Post on 03-Feb-2016
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The Dvorak TechniqueThe Dvorak Technique
Originally By: TSgt Johnson (JTWC Satellite Operations)
Updated by Mr. Paul McCrone (HQ AFWA/XOGM)
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The Dvorak TechniqueThe Dvorak Technique
• Positioning• Intensity Estimation
– Final T-number• Data-T• Pattern-T• Model-T
– Current Intensity• Coding
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PositioningPositioning• Eye• Exposed Low Level
Circulation Center (LLCC)
• Cold Dense Overcast (CDO)
• Embedded Center (EMB CTR)
• Spiral Curved Band (SBC)
• Partially exposed LLCC• Cloud minimum wedge• Central Cold Cover
(CCC)• Cirrus outflow• Circle method• Conservative feature• Animation• Extrapolation
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Common AbbreviationsCommon Abbreviations• Low Level Circulation CenterLow Level Circulation Center LLCC• Low Level Cloud LinesLow Level Cloud Lines LLCLS• Upper Level Circulation CenterUpper Level Circulation Center ULCC• Cold Dense OvercastCold Dense Overcast CDO• Embedded CenterEmbedded Center EMB CTR• Spiral Band CurvatureSpiral Band Curvature SBC• Central Cold CoverCentral Cold Cover CCC• Enhanced Infrared Enhanced Infrared EIR• Convection Convection CNVCTN
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Eye Fixes Visual (VIS)Eye Fixes Visual (VIS)• Dark cloud free spot• Shadowy spot for cloud
filled eye• Without LLCC showing
within eye, fix on center of eye
• Measure width • Evaluate shape
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Eye Fixes Infrared (IR)Eye Fixes Infrared (IR)• IR Warm spot
– As a guideline look for 2 shades warmer on the BD curve (MUST use BD CURVE!)
– Use warmest spot.– Eye boundary (eye
wall)defined by the tightest temperature gradient
• Measure width and shape independent of Visual.
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• Look for tightening cyclonic low clouds.
• The center will be within the tightest circle of clouds.
• Much easier to find with VIS imagery
Exposed LLCC FixesExposed LLCC Fixes
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CDO FixesCDO Fixes• VIS only (The term
“CDO” implies “VIS only” - no exceptions!
• Look for low level cloud lines to extrapolate underneath convection
• Look for overshooting tops - bias LLCC toward tallest tops!
• Look for SBC pattern in texture of CDO
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EMB CTREMB CTR• Look for a warm spot• Look toward the edge
with the tightest temperature gradient
• Don’t forget continuity with past positions
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• Draw Streamlines on the image.
• Place each streamline so the curve lies as close as possible to the low level cloud lines (LLCLS) and convective bands.
• Follow the streamlines to the center.
SBC Fixes VISSBC Fixes VIS
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• Draw Streamlines on the image.
• Place each streamline so the curve lies as close as possible to the low level cloud lines (LLCLS) and convective bands.
• Follow the streamlines to the center.
SBC Fixes VISSBC Fixes VIS
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SBC Fixes IRSBC Fixes IR• Draw Streamlines on the
image.• Place each streamline so
the curve lies as close as possible to the low level cloud lines (LLCLS) and connective bands.
• Follow the curves to the center
• Same idea as VIS
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Partially Exposed LLCC Partially Exposed LLCC Fixes VISFixes VIS
• Defined as “Less than half of the LLCC exposed”
• Includes cirrus obscuration• The center will be within
the tightest circle of clouds.• Similar to the Fully
exposed LLCC, just harder - less obvious.
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• Again…. “Less than half of the LLCC exposed”
• Same idea as visual, except this can be even harder
• LLCLS don’t show up well in GOES/GMS EIR (but they show up fairly well in DMSP Thermal imagery).
Partially Exposed LLCC Partially Exposed LLCC Fixes IRFixes IR
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
Dry SlotDry Slot
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
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• The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.
Cloud Minimum WedgeCloud Minimum Wedge
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• Rare; to be used with VIS imagery ONLY
• Typically, storm exhibits a milky cirrus top - few convective cells visible
• Only use if there is no evidence of the CDO or curved lines visible through the cirrus.
• Center placement based mostly on continuity.
CCC Fixes VISCCC Fixes VIS
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• Very difficult to accurately locate center.
• Center placement based mostly on continuity.
CCC Fixes IRCCC Fixes IR
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• Use only when low clouds are not visible.
• Follow the cirrus outflow anticyclonically back to the center.
