Friday, September 27, 2013

Email Weather Briefing
Courtesy: NOAA/NWS, Portland, OR
September 27, 2013
Emergency Managers and Public Safety Officials,
This is an update to our email briefing we sent yesterday (Sep 26). The most significant item to add to today’s briefing is another strong weather system is expected on Sunday. This system will have the potential to produce the strongest winds of the weekend as well as some dangerous conditions in the surf zone.
Expect winds on the coast of 65 to 80 mph, inland valleys 40 to 50 mph during the day on Sunday. Also, high seas (20 to 25 ft seas) and dangerous conditions in the surf zone are expected Sunday and Monday.
The impacts from the first two storms we discussed yesterday remain relatively unchanged. More details below.
SYNOPSIS: A significant change to a very wet weather pattern is underway. The first storm is moving into the region today (Sep 27) with rain becoming steady later this afternoon and evening.
Another system is expected to move over the area Saturday (Sep 28) into Saturday night which will bring heavy rain and strong winds to the region. Rich sub-tropical moisture from an old typhoon has been entrained into this weather system, so heavy rainfall over the region is expected. Rain will increase during the day on Saturday with flooding on small streams likely as well as urban and street flooding. Winds will become strong on the coast in the late morning into afternoon (50 to 65 mph) and throughout the afternoon in the valleys (30 to 40 mph). There may be a brief break in the rainfall and winds late Saturday night into early Sunday morning before a third storm moves in.
Yet another weather system is expected Sunday that may perist into early Monday. This system is expected to produce the strongest winds along the coast (65 to 80 mph) and inland (40 to 50 mph) Sunday into Sunday evening as well as continued rainfall.
Rainfall amounts are for late Friday through late Sunday. Precipitation graphics are included in the attached word document.
  • Coast/Coast Range: Heavy Rain - (3 to 7 inches)
  • Valleys/Gorge: Heavy Rain - (2 to 4 inches)
  • Foothills/Cascades: Heavy Rain - (5 to 10 inches)
  • Coast/Coast Range (mid morning through evening)
    • 60 to 70 mph (headlands)
    • 50 to 60 mph (coastal communities)
  • Valleys (afternoon/evening)
    • 30 to 40 mph.
  • Coast/Coast Range (morning/afternoon):
    • 70 to 80 mph (headlands)
    • 60 to near 70 mph (coastal communities)
  • Valleys (afternoon/evening)
    • 40 to near 50 mph.
Sea conditions
Sunday into Monday
  • 20 to 25 ft seas
  • Dangerous conditions in the surf zone
  • Heavy Rain:
    • Although rivers and streams are near base flow, there could be sharp rises on smaller creeks and streams and moderate rises on rivers.
    • Flooding on small streams and pasture lands.
    • Likely some urban street flooding as leaves are just beginning to fall and may clog some storm drains. Rainfall rates may be high at times which may cause local street flooding at times.
  • Winds
    • Local power outages likely on the coast and in the valley as strong winds could break weakened tree branches and limbs.
  • Surf Zone
    • Dangerous sneaker waves and rip currents
- High Confidence:
o Heavy rainfall over the area
o Strong winds along the coast and inland
o Sea and surf zone conditions
- Low Confidence:
o Whether flooding will only be confined to small streams and urban areas
UNCERTAINTIES: There is some uncertainty whether the axis of heavy precipitation may stall for a few hours somewhere over the region during the weekend. There is also some uncertainly whether there will be a brief break in rainfall late Saturday night.
Monitor river conditions and forecasts at, and
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