# Presentation: 067000

## Lab 2b: A cold season case: 27June 2007	

- Session 3, 9 October 2007
- Bill Bua, UCAR/COMET
- and
- Rich Grumm, NOAA/NWS

## Objectives

**Learn how the cold season, dominated by extratropical processes, differs from the warm season.  **
**Assess the risk of significant weather in the cold season.  **
**Use the GEFS and NAEFS in the cold season forecast process to see alternative solutions to those provided by the deterministic GFS.**

## Web Browser Instructions

- We’ll be using both the Severe Weather Forecast Demonstration Project (SWFDP) and the Ensemble Browser for this lab
- Find SWFDP at
- _[http://www.emc.ncep.noaa.gov/gmb/wd20bb/swdfp_27Jun2007/index.html](http://www.emc.ncep.noaa.gov/gmb/wd20bb/swdfp_27Jun2007/index.html)_ (all one line)
- Find ensemble browser at
- http://eyewall.met.psu.edu/rich/Africa/view/jun.html

## Each case has its own viewer
Red box  animation controls
Pulldown menu on left controls animation speed
Click in animation toggle to turn animation on or off
Four right hand buttons control movement through the graphics (1st button goes to 1st time step, 2nd button  is move back one time step, 3rd button is move forward one time step, 4th button goes to last time step

- Each case has its own viewer
- Red box  animation controls
- Pulldown menu on left controls animation speed
- Click in animation toggle to turn animation on or off
- Four right hand buttons control movement through the graphics (1st button goes to 1st time step, 2nd button  is move back one time step, 3rd button is move forward one time step, 4th button goes to last time step

- The Ensemble Viewer

## Blue box  date/cycle controls
Select a date pulldown menu
Select a cycle pulldown menu
Select a parameter from...
PWAT
MSLP
500-hPa Hgt
925 & 850 hPa Temp
Prob 2m-T < 4°C
Precipitation thresholds for 6, 12, 24, 36, and 48 hours

- Blue box  date/cycle controls
- Select a date pulldown menu
- Select a cycle pulldown menu
- Select a parameter from...
- PWAT
- MSLP
- 500-hPa Hgt
- 925 & 850 hPa Temp
- Prob 2m-T < 4°C
- Precipitation thresholds for 6, 12, 24, 36, and 48 hours

- The Ensemble Viewer

## Ensemble Viewer Graphics

- Top panel:
- Spaghetti diagram for different contours
- Grey shading represents spread
- Bottom panel:
- Ensemble mean and climate anomaly (in standard deviation units)

## Cold Season Characteristics

- Synoptic scale, baroclinic waves
- Sensitive to initial conditions
- Amplification through temperature advection and differential vorticity advection
- Strong dynamical forcing from
- Vorticity advection
- Temperature advection
- Effects of physical processes are **generally **small relative to dynamics
- May become important in situations where baroclinicity is increased by physical processes, such as convection  latent heat release  increased warm advection downstream of convection  lowers pressure when occurring in conjunction with cyclogenesis

## Exercise 1:  Assess the deterministic GFS model uncertainty

- Use the Severe Weather Forecast interfaces for June 21, 22, 23, 24 and 25, linked from the table found at:
- _[http://www.emc.ncep.noaa.gov/gmb/wd20bb/Africa_20070627/](http://www.emc.ncep.noaa.gov/gmb/wd20bb/Africa_20070627/)__ _
- Note the features that move through the southern portion of Africa in the mid-troposphere (500-hPa).  What are the forecast problems for June 26-27, 2007 over South Africa in particular and adjacent areas in general?
- Note the amount of variability at 500-hPa from run to run for the same valid time (say about 00-06 UTC June 27, 2007).

## Exercise 2:  What would you forecast ...

- Based on the deterministic GFS for the 00 UTC forecast run on 22 June 2007, what would you forecast for Johannesburg for the period from 18 UTC 26 June to 06 UTC 27 June? Based on the run from 23 June? 24 June? 25 June?
- Use the powerpoint template you can directly download from the web page linking to the model forecasts to draw in your forecasts

## Forecast Template: 26-27Jun07 (Pretoria, SA)

**Wind:**
** ****Expected: **
** ****Direction**
** ****Speed (kt)**
**Precip:**
** ****Expected amount (mm)****.**
** ****P >0.1mm (%)**** **
**Temperature**
**(max/****min****)**
**Expected maximum**
**Expected minimum**

- 20°
- 10°
- 0°

- Forecast from:
- Example:        22 June                23 June            24 June           25 June

- SW
- 12
- S-SW
- 9-13
- 0.00
- 1.5
- 0.00
- 40%

- not applicable

- not applicable

## Exercise 3:  What do the ensemble forecasts tell us?

- Now examine the ensemble forecasts for the same period using the Ensemble Browser found at:
- _[http://eyewall.met.psu.edu/rich/Africa/view/junx.html](http://eyewall.met.psu.edu/rich/Africa/view/junx.html)_
- Identify the atmospheric features in the ensemble forecasts that you considered important in the GFS deterministic forecasts.
- How much uncertainty is there in the ensemble forecasts of these features?
- Are there any trends that you notice in the ensemble forecasts as their initial time gets closer to the time of interest?
- How do these match the GFS deterministic forecasts over the same periods?

## Exercise 4:  What would you forecast ...

- Based on the probabilistic GENS after the 00 UTC EPS forecast run on 22 June 2007 for Johannesburg for 26-27 June 2007? From the run on 23 June? 24 June? 25 June?
- Use the printed forecast template you can directly download from the web page linking to the model forecasts to draw in your forecasts

## Forecast Template: 26-27Jun07 (Pretoria, SA)

**Wind:**
** ****Most likely: **
** ****Direction**
** ****Speed (kt)**
**Uncertainty**
** ****Direction**
** ****Speed**** **
**Precip:**
** ****Most likely amount (mm)**
** ****Maximum and minimum amt.**
** ****P >0.1mm (%)**
**Temperature**
**(max/****min****)**
**Highest possible**
**Most likely**
**Lowest possible**

- 20°
- 10°
- 0°

- Forecasts from:
- Example:        22 June                23 June            24 June           25 June

- SW
- 12
- S-SW
- 9-13
- 0.00
- 1.5
- 0.00
- 40%

## Verification: 00 UTC 27Jun07

## 27 June 07 was coldest of last 365 days

- From CPC website temperature monitoring
- Note that last 365 days have averaged 1.8C or so above normal.
- Max temp on 27/06/07 was about 5C

## Post-Mortem: 20 June 2007 ensemble forecasts

## Post-Mortem Discussion: 21Jun07 GFS forecasts

- 12z ens mean

- 00z ens mean

## Post-Mortem Discussion: 21Jun07 GFS forecasts

## Post-Mortem: 21Jun07 forecasts

## Post-Mortem: 21Jun07 forecasts

## Slide 21

## Post-Mortem: 22Jun07 GFS

## Post-Mortem: 22Jun07 GENS

## Post-Mortem: 22Jun07 500-hPa heights

## Post-Mortem: 22Jun07 GENS 850-T

## Post-Mortem: 23Jun07 GFS

## Post-Mortem: 23Jun07 GEFS 850 T

## Post-Mortem: 24Jun2007 500hPa heights