• This locates the Upper Level Circulation Center (ULCC)
• ONLY USE AS A LAST RESORT.
Cirrus Outflow FixesCirrus Outflow Fixes
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• To be used with weak or very broad systems.
• Use all available curvature to find center.
• Where most circles meet, indicates most likely LLCC.
Circle Method FixesCircle Method Fixes
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• If you had good reason to believe the LLCC was located at a certain point in relationship with a persistent feature, the LLCC will remain in the same relative location for up to 12 hours (at the very furthest in time)
Conservative Features FixesConservative Features Fixes
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• Self explanatory• Use with all type of fixes when available.• Use animation alone only when still imagery
gives no indication of LLCC.
Animation FixesAnimation Fixes
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• Extrapolate past few fixes to determine where current position should be located.– Limited by the accuracy of the
past fixes– Don’t technically need a
satellite image to do this– This is a mathematical “dead-
reckoning” approach.– This method is not
encouraged as an analysis method
Extrapolation FixesExtrapolation Fixes
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Intensity EstimationIntensity Estimation
• Step 1 - Locate Cloud System Center (CSC)
• Step 2 - Determine the Data Type (Data-T)
• Step 3 - CCC• Step 4 - Past 24 hour
trend• Step 5 - Model Expected
T-number (MET)
• Step 6 - Pattern T-number (PT)
• Step 7 - T-number determination
• Step 8 - Final-T• Step 9 - Current
Intensity (CI)• Step 10 - Final-T/CI
encoding
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Step 2, Data-TStep 2, Data-T
• Step 2A Curved Band• Step 2B Shear Pattern• Step 2C Eye Pattern• Step 2D CDO• Step 2E Embedded Center
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Step 2A, Curved BandStep 2A, Curved Band
• Use a LOG10 spiral overlay.• The spiral should lie along
the axis of the of the band, and roughly parallel the inside edge of the band.
• Measure the arc length.
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Step 2A, Curved BandStep 2A, Curved Band
• Use a LOG10 spiral overlay.• The spiral should lie along
the axis of the of the band, and roughly parallel the inside edge of the band.
• Measure the arc length.
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Step 2A, Curved BandStep 2A, Curved Band• Measuring the arc length:
– Follow the convection, not cirrus blow-off
– Easier to do with Visual than Enhanced IR.
– You may have small breaks in convection and draw through
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Step 2A, Curved BandStep 2A, Curved Band
• Use a LOG10 spiral overlay.• The spiral should lie along
the axis of the of the band, and roughly parallel the inside edge of the band.
• Measure the arc length.
LOG10Spiral
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Step 2A, Curved BandStep 2A, Curved Band• Measuring the arc length:
– Can be very subjective– Inexperienced analysts tend to
go too high (fooled by cirrus).– This storm is somewhere
between 0.70 and 0.85.
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Step 2A, Curved BandStep 2A, Curved Band
Note: Southern Hemisphere Example
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Step 2A, Curved BandStep 2A, Curved Band
Note: Southern Hemisphere Example
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Step 2A, Curved BandStep 2A, Curved Band
Draw your banding line from the outside , then in.
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Step 2A, Curved BandStep 2A, Curved Band
0.100.20
0.300.40
0.50
0.60
0.700.80
Start from yourLLCC and count “pie slices”or log10 sectors.
They are counted in tenths.
360 degrees around equals “1.00” wrap
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Step 2A, Curved BandStep 2A, Curved Band
0.100.20
0.300.40
0.50
0.60
0.700.80
A wrap of 0.80would equal a Data T of T3.5
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0.100.20
0.300.40
0.50
0.60
0.700.80
I could have addedI could have addedan additional 0.05an additional 0.05for this portion of for this portion of wrap, giving a totalwrap, giving a totalwrap of 0.85wrap of 0.85- Judgement call.- Judgement call.
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Step 2B, Shear PatternStep 2B, Shear Pattern• Measure the distance from
the LLCC to the nearest convection.
• In IR, use the dark gray (DG) on BD Curve ONLY shade to identify convection.
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Step 2B, Shear PatternStep 2B, Shear Pattern• Measure the distance from
the LLCC to the nearest convection.
