Transcript Document

Tracking and Extrapolating
Precipitation Episodes in the
National Convective Weather
Forecast
D. Ahijevych, S. Trier, C. Mueller,
D. Megenhardt
Warm Season Precipitation Episodes
Rainfall Streaks
Potential Predictability
Coherent regeneration of convective
rainfall
Anchored to diurnal cycle and
topography
Frequent when forecast skill is lowest
Can we identify and track long-lived
episodes in real time?
Rainfall Streak Detection
TITAN Software
Finds coherent
precipitation zones
in smoothed radar
reflectivity (>10dBZ)
Extrapolates based
on last 6 hours of
propagation
Extrapolated Precipitation Zone
6 hours later…
6 hours later…
Extrapolation issues
Mergers and splits
Back building &
sudden southward
propagation
Dissipation Issues
False alarm rate
Use new episode climatology based on
TITAN track history
Filter by time-of-day and longitude with
current rain streak climatology
Probability of Rain Streak
Continuance (red=high blue=low)
Final Thoughts
Implementing in NCWF
Best lead time to use (3-9h?)
Blending with numerical model
Regime dependency?
Some periods work better than others