THERMAL SOARING FORECASTING

Richard Kellerman

rkellerman@nkhome.com

www.nkhome.com

THERMAL SOARING FORECASTING

PART 1: WHY BOTHER?

PART 2: SKEWT TUTORIAL

PART 3: THE CONVECTIVE BOUNDARY LAYER

PART 4: A LITTLE BIT OF PHYSICS

PART 5: TOOLS

PART 6: MAKING THE FORECAST

PART 7: RECONCILIATION

PART 1

WHY BOTHER?

WHY?

• DR JACK’S BLIPMAP FORECASTS

• FORECASTS ARE ALWAYS WRONG ANYWAY

WHO NEEDS FORECASTS ANYWAY?

PART 2

SKEWT TUTORIAL

WHAT’S THIS?

SKEWT’S

• COMPACT DATA DISPLAY (GRAPHS) BALLOON SOUNDINGS (T, DP, WIND) MODEL SOUNDINGS

• CALCULATORS DALR, SALR, MIXING RATIO

• IDEAL FOR THERMAL SOARING FORECASTS

TEMPERATURE AND PRESSURE AXES

ADD DRY ADIABATS

ADD CONSTANT MIXING RATIO LINES

MAKING CLOUDS

LAPSE RATES AND ADIABATS

• TEMPERATURE LAPSE RATE (MEASURED)

• DEWPOINT LAPSE RATE (MEASURED)

• DRY ADIABATIC LAPSE RATE (CALCULATED)

• SATURATED ADIABATIC LAPSE RATE (CALCULATED)

• IN THE CONVECTIVELY MIXED BL:

THE TEMPERATURE LAPSE RATE = DALR

TEMPERATURE AND DP ALOFT

GOOD DAY WITH CU

“CUMULUS POTENTIAL”

GOOD DAY – NO CU

WHEN GOOD CLOUDS GO BAD, 1

WHEN GOOD CLOUDS GO BAD, 2

PART 3

THE CONVECTIVE BOUNDARY LAYER

BOUNDARY LAYER EVOLUTION

• RUC MODEL SOUNDINGS FOR A TYPICAL GOOD SOARING DAY IN THE LEHIGH VALLEY

• DATA IS FOR ABE JULY 3 2005 AT 6:00, 8:00, 11:00 AM AND 2:00 5:00 PM

6:00 AM

8:00 AM

9:00 AM

11:00 AM

2:00 PM

5:00 PM

COMPOSITE, MORNING

6:00 AM

8:00 AM

11:00 AM

COMPOSITE, AFTERNOON

5:00 PM

2:00 PM

11:00 AM

PART 4

SOME INTERESTING PHYSICS

GLIDER DISSIPATION

• AT 75 KTS (~40 M.S-1) MY ASW27 LOSES ALTITUDE AT ~1 M.S-1

• IT HAS A MASS OF ABOUT 350 KG• IN UNACCELERATED FLIGHT THAT’S A

FORCE OF ~3,400 N• POWER = 3,400 x 1 = 3,400 W (~4.5 HP)

MAKING THERMALS

• SUMMER INSOLATION IS ~ 1,000 W.M-2 @ N40º

• ABOUT ½ OF THIS MAKES IT TO THE GROUND

• THE GROUND GETS HOT

• THE AIR GETS HOT

NUMBERS

• IT TAKES A FEW HOURS OF INSOLATION TO HEAT THE TOP FEW CENTIMETERS OF THE GROUND BY 20Cº OR MORE

• IT TAKES JUST 2 SECONDS OF SUNLIGHT TO PROVIDE THE ENERGY TO RAISE THE TEMPERATURE OF THE THE FIRST 1 M OF AIR BY 2Cº

• A 500 M x 500 M x 1 M SLAB OF AIR WEIGHS 250 TONS

• INSOLATION IS ON THIS SLAB IS ~1.25E8 W (THAT’S MEGAWATTS)

