Anticipating Mesoscale Band Formation in Winter Storms David Novak, Jeff Waldstreicher NWS Eastern Region, Scientific Services Division, Bohemia, NY Lance Bosart, Daniel Keyser University at Albany, State University of New York, Albany, NY / /0300

C S T A R Collaborative Science, Technology and Applied Research Topics  Climatology  Composites  Conceptual Models  Application to 6-7 January 2002

Why study bands? Forecast details matter to the public  Precipitation amount  Precipitation intensity  Precipitation timing New data sets enable comprehensive investigation  Unified Precipitation Dataset – 0.25°, daily  WSR-88D – 2 km, 5 minute

Methodology Cold season: October through April Study Period: October 1996 – April 2001 Northeast U.S. © ©1995

Methodology Case thresholds: >25 mm rainfall or >12 mm liquid equivalent at a location in study area for at least one 24 h period

Single Band >250 km length km width 30 dBz minimum 2 h minimum /0000

Band Distribution Identified 48 Events ~80% of bands in NW quadrant

Composite Methodology NCEP ETA model analysis and 6-h forecast fields 80 km analysis grid – smooth analysis and uniform dataset Resolves frontal environment – NOT the band Cyclone-relative, from –12 h to +12 h Class TypeIncorporated Events NorthwestMajority of band length in NW quadrant NonbandedCase exhibited no type of banding

Northwest Composite Summary

Nonbanded Composite Summary

Corroborates Nicosia and Grumm (1999)

Composite Cross-Section Comparison Northwest Nonbanded

Conceptual Models BandedNonbanded

Cross Sections BandedNonbanded 1000 km

Forecast Framework

Forecast Strategy 1–2 Days: assess forecast synoptic flow pattern  Strength of cyclogenesis?  Closed midlevel circulation?  Significant deformation / frontogeneis? VS.

Forecast Strategy 6–24 h: assess approximate band location  Location/magnitude of midlevel frontogenesis maximum?  Strength and depth of frontogenesis?  Weak conditional or symmetric stability?  Narrow, strong vertical velocity signature? VS.

Forecast Strategy 0–6 h: anticipate band evolution by monitoring short- range guidance  How is the frontogenesis field expected to evolve?  Is the band developing?

Assess Forecast Synoptic Flow 00 UTC 6 January 2002  Cyclogenesis  Closed midlevel circulation  Deformation/ frontogenesis

 Cyclogenesis  Closed midlevel circulation  Deformation/ frontogenesis Approximate Band Location 12 UTC 6 Janaury 2002

Approximate Band Location 18 UTC 6 Janaury 2002  Cyclogenesis  Closed midlevel circulation  Deformation/ frontogenesis

Approximate Band Location  Strength and depth of frontogenesis  Weak conditional/ symmetric stability  Narrow, strong vertical velocity signature

Frontogenesis evolution Is the band developing SPC Discussion 20 UTC 6 Jan “HEAVY SNOWFALL WILL EXIST WHERE STRONGEST FRONTO- GENETICAL FORCING IN THE 750 TO 650 MB LAYER IS MAXIMIZED FROM UNV TO BGM TO ALB THROUGH 07/02Z.” Anticipate Band Evolution 21 UTC 6 January 2002

Observed

25

Conclusions Composites and case studies show how the process of cyclogenesis influences the magnitude and location of deformation and subsequent frontogenesis maxima Cross-section analyses suggests frontogenesis in the presence of weak conditional stability is the “smoking gun” of band formation Forecast process placing band formation in the context of cyclogenesis, and subsequent deformation/frontogenesis may be successful