WEATHER SUMMARY AND FORECAST DETAILS
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FOR 5/18/2020 - from Medford NWS
Showers and isolated thunderstorms yesterday brought a significant amount of precipitation to many areas. The heaviest precipitation was around the Mount Shasta region where it picked up well over an inch of precipitation in the past 24 hours. The south end of the Shasta Valley also picked up between 0.30 and just over an inch with the highest amounts near and at Weed. The core of the heaviest rainfall in Oregon was along a corridor from Southeast and Eastern Jackson County running north to northeast along the Cascades and Northwest Klamath County. Even portions of the eastside got into the action with Summit Raws site in Eastern Klamath County picking up 0.50 of an inch in the past 24 hours. Rainfall totals for Curry County were pretty significant as well ranging from 0.80 to just over an inch.
Despite the significant amount of rain, no record were set, but it was close in Mount Shasta where the record was missed by 0.03" of an inch. All this rain is good news because of the lingering drought conditions and the amount we picked up since Friday afternoon and the last round the first part of the month certainly helps.
The latest satellite image shows the upper low closer to shore with plenty of shortwave energy rotating around it up into our area. So we can expect pretty much the same with showers at a relative minimum this morning, then increasing coverage as the upper low moves inland and brings the colder air aloft with it. At the same time daytime heating will once again provide the opportunity for isolated thunderstorms this afternoon and early evening for most of the area. The exception will be in Northwest Douglas and Northern Coos County where it`s expected to be more stable. However it not expected to be widespread as yesterday. It will be one of those days where we`ll have plenty of showers with isolated thunderstorms. The upper low will weaken and move south of the area tonight. The coldest air aloft will be south and we`ll actually have some warming aloft. So as we lose daytime heating, showers will begin to diminish around sunset with not much more then a few isolated showers lingering in the overnight period.
Tuesday, the upper low will weaken as it moves further inland and moves southeast of our area. Despite this, surface heating will result in enough instability for showers to increase in coverage mainly along the Cascades and east side Tuesday afternoon. Although a moist northwest flow on the backside of the upper low could bring a few showers to the coast and Douglas County. Wednesday will be transition day as the upper low finally moves east of our area and weak ridging builds in. Most areas will be dry, but could not rule out isolated showers in the Northern Cascades and Northern Douglas and Coos County.
The operational ECMWF and GFS forecast computer models are in similar agreement showing another upper low moving southeast into Northwest Washington state Thursday afternoon with an increasing west to northwest flow in our area. A cold front will also drop south, but moisture is lacking which makes sense given the trajectory of the upper low. The operational models show the best chance for showers mainly north of the Umpqua Divide and northern Cascades. The models show the upper trough dropping south into the area on Friday. However the GFS has backed off on the over water trajectory of the upper trough and has it inland over our area. The ECMWF shows the upper trough swinging northeast of our area which typically results in a dry cold front passage. Therefore the chances for shower activity have been cut back and could very well be cut back further. Note: A closer examination of the GFS and ECMWF individual ensemble members are showing little or no precipitation south of the Umpqua Divide on Friday. (Note from Rogueweather - I spotted that trending coming an had a much drier forecast for Friday than NWS did last night. They have now come in line with the forecast I have for Friday.)
All in all, most areas and hours will be dry Friday, then the majority of the individual ensemble members (ECMWF and GFS) are pointing towards dry and warmer weather for the Memorial Day holiday weekend. Of note: The operational ECMWF shows a frontal boundary remaining north of our area and nearly parallel to the upper flow which would keep it there. The GFS shows more troughing and a very slight chance for showers Sunday and Monday, but as mentioned the majority of the individual GFS and ECMWF ensemble members don`t show anything. Treating the GFS main as an outlier and have forecasts dry through Monday Memorial Day.
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