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Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection

Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection. Jack Kain ASP Summer Colloquium July 2006. Getting the Convective Boundary Layer Right in models : How it impacts Human Forecasts of Deep Convection. Jack Kain ASP Summer Colloquium July 2006.

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Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection

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  1. Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection Jack Kain ASP Summer Colloquium July 2006

  2. Getting the Convective Boundary Layer Right in models: How it impacts Human Forecasts of Deep Convection Jack Kain ASP Summer Colloquium July 2006

  3. My Background… I am a numerical modeler by training, but I have spent the last several years working at the interface of research and daily operations – with forecasters from the NCEP/Storm Prediction Center (SPC) and researchers from the NOAA/National Severe Storms Laboratory (NSSL)

  4. CAPE CIN Why the Boundary layer?

  5. CIN Why the Boundary layer? CAPE

  6. Small changes in Boundary Layer Temperature and Moisture can have a Big Impact on CAPE and CIN…Also, the Temperature Profile just above the top of the BL strongly affects CIN But do forecasters actually care about small-scale details in forecast-sounding structure? Yes! Consider a sampling of DAY 2 OUTLOOKs, a product that SPC forecasters use to provide guidance to local forecast offices…

  7. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1111 AM CST SAT APR 01 2006 VALID 021200Z - 031200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF IA...MO AND MUCH OF IL... …FORECAST SOUNDINGS INDICATE A POTENT COMBINATION OF INSTABILITY AND VERTICAL SHEAR ACROSS MODERATE RISK AREA...WHICH SHOULD SUPPORT INTENSE SUPERCELL DEVELOPMENT WITH THE POTENTIAL FOR A FEW STRONG TORNADOES IN ADDITION TO VERY LARGE...DESTRUCTIVE HAIL AND DAMAGING WINDS. WITH TIME...STORMS MAY EVOLVE INTO BOWING LINE SEGMENTS OR A MESOSCALE LEWP STRUCTURE WITH CORRIDORS OF DAMAGING WINDS POSSIBLE EWD ACROSS THE OH VALLEY SUNDAY NIGHT… …FORECAST SOUNDINGS INDICATE A POTENT COMBINATON OF INSTABILITY AND VERTICAL SHEAR ACROSS MODERATE RISK

  8. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1239 PM CDT MON APR 03 2006 VALID 041200Z - 051200Z ...NO SVR TSTM AREAS FORECAST... ...EARLY MORNING -- TX/SERN NM... …MRGL/CONDITIONAL HAIL PROBABILITIES EXIST OVER THIS REGION FOR FIRST FEW HOURS OF PERIOD...AMIDST EXTENSION OF LATE DAY-1 WAA/MOISTURE RETURN REGIME. ELEVATED BUOYANCY IS FCST TO BE SMALL – GENERALLY AOB 500 J/KG MOST AREAS. HOWEVER...ANY SUSTAINED CONVECTION WILL HAVE POTENTIAL FOR HAIL GIVEN STRONG VEERING AND SPEED SHEAR WITH HEIGHT THROUGH CONVECTIVE COLUMN...WHICH SHOULD BE ROOTED IN 800-850 MB LAYER BASED ON FCST SOUNDINGS. ACTIVITY SHOULD DIMINISH DURING LATE MORNING AS LLJ WEAKENS… ELEVATED BUOYANCY CONVECTION SHOULD BE ROOTED IN 800-850 MB LAYER BASED ON FCST SOUNDINGS.

  9. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1237 PM CDT TUE APR 04 2006 VALID 051200Z - 061200Z ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NRN PLAINS... ...NRN/CENTRAL PLAINS... …WIDELY SCATTERED TSTMS SHOULD DEVELOP FROM MID/LATE AFTERNOON INTO EARLY EVENING ACROSS NRN HIGH PLAINS...FROM SRN MT POTENTIALLY AS FAR E AS INVOF BLACK HILLS. ACTIVITY INITIALLY SHOULD BE HIGH-BASED...SUPPORTED BY MRGL BOUNDARY LAYER MOISTURE...STEEPENING MIDLEVEL LAPSE RATES ASSOCIATED WITH APCHG TROUGH...STRENGTHENING DEEP-LAYER SHEAR...AND DIABATIC SFC HEATING. DEEPLY MIXED SUBCLOUD LAYERS IN FCST SOUNDINGS SUGGEST POTENTIAL FOR BOTH DAMAGING DOWNDRAFTS AND LARGE HAIL TO REACH SFC. DEEPLY MIXED SUBCLOUD LAYERS IN FCST SOUNDINGS SUGGEST POTENTIAL FOR BOTH DAMAGING DOWNDRAFTS AND LARGE HAIL TO REACH SFC…

