Observed and Simulated Multi-bands in Northeast U.S. Winter Storms S ARA A. G ANETIS 1, B RIAN A. C OLLE 1, S ANDRA E. Y UTER 2, AND N ICOLE C ORBIN 2

Observed and Simulated Multi-bands in Northeast U.S. Winter Storms

SARA A. GANETIS1, BRIAN A. COLLE1, SANDRA E. YUTER2, AND NICOLE CORBIN2

1 School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York

2 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

NROW XV 12 November 2014 1


Previous Work on Snowbands

Moisture Instability

Lift

Single Band

Single Band Nonbanded

Nonbanded

Novak et al. 2004• Climatology of banded structures in

Northeast U.S. extratropical cyclones for 5 years (1996-2001) that identified 88 cases, 75 banded, 48 single bands & 13 nonbanded

Novak et al. 2010• 75 cases, 30 single-banded cases for 2002-08• Band-relative composites using 3-hourly 32-

km (NARR) data and hourly 20-km RUC data


Previous Work on Microphysics within East Coast Storms

Stark et al. (2013)• Case studies examining microphysical evolution of snowbands


Novak et al. 2009• Confirmed the capability of a mesoscale model in simulating single-banded storms

Observation

4-km MM5 Simulation

Previous Work on Utilization of Mesoscale Models


What about Multi-bands?

Reflectivity [dBZ]

26-27 Dec 2010 OKX 0.5° Reflectivity


Fewer studies have focused on or discussed smaller-scale multi-bands found in the comma head of cool season (Oct – Mar) extratropical cyclones and include

• observational studies• e.g. Uccellini and Koch 1987; Shields et al.

1991; Nicosia and Grumm 1999• theoretical and/or idealized studies

• e.g. Xu 1992; Pizzamei et al. 2005; Morcrette and Browning 2006

Previous Work on Multi-bands

Novak et al. 2006

Cross-section of vertical velocity for a saturated region in the presence of negative moist geostrophic potential vorticity (Xu 1992).

Stable Unstable

VT


Science QuestionsWhat are the frequency of occurrence and characteristics

of observed banded precipitation structures in Northeast U.S. winter storms and are they in agreement with those of previous studies?

• How often do multi-bands transition into a single band and vice-versa?

How do environmental parameters differ among the different banded precipitation structures and how could the differences be used to enhance conceptual knowledge?

• Do multi-bands always form in an environment of instability?

Can a mesoscale model run down to 1.33-km grid spacing simulate the different observed precipitation structures?


Dataset Creation Methodology

123 Cyclone DatesReporting ≥ 1” snow

in 24 h

71 Cyclone Dates w/ Radar Data from KDIX, KOKX, KBOX

Source: US Census Bureau

• Coastal Northeast U.S. cool season (Oct – Mar) snow storms from 1997-2014• Goal Using stitched radar data (NCState) from DIX, OKX, BOX:

Classify events or time periods during which different banded precipitation structures were observed within cases

50 Cyclone cases with radar data available for entire duration of storm

Terrain Height [m]


Band Description

Band Type

Single bandLinear structure 20–100 km in width, >250 km in length, with an intensity >30 dBZ maintained for at least 2 h

Multi-bands

>3 finescale (5–20-km width) bands with periodic spacing

and similar spatial orientation, with intensities

>5 dBZ over the background reflectivity maintained for at

least 1 h

Both single band and

multi-bands

Both above single band and multi-bands criteria are met

within 250 km

Nonbanded

None of the above criteria are met and this may also be classified as "cellular" where reflectivity features >30 dBZ are not ellipsoidal in shape

to be classified as multibands

Classification Methodology

Single band


Classification Methodology Band Description

Band Type


Multi-bands




least 1 h


multi-bands


within 250 km

Nonbanded



Multi-bands



Band Type


Multi-bands




least 1 h


multi-bands


within 250 km

Nonbanded



Both Single & Multi-bands



Band Type


Multi-bands




least 1 h


multi-bands


within 250 km

Nonbanded



Non-banded


Preliminary Event Results

Terrain Height [m]

68 Events• 12 Single bands (18%)• 22 Multi-bands (32%)• 14 Both single bands and multi-bands (21%)• 20 non-banded (29%)

Comparison to previous studies• Less events over a longer time period

compared to Novak et al. 2004 • 162 events, 48 exhibited single bands

Multi-band Transitions within 13 cases• Both Multi: 4• Multi Both Multi: 2• Multi Both: 2• Single Both: 2• Multi Both Single: 1• Multi Single Both: 1• Single Both Single: 1

Spatial Distribution

Moisture Instability

Lift


Composite Methodology

• 3-hourly NARR Data (1997-2014)• One NARR file per event, but cyclone can be

sampled more than once

N-3 N0 N+3Multi-bands Both Single & Multi-bands

Multi-bands Both Single & Multi-bands


Composite Results: 300 mbSingle Band Multi-bands


Non-bandedWind Speed [kt]


