a case study of heavy precipitation occurring in continental environment to investigate a case of a...
TRANSCRIPT
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