• In EIR, use the dark gray (DG) on BD Curve ONLY shade to identify convection. 70nm = T1.570nm = T1.5
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Step 2C, Eye PatternStep 2C, Eye Pattern• Terms
– E#: Eye Number– Eye adj: Eye adjustment – CF: Central Feature– BF: Banding Feature
• CF Formula: CF = E# + Eye adj• Data-T Formula: DT = CF + BF
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Step 2C (E# VIS)Step 2C (E# VIS)• Determine if Eye is banding type or not.• Measure the embedded distance of the eye, or the average band
width if eye is a banding type. • For small eyes, measure distance from center.• For large eyes (> 30 nm) measure from edge.• Apply Values to E# Table
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CDO type eyeCDO type eye
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CDO type eyeCDO type eye
CDOCDO
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CDO type eyeCDO type eye
CDOCDO
Measure narrowest distanceMeasure narrowest distance(This is for a Large eye,(This is for a Large eye,which defined as which defined as 30 nm or30 nm ormore inclusivemore inclusive))
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CDO type eyeCDO type eye
CDOCDO
Measure narrowest distanceMeasure narrowest distance(This is for a SMALL eye,(This is for a SMALL eye,which defined as which defined as 29 nm or29 nm orlessless))
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Banding EyeBanding Eye
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Banding EyeBanding Eye
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Banding EyeBanding Eye
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Banding EyeBanding Eye
Use average distance around thebanding eye
(Outline the band if you need to)
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Banding EyeBanding Eye
Use average distance around thebanding eye• Don’t use the smallest or largest• Can be subjective
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Step 2C (Eye adj VIS)Step 2C (Eye adj VIS)
• For poorly defined or ragged eyes subtract .5 if E# < 4.5, and subtract 1.0 if E# > 4.5.
• Add .5 or 1.0 if the eye is well defined, circular, and embedded in a smooth, very dense canopy
• Add .5 or whole 1.0, IF the MET > 6.0, & the CF is less than the MET.
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Step 2C (BF VIS)Step 2C (BF VIS)
• Dense, mostly overcast band that curves at least 1/4 distance around the central feature.
• Rarely used if CF is greater than 4.5.• Compare to chart.
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Step 2C (E# IR)Step 2C (E# IR)• Find the shade of the coldest ring completely surrounding the eye. MUST
USE BD CURVE!• Measure the distance from the edge of the coldest color band to the outside
edge of the coldest surrounding ring.• For EIR, DO NOT USE center of eye ever (center is only used in
VISUAL)!• Apply Values to E# Table
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Step 2C (E# IR, Example)Step 2C (E# IR, Example)
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Step 2C (E# IR, Example)Step 2C (E# IR, Example)
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Step 2C (E# IR, Example)Step 2C (E# IR, Example)
43 nm
9 nm
18 nm
In this Example,use White.Cold Medium Gray is not wide enough(18 nm!)
Eye # is 6.0
Confused?
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Step 2C (E# IR, Example)Step 2C (E# IR, Example)
43 nm
9 nm
18 nm
Why is it that Cold Medium Gray (CMG) is not wide enough?
The colorband youpick mustmeet thedistance criteriain the table(at thebottomleft)!
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Step 2C (E# IR, Example)Step 2C (E# IR, Example)
43 nm
9 nm
18 nm
43 nm ofdistance on the white band meets the 6.0requirement
The colorband youpick mustmeet thedistance criteriain the table(at thebottomleft)!
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Abbreviations:Abbreviations:
SurroundingRingTemperature
Eye TemperatureWMG Warm Medium GrayOW Off WhiteDG Dark GrayMG Medium GrayLG Light GrayB BlackW WhiteCMG Cold Medium GrayCDG Cold Dark Gray
• Each abbreviation on the EIR Eye adjustment chart comes from theBD enhancement curve, which Dvorak developed and used for EIR analysis on Tropical Cyclones (TC). • Each color is directly correlated to a temperature range.• It is a standard to use these shortened color terms rather that the temperature values themselves in TC Analysis.
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TemperaturesTemperatures
Abbreviation Gray Shade TemperatureRange ( C)
WMG Warm Medium Gray > +09OW Off White +09 to -30DG Dark Gray -31 to -41MG Medium Gray -42 to -53LG Light Gray -54 to -63B Black -64 to -69W White -70 to -75CMG Cold Medium Gray -76 to -80CDG Cold Dark Gray < -81
o
oooooooo
oooooooo
o
o
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Step 2C (Eye adj IR)Step 2C (Eye adj IR)• Determine the warmest shade in the eye and the
shade of the coldest ring surrounding the eye.• Do not use for eyes 45nm diameter or larger.• Apply to chart.
