Notes

Outline

The Dvorak Technique

The Dvorak Technique Positioning Intensity Estimation Final T-number Data-T Pattern-T Model-T Current Intensity Coding

Positioning Eye Exposed Low Level Circulation Center (LLCC) Central Dense Overcast (CDO) Embedded Center  (EMB CTR) Spiral Band Curvature (SBC) Partially exposed LLCC Cloud minimum wedge Central Cold Cover (CCC) Cirrus outflow Circle method Conservative feature Animation Extrapolation

Common Abbreviations Low Level Circulation Center LLCC Low Level Cloud Lines LLCLS Upper Level Circulation Center ULCC Central Dense Overcast CDO Embedded Center  EMB CTR Spiral Band Curvature SBC Central Cold Cover CCC Enhanced Infrared EIR Convection CNVCTN

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

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.

Exposed LLCC Fixes Look for tightening cyclonic low clouds. The center will be within the tightest circle of clouds. Much easier to find with VIS imagery

CDO 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

EMB CTR Look for a warm spot Look toward the edge with the tightest temperature gradient Don’t forget continuity with past positions

SBC Fixes VIS 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 VIS 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 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

Partially Exposed LLCC Fixes 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.

Partially Exposed LLCC Fixes IR 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).

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

Cloud Minimum Wedge The center will be halfway along a line drawn from the tip of the wedge straight across the comma head.

CCC Fixes VIS 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 IR Very difficult to accurately locate center. Center placement based mostly on continuity.

Cirrus Outflow Fixes 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.

Circle Method Fixes To be used with weak or very broad systems. Use all available curvature to find center. Where most circles meet, indicates most likely LLCC.

Conservative Features Fixes 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)

Animation Fixes Self explanatory Use with all type of fixes when available. Use animation alone only when still imagery gives no indication of LLCC.

Extrapolation Fixes 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

Intensity 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

Step 2, Data-T Step 2A Curved Band Step 2B Shear Pattern Step 2C Eye Pattern Step 2D CDO Step 2E Embedded Center

Step 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.

Step 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.

Step 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

Step 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.

Step 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.

Step 2A, Curved Band

Step 2A, Curved Band

Step 2A, Curved Band

Step 2A, Curved Band

Step 2A, Curved Band

Step 2A, Curved Band

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Step 2B, Shear Pattern Measure the distance from the LLCC to the nearest convection. In IR, use the dark gray (DG) shade on BD Curve ONLY to identify convection.

Step 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.

Step 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

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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Banding Eye

Banding Eye

Banding Eye

Banding Eye

Banding Eye

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.

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.

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

Step 2C (E# IR, Example)

Step 2C (E# IR, Example)

Step 2C (E# IR, Example)

Step 2C (E# IR, Example)

Step 2C (E# IR, Example)

Abbreviations: Surrounding Ring Temperature

Temperatures

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.

Step 2C (E Adj IR, Example)

Step 2C (E Adj IR, Example)

Step 2C (E Adj IR, Example)

Step 2C (E Adj IR, Example)

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.

Step 2C (E Adj IR, Example)

Step 2C (BF IR, Example)

Step 2C (BF IR, Example)

Step 2C (BF IR, Example)

Step 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.

Step 2C (E Adj IR, Example)

Step 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

Step 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.

Step 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

Step 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)

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”!

Step 6, Pattern T - PT (IR) Select the pattern in the diagram that best matches your storm picture; 100% SUBJECTIVE

Step 6, PT (VIS) Select the pattern in the diagram that best matches your storm picture; same as EIR PT

Final 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”

Final-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.

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.

Current Intensity (CI) 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

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.

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

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

Coding Exercise

Exercise Answers

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