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Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota

Warm Season Frontogenesis Forcing Applications and Implications for Convective Initiation (or Failure). Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota. Phil Schumacher Science and Operations Officer NWS/WFO Sioux Falls, South Dakota. Greg Mann, PhD

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Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota

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  1. Warm Season Frontogenesis Forcing Applications and Implications for Convective Initiation (or Failure) Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota Phil Schumacher Science and Operations Officer NWS/WFO Sioux Falls, South Dakota Greg Mann, PhD Science and Operations Officer NWS/WFO White Lake, Michigan Great Lakes Operational Meteorology Workshop – Toronto, Ontario 22 March 2010 NWS Duluth Minnesota

  2. Objectives 1) Review frontogenesis conceptual models 2) Review cold season frontogenesis applications 3) Establish a need for FGEN application during the warm season 4) Develop a warm season frontogenesis conceptual model 5) Warm season case example 6) A few thoughts about warm season “parameter space”

  3. C L F > 0 A B Synoptic Cyclone Frontogenesis Regions

  4. Frontogenesis Conceptual Models F > 0 F > 0 F > 0 Remember: By convention, we draw the front at the leading edge of the gradient - so FGEN > 0 on the cool side of the front. BUT… The ascending branch of the ageostrophic circulation resides to the warm side of the FGEN maximum (in the max F vector convergence) Cross Section A Cross Section B Cross Section C Dryline Movement Cold Frontal Movement Warm Frontal Movement

  5. Frontogenesis Conceptual Models We will focus on this area where “warm” frontogenesis is occurring L F > 0

  6. Review of Frontogenesis Concepts Thermal Gradient Frontogenesis Low Level Jet QPF on Cool Side L Banded Precip Low Level Jet Weak Stability or Instability needed for Heavy Precipitation

  7. Cold Season FGEN Conceptual Model 850 mb T/Wind/ Isotachs 800 mb/ FGEN Sfc Pres/ QPF Sfc Pres/ Temp

  8. Cold Season FGEN Conceptual Model 700 mb 500 mb 925 mb 850 mb FGEN (image), Isotherms and Wind

  9. Cold Season FGEN Conceptual Model EPV*/ Theta RH FGEN/ Theta-E T/ Omega south north X-Section Across Frontal Zone

  10. FGEN in the Warm Season? So, why are FGEN processes de-emphasized during the warm season? Presumably because… 1) Thermal gradients are weaker in the warm season 2) Frontal zones are shallower in the warm season 3) Synoptic waves are generally weaker during the warm season (weaker dynamic forcing) However… Instability is typically MUCH greater! …and strong low level jet interaction with a low level baroclinic zone (front or outflow boundary) is quite common

  11. Frequency of FGEN in Warm Season? From Bettwy/Donofrio/Lonka, et al for 2006 warm season MUCH more common that previously acknowledged! FGEN processes need additional scrutiny in the warm season as well

  12. Warm Season FGEN Conceptual Model 850 mb T/Wind/ FGEN MUCAPE Sfc Pres/ QPF Sfc Pres/ Sfc CAPE

  13. Warm Season FGEN Conceptual Model 700 mb 500 mb 925 mb 850 mb FGEN (image), Isotherms and Wind

  14. Warm Season FGEN Conceptual Model CAPE/ Omega RH FGEN/ Theta Theta-E/ Ageo Circ southwest northeast X-Section Across Frontal Zone

  15. Case Example: 13 August 2007 1630 UTC Categorical Outlook 1630 UTC Tornado Outlook 1630 UTC Hail Outlook 1630 UTC Wind Outlook

  16. Case Example: 13 August 2007 2030 UTC Categorical Outlook 2030 UTC Tornado Outlook 2030 UTC Hail Outlook 2030 UTC Wind Outlook

  17. 13 August 2007: Convective Initiation KDLH Reflectivity Loop 2159-2341 UTC

  18. 13 August 2007: Objective Analysis Surface CAPE 21Z Most Unstable CAPE 21Z

  19. 13 August 2007: Objective Analysis Surface CAPE 23Z Most Unstable CAPE 23Z

  20. 13 August 2007: Volumetric Reflectivity ~33,000 ft agl ~41,000 ft agl ~12,000 ft agl ~21,000 ft agl KDLH Reflectivity 4-panel 2353 UTC