  10. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1235 PM CDT THU APR 06 2006 VALID 071200Z - 081200Z ...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA... …INITIATE FRIDAY AFTERNOON...SUPERCELLS WILL BE LIKELY DUE TO THE STRONG VERTICAL SHEAR ASSOCIATED WITH THE MID-LEVEL JET. NAMKF FORECAST SOUNDINGS FOR TUPELO MS...FLORENCE ALABAMA AND HUNTSVILLE ALABAMA FRIDAY AFTERNOON SEEM REASONABLE WITH MODERATE TO STRONG INSTABILITY (MLCAPE VALUES 2500-3000 J/KG)...0-6 KM SHEAR VALUES AT/ABV 60 KT AND IMPRESSIVE LOW-LEVEL SHEAR PROFILES (0-3 KM SRH AT/ABV 350 M2/S2). IN THIS ENVIRONMENT...STORMS SHOULD REMAIN DISCRETE FOR THE LATE AFTERNOON AND EARLY EVENING HOURS. IN ADDITION...LCL HEIGHTS ARE FORECAST TO REMAIN LOW WHICH COMBINED… NAMKF FORECAST SOUNDINGS SEEM REASONABLE WITH MODERATE TO STRONG INSTABILITY

  11. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1235 PM CDT THU APR 06 2006 VALID 071200Z - 081200Z ...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA... …FAVORABLE FOR TORNADOES. LONG-TRACK STRONG OR EVEN VIOLENT TORNADOES WILL BE POSSIBLE ESPECIALLY WITH SUPERCELLS THAT TRACK ALONG ANY PRE-EXISTING BOUNDARIES OR CONVERGENCE ZONES. THE INSTABILITY...SHEAR AND STEEP MID-LEVEL LAPSE RATES NEAR 8.0 C/KM SHOWN ON THE FORECAST SOUNDINGS WILL ALSO BE FAVORABLE FOR LARGE HAIL AND WIND DAMAGE WITH THE SUPERCELLS. VERY LARGE HAIL WILL ALSO BE POSSIBLE WITH THE STRONGER SUPERCELLS… SHEAR AND STEEP MID-LEVEL LAPSE RATES NEAR 8.0 C/KM SHOWN ON THE FORECAST SOUNDINGS WILL ALSO BE FAVORABLE FOR LARGE HAIL AND WIND

  12. DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1235 PM CDT THU APR 06 2006 VALID 071200Z - 081200Z ...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA... …INSTABILITY IN THE AFTERNOON HOURS. THE NAM AND GFS INITIATE POST-FRONTAL CONVECTION EARLY IN THE AFTERNOON NORTH OF A FRONTAL BOUNDARY EXTENDING WSWD TO ENEWD ACROSS THE OH VALLEY. FORECAST SOUNDINGS FOR THIS AREA FRIDAY AFTERNOON SHOW SUFFICIENT INSTABILITY/SHEAR PROFILES AND STEEP LAPSE RATES THAT SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. FURTHER SOUTH ACROSS KY...SFC DEWPOINTS IN THE UPPER 50S TO NEAR 60 F SHOULD ALLOW MODERATE INSTABILITY TO DEVELOP. ALTHOUGH CONVECTIVE INITIATION MAY... FORECAST SOUNDINGS FOR THIS AREA FRIDAY AFTERNOON SHOW SUFFICIENT INSTABILITY/SHEAR PROFILES AND STEEP LAPSE RATES THAT SHOULD BE FAVORABLE FOR SUPERCELLS

