Rapid Update Cycle Model William Sachman and Steven Earle ESC452 - Spring 2006

Primary uses of RUC ► Making short range forecasts  Initialized with very recent data ► Monitoring hourly conditions with hourly analyses  Useful when overlaid with satellite, radar and other hourly observations ► Evaluating trends of longer range models  Used to confirm other models

History ► With the birth of an increase in automated observations from commercial aircraft and the newly developed wind profilers came the means to create short term forecasts based on the frequent observations. ► It was designed to provide accurate 0-12h forecasts for weather sensitive users such as the aviation community. ► Significant weather events occur in such a short time frame, including severe weather.

RUC Implementation ► Mesoscale Analyses and Prediction System (MAPS) was developed at the Forecast Systems Laboratory (FSL) and began testing in 1988  used only for research. ► RUC-1 was the first short range operational forecast model, September 1994 at NCEP  3h data assimilation cycle  60-km resolution and 25 levels ► RUC-2 developed in April, 1998  1h data assimilation cycle  40-km resolution and 40 levels ► RUC-20 April 16, 2002 ► RUC-13 June 28, 2005

RUC-20 ► Replaces RUC-2. ► 50 hybrid isentropic-sigma levels ► 20-km grid spacing Model Changes ► Model Changes  13-km resolution  Still has 50 levels ► New observations in data assimilation  METAR  Mesonet  Radio Acoustic Sounding System (RASS) ► Improved Post-processing  precipitation type, CAPE, visibility RUC-13

RUC-13 now provides a 9 hour forecast every hour, with a 12 hour forecast every third hour 1-hour version of the RUC model

RUC-20 Mean Orography

February 21, z More detailed coastline with 13km RUC Soil Moisture (Top 2cm)

Horizontal Domain ► Consists of a rectangular mesh (451 by 337 grid points) ► Grid length measures km at 35 o N and 12.4 km at 45 o N ► Grid length decreased to 10 km at the northern boundary ► East-West boundaries are well off the coastline providing good coastal forecasts ► Local circulation is better resolved including differential heating and orographic precipitation patterns ► Very detailed output  Could lead to problems?

Vertical Domain Sigma Coordinates Isentropic (Theta) Coordinates Surfaces are terrain following -resolve boundary layer well May not correctly portray weather events on the lee side of mountains Increases resolution in baroclinic regions -fronts and tropopause Incompletely depicts low level adiabatic flow

RUC-13 Vertical Resolution

Observations used to initialize RUC model

RUC Diagnosed Variables ► Relative Humidity ► Surface Temperature ► Dew Point ► Sea-level pressure ► Precipitation ► Snow accumulation ► Snow depth ► Precipitation type ► Freezing levels ► 3h Pressure changes ► CAPE/CIN ► Lifted Index ► Precipitable water ► Helicity ► Soil Moisture ► Tropopause pressure ► Vertical Velocity ► PBL depth ► Gust wind speed ► Cloud base height ► Cloud top height ► Cloud fraction ► Visibility ► Pressure of max Theta-E in column ► Convective cloud top height ► Equilibrium level height

Strengths of the RUC model ► Initializes every hour ► Hybrid isentropic-sigma vertical coordinates  Eliminates problem of isentropic (theta) surfaces intersecting the ground. ► Horizontal Domain  Finer definition of terrain features which leads to better representation of topographically induced features.

Weaknesses of the RUC model ► Hybrid isentropic-sigma vertical coordinates  Difficult to blend coordinates at their interfaces ► Horizontal Domain  Detailed (sometimes noisy) output compared to other models.  Resolution still insufficient to depict local details of most topographically induced circulations

In Conclusion... ► Operational forecast model that provides accurate short range forecasts. ► The most recent model is the RUC-13 model, providing a 13km resolution. ► RUC uses hybrid isentropic-sigma vertical coordinate system. ► Combines upper air and surface data to initialize model.

References ► FSL ► NOAA ► NCEP VOTE TODAY!!!!!