Winter Weather Forecast 20142015
How Windy Will in Be?
Professor Cliff Mass
University of Washington
What are the chances of getting a
major windstorm?
The Most Useful Tool for
Predicting the General
Characteristics of Northwest
Winters:
The Connection Between El Nino/La Nina
and Northwest Weather
Neutral
La Nina
Three Phases
An important measure of El Nino/La Nina
is the sea surface temperature anomaly in
the central tropic Pacific: the Nino 3.4
area
El Nino: >.5C
La Nina:<-.5C
Neutral: .5 to -.5
The Correlations
• El Nino years tend to be warmer and drier.
Fewer big storms.
• La Nina years tend to be cooler, wetter, and
snowier.
• Neutral (or La Nada) years tend to have
normal precipitation and temperature, but are
the years with the rare, but damaging, major
windstorms and floods.
El Nino, La Nina, La Nada and Major
Windstorms
•Major windstorms appear to avoid El Nino and La Nino years
•They like neutral winters.
This Year: Weak El Nino Winter
Forecasts by the Climate Prediction Center
65% probability of El Nino Conditions
But How Strong?
• The effects over the Northwest are greatly
influenced by its El Nino/La Nina strength
Central Pacific (Niño 3.4) Sea Surface
Temperature Outlook: Weak El Nino
• El Nino defined as positive temperature anomaly of greater than .5C
SST Outlook: National Weather Service LongTerm Forecast Model
The CFS.v2 ensemble mean (black dashed line)
predicts ENSO-neutral conditions (warm side of
neutral) through spring 2014.
Bottom Line
• Without a strong El Nino, the potential
for strong windstorms will be
undiminished.
Climate Prediction Center U. S. Seasonal
Outlooks
October – December 2014
Temperature
Precipitation
The seasonal outlooks combine the effects of long-term trends,
soil moisture, and ENSO (El Nino/La Nina).
City Light and its customers
can prepare better today for
windstorms because short
and extended range forecasts
have improved
Forecast Models are Now Showing
Useful Skill for 7-9 days Out
2012: Hurricane Sandy
125 dead, 60+ billion dollars damage in an area with a
population of tens of millions.
Well predicted, more than a
week ahead
ECMWF 6-day Forecast of Sea Level Pressure
Major Advances in Short-Term
Prediction: the High Resolution
Rapid Refresh (HRRR)
Best Forecast Next Few Hours: NOAA
HRRR Model
(http://ruc.noaa.gov/hrrr/)
Forecasts made
every hour
High resolution
15h prediction
Tailored Local Forecast Guidance
• The UW and the City of Seattle have worked
together to produce three web sites with
weather guidance for city personnel and
citizens:
– Rainwatch
– Snowwatch
– Windwatch
Seattle WindWatch: Upgraded for
2014 by Jeff Baars!
Seattle WindWatch (2014 Edition)
• Provides access to National Weather Service
and UW High Resolution Forecasts.
• Provides real-time warnings (e.g., email, txt
message) to city personnel when high winds
threaten.
• Now monitors observed winds.
• And includes the new HRRR forecasts (out 15
hr)
Warning Capabilities
• WindWatch electronically warns Seattle Light
personnel when observed or forecast winds
exceed specified thresholds.
A Now a REALLY Long Wind
Forecast
Will Global Warming produce
stronger winter winds here in
the Northwest?
City Light has supported the UW to examine
the output of long-term regional climate
models
The Answer Appears to Be No!
1970-2070
1970-2070
Next Issue
• Will lightning increase over our area as the
Earth warms?
Final Remarks
• Large uncertainty in seasonal forecasts. Think
of dice being weighted
• A weak to moderate El Nino this winter will
probably not weight the meteorological dice
heavily.
• So no reason to expect an atypical wind
season
• Forecast models continue to improve.
• Seattle WindWatch has substantially
enhanced capabilities.
The End