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Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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269 FXUS66 KMFR 162139 AFDMFR Area Forecast Discussion National Weather Service Medford OR 239 PM PDT Tue Jul 16 2024 .DISCUSSION...Upper low centered off of northern California this afternoon is spinning slowly northward and wrapping some drier mid level air into the region. Southerly winds gusting to 15-20 mph across the south and east so far but not yet surfacing in the Rogue Valley. The south wind is also evident from Ashland to Phoenix but may not happen around the airport and northward. We`ve got higher confidence in the west/northwest winds around 15 gusting to 25 mph by later in the day. The drier air is mainly seen moving into Siskiyou, Jackson, and western Modoc counties through 8 pm, then gradually overtaking the remainder of the CWA through about 2 am. Outside of this drier wedge, a 10 to 30 percent coverage of thunderstorms is expected, with the highest concentration over the east side and the eastern Douglas county foothills and Cascades around and north of Crater Lake. Gusty outflows OF 45-55 mph are again possible. The center of the upper low should be somewhere off the Coos coast by early Weds morning and showers and storms will have lifted north and east of the CWA. The area can expect slightly cooler and more stable weather over the area for a couple days with the western valley dipping into the mid to upper 90s, and east side areas into the upper 80s to around 90. Not a huge relief from the recent sweltering July, but some relief nonetheless. The upper high over the intermountain west will retrograde back toward the west coast Friday into the weekend with temperatures coming back up a little bit. We may see some of the east side and south flirt with Heat Advisory levels as the NWS Heat Risk indicates moderate to locally major levels Saturday and Sunday. The other thing to concern ourselves with by Saturday is another short wave in the SW flow forecast to scoot up the coast region. This pattern, as we`ve seen recently, can certainly bring thunderstorms to the area. Confidence in the details is low at this point with little ensemble consensus. Pops of 5 to 10 percent are forecast over the east side at this time and this should be monitored for fire weather concerns. Stavish && .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 200 PM 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/BR-y && .FIRE WEATHER...Issued 200 PM Tuesday July 16, 2024... There are two main fire weather threats today: First, abundant lightning from scattered thunderstorms across fire weather zones 616, 617, 623, 624, 625, and 285. Second, gusty winds and low humidity within and around the Rogue and Shasta valleys. The main change that was made for today was to include the eastern part of fire zone 616 (east of I-5) and most of fire zone 285 into the Red Flag Warning for abundant lightning on dry fuels for this afternoon into late this evening. The newest data this morning showed increasing evidence that storms could fire up in these areas this afternoon into this evening. An upper trough offshore is taking on a slight negative tilt which is concerning in that it will result in conditions being ripe for the pickings for thunderstorms to develop this afternoon and carry over into this evening. There`s some indications isolated storms could make they way all the way to the coast in Coos, northwest Douglas and portions of Fire zone 620 County later this afternoon into this evening, but storms in these areas should be isolated. 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 fire zone 616, east of the I-5 corridor. Additionally, storms this afternoon will tend to be fast movers which could result in additional forward momentum, meaning outflow winds could end up stronger than what we could typically see in slower moving storms. It`s also worth noting, some of the high res guidance suggest convection could also break out over the northern part of fire zone 622. Even though the Red Flag Warning covers the wind and RH component, additional information as been added to the headline to include the thunderstorm potential leading to new fire starts. As previously mentioned, 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 this afternoon. Tonight, the upper trough axis will move over the area and the threat of storms will shift north of our area ahead of the upper trough axis. We could see the last of the storms end or move out of the area between 11 pm and midnight tonight. 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. A dry and stable southwest flow sets up over the area Wednesday through Friday with no concerns for thunderstorms. However, afternoon relative humidities will trend lower for most interior locations with values in the single digits for portions of the eastside Wednesday, Thursday, and Friday along with the typical gusty afternoon and early evening breezes. This will result in near critical conditions for portions of Fire zones 624, 625 and 285, but at this time were not expecting the combination of wind and RH to result in Red Flag conditions. This weekend will warrant close watching. Some evidence is pointing towards another upper low moving up from the south on the backside of the four corners high and could tap into some monsoonal moisture as early as Saturday. Therefore there`s could be an increasing concern for thunderstorms. This is something that we`ll monitor, especially once we get past late this evening. Stay tuned. Petrucelli && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 11 PM PDT this evening for ORZ616-617-623>625. Heat Advisory until 8 PM PDT this evening for ORZ024-026. Red Flag Warning until 8 PM PDT this evening for ORZ622. CA...Red Flag Warning until 8 PM PDT this evening for CAZ281. Red Flag Warning until 11 PM PDT this evening for CAZ284-285. PACIFIC COASTAL WATERS...None. && $$