Jason Knievel ATEC Forecasters’ Conference, July and August 2006 1

Lake-effect precipitation from the

Great Salt Lake

Jason Knievel

Material contributed by: Greg Byrd, Josh Hacker, Scott

Halvorson, Daryl Onton, and Jim Steenburgh

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 2

Examples of lake-effect precipitation

From NASA

30 November 2004

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 3

Examples of lake-effect precipitation

Radar reflectivity

From U of Wyoming

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 4

Examples of lake-effect precipitation

Satellite-derived precipitation

11-12 November 1996

From NWS Buffalo

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 5

Locations of lake-effect-type precipitation

Great Lakes

Finger Lakes, NY

Chesapeake, Delaware, and Massachusetts

Bays

Gulf Stream

Sea of Japan

Great Salt Lake (GSL)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 6

Lake effect precipitation from the GSL

Radar reflectivity

From Jim Steenburgh

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 7

GSL and surroundings

From siteatlas.com

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 8

Lake-effect precipitation by month

L-E precipitation

occurs during all the

cool/cold months

Most distinct L-E

precipitation occurs

during autumn and

early winterFrom Halvorson (1999)

Data from Sep 1994 - May 1998

18 marginal cases in gray

16 distinct cases in black

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 9

Climate of GSL temperature

From Halvorson (1999)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 10

Significance of salinity and size of GSL

Lake-effect precipitation can occur over most of

the year

– Lake does not freeze

– Lake temperature responds quickly to forcing

Upstream, extant moisture may be important in

many cases

– Moisture from lake is limited

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 11

Synoptic setting

From Steenburgh et al. (2000)

Composite RUC analysis

for onset of L-E snowRH (%)

vorticity (x10-5s-1)surface parcel is dashed

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 12

Timing and duration of snows

Most episodes start and night and last 12-36 h

From Halvorson (1999)From Halvorson (1999)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 13

Mesoscale enhancement by land breeze

Warmer water

drives a land

breeze

Tlake Tland during lake-effect snows

From Halvorson (1999)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 14

Mesoscale enhancement by land breeze

Frequent nocturnal onsets may be from enhanced

forced ascent due to convergence over the GSL

from land breezes

From Michael Pidwirny

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 15

Role of static instability

Tlake T700 during lake-effect snows

From Halvorson (1999)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 16

Role of static instability

Tsfc T700 lapse rate during lake-effect snows

From Halvorson (1999)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 17

Wind direction and banding

Radar reflectivity

Terrain, Sfc obs

7 Dec 1998

From Steenburgh and Onton (2001)

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 18

Wind direction and banding

From Onton (2000)From Onton (2000)

1200 UTC 7 Dec 1998 0000 UTC 8 Dec 1998

Lake temperature

Modified parcel

Surface parcel

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 19

Summary of ingredients

Instability: Cold air over warm water to produce

conditional or absolute instability

Lift: Convergence, mountains, other mechanisms

for lifting parcels to level of free convection

Moisture: Supply of water for latent heating and

precipitation

Wind direction and lack of shear: Indicator of

precipitation location and banding

Persistence and intensity of these conditions

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 20

Lake-effect precipitation and RTFDDA

RTFDDA is capable of realistically predicting

lake-effect precipitation

1200 UTC 18 Apr 2006 1200 UTC 18 Apr 2006Obs WRF

From Carissa Edgar From Carissa Edgar

Jason Knievel ATEC Forecasters’ Conference, July and August 2006 21

Importance of lake temperature in RTFDDA

RTFDDA is also capable of over-predicting lake-

effect precipitation

11.75 ºC

From Josh Hacker

3.5 ºC

From NOAA

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Additional reading

Carpenter, D. M., 1993: The lake effect of the Great Salt Lake: Overview and forecast

problems. Wea. Forecasting, 8, 181–193.

Halvorson, S. F., 1999: Climatology of lake-effect snowstorms of the Great Salt Lake.

M. S. thesis, Dept. of Meteorology, University of Utah, 78 pp.

Onton, D. J., 2000: An observational and numerical modeling investigation of Great

Salt Lake effect snow. Ph. D. dissertation, Dept. of Meteorology, University of Utah,

131 pp.

Steenburgh, W. J., S. F. Halvorson, and D. J. Onton, 2000: Climatology of lake-effect

snowstorms of the Great Salt Lake. Mon. Wea. Rev. , 128, 709–727.

Steenburgh, W. J., and D. J. Onton, 2001: Multiscale analysis of the 7 December

1998 Great Salt Lake-effect snowstorm. Mon. Wea. Rev., 129, 1296–1317.