High Resolution Numerical Weather Prediction for High Impact and Extreme Weather Events in 2014 across Southern California Alex Tardy Alexander.Tardy@noaa.gov NWS San Diego Warning Coordination Meteorologist September 10, 2015 Floodplain Management Association Conference 2015 CANSAC WRF WRF-EMS ARW NAM4 HRRR
Motivation NWP has improved significantly and can be used to fine tune orographic and convective precipitation forecasts, however experience with timing, intensity and location is necessary otherwise the guidance can be misused operationally NWS tendency to forecast orographic signatures as default and rely on legacy NWP output (miss high impact signatures) Can the NWP be utilized in a wide variety of weather regimes (coastal, orograghic, convective, deserts, banded, elevated, etc)? High resolution NWP can significantly increase confidence in a forecast following the use of other tools such as analogs, anomalies (R-climate), ensemble spreads, reforecasts (M-climate) and synoptic scale patterns Floodplain Management Association 2015
NWS SGX Service Area Max Elevation 11, 400 feet MSL Max Elevation 6,200 feet MSL View from Office
Event 1 September 7 to 9, 2014
September 7 moisture surge
Coachella Valley morning 9-8-14
400 likes on Facebook View of San Bernardino from Crestline
La Quinta
Varner Road 9-9
Varner Road on 9-9
Most significant impacts Extensive road and channel damage in City of Riverside (Chicago and University), numerous large trees snapped and uprooted, storm survey done, standing water as deep as car roof tops, some room damage, and TV media coverage at site (national news) Local flooding and debris flows east of Hemet Local flooding in city of San Bernardino, several streets with standing and flowing water Extensive flooding in Coachella Valley, including Thousand Palms, Cathedral City and La Quinta, with mud flows as deep as 3 to 5 feet, many road closures, helicopter high water/debris rescues, many homes damaged and flooded in La Quinta (no estimate yet), flowing water on streets as deep as 2 to 3 feet with standing water up to car roof tops, complete closure of major roads in La Quinta, several sink holes, extensive local media coverage Clean up in Coachella Valley continues today with large trucking removal of dirt and street repairs with several closures still in place 2 to 3 inch rainfall in 1 to 2 hours all flooded areas (gage and radar), 1 in 200 to 1 in 500 year return intervals Elevated surf and high rip current risk continued with south swell
Meteorology High precipitable water values were separate plume ahead of the TC Norbert which arrived Saturday and Sunday (values up to 2.2 inches in the Coachella Valley Tropical Cyclone Norbert remnants stayed offshore of Baja and upper low remnants crossed Baja, to the south Separate upper level short wave (PRE type) moved across deserts early Monday (Coachella Valley flash floods) Isolate thunderstorms developed as early as Friday and in several mountain areas on Saturday Recognized run to run consistency of ECMWF (TC Norbert well offshore) versus GFS (TC Norbert remnants), and that this was the main forecast factor but rather the PW surge would still occur and be significant Recognized desert threat (opposed to just mountains) Participating on NHC calls in real-time and DSS WRH call on Friday
00 UTC and 12 UTC 6 Sept
12 UTC 7 and 00 UTC 8 Sept
Event 2 -high impact warm season convective NWP indicates big rain potential WRF-EMS 12 UTC August 1 NAM4 12 UTC August 1 4.5 inches 8 inches or 200 mm RUN Total QPF Caution with location 6 inches 5 inches 125 mm CANSAC WRF 00 UTC August 1 WRF-EMS large domain 12 UTC August 1
00 UTC 2 August 2014 Local 5 inches (125 mm) totals forecast 72-h run total 2.5 to 5 inches
Summary of Advantages The information in the high resolution NWP can and should be used to effectively communicate the threat during impact decision support services (especially less than 60-h) High resolution NWP effective in low and high impact, or lowend and significant precipitation events (gives you the correct threat even if location is wrong or variable run-to run) High Resolution Ensemble (e.g., EHRRR) should help. High resolution NWP very valuable for local orographic enhancement and downslope effects (wind or QPF) High resolution NWP effectively can locate small scale features (micro and mesoscale QPF patterns) and magnitude, as well as non-climatological patterns (rare) High resolution NWP (convection allowing) far superior to all other legacy QPF guidance for stratiform and convective precipitation regimes in southern California Apply with other ingredients and conceptual models American Meteorological Society WAF conference, Chicago Alexander.Tardy@noaa.gov
Floodplain Management Association 2015 Alexander.Tardy@noaa.gov Summary of Limitations High resolution NWP can overproduce QPF in shallow instability forced across terrain High resolution NWP needs to be used with other tools such as anomalies, analogs, ensemble extremes, percentiles and conceptual models High resolution NWP still highly dependent on the synoptic scale patterns correctly timed and resolved Variability in convection allowing NWP and extremes can be misleading (Storm-Scale Ensemble will improve) Poor performance in elevated convection (e.g., August 20)