Regional Models Lake Victoria Model Prepared by C. Tubbs, P. Davies, Met Office UK Revised, delivered by P. Chen, WMO Secretariat SWFDP-Eastern Africa.

Regional Models

Lake Victoria Model

Prepared by C. Tubbs, P. Davies, Met Office UK Revised, delivered by P. Chen, WMO Secretariat

SWFDP-Eastern Africa Training Workshop Bujumbura, Burundi, 11-22 November 2013

MINISTRY OF WATER, LANDS AND ENVIRONMENT,DEPARTMENT OF METEOROLOGY,P.O. BOX 7025,KAMPALAUGANDA

Mobile Weather Alert - Uganda Pilot

Lake Victoria - motivation

Major convective storms driven by lake/land differences in temperature over Lake Victoria are believed to contribute to an estimated several thousand deaths each year of fishermen and small boat operators. A collaboration between WMO Uganda Department of Meteorology (UDoM) and other partners has been implementing a ‘Mobile Weather Alerts’ project to help address this danger. As a contribution to this project the Met Office has developed a 4km model over the Lake Victoria region.

© Crown copyright Met Office

Incidents on Lake Victoria in 2010

18 kids drown in

Lake Victoria

“…preliminary reports have it that

the boat was over-loaded and

there were strong winds at the

area.” Daily News, Tanzania, 5

August 2010

50 Feared dead on Lake Victoria “The period between April and

September is tough for fishermen

on the lake due to the strong

winds and turbulent waves.”

Daily Monitor, Uganda, 22 July

2010

15 Passengers feared dead as boat capsizes“Local fishermen were quick to attribute the incident to a storm, locally known as “nyakoyi”, that engulfed the lake, forcing the boat to capsize.” Daily Nation, Kenya, 1 November 2010

© Crown copyright Met Office

The latest weather and climate science

High resolution weather forecast models

Satellite Observations

© Crown copyright Met Office

Tailoring forecasts to the needs of fishermen

ALERT STATE:

GREEN YELLOW ORANGE RED

Mean Wind

0 – 5 KT 6 – 10 KT 11 – 20 KT Over 20 KT

Wind gusts

5 – 10 KT 11 – 20 KT 21 – 30 KT Over 30 KT

Thunder-storms

Light Moderate Strong Severe

Visibility > 1Km 500 – 1000m 100 – 500m < 50m

Hazard threshold:

Very Low Low Moderate High

Advice Nil Be Aware

BePrepared

TakeAction

Courtesy: Paul Davies, Met Office

© Crown copyright Met Office 2011 © Clare Wise de Wet

Launch of the Mobile Weather Alert Service

Lake Victoria Model

Lake Victoria – model summary

Initial model fields are downscaled (no data assimilation) from the 25km global configuration of the Met Office Unified Model (UM) to a 4km (0.036°), 70 level, partially convection-resolving configuration of the UM over the Lake Victoria basin. The model lid is at a height of 40km and the timestep is 100 seconds.

The model runs twice per day (by 0000UTC, 1200UTC), out to T+48.

Lake surface temperatures are taken from the OSTIA model, which uses satellite measurements to produce a daily analysis of global lake and sea-surface temperatures.

Soil moisture is interpolated from an earlier global analysis.

Daily forecasts from both cycles of the Lake Victoria model are available from www.metoffice.gov.uk/weather/africa/lam.

Lake Victoria – model science

Science configuration currently follows that of latest Met Office UK4 and Euro4 4km 70 level operational NWP configurations.

Uses the JULES land surface scheme.

There is no data assimilation, due to lack of in situ observations in the region.

4km resolution allows partially-resolved convection - resolved deep, parametrized shallow. Lower model resolutions, e.g. 12km, are fully parametrized. Higher resolutions, e.g. 1.5km, can be fully explicit/resolved.

Lake Victoria – strengths and weaknesses

High-resolution orography represents local topography well, which improves surface temperatures and orographic precipitation.

4km models can begin to resolve convective activity and produce better (higher) peak precipitation, compared with lower resolution models.

However, 4km not as good as 1.5km (UKV has fully explicit convection). Onset of convection is too slow as early small-scale stages of convection cannot be resolved, resulting in too few cells that are too large and too intense.

Land-lake breezes and day/night differences in convection are represented, i.e. convection usually only over lake at night due to convergence.

General pattern of convective cells can look “realistic” but detail of cell location/number/size cannot be assumed to be accurate.

Lake Victoria - orography

Model orography is at a resolution of 4km, generated from Globe30 data.

Lake Victoria and the surrounding 8 largest lakes are included in the domain (see lake temperature slide).

Height of orography (m)

NWP convection switched on….

NWP convection switched off….

Lake Victoria – lake temperatures

Lake surface temperatures are based on satellite measurements.

These are ingested by the OSTIA model to produce a daily high-resolution global analysis of lake and sea-surface temperatures.

The “foundation temperature” that is produced is valid for a 24 hour period. Lake temperatures do not change through the forecast period.

If observations are missing, lake temperatures are relaxed to climatological values.

Lake surface “foundation” temperature (K)

Lake Victoria – soil moisture

Soil moisture content (on 4 model levels, covering a depth of 3 metres) is interpolated to 4km resolution from the earlier global model analysis.

Soil moisture content (kg/m2)

Lake VictoriaValidation of model: Case study 17th December 2012

4km modelGlobal model Observations

MSG Satellite OLR 17/12/2011 0600UTCT+18 forecast T+18 forecast

• The global model was able to indicate that some event might take place, but the 4km model was able to add detail to the case and increase forecast confidence

• The 4km model is able to represent fine scale processes in a more explicit way. Due to the size of the grid points, it is also able to represent small scale events in more detail than the global model

• We still need skill in the global model as the 4km relies on it for large scale forcing

Global UM

4km UM

4th March 2012: Storm over Lake Victoria caused the deaths of 2 fishermen when a boat capsized

The Global UM showed some indication of the event in T+6 forecast

The 4km UM showed increased indication of the storm in T+6 forecast

Lake VictoriaValidation of model: Case study 4th March 2012

• Objective analysis (automated ‘storm’/ ‘no storm’ decision made by an algorithm) was conducted on model data from February and March 2012

• The 4km model was able to capture more storms than the global model

• The 4km model especially ‘added value’ at longer lead times 18-24 hour forecasts, though it did add some more false alarms. Good forecasts are always a balance between getting fewer false alarms without getting more missed events

Lake VictoriaValidation of model: Objective analysis

SHORTER LEAD TIME LONGER LEAD TIME

Lake Victoria – future plans

Lake temperatures – in future OSTIA developments, diurnal variation and in situ lake temperatures may be added.

Model science – investigations into whether forecast performance can be improved for the tropics, with adjustments to the model settings (e.g. turbulence scheme). Lightning forecasting capability will be trialled.

Web – website will be updated shortly, with more interactive model and satellite imagery.