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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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626 FXUS66 KMFR 180537 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1037 PM PDT Sat Aug 17 2024 ...Updated AVIATION discussion... .DISCUSSION...Pretty busy day on the radar today. There were a handful of strong and severe storms in the region today, though hail reports so far range from pea sized to around 1/2". One cell passed through Medford area, dumping heavy rain in a short amount of time and we recieved reports of downed trees and tree limbs in the Phoenix area from strong winds. A rough count on lightning strikes indicates about 1800 strikes recorded today, focused along and west of the Cascades. Rainfall amounts range from 0.25"-0.50" with some places recording 0.75" and even close to an inch. Even the wildfires burning in Douglas County received some precipitation, but amounts vary with the western fires (Homestead Complex) receiving considerably more rain than the eastern fires (Diamond Complex). Despite the lower amounts, fire activity should be reduced, even if only temporarily, and this should bring a reprieve from the persistent smoky conditions. Thunderstorm activity has largely come to an end for the evening. There are a few isolated showers on radar still, and satellite indicated lightning detection does show a few cloud to cloud strikes lingering in the region. Isolated showers are likely to continue overnight, becoming more confined to areas west of the I-5 corridor. Quieter conditions are expected for Sunday and into next week. For more details, please see the previous discussion below. /BR-y && .AVIATION...18/06Z TAFS...Thunderstorm activity has calmed for the moment across northern California and southern Oregon. A few isolated showers indicate that moisture and energy remain in the atmosphere, so stray thunderstorms and showers cannot be ruled out overnight. Any overnight activity that does develop would most likely be west of the Cascades. Ceilings along the coast vary, with Brookings solidly at LIFR levels and North Bend currently going between VFR and MVFR ceilings. Slight shower chances (30-50%) will persist over coastal areas through Sunday morning but should be cleared out by Sunday evening. Inland areas are expected to remain at VFR through the TAP period. -TAD && .MARINE...Updated 900 PM Saturday, August 17, 2024...Relatively calm conditions are expected for the next several days with light to moderate winds and seas remaining 5 feet or less. A rather strong upper low for this time of the year is bringing showers and storms today. While storms will dissipate this evening, showers may continue into early Sunday morning. && .PREV DISCUSSION... /Issued 434 PM PDT Sat Aug 17 2024/ ..Updated AVIATION discussion... DISCUSSION... Lots of fast moving thunderstorms on radar this afternoon as an upper level low off the coast and embedded short wave kick off thunderstorms across the region. They haven`t looked very impressive over the last few hours, perhaps because a lack of convective available potential energy. However, there is plenty of directional shear for these thunderstorms and models are still predicting some stronger storms later this afternoon and evening mostly in the Cascades. In general, we`ve seen wind gusts mostly around 45 mph with one gust up to 58 mph over higher terrain with mostly pea size hail. However, that could change in the coming hours as models are still initiating convection through 3Z. Because of this, a severe thunderstorm watch has been issued until 9 pm for Jackson, Douglas and Siskiyou Counties. Storms will move north through the evening and decrease in coverage overnight. A few models are still holding onto storm activity along the Cascades. In addition, the latest NBM does have some low(15%) chance of thunder probabilities along the coast overnight. By Sunday, the low bringing all the weather is starting to move north and the weather should be more fall like with only a few showers lingering around Douglas County Sunday morning. Conditions will continue to dry into Sunday evening with some cooler than normal temperatures persisting. The cooler westerly winds will remain in place for Monday and Tuesday, which will result in highs in the lower 80`s and some cooler lows overnight. The low bringing all this weather will eventually shoot eastwards and high pressure will build in it`s wake east of Oregon on Wednesday. Temperatures won`t warm up too much, but the ridge will block the progression of the next upper level low. Deterministic models and likely some ensemble members are anticipating another low to sit off our coastline around Thursday. This type of pattern during the summer usually means a few thunderstorms. The NBM probability of precipitation increased