IMPROVING PREDICTION OF HEAVY RAINFALL WITH ELEVATED CONVECTION

Transcription

1 IMPROVING PREDICTION OF HEAVY RAINFALL WITH ELEVATED CONVECTION Patrick Market, University of Missouri Laurel McCoy, University of Missouri and NOAA/NWS, Portland, OR Chad Gravelle, CIMSS/SSEC University of Wisconsin, Madison, WI Charles Graves, Saint Louis University, St. Louis, MO Presented to the National Weather Association Annual Meeting 21 October 2014, Salt Lake City, UT

2 Acknowledgements Funding for PRECIP Collaborators NOAA/NWS/ Weather Prediction Center Mike Bodner SUNY-College at Brockport Dr. Scott Rochette

3 PRECIP Project Use McCoy s forecast method to predict where heavy-rain-producing elevated thunderstorms will occur Deploy teams to collect observational data from storm environment or

4 Introduction

5 Colman (1990a,b) Initiated the modern era of elevated convection studies Showed the preferred region of elevated convection in US northeast of a surface cyclone north of its attendant warm front

6 Later work Corfidi et al. (2006) examined the nature of altocumulus castellanus determined that the division between elevated and surface-based [convective] activity is rarely distinct.

7 A Hierarchy of Elevated Convection Pure: τ > f -1 ex: wraparound Surface influences on mid-level parcels reduced or eliminated because of their 1) vertical location and/or 2) temporal history Hybrid: τ ~ f -1 ex: north of warm front Surface influences on mid-level parcels (if any) mitigated by their arrival over frontal inversion Mixed: τ < f -1 ex: warm sector castellanus Surface influences on mid-level parcels unrestricted

8 A Hierarchy of Elevated Convection Pure Mixed

9 Objectives

10 Objectives Analyze average environment Compare to previous research Create method for forecasting heavy-rainfallproducing elevated thunderstorms in this region

11 Methodology

12 Methodology Composite events within following National Weather Service County Warning Areas (CWAs): Kansas City/Pleasant Hill (EAX) Springfield, MO (SGF) Tulsa (TSA) Wichita (ICT) Topeka (TOP)

13 Methodology Event criteria: Produced over 2 rain in 24 hrs. Local rainfall maximum within CWA boundary

14 Methodology Used North American Regional Reanalysis (NARR) data to find event times Event time defined as NARR time-step with heaviest rainfall occurring over next 3 hours Used NARR data to evaluate if event was elevated 2-meter θ e and precipitation maximum NARR sounding from rainfall max

15 Creating Composites Lists created including: Event time Coordinates for local rainfall max Composited using software from SLU NARR grid layers overlaid with coordinates centered on centroid of CWA Parameters averaged over 207 x 207 grid Grid squares = 32 km 2

16 Generate Plots Composites show average environmental conditions for elevated thunderstorm events Created composites for: The event time (t=0) 6-hours prior (t-6) 12-hours prior (t-12)

17 Some of the Parameters Evaluated 250-mb Wind and Divergence (Upper-Level Jet) 500-mb Absolute Vorticity 850-mb Wind (Low-Level Jet) 850-mb θ e Advection and 2-meter θ e (Surface Boundary Location and Transport Maximum) mb Thickness Mean-Sea-Level Pressure Precipitable Water Most-Unstable CAPE K-Index

18 Results

19 Results- Kansas City 250-mb Wind (color-filled), heights (black), and divergence (dashed)

20 Results- Kansas City 250-mb divergence - Interquartile Range (IQR) plot T=00

21 Results- Kansas City 850-mb θ e advection (color- filled) and 2-meter θ e (brown)

22 Results- Kansas City 850-mb θe advection & 2-m θe - IQR plots, T=00

23 Results- Kansas City mb Thickness (brown), Mean-Sea-Level Pressure (black), and Precipitable Water (colorfilled)

24 Results- Kansas City Precipitable water - IQR plots, T=00

25 Results- Kansas City MUCAPE (color-filled) and K-Index (purple)

26 Results- Kansas City K Index - IQR plots, T=00

27 Cross-Section Kansas City The X

28 Conclusions

29 Conclusions Unique patterns to look for when forecasting heavyrainfall-producing elevated thunderstorms: Strong signal; strong variability Upper-level jet streak to the northeast of the region Divergence > 3 x 10-5 s -1 (lift) Event located within or just south of 850-mb θ e advection maximum (convergence max) Signals LLJ from the SSW (moisture; lift; instability) Strong signal; small variability >30 K-index values (instability) Precipitable water values > 1.6 (moisture) 2-m θ e pattern (confirms elevated convection)

30 Conclusions Prior work largely corroborated. However, some novel findings as well MUCAPE decreases while K Index increases X marks the spot in cross sections Interquartile ranges - enhance confidence in forecasting heavy rain events with elevated convection

31 Conclusions 250-mb Jet Core > 70 kt Moisture PWATs > 1.6 (~40 mm) Lifting 250-mb DIV > 3 x 10-5 s -1 Instability K Index > 32

32 Future work Find analogs to composite grids Find null events Discover parameters differing for heavy-rainfall vs non-heavy-rainfall events

33 PRECIP Project Use McCoy s forecast method to predict where heavy-rain-producing elevated thunderstorms will occur Deploy teams to collect observational data from storm environment or