• For elongated eyes, subtract .5 if none subtracted by chart.
SurroundingRingTemperature
Eye Temperature
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)Here, distancedoesn’t matter.Use theCold DarkGray (CDG)for thesurrounding ring temp.Use Black for the eye.
Of course,the eyeadjustdiagram only goesto CMG,so use CMGinstead.
Cold DarkCold DarkGray onlyGray onlyneeds to needs to surroundsurroundfor eyefor eyeadjustmentadjustment.
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)WMG OW DG MG LG B W
OW 0 -.5
DG 0 0 -.5
MG 0 0 0 -.5
LG +.5 0 0 0 -.5
B +1.0 +.5 0 0 0 -.5
W +1.0 +.5 +.5 0 0 -1.0 -1.0
CMG +1.0 +.5 +.5 0 0 -.5 -1.0
So, for a Black eyeand CMG surroundring temperature,the eye adjustment is -0.5.-0.5.
Surround. Temp Ring
Eye Temp
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)
So, the E# was 6.0, based on a whiteband, and the eye adjustment was -0.5,-0.5,based on based on a Black eyeand CMG surroundring temperature.
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)Again,E# = 6.0 Eye adj= -0.5-0.5(don’t forget minus!)
Now use the formulafor the CENTRALFEATURE (CF):
CF Formula: CF = E# + Eye adj
Here, CF=6.0 +(-0.5)=5.5
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Step 2C (BF IR)Step 2C (BF IR)• Use only when the CF is 4 or more and the CF is lower than
the MET without adding the BF.• Band must curve 1/4 distance around, be MG or colder, and
have a DG or warmer wedge.• Measure Wedge.• Apply Chart.
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)Remember:
Here, CF=6.0 +(-0.5)=5.5
There is no banding feature on this storm.
BF=0
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Step 2C (BF IR, Example)Step 2C (BF IR, Example)This stormDOES have a Banding Feature…..
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Step 2C (BF IR, Example)Step 2C (BF IR, Example)This stormDOES have a Banding Feature
Here:
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Step 2C (BF IR, Example)Step 2C (BF IR, Example)This stormDOES have a Banding Feature
Here:
(This would be about BF=0.5)
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Step 2C, Eye PatternStep 2C, Eye Pattern
• Run the following Formulas:– CF Formula: CF = E# + Eye adj– Data-T Formula: DT = CF + BF
• When calculating with VIS, eyes with a diameter > 30nm limit DT to 6.0 for well defined eyes, and 5.0 for all others.
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Step 2C (E Adj IR, Example)Step 2C (E Adj IR, Example)Remember:
Here, CF=5.5
BF=0
Data-T Formula: DT = CF + BF
DT=5.5+0.0=5.5
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Step 2D, CDOStep 2D, CDO• Only used with VIS images.• Determine if CDO is well defined.• Measure CDO diameter and apply to chart.
• Always Add any Banding Feature
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Step 2E, EMB CTRStep 2E, EMB CTR• Only used with IR images and when Final-T from
12 hours previous was > 3.5.• Determine distance at which the center is
embedded into the shades of the BD curve and apply to chart.
• Add Banding Feature.
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Step 3, CCCStep 3, CCC
• When past Final-T < 3, use MET for 12 hours then hold same.
• When past Final-T > 3.5, hold same.• Use as Final-T and go to Step 9
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Step 4, 24-Hour TrendStep 4, 24-Hour Trend
• Compare current image to image 24 hours ago.• Determine if the cloud features in the current
image look better defined, the same or worse.– If better, the trend is Developed (D)– If the same, the trend is Same (S)– If worse, the trend is Weakened (W)
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Step 5, Model-T (MET)Step 5, Model-T (MET)
• For systems with a 24-Hour Trend of D or W, determine Pattern Evolution and apply appropriate number to Final-T from 24 hours ago.
» - Slow (+ .5)» Normal (+ 1.0) » + Rapid (+ 1.5)
• ASSUMES you are routinely doing Dvorak intensity estimates - can’t do a “one-timer”!
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Step 6, Pattern T - PT (IR)Step 6, Pattern T - PT (IR)• Select the pattern in the diagram that best matches
your storm picture; 100% SUBJECTIVE
A
B
C
PatternType:
Pattern T number.
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Step 6, PT (VIS)Step 6, PT (VIS)• Select the pattern in the diagram that best
matches your storm picture; same as EIR PT
A
B
C
PatternType:
Pattern T number.
