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Adapting the P-Type Nomogram to the GFE

Adapting the P-Type Nomogram to the GFE. Patrick D. Moore NWS Greenville-Spartanburg. Motivation. Add some science to the “dark art” of creating Wx grids for winter precipitation events… …by applying proven techniques to every grid box in the forecast area…

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Adapting the P-Type Nomogram to the GFE

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  1. Adapting the P-Type Nomogramto the GFE Patrick D. Moore NWS Greenville-Spartanburg

  2. Motivation • Add some science to the “dark art” of creating Wx grids for winter precipitation events… • …by applying proven techniques to every grid box in the forecast area… • …while keeping the forecaster engaged in the process… • …and maintaining database integrity.

  3. What we want to avoid…

  4. Two techniques have been adapted to the GFE to accomplish this task • Predominate Precipitation Type Trends Technique • Kermit Keeter (WFO Raleigh) • Top-Down Method of Precip. Type Forecasting • Dan Baumgardt (WFO LaCrosse) Image courtesy of Dr. Baker Perry, Flat Springs, NC

  5. The TREND Technique and thePartial Thickness Universal Nomogram • Empirical technique developed by correlating data from upper air soundings and surface observations taken at GSO (elevation 897 ft.) • Specifies and verifies the occurrence of p-types continuously over six hour intervals • Accounts for trends in the evolution of p-types References: Keeter and Cline (1991) See also http://www4.ncsu.edu/~nwsfo/storage/trend/

  6. Before the NDFD…A Problem…Where do we put transitions?

  7. With the Digital Forecast Database…Transitions are easier to define • We could draw transitions between precipitation types that don’t conform to zone boundaries • However, this is very tedious • How to maintain consistency?

  8. In the GFE… • Model data is ingested and interpolated to grids which can be used to populate database • Partial thickness values can be calculated at each grid box

  9. The Nomogram Adapted to the GFE • Using partial thickness values from grids, find position within Nomogram at every grid box • Display on PTypeNomogram grid in the GFE

  10. The Nomogram Adapted to the GFE • Using partial thickness values from grids, find position within Nomogram at every grid box • Display on PTypeNomogram grid in the GFE • Indeterminate split between RA and SNra

  11. Task of creating Wx grid is broken up into two main steps • Creating PTypeNomogram grid using CreatePTypeNomogram procedure • ThickH100toH85, ThickH85toH70 • Creating Wx from PTypeNomogram grid using WxFromNomogram procedure • PtypeNomogram, PoP, T, QPF, FzLevel, Snowlevel

  12. Changes to Nomogram P-Types • If elevation of grid box is… • above FzLevel, change all p-types to SN • below SnowLevel, change all p-types to RA or ZR, depending on T • within melting layer, allow RA and SN to coexist accordingly • Surface temperature controls RA or ZR Image adapted from SRH JetStream

  13. The WxFromNomogram Procedure • Conditional probability of primary precipitation type taken from PoP grid • Conditional probability of a secondary precipitation type selected by user • Intensity taken from QPF grid according to FMH-1

  14. The WxFromNomogram Procedure • Combine attribute and duration qualifier selected by user • Initial distribution of p-types taken from PTypeNomogram grid • Final distribution of p-types modified by surface temperature and grid box elevation relative to FzLevel and SnowLevel, if desired

  15. Creating Wx from the NomogramSome things to consider… • Incorporation of FzLevel and SnowLevel allows the technique to be extended to high elevations with reasonable results • Wx grids of less than 6-hr length violate the experimental design of the Nomogram!!! • Does not account for very shallow arctic air masses • Does not account for cloud microphysics issues • Will maintain internal consistency among elements!

  16. The Problem With The Wx GridOr, why do my Wx grids look like hell? • The Wx grid is a catch-all for… • Conditional probability • Precipitation type • Temp aloft • Temp at surface • Intensity, Visibility • Attributes Wx = probability: ptype : intensity : visibility: attribute + prob2 : ptype2 : intensity2: visibility2 : attribute2

  17. The World is a messy place…

  18. Operational Considerations… • Beyond forecast hour 36, consider choosing WxFromNomogram because of its built-in climatology • Create a new weather element group for winter weather grids • Configure colors and shades for different precipitation types

  19. Other Important Considerations... • These are “advanced” techniques! (Not simple Wx-from-PoP tools, but a methodology) • Objective application of techniques used in a subjective process… (Grids will sometimes appear “messy”) • The Procedures will only take you so far down the road… (May need to finish up with “Showerize” or “RemoveWx”) • Impact on forecast process… (Should be done later instead of earlier) • How will text formatters react? (Really intended for a point-and-click forecast)

  20. Questions?

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