Hazardous Weather Ahead and

Outlook for Winter 2009-2010

Dave Reynolds -MTRDan Keeton - STOMeteorologists in

Charge

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or /Sacramento

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San Francisco Lightning

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WFO Product Timeline7-Day Forecast

3-5 Day Outlook

Special Weather StatementHazardous Weather OutlookMarine Weather Statement

Hydrologic Outlook

Hazard Watch12 to 48 hours ahead

Hazard Advisory Hazard Warning

potential

imminent

Nuisance Life and/or property threatening

• 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.

Developing Stormy Pattern for California

MJO Index -- Recent Evolution

The MJO has continued to propagate eastward.

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

Storm track and moisture source often associated with the MJO

Setup for Atmospheric River

SSMI shows AR stretching across Pacific to Central California

Central CA>15 inches rain

Atmospheric River

Series of Storms Starting Sunday Night

First Storm: Sunday Night – Monday NightMore Storms: Tuesday – Next Week Week

Remnants of Typhoon NIDA

MJO driven thunderstorms

Enhanced Jet

Cold arctic air to move south and west Sunday

H

(knots)

ECMWF 156-hr forecast 250 mb winds valid 12Z Wed 09 Dec

In general there is widespreadagreement on strong zonal flow into California next week. MaybeCentered south of Bay Area.

Valid 4pm Wednesday Dec 09

Details still to be determined on timing and location of impacts

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 TropicsLocated 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 El Nino

Weak/ModEl Nino

NeutralWeak/ModLa Nina

Strong La Nina

Where are we now? Years with closest fit

DECJAN

JANFEB

FEBMAR

MARAPR

APRMAY

MAYJUN

JUNJU

L

JULA

UG

AUGSEP

SEPOCT

OCTNOV

NOVDEC0

10

20

30

40

50

60

70

MEI Ranking

1972-73

2009-10

1965-66

1957-58

Monthly Pairs

Rank

ing

1-60

72-73 WY = +.5965-66 WY = -.2557-58 WY = +.67

U.S. Precipitation Tends Forecast for El Niño 09-10

weather.gov/SanFrancisco

Hazard map – clickableSatelliteRadarRiver ForecastsForecast Discussion

Media Briefing

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Current state of ENSO

• Last year moderate La Niña

• Currently, moderate El Niño

Winter Predictionsfor 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