# Presentation: 504884

## NAEFS and forecasting significant weather events over Africa

**Richard H. Grumm **
**And **
**William Bua**

## Overview

**We will need to define a significant weather event**
*Varies about the globe*
**We will need to look at some fields that relate to significant weather**
*Focus heavy rain and unusual cold in this lecture*
**We will look at some relevant NCEP/NAEFS products related to this**
*QPF probabilities and key mechanisms*
**We will explore some future concepts related to this**
*There is work to be done!*

## Definitions

**A significant weather event is an event that produces (***regionally or locally***)**
*Record or near record heat or cold*
*Record or near record rainfall or flooding*
*Widespread severe weather from organized convection*
*Produces costly damage to crops and infrastructure*
**Has significant cost/loss associated with it.**
*This will vary country to country and*
*Province to province*
*Some are on scales of ours or days and others are more episodic or climatic in nature**** drought*

## Significant Weather here

**We will focus on shorter term events**
*Appear 3-7 days out in lead-time*
*Duration typically on the order of *
*Hours*
*Or a few days*
*Droughts last on the order of months*
**Key cost loss:**
*Heavy rains and flooding events*
*Severe weather events*
*Cold and drought can impact agricultural activities*

## A few points

**You all may have your own definition of such events**
*Not one size fits all*
*Regional and locally issues.*
**It is geographical and experiential**
*Location *
*Based on local knowledge and experiences*
**Some user input on regional significant events******** ***heavy rains and flooding appears to be a world wide problem in many natural disasters.*

## Forecast Parameters

**Heavy Rain******
*Moisture best quantified by Precipitable water (PW)*
*Strong low-level winds*
*Moisture flux, convergence, and from moisture source*
*Association of winds and PW *
*To terrain features*
*Other parameters:*
*Favored indices such as KI and TTI*
*Model QPF*
***Ever wonder what is a significant QPF? Is 50mm or 100mm abnormal in 24 hours or 48 hours?***

## Forecast PatternsHeavy Rain

***Monsoon depressions***
***Tropical cyclones***
*Uniquely strong winds*
*Unique ability to transport moisture which is abnormally high for a region and replenish it*
***Regionally known and specific patterns***
***Good news*****
*We can get the patterns correct 3-7 days out*
*We can typically get the larger systems 2-7 days out*
***Bad news*********
*Details on threat areas change*
*Storm tracks/paths change *

## Forecast Parameters Severe Weather

*Moisture best quantified by Precipitable water (PW)*
*Instability by CAPE,KI,TTI*
*Strong low-level winds*
*Convergence and moisture transport*
*CAPE ~PW*
*Stronger winds better ability to transport damaging winds to surface*
*Shear profile plays role in storm types***
*More important N/S of about 30 degrees latitude*
*Geographic features*
*Terrain and water bodies modulate thunderstorm activity locally*

## Severe Convective Weather

***Organized events ***
*Should be a cooler / transition season problem south of 25-30S*
*Stronger fronts and winds*
***Regionally known and specific patterns***
***Bad news**********:*
*Convection is a mesoscale problem*
*NAEFS EPS data will give the broad regions not the details!*

## A few other event types

**Cold and warm episodes**
*Have distinct patterns*
*We will show an example here*
_*Can have impact on sensitive crops*_
*Good news:*
*Large ridges and synoptic fronts generally well forecast*
*Patterns of these events should be relatively well forecast*

## Things we will not cover

**Droughts******
*Should and do have distinct patterns and anomalies*
***Can severely impact crops and agricultural activities***
*Are more episodic in nature linked to climate signals*
*Known ENSO links to parts of Africa and drought (****next slide****)*

## ENSO Impact Map

## Decision Supportkey component of ensembles

- Most of the previously defined significant weather types create risks ($)
- Forecasts with probabilities help mitigate loss
- Take action to mitigate loss  Cost ($)
- Take no action to mitigate loss  Cost ($)
- Take some action to mitigate risk  Cost ($)
- Cost-Loss need probabilities to facilitate this and ensembles provide this.

## Heavy rainfall example

- System produced Severe weather and flooding in South Africa
- Dec 2006-Jan 2007
- Severe flooding in Pretoria on the 28th
- Rainfall locally of 80-100 mm
- _[http://www.weathersa.co.za/Pressroom/2006/2006Dec29SevereThunderstorms.jsp](http://www.weathersa.co.za/Pressroom/2006/2006Dec29SevereThunderstorms.jsp)_
- Heavy rains in Mozambique 2-4 January

## Short term forecast

- Hints of 50mm of rainfall in South Africa
- Potentially heavy rain
- Good first approximation
- Lets looks at more heavy rain

## Slide 16

## EPS Tools

- Obvious choice probability of heavy rainfall
- 50 mm in 24 hours
- 100 mm in 24 and 48 hours
- Other tools
- Parameters and patterns

## 28 December Low Probability of over 100 mmgot area but too low on amounts

## Forecasts from 29 December

## 30 December Forecasts

## 31 December

## Overview of Case

- 50 mm near Pretoria on the 28th was forecast
- Trouble with the location of heavy rain over Mozambique from forecasts
*Initialized 28-31 December*
*Concept of some heavy rain was there*
*Lots of uncertainty with the location and timing.*
*The details were a bit elusive*
- How do we improve upon forecasting heavy rains?
*Patterns and parameters may help us.*