  13. What components of a modeling system most strongly affect (pre-convective) CAPE/CIN and BL structures? • Parameterizations of: • Boundary Layer/Turbulence* • Shallow moist convection* (do we need this with ~1-4 km grid spacing?) • Surface processes • Atmospheric radiation • Advection

  14. Consider two very different shallow Convective Parameterizations (both used in the NCEP SREF) • Kain-Fritsch scheme: a “mass-flux” convective adjustment scheme • Betts-Miller-Janjic (BMJ) scheme: a “static profile” convective adjustment scheme

  15. KF scheme: Checking for the possibility of deep (precipitating) convection…can a parcel reach its LFC and form a deep cloud?

  16. KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?

  17. KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?

  18. KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?

  19. KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?

  20. Updraft path Detrainment Layer Entrainment Layer Updraft mass-flux profile KF scheme: determining shallow-convection adjustment profiles Cloud-base mass flux: At what rate is mass is processed by moist shallow convection? Currently scaled as a function of TKE in the BL

  21. KF shallow convection parameterization…requires many assumptions • We think we have a good handle on: • Cloud-base thermodynamic properties • Cloud base, cloud top • Adjustment time scale • We have less confidence in assumptions related to: • Cloud-base mass flux – how much of the BL mass participates in moist convection? • Vertical profiles of entrainment, detrainment and vertical mass flux, which determine profiles of heating and drying.

  22. …It’s cloud illusions that I recallI really don’t know clouds at all… - Joni Mitchell

  23. KF scheme adjustment profiles

  24. The Betts-Miller-Janjic (BMJ) parameterization: based on the philosophy of Alan Betts (Alan knows clouds): • The fundamental characteristics of updrafts and downdrafts depend on internal cloud dynamics and microphysics, which cannot be represented adequately by simple sub-models used in mass-flux parameterizations • Observations and theoretical considerations tell us that convecting atmospheres never stray too far from definable profiles. • Convective sources of heat and moisture can be defined in terms of these profiles.

  25. Like the KF scheme, the BMJ scheme first checks for the possibility of deep (precipitating) convection • As with all convective parameterizations, CAPE is a necessary condition for activation of deep convection, but the BMJ scheme reverts to shallow (non-precipitating) convection if • The cloud (unstable) layer is too dry • The cloud layer is too shallow

