UFSP 100Weather Forecasting

Ross A. Lazear

Why is forecasting the weather so difficult?

• Imagine a rotating sphere 8,000 miles in diameter

-Has a bumpy surface-Surrounded by 40-km deep mixture of

different gases whose concentrations vary both spatially and over time

-Heated, along with its gases, by a nuclear reactor 93,000,000 miles away

• Sphere is revolving around the nuclear reactor

-Some locations are heated more during one part of the revolution than others

• Mixture of gases receives inputs from the surface below

-Generally calmly; sometimes violently!

Why is forecasting the weather so difficult?

Why is forecasting the weather so difficult?

.....Now, imagine that after observing this gaseous mixture, you are expected to predict its state at multiple locations on the sphere one, two, or more days into the future.

This is essentially the task encountered every day by a weather forecaster!

Adapted from Ryan, 1982, Bulletin of the American Meteorological Society

Why the discrepancy?

Forecasting is often extremely challenging!

There are *many* forecasts made available to the public…

*National Weather Service*The Weather Channel*AccuWeather*Wunderground*Your iPhone…etc…

*Nowcasting (Up to six hours)

*Short/medium range (Up to 7-10 days)

*Long range/intraseasonal/seasonal

*Climate (IPCC)

Types of Forecasts

*Nowcasting (Up to six hours)

*Short/medium range (Up to 7-10 days)

*Long range/intraseasonal/seasonal

*Climate (IPCC)

Types of Forecasts

When will the thunderstorm hit?

When will the snow taper?

When will the rain change to snow/sleet/freezing rain?

Nowcasting

Radar Satellite Soundings

Nowcasting Tools

Nowcasting Tools

Surface (airport) observations

*Nowcasting (Up to six hours)

*Short/medium range (Up to 7-10 days)

*Long range/intraseasonal/seasonal

*Climate (IPCC)

Types of Forecasts

Short/Medium Range Forecasting

Computer models needed!

Models use:-Current surface observations-Upper air observations-Previous forecast

…and then…

Short/Medium Range Forecasting

From MetEd / UCAR

Models

GFS - 16 days, global, U.S.A.NAM - 84 hours, N. America, U.S.A.HRRR/Rapid Refresh, 18 hours, U.S.A.ECMWF - 10 days, global, U.K.UKMET - global, U.K.NOGAPS - global, U.S.A. (Navy)JMA - JapanCMC - Canada

WRF - Multiple domains, also run locally at Albany!

*Nowcasting (Up to six hours)

*Short/medium range (Up to 7-10 days)

*Long range/intraseasonal/seasonal

*Climate (IPCC)

Types of Forecasts

Long Range/Intraseasonal/Seasonal

Various global “signals” that help meteorologists forecast on longer time scales.

-ENSO (El Niño/La Niña)

Long Range/Intraseasonal/Seasonal

Also…

-Lots of other complex atmospheric waves in the tropics…

From Dr. Paul Roundy, UAlbany

Hurricane Sandy, October 2012

National Hurricane CenterForecast for Hurricane Sandy5 PM EDT October 24, 2012

Evening of October 25, 2012

Other forecast challenges: Precipitation type!

Forecast temperature profile for March 19, 2013 winter storm

ACTUAL temperature profile for March 19, 2013 winter storm...Close call for a heavy sleet storm!

Other forecast challenges: Precipitation type!