Predecessor Rain Events Ahead of TC Ike and TC Lowell on 11–14 September 2008 Lance F. Bosart, Thomas J. Galarneau, Jr., Jason M. Cordeira, and Benjamin J. Moore Department of Atmospheric and Environmental Sciences University at Albany, SUNY Albany, NY th Annual Northeast Regional Operational Workshop Albany, NY 4–5 November 2009

Motivation Predecessor Rain Events (PREs) are high-impact weather events that can result in significant inland flooding High-impact PREs occurred with TS Erin (18–19 Aug 2007), TC Ike (12–13 Sep 2008), and TC Rita (24–26 Sep 2005) PREs represent a big forecast challenge for models and humans alike Dynamics and thermodynamics governing PREs need to be better understood

TS Erin PRE 18–19 Aug 2007 Example of High-Impact Nature of PREs Photo from Minneapolis Star Tribune Photo from NWS La Crosse, WI

Outline Brief synopsis of PRE/TC relationships Synoptic overview of Lowell/Ike PREs – Rainfall and satellite signatures – Upper-air analyses – Precipitable water (PW) and sounding analysis Regional perspective – Ike moisture, PRE, and downstream jet – Trajectory analysis – Cross section analysis Summary

Predecessor Rain Events (PREs) Coherent area of rain displaced poleward of TC Moisture transport from TC toward PRE Event duration ~ 12 h Maximum rainfall rates typically ≥ 100 mm (24 h)  1 Time lag between PRE and TC passage ~ 36 h ~1000 km Bosart and Carr (1978) conceptual model of antecedent rainfall for TC Agnes (1972) Detailed study of PREs in Cote (2007) and Galarneau et al. (2009, submitted to MWR)

200 hPa h mean (dam) and anomaly (σ), mean wind (kt), and TC tracks TC Ike TS Lowell = 00Z position 8–14 September 2008 Data: 2.5  NCEP–NCAR Reanalysis

72-h Quantitative Precipitation Estimates (inches) Ending 1200 UTC 14 Sep Lubbock, TX (LBB), 11 Sept, mm - broke all-time 24-h rainfall record of mm set on 18–19 Oct Wichita, KS (ICT), 12 Sept, mm - broke all-time 24-h rainfall record of mm set on 8 Jun Chicago, IL (ORD), 13 Sept, mm - broke all-time daily rainfall record of mm set on 14 Aug

00Z/13 06Z/13 12Z/13 18Z/13 ORD rainfall in 6-h periods: 00–06 UTC 13  5.1 mm 06–12 UTC 13  75.4 mm 12–18 UTC 13  72.6 mm 18–00 UTC 13  19.8 mm PRE Ike Ike tropical moisture arrives by 06 UTC L L L L WSR-88D base reflectivity mosaic Source: NCAR case-selection archive ORD

06Z/14 12Z/14 15Z/14 18Z/14 ORD rainfall in 6-h periods: 00–06 UTC 14  1.3 mm 06–12 UTC 14  5.6 mm 12–18 UTC 14  25.7 mm 18–00 UTC 14  5.3 mm Ike ORD WSR-88D base reflectivity mosaic Source: NCAR case-selection archive

1200 UTC 9 September UTC 10 September 2008 Infrared Satellite Imagery source:

1200 UTC 11 September UTC 12 September 2008 Infrared Satellite Imagery source:

1200 UTC 13 September UTC 14 September 2008 Infrared Satellite Imagery source:

SLP, 1000–500 hPa Thickness, 250 hPa Wind 1200 UTC 8 September 1200 UTC 9 September SLP (solid contours every 2 hPa), 1000–500 hPa thickness (red dashed contours every 3 dam) and 250 hPa wind speed (shaded in m s −1 ) L L I I I = TC Ike L = TC Lowell

SLP, 1000–500 hPa Thickness, 250 hPa Wind 1200 UTC 10 September 1200 UTC 11 September SLP (solid contours every 2 hPa), 1000–500 hPa thickness (red dashed contours every 3 dam) and 250 hPa wind speed (shaded in m s −1 ) L L I I I = TC Ike L = TC Lowell

SLP, 1000–500 hPa Thickness, 250 hPa Wind 1200 UTC 12 September 1200 UTC 13 September SLP (solid contours every 2 hPa), 1000–500 hPa thickness (red dashed contours every 3 dam) and 250 hPa wind speed (shaded in m s −1 ) I I I = TC Ike L = TC Lowell

SLP, 1000–500 hPa Thickness, 250 hPa Wind 0000 UTC 14 September 1200 UTC 14 September SLP (solid contours every 2 hPa), 1000–500 hPa thickness (red dashed contours every 3 dam) and 250 hPa wind speed (shaded in m s −1 ) I I I = TC Ike L = TC Lowell

DT Analysis and Low-Level Frontogenesis DT pressure (shaded in hPa), DT–850 hPa wind shear (barbs in kt), 925–850 hPa ζ (contours every 2.0×10 −5 s −1 ) 1200 UTC 12 September hPa h (solid contours every 2 dam) wind (barbs in kt), θ (dashed contours every 2 K), frontogenesis [shaded in K (100 km) −1 (3 h) −1 ] I I I = TC Ike

DT Analysis and Low-Level Frontogenesis DT pressure (shaded in hPa), DT–850 hPa wind shear (barbs in kt), 925–850 hPa ζ (contours every 2.0×10 −5 s −1 ) 1200 UTC 13 September hPa h (solid contours every 2 dam) wind (barbs in kt), θ (dashed contours every 2 K), frontogenesis [shaded in K (100 km) −1 (3 h) −1 ] I I I = TC Ike