  26. SPC AC 011711 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1111 AM CST SAT APR 01 2006 VALID 021200Z - 031200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF IA...MO AND MUCH OF IL... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES SWD INTO THE MID SOUTH AND ARKLATEX... --POTENTIALLY SIGNIFICANT SEVERE WEATHER EPISODE IS BEING FORECAST ACROSS THE MIDWEST AND MID MS VALLEY SUNDAY AND SUNDAY NIGHT-- ...SYNOPSIS... MID AND UPPER-LEVEL TROUGH NOW OVER THE PACIFIC NW AND GREAT BASIN WILL TRANSLATE EWD INTO THE GREAT PLAINS LATE SATURDAY NIGHT INTO SUNDAY MORNING...PRIOR TO INTENSIFYING INTO A CLOSED CIRCULATION OVER THE UPPER MIDWEST SUNDAY NIGHT. AS THIS OCCURS...ACCOMPANYING MID AND HIGH-LEVEL JET STREAKS WILL PROPAGATE THROUGH THE TROUGH BASE INTO MO AND IL/IND SUNDAY AFTERNOON AND EVENING. IN THE LOW-LEVELS...PRIMARY SURFACE LOW INITIALLY OVER ERN NEB WILL DEVELOP ENEWD INTO LOWER MI BY MONDAY MORNING. ASSOCIATED WARM FRONT WILL CONCURRENTLY LIFT NEWD THROUGH THE OH VALLEY AND GREAT LAKES WHILE TRAILING COLD FRONT SURGES EWD THROUGH THE MID/LOWER MO AND MS VALLEYS AND INTO THE OH AND TN VALLEYS THROUGH THE FORECAST PERIOD. ...MID/LOWER MO VALLEY INTO THE GREAT LAKES...MID MS AND OH VALLEYS... A NW-SE ORIENTED BAND OF MAINLY ELEVATED TSTMS IS EXPECTED TO BE ONGOING 02/12Z FROM VICINITY OF THE SURFACE LOW OVER ERN NEB/WRN IA INTO WRN KY AND MIDDLE TN...LARGELY DRIVEN BY WAA ALONG BROAD SWLY LLJ. THIS ACTIVITY WILL LIKELY CONTINUE THROUGH THE PERIOD AHEAD OF RETREATING WARM FRONT INTO THE GREAT LAKES WITH THE STRONGEST STORMS CAPABLE OF MAINLY LARGE HAIL. IN THE WAKE OF THIS INITIAL ACTIVITY...THE PRESENCE OF STEEP MID-LEVEL LAPSE RATES / 7-8 C/KM / COUPLED WITH BOUNDARY-LAYER DEWPOINTS IN THE LOW TO MID 60S WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS ACROSS SYSTEM WARM SECTOR WITH MLCAPES INCREASING TO 1500-2500 J/KG FROM SERN SE/CNTRL MO SWWD INTO THE ARKLATEX AND LOWER MS VALLEY. INCREASED FORCING FOR ASCENT AHEAD OF MID-LEVEL TROUGH AND EXIT REGIONS OF ACCOMPANYING JET STREAKS WILL CONTRIBUTE TO RAPID SURFACE-BASED TSTM DEVELOPMENT BY EARLY TO MID AFTERNOON FROM NEAR SURFACE LOW OVER WRN OR CNTRL IA SWD ALONG COLD FRONT INTO MO. ADDITIONAL SURFACE-BASED STORMS WILL ALSO BE POSSIBLE AT THIS TIME ALONG WARM FRONT. FORECAST SOUNDINGS INDICATE A POTENT COMBINATION OF INSTABILITY AND VERTICAL SHEAR ACROSS MODERATE RISK AREA...WHICH SHOULD SUPPORT INTENSE SUPERCELL DEVELOPMENT WITH THE POTENTIAL FOR A FEW STRONG TORNADOES IN ADDITION TO VERY LARGE...DESTRUCTIVE HAIL AND DAMAGING WINDS. WITH TIME...STORMS MAY EVOLVE INTO BOWING LINE SEGMENTS OR A MESOSCALE LEWP STRUCTURE WITH CORRIDORS OF DAMAGING WINDS POSSIBLE EWD ACROSS THE OH VALLEY SUNDAY NIGHT. ...MID SOUTH INTO ARKLATEX... AS MENTIONED ABOVE...PRE-FRONTAL AIR MASS IS FORECAST TO BECOME MODERATELY UNSTABLE BY AFTERNOON OWING TO STEEPENING LAPSE RATES AND A MOIST BOUNDARY-LAYER. GIVEN A STRONGER CAP AND THAT LARGE-SCALE FORCING FOR ASCENT AND LOW-LEVEL FRONTAL CONVERGENCE WILL TEND TO WEAKEN WITH SWD EXTENT...SOME UNCERTAINTY EXISTS WITH REGARD TO EVENTUAL CONVECTIVE COVERAGE AND INTENSITY ACROSS REGION. LATEST SHORT TERM MODEL GUIDANCE SUGGESTS THAT TSTMS SHOULD BEGIN TO BUILD SWWD ALONG FRONT BY MID TO LATE AFTERNOON FROM NEAR THE CONFLUENCE OF THE OH AND MS RIVERS INTO PORTIONS OF ERN AR...WRN TN AND PERHAPS SWD INTO NRN LA AND NRN MS. THE COMBINATION OF MODERATE INSTABILITY AND 45-55 KT WLY MID-LEVEL FLOW SUGGEST THE THREAT FOR A FEW SUPERCELLS AND BOWING LINE SEGMENTS CAPABLE OF DAMAGING WINDS...LARGE HAIL AND A FEW TORNADOES. THIS SEVERE THREAT WILL LIKELY CONTINUE SUNDAY NIGHT ACROSS THE TN VALLEY AND NRN PORTIONS OF MS AND AL. ..MEAD.. 04/01/2006 CLICK TO GET WUUS02 PTSDY2 PRODUCT NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0800Z Conceptual basis for BMJ shallow-convection parameterization - from Betts (1986 – QJRMS)