significantly compared to 24 hours ago and we added a slight chance of thunderstorms in there as well. Ensembles are hanging onto the 20% chance of showers or thunderstorms by Friday into the weekend. These upper level lows like to wobble and things will probably change between now and early next week. -Smith FIRE WEATHER...Offshore low pressure will continue to send shortwaves northward across NW California and SW Oregon into this evening, providing plenty of forcing/lift for thunderstorms. Satellite and radar are showing numerous showers and thunderstorms developing early this afternoon as the shortwave encounters good moisture and instability with steep mid-level lapse rates near and west of the Cascades. These storms will move to the north (or even NNW) at a pretty good clip. A recent timed cell had a storm motion at 35-40 mph. Initially, individual fast-moving cells are likely to produce lightning, possibly outside of rain cores which could result in numerous new fire starts. As such, a Red Flag Warning remains in effect for abundant lightning on dry fuels for FWZs 616, 617, 620, 621, 622, and 623 in Oregon and FWZs 280 and 281 in California. In addition to frequent cloud to ground lightning, storms today will also have the ability to produce strong (40-57 mph) to perhaps severe (>58 mph) wind gusts and large hail in excess of 1 inch in diameter and the Storm Prediction Center has much of the aforementioned area in a marginal (5-14%) to slight risk (15-29%) for severe storms. These storms are also likely to become significant rain producers with PWs in the 0.75-1.00 inch range (even up to 1.25 farther north). Eventually, individual cells could organize into clusters or even train for a while over similar areas. This could result in heavy rain rates (>0.25"/hr at times) with peak rates of 0.50-0.75"/hr. By the time the storms end, most of the area from the Cascades west will have had a wetting rainfall of >0.25" (60-90% chance). Areas that get under training cells may receive more than 1.00 inch of rain today. While we aren`t expecting widespread flash flooding, there is a small possibility (5% chance) of a flash flood/debris flow (best chance is near the more significant fires in eastern Douglas County). All of these risks are safety concerns, and important details for aircraft and ground resources/personnel to be aware of. Please be safe out there this afternoon/evening. The Red Flag warning ends at 9 pm PDT this evening, but activity could end a little sooner than that in NorCal (6-8 pm) as it moves off toward the north. Farther east, a strong mid-level jet well in advance of the offshore low will bring strong, gusty S-SW winds into this evening for NE Cal and south-central Oregon. Guidance still shows sustained wind speeds of 15-30 mph with gusts in the 35-50 mph range. Model probabilities are showing 60-80% chances of wind gusts exceeding 40 mph and in-house fire weather RAWS guidance is showing peak wind gusts 40-50 mph for some of our more exposed RAWS locations. A Red Flag warning remains in effect until 8 pm PDT for FWZ 285 (Modoc) in California and FWZs 624/625 in Oregon. This also includes the Warner Peak fire in eastern Lake County. Winds will also be gusty in the Shasta Valley up into portions of the Klamath Basin into this evening, but humidities there should be slightly higher. Shower activity should wane overnight west of the Cascades. By Sunday, the offshore low will wobble a bit more and lift northward, so while there is still a chance of showers near and west of the Cascades, most areas will be dry. It will be breezy again over portions of the East Side and humidity will continue to be down around 15%. Even so, wind gusts should be a good 10-15 mph lower than today. We`ll maintain the headline for this in the Fire Weather Planning forecast. Beyond that, things should calm down a bit with the low moving northward toward Vancouver Island Monday, then opening up into a trough Tuesday and eventually onshore Tuesday night. This should put the area in a mostly dry SW flow aloft with maybe some cumulus buildups Tuesday afternoon. Models do show another shortwave moving through NorCal Tuesday night into Wednesday, so we`ll have to watch for some shenanigans with that. Right now, it appears to be moving through in the morning, which isn`t favorable for precipitation, but some slower/stronger solutions generate a slight thunder risk east of the Cascades Wednesday afternoon/evening. After that, yet another upper low is shown to drop south along the British Columbia Coast mid next week, then offshore the PacNW coast Thu/Fri. There are still some position/strength detail uncertainties to be worked out with this system, so we`ll be watching that as we head into next week. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. PACIFIC COASTAL WATERS...None. && $$ MNF/TAD/MAS/CZS