• SPECIFIC HEAT OF BOTH AIR AND DRY SOILS IS ~1 x 103 J.KG

• LATENT HEAT OF WATER IS 2.27 x 106 J.KG

PART 5

TOOLS

TOOLS

• BLIPMAPS

• DALE KREMER’S BMAPPER

• BILL MONINGER’S FSL JAVA SITE

• RAOB 5.7

• OMENS

BMAPPER

BAD OMENS

PILEUS CLOUD

SHOOTING CU

ALTOCUMULUS CASTELLANUS

GOOD OMENS

• DIURNAL TEMPERATURE SPAN >20ºF

• SURFACE (T – DP) SPREAD > 20ºF

• SURFACE WIND DIRECTION 270º - 030º (AT LEAST IN THE EASTERN HALF OF THE COUNTRY)

PART 6

MAKING THE FORECAST:

SYNOPTICS

SURFACE ANALYSIS CHART

SA SATELLITE COMPOSITE CHART

SA RADAR COMPOSITE

SURFACE DP FIELD

SATELLITE IMAGERY

FXUS61

• “FORECAST DISCUSSION”• ISSUED BY EVERY NWS OFFICE IN EVERY STATE• WRITTEN BY PROFESSIONALS FOR

PROFESSIONALS BUT AVAILABLE TO ALL• SYNOPTIC AND PROGNOSTIC ASSESSMENTS –

NOT MERELY SUMMARIES• NUMERICAL MODEL PERFORMANCE• ISSUED TWICE DAILY AND UPDATED WHENEVER

NEEDED, SOMETIMES FREQUENTLY• ESSENTIAL READING

MAKING THE FORECAST

PROGNOSTICS

500 HPA CHART FORECAST

SURFACE FORECAST CHARTS

SURFACE T AND DP - ACCUWEATHER

SURFACE T AND DP, MOS

SOUNDINGS

• RUC IN THE MORNING

• NAM OUT TO 60 HOURS

• GFS OUT TO FIVE DAYS

• GFSX OUT TO 10 DAYS

ANALYZE THE SOUNDINGS

• CONSTRUCT THE SURFACE DRY ADIABAT

• ENTER THE BEST ESTIMATE OF SURFACE DP

• DETERMINE CCL

• LOOK FOR SPREADOUT

• LOOK FOR VERTICAL OD

• ASSESS SENSITIVITY TO CHANGES IN T, DP

SURFACE ADIABAT

PART 7

RECONCILIATION

RECONCILIATION

The process of making consistent or compatible

An act of self-mortification or devotion performed

voluntarily to show sorrow for a sin or other wrongdoing.

CLOUDBASE AND RAIN PROBLEMS

BLIPMAP CLOUDBASE 18Z 5/20/2006

BLIPMAP CLOUDBASE 21Z 5/20/2006

DATE UCT

DEG/KT DEG/KT

30,000 300/64 310/9625,000

20,000

15,000

10,000 290/209,000

8,000

7,000

6,000 305/28 300/305,000 300/25 300/294,000 300/24 300/283,000 300/22 300/252,000 295/19 300/22

SURFACE 295/10 300/13

UTC 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 1800 2100LOCAL 11AM 12 1PM 2PM 3PM 4PM 5PM 6PM 7PM 8PM 2PM 5PM

CLOUDBASE 3927 4382 5064 5518 5973 6427 6655 6655 0 0LIFT, KTS** 3 -4 3 -5 4 - 6 3 - 5

SURFACE T, °F 53 54 56 57 58 60 60 59SURFACE DP, °F 41 40 39 38 37 37 36 35

SURAFCE T, °C 11.7 12.2 13.3 13.9 14.4 15.6 15.6 15.0SURFACE DP, °C 5.0 4.4 3.9 3.3 2.8 2.8 2.2 1.7

STABILITY AND CLOUDSWINDS

7000

RVL (MIFFLIN COUNTY AIRPORT) GLIDING FORECAST

May 20 2006 7:53

CONTEST DAY 2

MSL, FT

BL TOP* 6500 6500

MY FORECAST

MAY 17, 2005, DEWPOINT PROBLEMS

RUC 18Z SOUNDING

BL TOP

CUMULUS POTENTIAL

18Z SOUNDING WITH MODIFIED SURFACE DP

MY FORECAST

CONCLUSIONS

• DON’T TAKE FORECASTS FOR GRANTED– LOOK UNDER THE HOOD

• DATA RULES, NOT MODELS– MAKE USE OF THE RELTIME DISSEMINATION

OF DATA

• FLY MORE OFTEN– IT’S USUALLY BETTER THAN FORECAST