WEATHER SUMMARY AND FORECAST DETAILS
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FOR 6/20/2018 - compiled by staff meteorologists from Medford NWS
Moisture and instability will increase today in advance of a potent short wave disturbance associated with an upper level trough off the Northern California coast. Mid-level cooling is forecast to arrive with the shortwave at max surface heating this afternoon will lead to a very volatile atmosphere. The result will be widespread thunderstorms with scattered strong to isolated severe thunderstorms over portions of the forecast area this afternoon and evening. The main threat area will be from the Cascades near Lake of the Woods north and northeastward across far Eastern Douglas County, Northern Klamath and northern Lake Counties. We could also see the development of strong to an isolated severe storm back into Northern California.
Storms are expected to begin forming from Noon-2 pm with the most robust development expected from 2-11 pm tonight. Storms are likely to initiate over the mountains in the Southern Oregon Cascades, Siskiyous and western Siskiyou County early this afternoon, and then spread north and northeast late this afternoon and evening across Klamath and Northern Lake Counties. Recent runs of the convection allowing models show a threat period of 3-7 pm for the Rogue Valley (especially south and east sections), which falls in line with the data. The main threats with storms today will be frequent cloud to ground lightning, locally heavy rainfall, and the possibility of damaging wind gusts and hail. Most of the convection should stay east of a line from Roseburg to Grants Pass. However, given the situation for today and based on what we saw happen this weekend, I will say that there is a possibility we could see storms fire up anywhere inland from the coast. Make sure to keep an eye to the sky and have a plan if thunderstorms threaten. Seek shelter until the storms pass completely.
There may be some drizzle along the coast with a deepening marine layer tonight. This will also mean more clouds farther inland into the Umpqua Basin. Cooling behind today`s system will be minor, perhaps not even noticeable in most places, but with more clouds due to the marine layer, places like Roseburg will likely feel the most change from today to tomorrow. Overall, Thursday to Saturday will be warm and probably dry for inland areas with temperatures about 5-8 degrees above normal. Another shortwave disturbance will move through Thursday afternoon. Right now, moisture doesn`t look robust enough to include a slight chance of thunderstorms, but there could be some buildups over the East Side. Something to keep an eye on.
Models continue to show a spike in heat Sunday with forecast upper atmosphere temps in the 23-25 C range. This would put highs in the upper 90s here in Medford and near 90 in the Klamath Basin. 100F is in the range of high end data output for Medford, but 100 is a high outlier at this point. The current forecast has a high of 97 degrees for Medford on Sunday. That may change if the data comes into better consensus. This bout of heat will be short-lived, however, as the next Pacific trough is expected to move in early next week. This will bring a period of gusty afternoon west-northwest winds as the
trough moves onshore Monday. Without significant moisture, however, we are not expecting any precipitation. While we`ll take the edge off the heat Monday and Tuesday, we`ll still be about 5-8 degrees above normal.
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