  21. Is the Frontal Zone Active? Wind(green barbs)/Wind Isotachs (peach lines) and Divergence (image)

  22. Active Part of Frontal Zone Cold Season Warm Season Frontolysis/Frontogenesis couplet indicates active part of the frontal zone (Sawyer-Eliassen Equation)

  23. Ageostrophic Response Cold Season Warm Season Active Frontogenetic/Frontolytic circulations develop

  24. Impact on Parcel Trajectories Cold Season Warm Season Parcels hit a “speed bump” and weak subsidence just before entering the ascending branch of the frontogenetic circulation resulting in further dynamic strengthening of an already strong cap

  25. Layer Lifting Processes From: Bryan et al Significant limitation of Parcel Theory: Layer Lifting Processes Parcel Computed CAPE can underestimate Actual Realized CAPE by 2 to 4 times!!

  26. CI: 13 August 2007 Case - 21 UTC Surface Warm Front Location of Initiation

  27. CI: 13 August 2007 Case - 22 UTC

  28. CI: 13 August 2007 Case - 23 UTC

  29. CI: 13 August 2007 Case - 24 UTC

  30. Thermodynamics North of Boundary * Location of Initiation

  31. North of Boundary: Initial Profile Sustained Layer Forced Ascent due to frontogenesis MU layer: ~860-830 mb 2100 UTC CAPE: 491 CIN: 455 LFC: ~16000 ft/agl ~570 mb 2100 UTC

  32. North of Boundary: Profile Changes Sustained Layer Forced Ascent due to frontogenesis MU layer: ~850-830 mb 2200 UTC CAPE: 980 CIN: 276 LFC: ~14400 ft/agl ~602 mb 2200 UTC

  33. North of Boundary: Profile Changes Sustained Layer Forced Ascent due to frontogenesis MU layer: ~820-780 mb 2300 UTC CAPE: 1320 CIN: 130 LFC: ~13800 ft/agl ~616 mb 2300 UTC

  34. North of Boundary: Profile Changes Sustained Layer Forced Ascent due to frontogenesis MU layer: ~810-790 mb 2400 UTC CAPE: 1737 CIN: 72 LFC: ~13205 ft/agl ~630 mb 2400 UTC

  35. Sustained Layer Forced Ascent North of Boundary: Forcing Modifications MU Parcel Layer 3 Hour Change CAPE: 1737 (+1247) CIN: 72 (-383) LCL/LFC heights lower by ~3000 feet!

  36. Thermodynamics South of Boundary * Warm Sector Profile

  37. South of Boundary: Initial Profile 2100 UTC CAPE: 3605 CIN: -125 LFC: ~10745 ft/agl ~694 mb 2100 UTC Sustained Layer Forced Weak Subsidence due to Frontolysis

  38. South of Boundary: Profile Changes 2200 UTC CAPE: 3717 CIN: -129 LFC: ~10745 ft/agl ~694 mb 2200 UTC Sustained Layer Forced Weak Subsidence due to Frontolysis

  39. South of Boundary: Profile Changes 2300 UTC CAPE: 3756 CIN: -133 LFC: ~10745 ft/agl ~694 mb 2300 UTC Sustained Layer Forced Weak Subsidence due to Frontolysis

  40. South of Boundary: Profile Changes 2400 UTC CAPE: 3919 CIN: -147 LFC: ~10700 ft/agl ~695 mb 2400 UTC Sustained Layer Forced Weak Subsidence due to Frontolysis

  41. South of Boundary: Forcing Modifications MU Parcel 2200 UTC CAPE: 3919 (+314) CIN: 147 (+22) LCL/LFC height nearly unchanged Sustained Layer Forced Weak Subsidence

  42. Dynamic Cap Strengthening: CI Failure Agrees well with Weisman/Wieseler Study (St. Cloud State University) CI cases = red CI failure cases = green Dynamic Cap Strengthening

  43. Parameter Space vs. Processes Parameter “Sufficiency” + Maximized Processes Severe Weather Parameter Space is Maximized Sharp precip/cloud cutoff on warm side of boundary

  44. Thanks For Your Attention Questions/Comments/Discussion? dan.j.miller@noaa.gov

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