Weather Prediction and Usefulness for Forecasting

1. Weather Prediction and Usefulness for Forecasting Howie Bluestein David Parsons

2. Overview of Strategies and Issues • We did not really break out instrumentation by new and existing, but some themes emerged. • Radar developments: C and X band with polarization and refractivity on low cost systems in network or on mobile systems and rapid scale • Growth in airborne remote sensing capabilities (winds from lidar and radar, water vapor lidar, radio occultation) • Strong interplay of modeling, assimilation and observations • Discussion of new platforms (UAVS, driftsonde and HIAPER) • We tried to work both in terms of physical phenomena and predictive scale • The group (esp Howie and Morris) had a convective weather bias in expertise relative to expertise in pollution studies, fire weather, and tropical cyclones. • Three scales: • Synoptic and global numerical prediction -- relied on THORPEX/T-PARC ideas • Mesoscale -- relied on previous mesoscale breakout (just filled holes) • Nowcasting -- devoted relatively more time to this subject

3. General Comments • Make greater use of observations taken by testbeds and semi-permanent university observations, esp for nowcasting and mesoscale problems (models, lightning network, profilers, surface sites, radars, radiometers, GPS, all exist at the universities and other institutions (from TV stations to NCAR) -- relevant to Long-term obs WG, but for weather • Work needs to be done at the time-scale between nowcasting and the few hour time-scale where NWP starts to work. • The questions of the limits of predictability and what factors limit our predictive skill are important over a range of phenomena and over the range of time and space scales • Adaptive observing strategies is an issue for all scales. Explore adaptive convection for warm season convective ahead of storm formation, need work at mesoscale and global time-scales (limited by linear assumptions of mathematical techniques) and across scales (local vs “upstream” measurements)

4. Synoptic and Global Prediction • Hypothesis: Are adaptive measurements strategies useful for real prediction problems (location of lee low pressure systems and warm season severe wx outbreaks) or can they be improved what already works (e.g., improve the already promising work on tropical cyclone targeting) ? • Hypothesis: Can we improve the prediction of the excitation of Rossby waves (interaction with the wave guides with cyclogenesis and tropical convective events) • Hypothesis: Test and improve assimilation techniques (hot and cold starts, difficulty in assimilating water vapor) • Hypothesis: Predictive skill is limited by obs/physics on the local scales or is it by upstream sensitive regions or inaccurate boundary conditions • Hypothesis: Predictive skill of cold air outbreaks, winter cyclogenesis, precipitation amounts, temperatures extremes is limited by model physics (surface and boundary layer processes, atmospheric radiative processes (radiative balance), parameterization of convection)

5. Instruments for synoptic and global prediction studies • Vertical profiles from airborne wind lidar/Doppler radar • Satellite -- validation of measurements and assimilation techniques and improved utilization, improved access • Variables that are new for assimilation - Examples water vapor and balloon borne radio occultation • HIAPER holds a unique place for certain problems such as tropical convection and Rossby wave triggering • New platforms • Larger UAVs (Long term potential, keep exploring the constraints in usage with a careful examination and involvement of the broader community of the aviation constraints for weather studies (clouds, long distance flights), power, cost relative to other techniques vs benefits for weather research is needed) • Long duration stratospheric balloons (deploying driftsonde and carrying remote sensing) are ready now, but not part of GAUS in the facility pool

6. Mesoscale • Hypothesis: Predictive skill of mesoscale environments for subsequent high impact wx (cyclogensis, convection etc) over the eastern continental US, for example, is limited by the characterization of initial conditions and the model treatment of physical processes over the Rockies • Question: Are we observing the critical scales, critical heights and critical variables that produce high impact weather on the mesoscale (requires oversampling)? • Hypothesis: The prediction of pollution events be improved by improved initialization of pollutants and aerosols (increased interactions of the air chemistry and mesoscale communities, feedback of this information on forecast skill (e.g., surface temperatures, clouds, precipitation). • Other critical mesoscale problems (storm surge, precipitation issues ranging from hydrometer type (hail, rain-snow line) to precipitation amounts deserve attention

7. Mesoscale Instrumentation • Mesoscale instruments are to a large degree a marriage of the nowcasting and NWP observations, but some special additions • Example -- The orographic problem mentioned earlier would benefit from examination of the forecast impacts from networks of profilers and stability profiles (dropsondes, upsondes, longer wavelength profilers) within and upstream of the mountains. Another possibility is to just use a well instrumented HIAPER (wind lidar, dropsondes). Such obs would also benefit prediction studies of local weather events, wind storms, snowfall, etc).

8. Nowcasting • Hypothesis -- how to assimilation data for storm-scale prediction, what measurements and how to assimilate (water vapor, for example), • Phenomena: Fire Weather, tropical cyclones (nowcasting for tornadic cells, rainbands, eyewall), severe convection, flooding, winter storms • Rapid scan radar • Tornadoes evolve on scale of minutes, severe convection, small-scale structure within tropical cyclones, flooding • Polarmetric radar on mobile or networks of C-band and x-band -- microphysics, hail, winter storms, precipitation estimates (OBSERVE THE BOUNDARY LAYER)

9. Nowcasting • Hypothesis -- Can the X and C-band radars be used at these wavelengths for the multitude of needs for hydrometer type and rainfall intensity • Phenomena: Local and widespread flooding, severe convection (hail detection), winter storms (rain-snow line, freezing rain), important at the mesoscale also • Explore polarimetric radar techniques on C-band and X-band with parameterization • Goal of mobile or fixed site, low power networks (CASA) C-band and X-band (AGAIN OBS THE PBL) • Surfave observations are needed for verification

10. Nowcasting • Phenomena: Preconvective environment and convective initiation studies • Hypothesis: Boundaries are critical for convective initiation, what techniques/instruments are best to determine which fine-lines will become dynamically active • Mobile mesonets and soundings/profilers, radars with sensitivity and refractivity for boundaries, • Refractivity is well suited for CASA-type observations due to range limitations • Small UAVs • Long-term need -- temperature, humidity and winds in 3-D near the ground, for now mobile obs (clutter reduction for profilers) • Explore rapid scan and thermodynamic retrievals for the long-term need or wind and water vapor lidars