ETA 6-hr fcst. Valid 18z 02/19/02 Will it rain at MEM, JAN at 00z???

Association: Radar to 700 RH PRECIP FORECASTING Radar: 18z6-hr ETA 700mb RH fcst: 18z Observations Short-term model output

Association: Radar to 700 RH PRECIP FORECASTING 6-hr ETA 700mb RH fcst: 18z12-hr ETA 700mb RH fcst: 00z * Raining in Memphis,TN? Jackson, MS? at 00z *

Association: Radar to 700 RH PRECIP 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 RH CLOUD 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 Forecasting 850 mb method Adding 13.5C to 850mb temp = dry rate to 1000mb

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 (1 st 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? 20C What was the 850mb temp 18z yesterday? 14C What was Chicago’s high yesterday? KORD Z 10SM FEW200 24/14 A 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 5 th : -> Highest 2m temp on the 6 th : -> Average 850mb temp on the 5 th : -> Average 850mb temp on the 6 th : 71F 77F 12C 17C Change=? The ‘Delta Method’: Temperature Forecasting

PIT Observations 23.9C=75F PIT High on the 5 th : 75F+6F=81F Predicted High on the 6 th (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-

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 4 th : -> 18z 2m Dew Point on the 5 th : 69F 55F Change= -14F

The ‘Delta Method’: Dew Point Forecasting MDT’s Dew Point 18z on Sept. 4th? MDT’s Dew Point on Sept. 5th? 70F SEPTEMBER 4, 2001

The ‘Delta Method’: Wind Forecasting -> Highest Wind on the 5 th : -> Highest Wind on the 6 th : 13 kts 19 kts -> Highest Wind on the 5 th : -> Highest Wind on the 6 th : 17 kts 28 kts SUSTAINED WIND: 10m method SUSTAINED WIND: 850 method CASE EXAMPLE: DDC

The ‘Delta Method’: Wind Forecasting CASE EXAMPLE: DDC Maximum Sustained Wind: 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