# Presentation: 918603

## Summer Precipitation Regimes over North America and Prediction

***Kingtse C. Mo & Jae Schemm***
- Climate 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 mode

- REOF 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

- Northern Plains GPLLJ

- Southern Plains

-  Beryle &Paegle 2003

## Slide 16

## 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 ForecastsCase 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

## Slide 23

## Seasonal Forecasts  (July-September)

- GFS model  92 day forecasts
- 8- member ensemble  ICs 6 h apart
- T62L28, T62L64 and T126L28
- Observed SSTs
- 1999 summer

## Slide 26

## Slide 27

## 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