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
Acknowledgements Funding for PRECIP Collaborators NOAA/NWS/ Weather Prediction Center Mike Bodner SUNY-College at Brockport Dr. Scott Rochette
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 http://weather.missouri.edu/precip or https://www.facebook.com/precipresearchprogram
Introduction
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
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.
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
A Hierarchy of Elevated Convection Pure Mixed
Objectives
Objectives Analyze average environment Compare to previous research Create method for forecasting heavy-rainfallproducing elevated thunderstorms in this region
Methodology
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)
Methodology Event criteria: Produced over 2 rain in 24 hrs. Local rainfall maximum within CWA boundary
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
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
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)
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) 1000-500-mb Thickness Mean-Sea-Level Pressure Precipitable Water Most-Unstable CAPE K-Index
Results
Results- Kansas City 250-mb Wind (color-filled), heights (black), and divergence (dashed)
Results- Kansas City 250-mb divergence - Interquartile Range (IQR) plot T=00
Results- Kansas City 850-mb θ e advection (color- filled) and 2-meter θ e (brown)
Results- Kansas City 850-mb θe advection & 2-m θe - IQR plots, T=00
Results- Kansas City 1000-500-mb Thickness (brown), Mean-Sea-Level Pressure (black), and Precipitable Water (colorfilled)
Results- Kansas City Precipitable water - IQR plots, T=00
Results- Kansas City MUCAPE (color-filled) and K-Index (purple)
Results- Kansas City K Index - IQR plots, T=00
Cross-Section Kansas City The X
Conclusions
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)
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
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
Future work Find analogs to composite grids Find null events Discover parameters differing for heavy-rainfall vs non-heavy-rainfall events
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 http://weather.missouri.edu/precip or https://www.facebook.com/precipresearchprogram