A Case Study of Heavy Precipitation Occurring in Continental Environment

To investigate a case of a heavy winter precipitation event of 7 January 2002 that was a challenge to operational forecasters.

John R. Gyakum, McGill Paul A. Sisson, NWS Ron McTaggart-Cowan, McGill Garry Toth, Met Svc Canada Peter Lewis, MSC John K. Parker, MSC

A Cooperative program for Operational Meteorology, Education, and Training

(COMET) Cooperative Outreach Project

McGill University

Montreal, QC, Canada

National WeatherService

Burlington, VTUSA

Cold-Season Quantitative Precipitation Forecasting for the

Burlington, Vermont Region

Outline

Synoptic Overview Diagnosis Mesoscale Modelling using MC2 Summary

Synoptic Overview Summary

12-18” Snowfall in 3-6hrs in narrow mesoscale band KALY-KVSF-KLEB

Little if any orographic enhancement 16:1 Snow to water ratios 3-4”/hr snowfall rates for ~3 hrs Cloud to ground Lightning detected at KPOU. Surface Low Track ACY-ISP-PVD-PYM Intense Upper-level mesoscale trough

Snowfall ending 12 UTC 7 Jan 02

KBTV

KLEB

KVSF6 inch

6 inch

12 inch

12 inch

12 inch

12 inch

6 inch

3 inch

3 inch

3 inch

3 inch

3 inch

3 inch

24-h Precipitation (in) ending 12 UTC 7 January 2002

KBTV

KVSF 070654Z AUTO VRB04KT 2 1/2SM -SN BR BKN012 OVC021 00/M01 A2946 RMK AO2 SLP983 P0012 T00001006=

KVSF 070554Z AUTO 35004KT 1/4SM +SN FG OVC002 00/M01 A2949 RMK AO2 SLP990 P0020 60068 T00001006 10000 21011 56039=

KVSF 070454Z AUTO VRB03KT 1/2SM SN FG OVC003 00/M01 A2949 RMK AO2 SLP993 P0019 T00001006 400281033=

KVSF 070354Z AUTO 00000KT 1/4SM +SN FZFG OVC002 M01/M01 A2954 RMK AO2 SLP010 P0014 T10061006=

KVSF 070254Z AUTO 36003KT 1/2SM SN FZFG BKN003 OVC010 M01/M01 A2960 RMK AO2 PRESFR SLP032 P0008 60015 T10061011 58047=

KVSF 070154Z AUTO 00000KT 3/4SM -SN BR VV004 M01/M01 A2966 RMK AO2 SLP052 P0006 T10061011=

KVSF 070054Z AUTO 00000KT 1 1/2SM -SN BR OVC014 M01/M02 A2970 RMK AO2 SLP066 P0001 T10111017=

Springfield VT ASOS (KVSF)0.80” = 12.0” Snow

Hourly Precipitation

1.3

.12.01 .06 .20.19.14.08

2.1

3.23.02.2

0.21.0

0.0

1.0

2.0

3.0

4.0

0 1 2 3 4 5 6 7

Hour (UTC)

Inches

Liquid Snow

Reflectivity (dbZ) 02-09 UTC 7 Jan 2002

03 UTC 7 January CG LightningRUC SLP METAR

KPOU

500 hPa Heights at 00Z 7 Jan 2002

SLP 06 UTC

Albany Sounding 00 UTC 7 Jan 2002

ETA Analysis at 500 hPa

ETA Analysis at 500 hPa

ETA Analysis at 500 hPa

ETA Analysis at 500 hPa

ETA 36 hr Forecast From

NCEP Short Range Ensemble Forecast (SREF) from 21 UTC 5 Jan 2002

Mesoscale Modeling

MC2 version 4.9.3Non-hydrostatic, semi-implicit time

step, semi-Lagrangian advectionKain-Fritsch Convective

Paramertization(36km,12km)Three one-way nest domains(36km,12km,3km)

Model Description

Nesting Strategy

36km

12 km3 km

KBTV

MC2 36-h Forecast 12-h Precipitation Accumulation (mm) valid 12 UTC 7 January 2002

36-km

12-km

Precipitable Water (mm)

24-h Forecast valid 00 UTC 7 Jan 2002

36-km 12-km

Dynamic Tropopause (DT)

Defined as 1.5 Potential Vorticity unit surface (where 1 PVU is 1.0 X 10-6 K m2 kg-1 s-1) DT separates high PV air in the stratosphere from

lower PV in the troposphere Useful for a concise display of jets and upper

troughs which usually are at a maximum at the DT Advections of lower potential temperature (higher

pressure) on the DT are favorable for cyclogenesis

Potential Temperature (K) Dynamic Tropopause (DT;1.5 PVU)24-h Forecast valid 00 UTC 7 Jan 2002

36-km 12-km

Dynamic Trop 21 – 03 UTC

Dynamic Trop 21 – 03 UTC

Dynamic Trop 21 – 03 UTC

500 hPa Heights Vorticity 21-03 UTC

500 hPa Heights Vorticity 21-03 UTC

500 hPa Heights Vorticity 21-03 UTC

Coupling Index (CI)

Bosart and Lackmann MWR 1995 Theta(Dyn Trop) – Theta-e (850hPa)

“…crude measure of tropospheric lapse rate” “ …small positive or negative values indicate where

deep convection is possible, given the existence of a suitable lifting mechanism.”

MC2 variation of CI “Best” or most unstable CI using maximum theta sfc-850

hPa

Coupling IndexTheta(DT) – Theta-e max(850hPa)

00 UTC 7 January 2002

36-km 12-km

Time Lapse CI

Time Lapse CI

Time Lapse CI

Potential Vorticity (PVU) X-Section CYMX-KACKEquivalent Potential Temp (K) shaded27-hr fcst valid 3 UTC 7 Jan 2002

KLEB

Lowering DTConvectiveInstability

Poor? AWIPS substitutes

For CI use Showalter Index (SI) Temp (500 hPa) – Temp (lifted from 850 hPa)

For DT use single1.5 PVU contours on multiple theta surfaces

ETA Showalter Index3-hr fcst valid 0300 UTC 7 Jan 2002

Summary

The 7 January 2002 Heavy Precipitation Event was a challenge to Operational Forecasters Band of intense precipitation occurred north of forecasted

precipitation maximum 24-36-h in advance 12km MC2 captured important detail at the dynamic

tropopause Deep layer instability appeared to be important in location

and intensity of precipitation 36km MC2 did not capture this detail Precipitable Water may have been deficient at

12-km and contributed to lower QPF

Future Work

Nudge Precipitable Water near band location Move 3km grid to the heavy precipitation area Will use in a Warning Event Simulation for BTV

forecasters in 2002 Have forecasters look at the DT based Coupling

Index to assess tropospheric stability RUC use AWIPS Volume Browser Difference

Function; other NCEP models DT grids soon? Move MC diagnostics into AWIPS (via LDAD)

McGill University Real-Time MC2

http://132.206.43.151:5080/realtime/ Dynamic Tropopause and PV diagnostics 00Z Initial time