1 / 31

An Investigation of Null-Event Severe Convective Watches in the WFO Sterling Forecast Area

An Investigation of Null-Event Severe Convective Watches in the WFO Sterling Forecast Area. Lee Picard Student Volunteer, WFO LWX University of Miami, Coral Gables, FL Matthew Kramar Senior Forecaster, WFO LWX. Definitions. Severe thunderstorm watch

todd-boone
Download Presentation

An Investigation of Null-Event Severe Convective Watches in the WFO Sterling Forecast Area

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An Investigation of Null-Event Severe Convective Watches in the WFO Sterling Forecast Area Lee Picard Student Volunteer, WFO LWX University of Miami, Coral Gables, FL Matthew Kramar Senior Forecaster, WFO LWX

  2. Definitions • Severe thunderstorm watch • From SPC: “outlines an area where an organized episode of hail 1 inch diameter or larger and/or damaging thunderstorm winds are expected during a three to eight hour period.” • Tornado watch • From SPC: “includes the large hail and damaging wind threats, as well as the possibility of multiple tornadoes.”

  3. Definitions • Null watch • A watch, either severe thunderstorm or tornado, where the expected coverage and intensity of thunderstorms does not materialize

  4. Motivation • Provide guidance to forecasters as to synoptic patterns that would typically result in a null watch • Reduce the frequency of null watches and thereby decrease public desensitization

  5. Motivation

  6. Motivation

  7. Motivation

  8. Methodology • Assembled a database of convective watches issued in the WFO Sterling CWA from 2005-10 • Sorted through archived products to determine if severe weather occurred during watches in CWA • Eliminated null cases from list subject to: • Outside typical severe season (May-Sept.) • Small part of CWA affected • Thunderstorms occurred, but below severe threshold

  9. Methodology • Constructed synoptic composites using data from the NCEP/NCAR and NARR Reanalyses • Used 6-hour synoptic time immediately preceding watch initiation • Variables: • Geopotential height • Air temperature • Vector wind • Zonal wind • Meridional wind • Relative humidity • Precipitable water • Levels: • 100 mb • 250 mb • 500 mb • 700 mb • 850 mb • 925 mb • Surface

  10. Methodology • Chose 18 cases of very active severe convective weather watches from 2005-10 • Created a second set of composites to use as a baseline to contrast with null cases

  11. Methodology • Synoptic composites • NCEP/NCAR Reanalysis • Lower resolution • 2.5° x 2.5° lat./lon. grid • 6-hourly data • NCEP North American Regional Reanalysis (NARR) • Higher resolution • 1° x 1° lat./lon. grid • 3-hourly data

  12. 500-millibar variables Comparisons Null events Very active events

  13. 500-millibar variables

  14. 500-millibar variables

  15. 700-millibar variables

  16. 850-millibar variables

  17. 850-millibar variables

  18. 850-millibar variables

  19. 925-millibar variables

  20. 925-millibar variables

  21. 925-millibar variables

  22. Surface variables

  23. Surface variables

  24. Surface variables

  25. Precipitable Water

  26. Pattern Analogs • Analog searches provided by Greg Carbin (SPC) • Dates since 1979 with the patterns closest to those of null watches • RMS errors for geopotential height at 500 and 850 millibars • Grid difference for precipitable water • Selected dates that occurred as matches to both the 500- and 850-mb patterns • Ruled out dates before 1990 and those dissimilar to composite patterns based on manual inspection • Determined if severe weather occurred on analog dates

  27. Pattern Analogs • Of 6 national domain matches, three produced severe weather • Of 6 local domain matches, zero resulted in severe weather • National matches could be tied more heavily to the ridge/trough patterns across the country and could undervaluate local details that result in null events

  28. Results Null events Severe events Upper level More amplified ridge and trough Relative eastward wind maximum (upstate NY/Lake Ontario) Weaker wind maximum Dipole in meridional wind • Upper level • Less amplified ridge and trough • Relative westward wind maximum (southern Ontario) • Stronger wind maximum

  29. Results Null events Severe events Middle level More amplified ridge and trough More amplified 700-mb temperatures Weaker wind maximum • Middle level • Less amplified ridge and trough • Less amplified 700-mb temperatures • Stronger wind maximum • Additional wind maximum over Atlantic Ocean

  30. Results Null events Severe events Lower level Relative southward surface low pressure located (southern Ontario) Weak wind maximum off northeast seaboard Relative cooler temperatures Relative lower PW • Lower level • Relative northward surface low pressure center (northern Quebec) • Strong wind maximum off northeast seaboard • Relative warmer temperatures • Relative higher PW

  31. Local Domain 500 & 850 mb Geopotential Height Composites

More Related