eta 6-hr fcst. valid 18z 02/19/02

ETA 6-hr fcst. Valid 18z 02/19/02

Will it rain at MEM, JAN at 00z???

Association: Radar to 700 RHPRECIP FORECASTING

Radar: 18z 6-hr ETA 700mb RH fcst: 18z

Observations Short-term model output

Association: Radar to 700 RHPRECIP FORECASTING

6-hr ETA 700mb RH fcst: 18z 12-hr ETA 700mb RH fcst: 00z

*

Raining in Memphis,TN? Jackson, MS? at 00z

*

Association: Radar to 700 RHPRECIP FORECASTING

B

A

Which location is more likely to be raining at this time?

24-hr ETA 700mb RH fcst. Valid 12z the next day

Association: Cloud Forecasting

What’s the sky look like in ALB?

*

*

What’s the sky look like in n.MS?

Association: Satellite to 700 RHCLOUD FORECASTING

Correlation between cloud cover and 700mb RH ……

6-hr ETA 700mb RH fcst: 18z

Temperature Forecasting

• What causes temperature to change? DT/dt =

• Advection• Diabatic effects

– Radiative heating/cooling– Condensational heating/cooling

• Adiabatic effects– Compressional warming (Descent)– Expansional cooling (Ascent)

Temperature Forecasting850 mb method

Adding 13.5C to 850mb temp = dry rate to 1000mb

Effect of solar heating on boundary layer

Effect of solar heating on boundary layer

Effect of solar heating on boundary layer

Temperature Forecasting: 850mb method

• Would this method work the same for all seasons?– Add less during cold season– Add more during warm season

• Would this method work the same for all weather conditions?– Add less on cloudy, rainy days– Add more on bright, sunny days

Temperature Forecasting: 850mb method

• General Rules of Thumb– In summer:

• If mainly sunny -> 15/16C (13C-18C)• If cloudy -> 10C (6C-13C)

– In winter:• If mainly sunny -> 11C (9C-13C)• If cloudy -> 4C (-2C-7C)

Temperature Forecasting Methods

• Persistence– No change

• Modified Persistence– Persistence (1st guess) + any changes

• Advective changes?– Warm or Cold Advection?

• Adiabatic changes?– Upslope vs downslope?

• Diabatic changes? – More sun or less sun?

Temperature Forecasting Methods: Modified Persistence (850mb temp)

18z Today 18z Yesterday

Let’s predict Chicago’s max temp today!

What’s the predicted 850mb temp at 18z today?

20CWhat was the 850mb temp 18z yesterday?

14CWhat was Chicago’s high yesterday?

KORD 292356Z 10SM FEW200 24/14 A2996 10278 20239

Our prediction: 28C+6C=34C=93F

The ‘Delta Method’

• Modified persistence technique• Used in T, Td, winds forecasts• Correlates model tabular output to

observed conditions

Raw Model Output (tabular data)

-> Highest 2m temp on the 5th:

-> Highest 2m temp on the 6th:

-> Average 850mb temp on the 5th:

-> Average 850mb temp on the 6th:

71F

77F

12C

17C

Change=?

Change=?

The ‘Delta Method’: Temperature Forecasting

PIT Observations

23.9C=75FPIT High on the 5th:

75F+6F=81FPredicted High on the 6th (DELTA 2m):

Predicted High on the 6th (DELTA 850mb): 75F+9F=84F

The ‘Delta Method’: Temperature Forecasting

DELTA METHOD works best when:

• TEMPERATURE– Radiative character (DAY 1) = radiative

character (DAY 2)• Cloud cover between days is similar

– Low lvl winds (DAY 1) = low lvl winds (DAY 2)• Especially true near coast, mountains …WHY?

– Can work well in FROPA situations!

ETA 6 hr Forecast: Valid 18z 9/5/01

m415 web page- http://www.meteo.psu.edu/~m415mgr

ETA 30hr Forecast: Valid 18z 9/6/01

Is the radiative AND wind character similar?

Dew Point Forecasting

• What causes dew point to change? dTd/dt =

• Advection• Evaporation/Condensation• Adiabatic effects

• ADVECTION is the dominant term

The ‘Delta Method’: Dew Point Forecasting

-> 18z 2m Dew Point on the 4th:

-> 18z 2m Dew Point on the 5th:

69F

55FChange= -14F

The ‘Delta Method’: Dew Point Forecasting

MDT’sDew Point 18zon Sept. 4th?

MDT’sDew Point onSept. 5th?

70F

SEPTEMBER 4, 2001

The ‘Delta Method’: Wind Forecasting

-> Highest Wind on the 5th:

-> Highest Wind on the 6th:

13 kts

19 kts

-> Highest Wind on the 5th:

-> Highest Wind on the 6th:

17 kts

28 kts

SUSTAINED WIND: 10m method SUSTAINED WIND: 850 method

CASE EXAMPLE: DDC

The ‘Delta Method’: Wind ForecastingCASE EXAMPLE: DDC

Maximum Sustained Wind: Maximum Sustained Wind:15kts 15kts

Forecast for 9/6: 15+6=21kts Forecast for 9/6: 17+11=29kts

DELTA METHOD (WINDS) works best when:

• Low-level stability of period 1 = low-level stability of period 2 !

• In unstable/well-mixed environments, consider using 850mb for the Delta method!

Different Stabilities: Delta Method problems for wind