...VFR conditions prevail across the region this afternoon with the typical gusty afternoon breezes. Scattered cumulus with isolated showers have developed east of the Cascades, and there remains a 10 to 20% chance of thunderstorms there through this evening. Cloud bases are fairly high, so expect gusty outflow winds in the vicinity of these showers/thunderstorms. Marine stratus will make a return later this evening and overnight as an upper level trough approaches the Pacific Northwest. Expect the return of IFR/LIFR conditions along the coast between 03-06z, with ceilings lifting to MVFR late tonight/early Tuesday morning as the marine layer deepens and pushes inland. Marine stratus is expected to make a farther inland intrusion than previous nights, so we expect some MVFR cigs to make into the Umpqua Basin around 10- 12z. Clouds are likely to develop south of the Rogue-Umpqua Divide and into the Illinois and Rogue Valleys, ceilings should remain just above MVFR and confidence is low on how much the clouds will fill in and impact the Medford Airport. While conditions should generally improve later Tuesday morning, cloud cover will likely linger through the day as a weak front pushes through the area. /BR-y && .MARINE...Updated 830 PM Monday, May 27, 2024...Relatively calm conditions will continue into Tuesday. Northerly winds will turn westerly on Tuesday as an upper trough passes to the north, and swell will increase slightly, but remain unimpactful. A thermal trough will develop under upper level ridging on Wednesday afternoon, driving conditions through the rest of the week. North winds will return and bring wind-driven steep and very steep seas to all marine waters. Sustained winds will be in the 20 to 35 kt range at their highest, with the strongest winds expected south of Cape Blanco. Chances for gale gusts south of Cape Blanco will be very high (50-90%) from Wednesday afternoon through Friday afternoon, and there is a lesser (10-50%) chance of gales over the outer waters north of Cape Blanco as well. A Gale Watch is in place from Wednesday evening through Friday evening for all waters south of Cape Blanco where the chances are highest for gales. Meanwhile, steep seas and conditions hazardous to small craft are likely for all areas north of Cape Blanco during this time. Conditions could improve next weekend as a pattern change disrupts the thermal trough, and winds ease. -TAD/BR-y && .PREV DISCUSSION... /Issued 242 PM PDT Mon May 27 2024/ SHORT TERM...Satellite image shows clear skies west of the Southern Oregon Cascades, with cumulus buildups along and east of the Cascades and over the higher terrain in northern Cal. Regarding the thunderstorm potential later this afternoon and evening east of the Cascades and northern Cal. It still exist, but it could end up bring more of the exception and not the rule. Meaning a few isolated storms are possible, but odds are we`ll just have some building cumulus in these areas. Any storms will dissipate early this evening with dry weather likely for tonight. An upper trough will approach from the west Tuesday and could bring a few showers north of Cape Blanco, north of the Umpqua Divide and northern Cascades. Additionally, instability will be on the increase along with ample low level moisture, and strong enough trigger east of the Cascades that could bring another round of isolated storms. The general consensus shows convection breaking out and orientated from southwest to northeast from Mount Shasta northeast to southeast Klamath and central Lake County. Afternoon temperatures for the interior will be cooler and winds will be stronger east of the Cascades Tuesday afternoon and evening due to a tighter pressure gradient and stronger winds aloft (near 700mb). However, we`re not expecting winds to reach advisory criteria. Isolated storms will once again diminish and end early Tuesday evening with not much more than a few showers in northern Coos and Douglas County Tuesday night. The upper trough axis shifts east of the area Wednesday with a dry and stable northwest flow. Therefore it`s likely to remain dry for the entire forecast area, with gusty breezes in the afternoon and early evening hours for the interior westside valleys and east of the Cascades. Wednesday night, a thermal trough will set up along the south Oregon coast resulting in increased east to northeast breezes near and at the ridges for the coastal mountains in southwest Oregon and western Siskiyou County. It will remain dry with cooler overnight temperatures east of the Cascades and wind sheltered locations for the interior west side. -Petrucelli LONG TERM...Models and ensembles show high confidence for a high pressure ridge building into the area on Thursday and remaining in place on Friday. This will bring warming trend and dry weather across the area. Temperatures on Friday will be roughly 8 to 15 degrees warmer than the normals for this time of year in late May, although remain a limited heat risk to those sensitive to heat. High temperatures are forecast to be in the upper 70s to mid 80s across inland valleys Friday. Models also indicate a high potential for gusty northeast to north winds along the coast and over the coastal mountains during this period (Thursday and Friday), as surface thermal trough develops. This is likely to bring a warming and drying trend to the southern Curry coast, especially near Brookings. Guidance the National Blend of Models (NBM) supports temperatures in the mid 70s at Brookings Thursday. T The pattern may begin to change Saturday night into Sunday with ensembles showing a front and a shortwave upper level trough moving into the area. There is low confidence on the strength of this system and how much moisture it will bring. Currently, the National Blend of Models favors light rain, with best chances along the coast and into Douglas County on Sunday and Sunday night. NBM shows the probability of precipitation of 0.25 inches or more is only 20-30% along the coast and into Douglas County for Sunday and Sunday night, with lower chances 5-15% across other parts of southern Oregon and northern California. Temperatures are expected to trend closer to seasonal norms though on the weekend. -CC AVIATION...27/18Z TAFs...Stable weather will continue to support generally VFR conditions across northern California and southern Oregon. A marine stratus layer north of Cape Blanco is quickly breaking up and should be cleared out within the hour. The usual afternoon winds will develop across the area and will calm later this evening. Marine stratus will return tonight and could remain in place through the end of the TAF period. -TAD MARINE...Updated 230 PM Monday, May 27, 2024...Calm seas will continue through today and Tuesday. Northerly winds will turn westerly as an upper trough passes to the north, and swell will remain unimpactful. A thermal trough will develop under upper level ridging on Wednesday afternoon, driving conditions through the rest of the week. Northerly winds will return and bring wind-built steep or very steep seas to all marine waters. Sustained winds will be in the 20 to 35 kt range at their highest, with the strongest winds south of Cape Blanco. Chances for gale gusts south of Cape Blanco will be very high (50-90%) from Wednesday afternoon to Friday afternoon, and there are lesser (10-50%) chances of gales over outer waters north of Cape Blanco as well. A Gale Watch is in place for waters south of Cape Blanco from Wednesday at 5 PM through Friday at 5 PM to communicate the most active period of the thermal trough, but more complete hazard timing and areas will take more time to develop. A pattern change near the weekend will break the thermal trough up and is forecast to bring calm seas by Saturday. -TAD && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Gale Watch from Wednesday afternoon through Friday afternoon for PZZ356-376. && $$ MAS/MNF/MAP/CC/TAD