Mike Ekern, Sr. HAS Forecaster NOAA, National Weather Service

HydrometeorologicalAnalysis and Support Function Overview Mike Ekern, Sr. HAS Forecaster NOAA, National Weather Service California Nevada River Forecast Center

Hydrologist hydrologic expertise & judgment model guidance Forecast Inputs H A S Flood Forecast Guidance Precip (QPF) Snow Levels Temperature • Bulletins • Graphics parameters data Model Calibration Observing Systems www.cnrfc.noaa.gov Operational Flood Forecasting NWSRFS SAC-SMA SNOW-17

HydrometeorologicalAnalysis and SupportBasic Functions H A S • assimilation and quality assurance of observed and forecast data sets for use in the hydrologic modeling process • production of hydrometeorological discussions • coordination • interact with other offices on hydrometeorological inputs to hydrologic operations • serve as a liaison with WFOs and HPC to ensure full utilization of hydrometeorological data in the hydrologic modeling process

HydrometeorologicalAnalysis and Support H A S • Apply meteorological expertise to specialized activities above and beyond the basic HAS functions, such as… • QPF verification analysis • Development and improvement of hydrometeorological procedures

Forecast Inputs NWSRFS Forecast Inputs H A S Precip (QPF) Snow Levels Temperature

Forecasting Methodology

Mountain Mapper Software • Specify (QPF) - uses PRISM monthly precipitation climatology to distribute point QPF data to a 4km grid using inverse distance squared weighting • DailyQC (QPE) – uses PRISM monthly climatology to quality control observed precipitation. Compares gage data to its own estimate (based on surrounding gages) • Verify (QPF – QPE)

QPF Process Sequence National QPF – Hydrometeorological Prediction Center HPC

QPF Process Sequence National QPF – Hydrometeorological Prediction Center • QPF data are converted from HPC contours to grid • Grid  RFC QPF point data using bilinear interpolation and sent to RFCs as ASCII SHEF-encoded text file

Strengths/Weaknesses of PRISM method

CNRFC HAS Goals

Challenges . . . • Time constraints • QPF due in the hands of the hydrologists by 7:30 AM to get a hydrologic forecast out by 8:00 AM • 12 6-hour periods X 66 QPF points = 792 possible points to edit! • 5 Minutes per 6-hour period (4.5 secs/point) • limited time for WFO/HPC coordination

…more Challenges… • Disparity between model guidance and between model guidance and HPC • which model do you choose? • false alarms – when do you trust guidance?

…more Challenges… • Experience vs. Guidance • forecaster experience crucial in extreme events • requires coordination • Scrutiny of 10 WFOs using your QPF • Can impact watch/warning criteria

…and more challenges… • Information overload • WRF-NAM / GFS / UKMET / ECMWF / RUC / SREF / GFS Ensembles / CANSAC / Bufkit / CMC • Model continuity (06UTC vs. 00UTC) • more data and 12UTC WRF-NAM arriving during the forecast process • Limitations of the MM software • non-climatological distribution of precipitation • Credibility – if QPF/snow levels are wrong??? (NWSRFS Garbage In – Garbage Out)

…and still more challenges • Freezing Levels • based on GFS model guidance (from HPC) • difficult to observe/verify • HMT vertical radars help in short term • time intensive • competes for time with QPF • 12 periods X 66 points

Forecast Area Challenges… • Upper Sacramento • Balance between releases and runoff below dam • Russian/Napa • poor radar coverage • challenging QPF • East-side Sierra Nevada • lee-side “spillover” • San Diego • Reacts like “flash flood” • sensitive to low QPF

daily_qc (PRISM) • gage only • 676 Points • qc’d by hydrologists QPE

Mike Ekern, Sr. HAS Forecaster NOAA, National Weather Service

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