  27. 1) Find the LCL of cloud base and cloud top air 2) Draw a linear “mixing line” between these two layers 5) Draw qv,adj so that net moistening is zero. BMJ Scheme: determining shallow-convection adjustment profiles 3) Anchor Tadj to the sounding at cloud base, draw it parallel to mixing line 4) Slide Tadj so that net heating is zero

  28. Consider the impact of parameterized BMJ shallow convection in a “normal” diurnal cycle… Model Initial Condition Raob BMX 12 Z 11 May 2000

  29. 1 h forecast BMJ adjustment process (Eta model forecast)… Initial time

  30. 9 h forecast BMJ adjustment process (Eta model forecast)… 3 h forecast

  31. Compare Eta model forecast with raob at 00Z: 12 h forecast Model forecast Raob BMX 00Z 12 May 2000

  32. 12 h EtaKF forecast Raob BMX 00Z 12 May 2000 How about same 12h forecast using KF shallow convection instead of BMJ (EtaKF)?

  33. 24 h Eta/EtaKF soundings vs. DFW raob 00Z RAOB OpnlEta 00Z RAOB Etakf

  34. Shallow convection mean moisture tendencies 21h fcst Opnl Eta EtaKF

  35. Performance characteristics like this that are common knowledge to model developers are often a mystery (but potentially very useful) to forecasters…

  36. Interactions with forecasters convinced us that knowledge of these behavior characteristics could help forecasters interpret model forecast soundings, motivating us to…. • Document characteristic biases during 2001 Spring Program • Publish guidance for forecasters (Baldwin et al. 2002, Wea. Forecasting) - Provide formal SPC/WFO training on model forecast sounding interpretation - Introduce diagnostic versions of BMJ and KF schemes into the SPC’s NSHARP sounding analysis program

  37. 48 h EtaKF CAPE forecast Consider a real forecasting dilemma from several years ago… 48 h Eta CAPE forecast Wind barbs: 0-6 km shear vector

  38. 48 h Eta model forecast for SHV: BMJ T, Td reference profiles

  39. 48 h EtaKF model forecast for SHV…

  40. SPC forecasters identified the characteristic bias of the Eta model, boldly suggested the 48 h forecast sounding was “in error” SPC day 2 convective outlook valid 28 Mar 2002

  41. 48 h later: SHV observed sounding…

  42. Preliminary Summary: PBL structures, CAPE, CIN values, etc. are all quite sensitive to parameterization of shallow moist convection… • How about the sensitivities to PBL/turbulence parameterizations? Compare CBL soundings from dx~4km forecasts from • WRF-ARW using the YSU (Yonsei University) PBL • WRF-NMM using the MYJ (Mellor-Yamada-Janjic) PBL …without parameterization of moist convection

  43. MYJ PBL Param YSU PBL Param Possible Approaches for Parameterization of the Convective Boundary Layer - From Stull (1988)

  44. Sounding comparison: 24h forecast valid 00Z 24 May at DDC ARW with YSU PBL Good forecast… Model Raob NMM with MYJ PBL PBL too shallow, cold, & moist… clouds just broke up! Model Raob

  45. Sounding comparison: 24h forecast valid 00Z 18 May at DDC NCAR Too dry in PBL, too moist above; Where is the PBL top? EMC Good forecast… ARW with YSU PBL Model Raob NMM with MYJ PBL Raob Model

  46. Sounding comparison: 24h forecast valid 00Z 28 April at OUN NCAR Good in PBL, but CIN layer is washed out EMC PBL too shallow and moist, but CIN layer looks good ARW with YSU PBL Raob Model NMM with MYJ PBL Raob Model

  47. Quantifying errors in model-forecast soundings…simple comparison of T, qv values at a given pressure level is inadequate! Is the forecast sounding any good? What aspects of the sounding are predicted well?

  48. How does one quantify these errors? That one was way off!

  49. How does one quantify these errors?

  50. How does one quantify these errors? That one was BS! (Bad Sounding) S. Weiss

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