## PW and Wind fields with anomaliesnote above normal PW and southerly winds

- PW and Wind fields with anomalies*note above normal PW and southerly winds*

## Pattern Shows a signal

**Incredibly strong Low level jet (LLJ)**
*Both u and v-wind anomalies in the affected area.*
*Useful signal if in other events and other forecasts for this case.*
**Large PW anomalies too **
*In affected region*
*Another useful signal*

## 28 December Forecastspersistent anomaly and high PW image click

## 29 December Forecastspersistent anomaly and high PW image click

## 30 December Forecastspersistent anomaly and high PW 2 images clicks

## 31 December Forecastspersistent anomaly and high PW image click

## EPS Forecast the signal

**Strong LLJ 850 hPa wind fields**
**Large PW anomalies too **
**Earlier QPF**
**Not quite as good but showed some signal**
**Moisture is less skillful than mass**
**QPF is event less skillful**

## Heavy rain in Pretoriakey anomalies

## Wind signal was weak in Pretoria

## Concept-Example 1

**There may be a signal in the EPS data for big events**
*Need to leverage these signals*
**Strong boundaries**
- As indicated by the PW fields
- And strong winds
**Big anomalies**
- Based on 30-years of climate data
- Suggest above normal PW and southeasterly flow keeping moisture moving into the region
- Worked for this and similar cases (not shown).

## Heavy Rain Events

## Anomalies showed similar signals2 and 3 January 2007 image click

## January 2007 Rainfall

- _[http://www.ncdc.noaa.gov/oa/climate/research/2007/jan/hazards.html#Flooding](http://www.ncdc.noaa.gov/oa/climate/research/2007/jan/hazards.html#Flooding)_
**In Angola, heavy rainfall during January 21-24 produced flooding that caused at least 81 deaths (AFP). In Mozambique, flooding rains rendered more than 3,500 homeless during the 20th-23rd (AFP). **

## Slide 36

## Slide 37

## Brief look 17 Jan Forecasts this event had boundary and lots of convection click 3rd image

## Clues in QPFthis event had boundary and lots of convection

## May cold episode

- _[A cold front that swept across South Africa](http://www.ncdc.noaa.gov/img/climate/research/2007/may/SouthAfrica05212007.jpg)_ led to at least 21 fatalities and 54 weather records observed in many areas on May 21-22. Most of the records were for lowest maximum and minimum daily temperatures, with some locations reaching a low minimum temperature of -6°C (21°F) while in some other locations the lowest maximum temperature was 1.7°C (35°F) (Cape Times News). _[For additional information, see the South African Weather Service report](http://www.ncdc.noaa.gov/cgi-bin/good-bye.pl?src=http://www.weathersa.co.za/Pressroom/2007/2007May22IcyGrip.jsp)_.
- Snow covered the mountains such as Snow on the Outeniqua mountains in George. (click for image).

## Heavy rainfall front with cold

## ColdForecast 16-22 May

## Some rain nothing impressively significant

## Significant Wind anomalies

## Some high PW followed by very dry air behind the front...

## Anomalous 850 hPa temperaturesExtreme anomalies with record event

## June 2007 Snow and Cold 27-snow 27-30th Cold

- Cold and snowy weather characterized conditions across much of South Africa on **June 27**, where 25 cm (10 inches) of snow fell in parts of the country.
- Johannesburg, South Africa's largest city, received its first significant snowfall since **10 September 1981**. One fatality was attributed to the cold temperatures (SA/Reuters).
- Link: _[http://www.weathersa.co.za/Pressroom/2007/2007Jun27GautengSnow.jsp](http://www.weathersa.co.za/Pressroom/2007/2007Jun27GautengSnow.jsp)__ _

## 850 hPa temps20-21-22 June

## Forecasts from 23-24-25Cold air now forecast to be colder

## Review

**We defined a significant weather event**
*Focused on rainfall and cold here*
**We looked at some fields that relate to significant weather**
*Probability fields for big POPS*
*Anomalies for features associated with significant events*
**We looked at NCEP/NAEFS products related to define these events**
*Mainly for rainfall and record temperatures *
*Anomalies appeared to add value and purpose*
*May help with confidence of big event*
**Future concepts module******

## Future Concepts

**Define critical event types**
**Wind events** threhold values for probabilities of winds
**Rain events**threshold values for
- QPF in 12,24,48 hour increments
- Key features such as PW, winds, KI, and SLP
**Cold events**key temperature thresholds and anomalies
**Droughts** key patterns and anomalies
**Improve decision support for critical events**

## Slide 52

## Data Links

- _[http://www.cpc.ncep.noaa.gov/products/fews/rfe.shtml](http://www.cpc.ncep.noaa.gov/products/fews/rfe.shtml)_
- African Case links from South African Weather Service
- Other

## Favio Floods

- February 2007
- Intense storm with heavy flooding
- Struck Mozambique coast
- Not used.