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Hazardous Weather Ahead and
Outlook for Winter
2009-2010
Dave Reynolds -MTR
Dan Keeton - STO
Meteorologists in Charge
weather.gov/SanFrancisco
or
/Sacramento
Your NWS Weather Forecast Office
San Francisco Lightning
• Our goal:
Provide forecasts and warnings so people can make
informed decisions.
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7-Day Forecast
3-5 Day Outlook
Special Weather Statement
Hazardous Weather Outlook
Marine Weather Statement
Hydrologic Outlook
potential
Hazard
12 to 48 hours ahead
imminent
Hazard
Hazard
Developing Stormy Pattern for California
• This weather pattern, which features strong zonal flow aimed at
portions of the west coast, is likely to last up to a week and maybe
longer.
• The pattern may be related to ongoing activity in the tropics
associated with the Madden-Julian Oscillation.
• This weather pattern is likely to be more transient in nature than that
typically observed with El Nino.
• El Nino does favor additional events of this type – but typically they
occur later in the winter (January-February timeframe), and are
associated with an amplified wave pattern, eastward extension of the
Pacific Jetstream, and persistent pattern of storminess somewhat
farther to the south.
MJO Index -- Recent Evolution
 The axes (RMM1 and RMM2) represent
daily values of the principal components
from the two leading modes
 The triangular areas indicate the location
of the enhanced phase of the MJO
 Counter-clockwise motion is indicative of
eastward propagation. Large dot most
recent observation.
 Distance from the origin is proportional to
MJO strength
 Line colors distinguish different months
The MJO has continued to
propagate eastward.
Storm track and moisture source
often associated with the MJO
Setup for
Atmospheric River
SSMI shows AR stretching across Pacific to
Central California
Atmospheric River
Central CA
>15 inches
rain
Series of Storms Starting Sunday Night
H
Enhanced Jet
Cold arctic
air to move
south
and west
Sunday
Remnants of
Typhoon NIDA
MJO driven
thunderstorms
First Storm: Sunday Night – Monday Night
More Storms: Tuesday – Next Week Week
ECMWF 156-hr forecast 250 mb winds valid 12Z Wed 09 Dec
(knots)
In general there is widespread
agreement on strong zonal flow
into California next week. Maybe
Centered south of Bay Area.
Valid 4pm Wednesday Dec 09
Drought Relief is Coming
Winter Outlook
• Expect possible moderate strength El Nino
to persist through spring.
• Could bring recurrence to weather we will
see next week.
• May not see influence until January
• Impacts still not certain
Sea Surface Temperature
Anomalies – El Niño
Thunderstorm Activity Tropics
Located over SSTs > 28C
Mass of warm water under surface
should maintain or enhance El Nino
Animation of subsurface tropical
ocean temperatures
SST Outlook: NCEP CFS Forecast
Issued 8 November 2009
The CFS ensemble mean (heavy blue
line) predicts El Niño will last at least
through Northern Hemisphere spring
2010.
El Niño
El Niños feature a strong jet stream and storm track across the southern part of
the United States, and less storminess and milder-than-average conditions across
the North.
ENSO strength vs SFD WY rainfall and
sign of PDO Sept-Nov.
Strong La Nina
Weak/
Mod
La Nina
Neutral
Weak/
Mod
El Nino
Strong El Nino
Where are we now?
Years with closest fit
MEI Ranking
72-73 WY = +.59
65-66 WY = -.25
57-58 WY = +.67
70
60
Ranking 1-60
50
40
1972-73
2009-10
30
1965-66
20
1957-58
10
0
Monthly Pairs
U.S. Precipitation Tends Forecast for El Niño 09-10
weather.gov/SanFrancisco
Hazard map – clickable
Satellite
Radar
River Forecasts
Forecast Discussion
Media Briefing
• Any Questions??
Current state of ENSO
• Last year
moderate La Niña
• Currently,
moderate El Niño
Winter Predictions
for 2009-2010
So what does this forecast mean regarding
our current drought situation?
Most of California is
currently under
drought conditions
Current drought
conditions are likely to
improve over the next
several months
El Niño Generalities
• During El Niño rainfall and thunderstorm activity
diminishes over the western equatorial Pacific, and
increases over the eastern half of the tropical Pacific.
– This overall pattern of rainfall departures spans nearly one-half
the distance around the globe, and is responsible for many of
the global weather impacts caused by El Niño.
• El Niño episodes feature large-scale changes in the
atmospheric winds across the tropical Pacific, including
reduced easterly (east-to-west) winds across the eastern
Pacific in the lower atmosphere, and reduced westerly
(west-to-east) winds over the eastern tropical Pacific in the
upper atmosphere near the tropopause.
•
El Niño’s affect on the Atmosphere
• An eastward extension and equatorward shift of the jet stream
from the International Date Line to the southwestern U.S.
• A more west-to-east flow of jet stream winds across the U.S.
• A southward shift of the storm track to the southern part of the
United States.
• A southward and eastward shift of the main region of cyclone
formation to just west of California.
• Results: a better chance of a stormy winter and increased
precipitation across California and the southern U.S, and less
stormy conditions across the northern part of the U.S.
• Also, there is an enhanced flow of marine air into western North
America, along with a reduced northerly flow of cold air from
Canada to the U.S. These conditions result in a milder than
normal winter across the northern states and western Canada.
El Niño: pronounced eastward extension of deep tropical convection and heating
to well east of the date line which extends the subtropical ridges in both
hemispheres to well east of the date line. This results in a pronounced eastward
extension of the midlatitude jet stream to the extreme eastern Pacific and an
equatorward shift of the jet streams over the eastern Pacific. This in turn has a
major affect on the winter weather patterns and storm tracks.
Animation of subsurface tropical
ocean temperatures