Anticipating Mesoscale Band Formation in Winter Storms

David Novak, Jeff WaldstreicherNWS Eastern Region, Scientific Services Division, Bohemia, NY

Lance Bosart, Daniel KeyserUniversity at Albany, State University of New York, Albany, NY

001230/1800001230/1800 020107/0300020107/0300

C S T A RC S T A RCollaborative 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.

http://fermi.jhuapl.edu/states ©1995©1995

MethodologyCase 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

20-100 km width

30 dBz minimum

2 h minimum

010206/0000

Band DistributionIdentified 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 Type Incorporated Events

Northwest Majority of band length in NW quadrant

Nonbanded Case exhibited no type of banding

Northwest Composite Summary

Nonbanded Composite Summary

Corroborates Nicosia and Grumm (1999)

12

Composite Cross-Section Comparison

Northwest

Nonbanded

Conceptual Models

Banded Nonbanded

Cross Sections

Banded Nonbanded1000 km1000 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 Flow00 UTC 6 January 2002

Cyclogenesis

Closed midlevel circulation

Deformation/ frontogenesis

Cyclogenesis

Closed midlevel circulation

Deformation/ frontogenesis

Approximate Band Location12 UTC 6 Janaury 2002

Approximate Band Location18 UTC 6 Janaury 2002

Cyclogenesis

Closed midlevel circulation

Deformation/ frontogenesis

Approximate Band LocationStrength and depth of frontogenesis Weak conditional/ symmetric stability

Narrow, strong vertical velocity signature

http://cstar.cestm.albany.edu/coolmeso/atn5_0-42.pdf

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 Evolution21 UTC 6 January 2002

Observed

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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

http://cstar.cestm.albany.edu/coolmeso