1. Warm Season Frontogenesis Forcing Applications and Implications for Convective Initiation (or Failure) Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota Dan Miller Science and Operations Officer NWS/WFO Duluth, Minnesota NWS Duluth Minnesota Great Lakes Operational Meteorology Workshop – Toronto, Ontario22 March 2010 Phil Schumacher Science and Operations Officer NWS/WFO Sioux Falls, South Dakota Phil Schumacher Science and Operations Officer NWS/WFO Sioux Falls, South Dakota Greg Mann, PhD Science and Operations Officer NWS/WFO White Lake, Michigan Greg Mann, PhD Science and Operations Officer NWS/WFO White Lake, Michigan

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. Synoptic Cyclone Frontogenesis Regions LL F > 0 A A B B C C

4. Frontogenesis Conceptual Models Cold Frontal Movement Dryline Movement Dryline Movement Warm Frontal Movement The ascending branch of the ageostrophic circulation resides to the warm side of the FGEN maximum (in the max F vector convergence) 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… F > 0 Cross Section A Cross Section B Cross Section C

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

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

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

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

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

10. FGEN in the Warm Season? 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 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 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)

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 Sfc Pres/ QPF Sfc Pres/ QPF 850 mb T/Wind/ FGEN 850 mb T/Wind/ FGEN MUCAPE Sfc Pres/ Sfc CAPE Sfc Pres/ Sfc CAPE

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

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

15. Case Example: 13 August 2007 1630 UTC Hail Outlook 1630 UTC Wind Outlook 1630 UTC Tornado Outlook 1630 UTC Categorical 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 KDLH Reflectivity 4-panel 2353 UTC ~12,000 ft agl ~12,000 ft agl ~33,000 ft agl ~33,000 ft agl ~41,000 ft agl ~41,000 ft agl ~21,000 ft agl ~21,000 ft agl

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

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

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

24. Impact on Parcel Trajectories 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 Cold Season Warm Season

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

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 MU layer: ~860-830 mb 2100 UTC CAPE: 491 CIN: 455 LFC: ~16000 ft/agl ~570 mb 2100 UTC CAPE: 491 CIN: 455 LFC: ~16000 ft/agl ~570 mb 2100 UTC Sustained Layer Forced Ascent due to frontogenesis

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

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

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

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

36. Thermodynamics South of Boundary * * Warm Sector Profile

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

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

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

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

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

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

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