Composite Results: 700 mbSingle Band Multi-bands


Non-bandedRelative Humidity

[%]


Composite Results: Forcing for LiftSingle Band Multi-bands


Non-bandedFrontogenesis

[K (100 km 3 h)-1]

-5 -2 -1 1 2 5

Hypothesis:There is low-to-mid-level frontogenesis inducing an ageostrophic vertical circulation that provides forcing for lift for both single bands and multi-bands

850 mb Frontogenesis


Composite Results: InstabilitySingle Band Multi-bands


Non-banded

Hypothesis:There is larger instability in the low-to-midlevel environment for multi-bands

950-925

≤ 0

> 0


Mesoscale Modeling Methodology• 26-27 Dec 2010 Case

• Both single and multi-bands 26/1700 - 27/0800• Weather Research and Forecasting (WRF)

mesoscale model v. 3.6.1• 30-h Simulation 0600 UTC 26 – 1200 UTC 27• Initial and boundary conditions from 6-hourly 0.5° GFS• 1/12th degree SST data from NCEP• 4 one-way nested domains (36, 12, 4, 1.33 km)• 40 vertical levels with model top set to 50 hPa• 5-layer thermal diffusion surface layer scheme (Dudhia

1996)• Kain-Fritsch cumulus parameterization (Kain 2004)

• applied to 36 and 12 km domains only• explicitly resolves updrafts and downdrafts

Planetary Boundary Layer Parameterization Scheme

Microphysics Parameterization Scheme

MYJ (Janjic 1994)-- 1.5-order scheme with local mixing and used in operational NAM

Thompson (Thompson et al. 2008)--predicts graupel and also predicts the number concentration of ice in addition to the mass concentration, despite being a single-moment scheme

YSU (Hong et al. 2006)– Diagnostic non-local closure scheme

WSM6 (Hong and Lim 2006)– single moment that also predicts the mass concentration of graupel

Resultant dataset: 4 simulations run down to 1.33-km grid spacing of 26-27 Dec 2010 multi-bands

36 km

12 km

4 km

1.33


Mesoscale Model Results: 0000 UTC 27 Dec 2010 Simulated Reflectivity

OKX 0.5°

Reflectivity [dBZ]

MYJ PBL / Thom MP MYJ PBL / WSM6 MP

YSU PBL / Thom MP YSU PBL / WSM6 MP1-km AGL Stitched


Mesoscale Model Results: 0000 UTC 27 Dec 2010 OKX Sounding

MYJ PBL / Thom MP

MYJ PBL / WSM6 MP

YSU PBL / Thom MP

YSU PBL / WSM6 MP

OKX Sounding


Mesoscale Model Results: 850 mb Geopotential Height26/1800 27/0000

27/0300 27/0600

MYJ PBL / Thom MP

MYJ PBL / WSM6 MP

YSU PBL / Thom MP

YSU PBL / WSM6 MP


Mesoscale Model Results: Dec 2010 Simulated Reflectivity

00 UTC 27 Dec 2010

Reflectivity [dBZ]

OK

X 0

.5°

Ref

lect

ivit

y

WR

F 1

.33

-km

Do

ma

in 5

00

-m A

GL

S

imu

late

d R

efl

ec

tiv

ity

FH 18 Valid 00 UTC 27 Dec 2010



01 UTC 27 Dec 2010 03 UTC 27 Dec 2010

B

B’


FH 18 Valid 00 UTC 27 Dec



BB’

BB’

BB’

Reflectivity [dBZ]

-70 -30 0 30 70

Frontogenesis [K (100 km h)-1]

Simulated Reflectivity, θes, Circulation Vectors

Frontogenesis, θe, Circulation Vectors


Summary & Ongoing Work Multi-bands are found in 53% of 50 cyclones exhibiting ≥ 1”/h snowfall

amounts between 1997-2014 in the Northeast coastal region and are an important part of the precipitation structure evolution

Multi-bands occur during a less developed period of the baroclinic wave with weaker frontogenesis than single band times, but more instability.

The MYJ PBL & Thompson microphysics schemes provided the most representative simulation of multi-bands for 26-27 Dec 2010 case

Is this configuration true for a larger variety of similar cases? What about varying IC/BCs?

A high-resolution gridded dataset is necessary to quantify the evolution of stability, moisture and lift attributed to the evolution of the banded precipitation structures in these coastal cyclones

Thank [email protected]

http://flurry.somas.stonybrook.edu/band_study/

Documents

Observed and Simulated Multi-bands in Northeast U.S. Winter Storms S ARA A. G ANETIS 1, B RIAN A. C OLLE 1, S ANDRA E. Y UTER 2, AND N ICOLE C ORBIN 2