textproduct: Medford

DISCUSSION

The forecast still separates into a period of dry weather through Wednesday (with little difference on Tuesday and Wednesday in comparison with today's conditions), and a relatively long period of active weather Wednesday night into next Monday (with impacts on the lower end of what is seasonably typical when expecting a series of disturbances).

The main feature of the short term is the Air Stagnation Advisory /PDXNPWMFR/ that remains in effect through Wednesday afternoon for all valleys east of the Coast Range. This has been most noticeable in Josephine and Douglas counties, where it naturally follows that stratus and patchy fog has been most persistent. Other characteristics of our short term weather under the ridge portion of a rex blocking pattern are light winds, strong valley inversions during the night and morning hours, dry air on ridges, chilly morning lows, and normal to above normal afternoon high temperatures.

Beyond Wednesday afternoon, continuing through Day 7, the NBM was utilized and is a highly appropriate solution in balancing a cadre of very weak, weak, or seasonable frontal impacts. There is around a 20% probability that each of the several disturbances will bring very weak, barely impactful weather to our area. There is a similar 20% probability that we will have more than an advisory level hazard or two or three worth advertising. Thus, leaving a 40% probability, the most likely, that an active pattern will bring periods of rain and mountain snow with snow levels on the high side of normal and precipitation amounts that are well worth noting but should keep impacts on the lighter side.

More specifically, we will begin Wednesday with the ridge beginning to nudge out of our area, a trough far offshore of southern California, and another trough in the Gulf of Alaska. Forecast confidence is high through Wednesday night, Above average for Thursday, and a little lower than average from Friday onward. Which, is actually typical given the complexity of the pattern. The Californian trough will track northeastward with southerly upslope flow bringing a chance of rain into our area before the end of Wednesday evening, particularly for southern and western Siskiyou County, and southern Curry County. This disturbance will likely continue across our area Thursday into Thursday evening. A minority of solutions (10-20%) are stronger, but slower with a track that sends a low northward farther to the west. A larger minority of solutions are weaker than the blended solution. The highest probability is for around an inch of precipitation in the Mount Shasta region and less elsewhere in our area through Thursday night with snow levels falling from around 8000 feet to around 7000 feet.

The highest probability for the strongest system of the batch comes from a developing low moving southeast out of the Gulf of Alaska before swinging northeast toward northern California. From Friday afternoon into early Saturday, precipitation amounts are forecast to be roughly double compared to Thursday's system...around 2 inches are forecast around southern/western Siskiyou County and southern Curry County. Snow levels are forecast to continue the slow downtrend from around 7000 feet to around 5000 feet during the event. The highest probability scenario would warrant Wind Advisories to be issued for the Shasta Valley and portions of the east side during Friday afternoon and night with southerly wind gusts of 35 to 55 mph.

An onshore, westerly flow is likely to follow for the weekend. This tends to be a showery pattern with at least slightly lower snow levels, most likely dropping to around 4000 to 5000 feet. The main uncertainty regards the strength and duration of breaks in- between shortwave disturbances. About 20-35% of ensemble solutions bring a stronger front with the passage of the axis of the upper level trough on Saturday.

Model uncertainty moves up a notch for early next week with the potential that the northern branch of the jet stream will be focused north of Oregon, allowing weak ridging into our area. Or a near equal probability for a continued showery pattern. All-in- all, from late this week into early next week, snow levels are likely to remain above the major passes for the bulk or possibly even all of these events. precipitation is unlikely to cause impactful rises on our rivers, and wind speeds will also not be overly noteworthy. For most of our area, this will bring higher low temperatures, but also lower high temperatures compared to the current pattern. Over the course of the 5 days from Thursday through Monday, around 6 inches of precipitation is forecast for southern Curry County, around 2.50 to 5 inches in southern and western Siskiyou County, an inch to 3 inches in Josephine County, around 2 inches for Coos County, around an inch for the Roseburg and Yreka areas, less than an inch for the Medford area, around 1.50 inches for the southern Oregon Cascades, and up to a half inch for the east side. For this time of year, that is nothing to write home about and doesn't appreciably help build the snow pack in much of our area. But, it is more beneficial than continuing our current dry weather.

In the Day 8 to 14 period, the pattern is likely to remain active, but the probability of stormy weather is lower than indicated by yesterday's suite of model data.

AVIATION...29/18Z TAFs

There is some high level cloud cover streaming over the region this morning along with gusty east to northeast winds across the terrain and along the coast. VFR prevails over most of the forecast area with some LIFR around Grants Pass and IFR around the Umpqua Valley. With the high clouds and lower sun angles, those areas will likely remain socked in with low clouds today. There is a low chance they could mix out as there is plenty of dry air aloft that could eat into the clouds.

Otherwise, we looked at fog potential in Medford, MFR, tonight and it seems the air could be too dry for any fog to form. High clouds will be around again through the evening and overnight hours, so that will be another check against fog formation. A persistence forecast would hint at more clear skies in the boundary layer tonight as not a whole lot will change tonight. So VFR remains more likely in Medford tonight, although there is still a low chance for some LIFR visibilities.

-Smith

MARINE...Updated 200 PM PST Monday, December 29, 2025

Westerly swells will start this afternoon and continue overnight. The weak thermal trough responsible for the northerly winds will shift northward tonight into Tuesday, bringing a brief period of southerly winds within 10-30 nm from shore. Stronger south winds begin late in the week ahead of the next series of frontal systems.

-Smith

MFR WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 4 PM PST Wednesday for ORZ023>026- 029>031.

CA...None.

PACIFIC COASTAL WATERS...None.