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Final T NumberFinal T Number
1. Use DT when it is clear-cut and representative.2. Use PT only when DT is not clear-cut and
representative, and PT is.– Often happens with Shear DT estimates (Shear DT often too high).– Remember that the Data T is often calculated, so it may be unrealistic.
3. Use MET only when PT and DT are not clear-cut and representative.– Thumb-rule: PT is NOT clear cut when you have difficulty distinguishing
amongst three different PT pictograms along the horizontal.– Example: on Vis PT diagram, you honestly have difficulty telling the
difference between an “A4.0”, “A5.0”, and “A6.0”
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Final-T Number ConstraintsFinal-T Number Constraints
• Initial Classification must be 1.0 or 1.5 (period).• During the first 48 hours of development Final-T
can not be lowered at night (but you can during day-light).• 24 hours after initial 1.0, Final-T must be < 2.5.• Final-T limits:
• < 3.5 =FT can change only 0.5 per 6 hours.• > 4.0 = FT can change only1.0 per 6 hours, 1.5 per 12
hours, 2.0 per 18 hours, or 2.5 per 24 hours.
• Final-T must be + 1.0 from MET.
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Current Intensity (CI)Current Intensity (CI)• Make the CI the same as Final-T during
development, but hold higher during weakening.• Do not lower CI until at least 12 hours have past.• CI will not be more that 1.0 greater than Final-T.
0
1
2
3
4
5
6
7
8
Final-T
CI
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Current Intensity (CI)Current Intensity (CI)Why hold CI higher during weakening?Why hold CI higher during weakening?
• Storm surface vorticity (spin) is conserved for a period of time, even though the cloud features seem unimpressive.
• CAREFUL! The storm will appear weak, but still maintain enough energy to have strong winds
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Short Term Trend (STT)Short Term Trend (STT)
• STT is the trend based on less than 18 hours.• Always use a STT when you have less than 18
hours of history.• In addition, you can use STT when the regular
trend does not tell the whole story.• NOTE: THERE IS NO MODEL T number
until the system is AT LEAST 18 hours old.
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Coding Coding
• DVORAK coding– FT/CI/Trend/Period– Example- T3.0/4.0/W1.5 24HRS
• STT coding– Trend/Period– Example - T2.0/2.0/STT: D0.5/15HRS
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Coding Coding
• What about those situations where the LLCC cannot be determined, but Dvorak Constraints keep us from finalling the system?– Enter TX.X for Final T– Keep last CI until Dvorak Constraints allow you to
eliminate the system– Should normally happen with very weak systems.– Example- TX.X/1.0/STT: S0.0/14HRS
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Coding ExerciseCoding ExerciseDVORAK CODE SST
FT/CI/TREND/PERIOD (TREND is change 18-30 hours)
Change < 18 hours
1/0530Z 1010 INIT
1/1130Z 1010 NA S00/06
1/1730Z 1010 NA S00/12
1/2330Z 2020 D10/18
2/0530Z 20
2/1130Z 25
2/1730Z 25
2/2330Z 30
3/0530Z 30
3/1130Z 25
3/1730Z 15
3/2330Z 10
4/0530Z 10
4/1130Z 10
4/1730Z 10
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Exercise AnswersExercise AnswersDVORAK CODE SST
FT/CI/TREND/PERIOD (TREND is change 18-30 hours)
Change < 18 hours
1/0530Z 1010 INIT
1/1130Z 1010 NA S00/06
1/1730Z 1010 NA S00/12
1/2330Z 2020 D10/18
2/0530Z 2020 D10/24
2/1130Z 2525 D15/24
2/1730Z 2525 D15/24 S00/06
2/2330Z 3030 D10/24
3/0530Z 3030 D10/24
3/1130Z 2530 S00/24 W05/06
3/1730Z 1525 W10/24 W15/12
3/2330Z 1020 W20/24
4/0530Z 1020 W20/24 S00/06
4/1130Z 1015 W15/24 S00/12
4/1730Z 1010 W05/24
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Questions?Questions?. Contact: .. Contact: .Paul J. McCrone, GS-12, Chief ForecasterHQ Air Force Weather Agency (AFWA) Meteorological Satellite ApplicationsOffice Code: XOGM106 Peacekeeper Dr. STE 2N3Offutt AFB, NE 68113-4039
Email: Paul.McCrone@afwa.af.mil and PaulJMC@aol.com
Phones: (402) 294-2821DSN: 271-2821Fax: (402) 294-5872