Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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523 FXUS66 KMFR 232342 AFDMFR Area Forecast Discussion National Weather Service Medford OR 442 PM PDT Mon Sep 23 2024 .UPDATED AVIATION Discussion... && .AVIATION...24/00Z TAFS...VFR conditions will prevail across the region through the TAF period with patchy high level clouds streaming through the area. LIFR/IFR cigs/vis are likely to return to the coast north of Cape Blanco between 03z-06z, then around Brookings for a brief period around 12-15z. /BR-y && .PREV DISCUSSION... /Issued 221 PM PDT Mon Sep 23 2024/ DISCUSSION (Today through Sunday)... Noteworthy items for this forecast include the well above normal temperatures (10+ degrees) expected tomorrow with some areas approaching 100 degrees. Additionally, we have a chance for rain showers with this incoming system starting Wednesday morning, but this should be confined to the westside with the best chance for accumulation along/near the coast. Also with this system, strong wind speeds (areas of 25+ mph sustained) are forecast on the eastside, and this will be coupled with low RH values, so we are looking at the threat for fire weather conditions Wednesday afternoon. Please see the latest fire weather discussion below for further information. Thereafter, we have seasonable temperatures and dry conditions forecast through the weekend. Further Details: A ridge of high pressure aloft will start to expand over the PacNW today and tomorrow. This will lead to well above normal temperatures in the afternoon hours. Brookings is currently at 90 degrees as of writing this (~2pm) thanks to an ongoing Chetco Effect. Here in the Rogue Valley, we are forecast to reach 90...or close to it. Medford will likely see temperatures passing 90 degrees tomorrow as we are currently forecasting 97 degrees. Temperatures in the 80s expected on the eastside for tomorrow. The probability for Medford to reach 100 degrees tomorrow is about 10%, so we may not reach triple digits tomorrow. The record for Medford on September 24th is 99 degrees, so we will be within record territory. The 500mb pattern will undergo a transition today into tomorrow as a Rex Block pattern develops tonight, and then transitions to an Omega Block pattern across the CONUS late Tuesday afternoon. Blocking patterns are tricky sometimes, but this Rex Block seems to be progressive in the sense its not really "blocking" the flow too much (pseudo blocking pattern?). However, we should probably keep an eye on this transition as the block could disrupt rainfall timing and chances. A closed low on westside of the Omega Block is expected to ride the western periphery of high pressure center over the Four Corners Region. This trough is progged to go north/northeast through the PacNW on Wednesday. This southwesterly flow will allow for rain showers to develop and spread west to east through the day on Wednesday. Showers are likely not going too far into the evening, and the current thinking is showers are unlikely after 9pm. Not expecting any thunderstorms to develop with instability forecast to be very low (<100 J/kg). Broadly speaking, this is one of those "high PoP, low QPF" scenarios for Wednesday. Rainfall might make it into eastern Douglas County and parts of Josephine County, but chances farther east really dwindle for rainfall. Along and near the coast has the best chance for rainfall accumulation, with the probability for greater than 0.10" over 12 hours around 10%-50%. That said, the chance for rain itself along/near the coast is about 35%-80%. In other words, expecting light rainfall amounts for areas west and north of a line from roughly Cave Junction to Roseburg. Areas south and east of this line will be lucky to get a couple hundreths (0.01") of rainfall. -Guerrero MARINE...Updated 200 PM Monday, September 23, 2024...A thermal trough remains in place over the Oregon coast. The trough will continue bringing gusty northerly winds through early Tuesday morning. A Small Craft Advisory remains in place for wind-built steep seas of water south of Bandon through Tuesday at 11 AM. Periods of very steep and hazardous seas are possible south of Pistol River late Monday night into early Tuesday morning. After the current Advisory ends, northwest swell will keep seas in the 7 to 8 foot range with longer periods keeping seas below Advisory levels in the middle of the week. Northerly winds will increase towards the end of the week and combine with the steep northwest swells. -TAD/Smith FIRE WEATHER...Issued 200 PM Monday, September 23, 2024... Offshore flow of recent days will ease today through tonight as the thermal trough that is present along the coast weakens. The thermal trough will shift northward and move inland on Tuesday. Where it is hot today (Brookings), it will be much cooler on Tuesday as marine air takes hold. However, inland areas will have the hottest day of the next 7 days. West side valleys will rise well into the 90s with a few spots flirting with the 100-degree mark. Winds on Tuesday will be fairly typical with afternoon gusts of around 15-20 mph and minimum RH values in the 15-25% range. The main fire weather risk comes on Wednesday as an upper trough swings through the PacNW. While the associated marine push will send some clouds and even a little rainfall onto the coast/Umpqua Basin (a few hundredths to a tenth of an inch for the Bottom Creek fire), gusty W-SW winds are expected in advance of the trough from the Cascades eastward. At least a few hours of windy conditions in portions of eastern Siskiyou, Modoc and into Klamath/Lake counties. Expect most of those areas to have 15-20 mph sustained winds during the afternoon with frequent gusts of 35 mph. Local RAWS guidance for some of our most exposed RAWS sites (Coffee Pot, Summit, Summer Lake, Timber Mtn) is showing peak wind gusts in the 40-45 mph range. The limiting factor though is that minRH values are shown to be in the 15-20% range, slightly too high for a Fire Weather Watch. We`ll continue to headline this risk though in the Fire Weather Planning Forecast. After that trough, there`ll be a break Thursday, then another weak trough/marine push is expected Friday afternoon/night. This one doesn`t look as strong as the Wednesday trough. The next stronger trough is shown to arrive over the weekend. This may increase W-SW winds again over the East Side/Modoc County Saturday afternoon/evening (winds may be similar to Wednesday) and RHs may be down a bit as well. This could then induce another thermal trough with a period of offshore NE winds Sunday into early next week. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Tuesday for PZZ356-370-376. && $$