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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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317 FXUS66 KMFR 161757 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1057 AM PDT Tue Jul 16 2024 .Updated AVIATION Discussion... && .AVIATION...16/18Z TAFS...Another surge of mid-level moisture and elevated instability will move into the region today. This will bring another round of isolated to scattered thunderstorms. Once again, these cells will have high bases and a very dry sub-cloud layer, so this will create the risk for strong outflow winds that can propagate a very far distance from the storms themselves. Wind gusts could be 35-45 kt in the stronger cells. And, with any thunderstorm, there is a risk of cloud to ground lightning. These could pop up just about anywhere, but are most likely in an arc from northern Josephine County, across Coos and Douglas counties, and southeast across Klamath, Lake, and Modoc counties...to the Warner Mountains. Also, gusts of 20 to 30 kt are likely this afternoon and evening without thunderstorms in the Shasta and southern Rogue valleys, strongest near Montague. Marine stratus has cleared from the coast north of Cape Blanco, but is slowly pushing northward along the coast, and is bringing IFR/LIFR to areas south of Cape Blanco. With a bit more onshore flow, expect stratus to be a bit more stubborn to break in some areas than yesterday, especially along the south coast. Main visibility reductions with the Shelly fire will be in the immediate vicinity of the fire. Otherwise, VFR will prevail in most areas for the next 24 hours. /BR-y && .MARINE...Updated 800 AM Tuesday, July 16, 2024...Low pressure offshore has disrupted the thermal trough pattern. A slight chance of thunderstorms will extend into the waters north of Cape Blanco this evening with gusty outflow winds possible. Otherwise, weak winds and low seas will persist into Friday morning. The thermal trough will restrengthen Friday into the weekend, with the strongest winds south of Cape Blanco. Advisory strength northerly winds and steep seas are possible Friday into Saturday, then gales and steep to very steep seas are possible on Sunday. -DW && .PREV DISCUSSION... /Issued 333 AM PDT Tue Jul 16 2024/ DISCUSSION...Heat will continue for the area today, with triple digit highs expected for all valleys west of the Cascades. Smoke may be a limiting factor for heat in some areas, but the effect should be small. Clouds, on the other hand, especially if convection gets started early, will make much more of an impact, perhaps keeping highs for some locations several degrees cooler than forecast. A Heat Advisory remains in effect for the valleys of Jackson and Josephine counties through this evening. The upper low off the coast will lift northward on Tuesday with a short wave wrapping from SW to N-NE across the forecast area. This, in conjunction with the ample moisture flowing into the region from the south, will produce a 20-30 percent chance for thunderstorms roughly along and north of a line from Lakeview to Roseburg, with a few stray thunderstorms possible across the rest of Douglas and coos counties. Not much rain is expected with the activity in general - mainly a tenth of an inch or less, but local amounts of a quarter are possible with some training cells. Outflow winds will be a concern, as shown by the thunderstorm activity Monday. Winds are a concern for Tuesday afternoon as the low moves north up the coast. Deep, very warm and dry layer of the atmosphere will be unstable and model indications are that lower atmospheric winds will be significant (greater than 20 kts) from the south and southwest. Should see some afternoon gustiness from the south then from the west over the West Side, and mainly southwesterly over the East Side. 15 mph gusting to 25-30 mph looks reasonable for most areas. Cooler weather by 5-10 degrees will prevail Wednesday through Friday in the wake of the low. However, the longer range solution supports high pressure strengthening over the area again with the NWS Heat Risk forecasts indicating more heat highlights possible starting again Saturday or Sunday. -Stavish/BPN FIRE WEATHER...Issued 300 AM Tuesday July 16, 2024... There are two main fire weather threats today: abundant lightning from scattered thunderstorms across fire weather zones 617, 623, 624, and 625, and gusty winds and low humidity within and around the Rogue and Shasta valleys. Red Flag Warnings are in effect for both of these areas. High pressure remains in control across the western United States. A weak trough offshore of California will move northward just offshore of the California coast, then pass over western Oregon today, before exiting to the north tonight. This will be the trigger for thunderstorm activity this afternoon and evening. The best chances for convection today looks to be along an arc from southern Lake County northwestward across Klamath County/Crater Lake into fire weather zone 617 and eastern Douglas County east of the I-5 corridor. Meanwhile, the trough will be taking on a negatively tilted orientation which is a common wind maker pattern for the area as well. Gusty south winds are expected across northern California, especially in the Shasta Valley as well as in the Rogue Valley, particularly between Ashland and Medford. These winds will combine with low daytime RHs to result in near critical to critical fire weather conditions for Tuesday afternoon. Tuesday night into Wednesday, low pressure finally swings through and out of our region. Given the negative tilt of the trough, it could kick off some nocturnal storms, but it looks more like a situation where storms develop along the Douglas/Lane County border and then moves north out of our area. Moisture looks to be well north and east of the region on Wednesday, so thunderstorm chances drop out of the forecast after Wednesday afternoon and typical summer weather conditions return. -BPN/BR-y && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this evening for ORZ616-617-623>625. Heat Advisory until 8 PM PDT this evening for ORZ024-026. Red Flag Warning from 2 PM this afternoon to 8 PM PDT this evening for ORZ622. CA...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this evening for CAZ281. Red Flag Warning from 2 PM this afternoon to 11 PM PDT this evening for CAZ284-285. PACIFIC COASTAL WATERS...None. && $$ MNF/BPN/DW