Forecast for next week — another Atmospheric River

This is a much longer and in depth forecast discussion than I usually post, but dangerous conditions are forecast so everyone needs to be focused on situational awareness and safety for themselves, their families, and their neighbors.

An approaching atmospheric river (AR) will begin to up the ante
later Monday and for the second time in one week. Models are
trending upward as to the strength of this AR. Integrated Water
Vapor Transport numbers around 700 kg/m/s, combined with a low-
level jet now showing the potential for 60 knots, is now making
this a strong AR. This will be similar to the AR that was just
experienced, if not stronger. Models have trended upward to
reflect the increase in intensity of both the winds and water
vapor associated with this plume of heavy moisture. Ensembles of
both the GFS, ECMWF and Canadian are all showing a majority of
members with heavy rainfall. Additionally, the EC originally was
showing a more northward track while the GFS showed a track
directed straight for the Bay Area. Those have come into better
alignment with the bullseye now being more focused to the Bay Area
and Central Coast region.

Due to this, a High Wind Watch is in effect from Monday evening
through late Tuesday night for southerly winds 25 to 40 mph with
gusts up to 50 mph in the valleys. Expect gusts from 55 to 70 mph
along the immediate coastline and in the hills above 1,000 feet.
This will be for the entire San Francisco Bay Area and Central
Coast. Fully saturated soils plus winds of this nature could
create a potentially dangerous situation. Trees and power lines
will fall easier than the last AR, putting everyone at risk.
Travel will be hazardous for the Tuesday morning and afternoon
commutes. It is best to delay travel.

Additionally, a Flood Watch is also in effect from Monday evening
through late Tuesday night for the San Francisco Bay Area and
Central Coast. This is due to flooding caused by excessive
rainfall being likely which will lead to creeks and streams
rising out of their banks. Extensive street flooding and flooding
of creeks and rivers is likely.

Further compounding this issue will be the elevated water levels
due to the most recent AR event. Areas such as the North Bay,
East Bay and South Bay will see renewed flooding. Additional
rainfall associated with this second AR will exacerbate ongoing
flooding across Monterey County. There is an extremely high level
of concern regarding the prolonged duration of flooding as all
mainstem rivers will be elevated before the next AR makes landfall.
Major interstates and highways can flood. Urban flooding, flash
flooding and mainstem river flooding will be worse than last week.
Widespread shallow landsliding is likely along with debris flows.
Once again, travel will be dangerous for the Tuesday morning and
afternoon commutes. Postpone travel! If you do travel (but don`t) turn
around, don`t drown!

Now is the time to prepare. Get gas for generators, food and
medications. Clean storm drains and gutters. Tie down or move
loose objects inside. Along with the trees falling, power outages
will happen, yet again. This is a potentially dangerous situation
as it comes so quickly on the heels of the last AR.

Expect prolonged, long-fused impacts associated with these back to
back storms even when the storm moves out of the area. This is
looking to be likely Wednesday with conditions continuing to dry
out into Friday. The dry air will usher in colder temperatures
with the potential for higher elevations to drop to around freezing.
After this, chances for rainfall could return for Friday and
Saturday, however, confidence is low at this time.

3 thoughts on “Forecast for next week — another Atmospheric River

  1. For a dramatic view of a river ..try the Palo Corona paths..there are two bridges offering unique view extending both upstream & down..powerful & of course beautiful sound. Take good care everybody

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