DT Analysis and Low-Level Frontogenesis DT pressure (shaded in hPa), DT–850 hPa wind shear (barbs in kt), 925–850 hPa ζ (contours every 2.0×10 −5 s −1 ) 1200 UTC 14 September hPa h (solid contours every 2 dam) wind (barbs in kt), θ (dashed contours every 2 K), frontogenesis [shaded in K (100 km) −1 (3 h) −1 ] II I = TC Ike

1200 UTC 11 Sep 2008 PW (shaded; mm), 250-hPa HGHT (black; dam), 700-hPa WND (kt), and 925–850-hPa REL VOR (magenta; every 0.5 x s -1 ) PW above 700 hPa onlyTotal PW

9−10 Sep11−12 Sep13−14 Sep mm m s −1 Total Precipitable Water Flux [mm m s −1 ] Data: 0.5  NCEP–GFS analyses 50 mm m s −1

Source: EPZ Santa TeresaDRT Del Rio MAF Midland 12Z 10 Sep 00Z 11 Sep12Z 10 Sep

TOP TopekaDVN Davenport ILX Lincoln 12Z 13 Sep 12Z 12 Sep12Z 13 Sep Source:

1200 UTC 13 September hPa h (dam) 925 hPa  e (K) 200 hPa wind speed (m s  1 ) 0000 UTC 13 September hPa h (dam), 700 hPa  (10  5 s  1 ) precipitable water (mm), 850–500 hPa mean wind (m s  1 ) L L Ike PRE 56 mm Data: 0.5  NCEP–GFS analyses

1200 UTC 13 September hPa h (dam), 700 hPa wind (m s  1 ) 700 hPa ascent (10  3 hPa s  1 ) 900–400 hPa relative humidity (%) 925 hPa h (dam), 925 hPa wind (m s  1 ) 925 hPa  e (K) 200 hPa wind speed (m s  1 ) Ike PRE H H Data: 0.5  NCEP–GFS analyses

Surface Observations and Base Reflectivity (dBZ) 0002 UTC 13 Sep UTC 13 Sep 2008 NE SD MN WI IL IA KS MO NE SD MN WI IL IA KS MO

72-h Backward Air Parcel Trajectories LBB: 00Z / 12 Sep ICT: 12Z / 12 Sep hPa dBZ Backward trajectories released from latitude and longitude of station every 100 hPa Circles represent 00Z locations t − 72h position of IKE t − 72h position of LOWELL Data: 0.5  NCEP–GFS analyses

72-h Backward Air Parcel Trajectories TOP: 18Z / 12 Sep CHI: 12Z / 13 Sep hPa dBZ Backward trajectories released from latitude and longitude of station every 100 hPa Circles represent 00Z locations t − 72h position of IKE t − 72h position of LOWELL Data: 0.5  NCEP–GFS analyses

Potential vorticity (PVU), θ (K), wind (kt)Relative humidity (%), θ (K), and upward vertical motion (10 −3 hPa s −1 ) A B ABAB UTC 12 September Data: 0.5  NCEP–GFS analyses Source: NCAR case-selection archive

Potential vorticity (PVU), θ (K), wind (kt) A B Frontogenesis [K (100 km) −1 (3 h) −1 ], θ (K), and upward vertical motion (10 −3 hPa s −1 ) ABAB 6 9 Source: NCAR case-selection archive 1200 UTC 12 September Data: 0.5  NCEP–GFS analyses

Cross Section Analysis 1200 UTC 13 Sep Potential vorticity (PVU), tangential circulation vectors, potential temperature (K) PVU C D C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa) 10 m s −1 10 cm s −1

Cross Section Analysis 1200 UTC 14 Sep Potential vorticity (PVU), tangential circulation vectors, potential temperature (K) PVU C D C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa) 10 m s −1 10 cm s −1

Cross Section Analysis 1200 UTC 13 Sep Mixing ratio (g kg −1 ), wind speed (kts), tangential circulation vectors, potential temperature (K) g kg −1 C D kts C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa) 10 m s −1 10 cm s −1

Cross Section Analysis 1200 UTC 14 Sep Mixing ratio (g kg −1 ), wind speed (kts), tangential circulation vectors, potential temperature (K) g kg −1 C D kts C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa) 10 m s −1 10 cm s −1

Cross Section Analysis 1200 UTC 13 Sep K (100 km) −1 (3 h) −1 C D C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa) Petterssen frontogenesis (K (100 km) −1 (3 h) −1 ), upward vertical velocity (μb s −1 ), potential temperature (K)

Cross Section Analysis 1200 UTC 14 Sep Petterssen frontogenesis (K (100 km) −1 (3 h) −1 ), upward vertical velocity (μb s −1 ), potential temperature (K) K (100 km) −1 (3 h) −1 C D C D 0.5°x0.5° NCEP GFS analysis Pressure (hPa)

Summary of TC Ike/Lowell PREs PREs fed off deep moisture from Ike and middle- and upper-level moisture from Lowell PREs occurred along low-level baroclinic zones well poleward of Ike and Lowell PREs were best defined where intense frontogenetical forcing was concentrated PREs were driven by deep ascent in equatorward jet-entrance regions Downstream jet strengthened considerably due to PRE- and Ike-driven diabatic heating