Colorado Flood-A few images and thoughts

Richard GrummNWS State College PA 16803

Where it rained-black dot is BoulderStage-IV data; NMQ Q2 and CCPA was used not shown here

When it rained

Timing is EVERYTHING

Why it rained strong ridge weak front easterly flow into terrain convectively favorable environment

Deep moisture PW +4sHow would this look in PDF not s

Easterly flow into the terrain +4s

Pattern of heavy rainfallPontrelli et al 1999: a) Madison County 1995, b) Fort Collins 1997, c) Rapid City 1972 and d) Big

Thompson Canyon 1977

Fronts and winds same 4 Cases

Idealized pattern for orographic record rainfall Pre-standardize anomaly era

Predictable? EC Forecasts QPF

EC Patternall models were quite similar

EC PW patternsimilar to SREF/GFS/NAM

EC Windshmm…SREF is next….

SREF WindsLarger anomalies Batman

GFS QPFwhat is a record event in this time frame in the GFS M-CLIMATE?

SREF Probability of 150 mmBoulder is a red dot…..

Prob 100 mm

Mean QPF and 50mm contours by member

SummaryPatterns and Probabilities

• Pattern known to be associated with upslope and similar to many heavy rain events involving terrain– Well research and good examples of historic events from the past.

• Pattern well predicted by any system we looked at.– Standardized anomalies may have provide clue about high PW and strong easterly flow– Good pattern with good anomaly signature– Trevor could likely provide PDF of the PW and u-winds in affected region

• QPF:– variable in spatial and temporal distribution– Many uncertainty issues along with clues to the rainfall potential– EC in key time was not a silver bullet (EC-lite)– We need internal model climatology M-Climate so EFI like products alert use to near record or

record QPF in every forecast system verse it’s internal a climate

• Link: http://cms.met.psu.edu/sref/severe/2013/12Sep2013.pdf

Future things to consider in 0-8 hours

• Rainfall verse NOAA-14 data for alerts

• Forecasts of Rainfall verse NOAA-14 for alerts– Russ Schumacher sites and examples here

• Flash Flood guidance and NOAA-14 data for alerts and heads up at critical thresholds.

• Better storm scale ensembles

Stage-IV verse NOAA-14 return periods

13 Sept