Summer Precipitation Regimes over North America and Prediction

Kingtse C. Mo & Jae SchemmClimate Prediction Center

NCEP/NWS

Purposes

• 1. Identify Summer Precipitation Regimes over Mexico and the United States

• 2 Determine P regimes are related to Tropical convection

• 3. Influence of soil moisture on P regimes

• 4 Week2 to Seasonal Forecasts

Data sets

*Precipitation over Mexico and the United States

(1968-2002)

* Circulation anomalies: CDAS/reanalysis R1

1968-2002

* OLRA : 1979-2002 ( Total & IS 10-90 day filtered)

* Qfluxes (vertically integrated moisture flux)

from CDAS 1968-1996, RSM 1991-2000

* Soil moisture and E from an off line NAOH model

1968-1998 (Huug van Den Dool et al. 2003)

Methods

Pentad precipitation data from June-September

1979-2002 Square root transformation to make rainfall

close to a normal distribution Perform EOF analysis Rotated EOF 5 day running mean of P and take square root take out the mean and project onto REOF to get RPCs.

Northern Great plains Southern Mexico

NW Mexico & SW Southern Plains

Weak Tropical linkage ,Zonal pattern

RPC 1 Southern Mexico

Both ENSO & MJO can influence REOF 3

Meridional modeREOF 2 REOF 5

MJO

When suppressed convection shifts to the central Pacific, Central America is likely to be wet (REPF 3), more rainfall over northwestern Mexico & less rainfall over southern Great Plains (REOF 2)

OLRA

REOF 5

Submonthly mode

Four REOF patterns related to the NAMs

REOF 1- Continental Zonal pattern, weak tropical influence

REOF 3- Southern Mexico Both ENSO and MJO influence

REOF 2 & REOF 5- Phase reserval Northwestern Mexico & southern Plains – Intraseasonal oscillations influence

Northern & Southern Great Plains

• They belong to two REOFs (REOF 1 & 5)

• They both are controlled by the Great Plains LLJ

• REOF 1 rainfall is influenced by soil moisture at the entrance region of the GPLLJ,but not REOF 5

Northern Plains GPLLJ

Southern Plains

RPC 1 Continental P pattern

• Zonal pattern (Cavazos et al2002)• Strong GPLLJ & weak GCLLJ• Associated with strong upper level wind over the

west region. (Beryle & Paegle2003)• Weak tropical convection• Wet soil moisture anomalies near the entrance of

the GPLLJ 10 days before positive events

REOF 3 – Southern Mexico

• Strong influence from tropical convection in the tropical Pacific. Both the MJO and ENSO can influence rainfall over Central America and REOF 3

REOF 2 & REOF 5 Northwestern Mexico, the

Southwest & southern Plains• Phase reversal between the GPLLJ and the

GCLLJ

• Meridional pattern

• No precursor of soil moisture influence

• Influenced by tropical intraseasonal oscillations

Monthly ForecastsCase studies

• July 1999 – A very wet Southwest

• August 2000- A dry Southwest

• Four members in the ensemble

• T62L28 forecasts– 50 km RSM downscaling

1999July 2000Aug

Seasonal Forecasts (July-September)

• GFS model 92 day forecasts

• 8- member ensemble ICs 6 h apart

• T62L28, T62L64 and T126L28

• Observed SSTs

• 1999 summer

Seasonal Forecasts

• High resolution model is needed to capture rainfall over the Southwest

• Future Plans

a) Systematically test the impact of model resolution (T126L64, T170L28)

b) Radiation & diurnal cycle

c) Test of convection

d) T62L28 downscaling with RSM & T170L28

30 day forecasts (calibration run)Jae Schemm

• JJAS from 1998-2002

• T126L28 for 7 days T62L28 to 30 days

• Errors for T126L28 and T62L28 are very different

REOF 1 black

REOF 2

Green

REOF 3

Red

REOF 5

blue