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An Investigation of Model-Simulated Band Placement and Evolution in the 25 December 2002 Northeast U.S. Banded Snowstorm. David Novak - PowerPoint PPT Presentation
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An Investigation of Model-Simulated Band Placement and Evolution in the 25 December 2002 Northeast
U.S. Banded Snowstorm
David NovakNOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York Stony
Stony Brook University, State University of New York, Stony Brook, New York
Brian ColleStony Brook University, State University of New York, Stony Brook, New York
Daniel KeyserUniversity at Albany, State University of New York, Albany, New York
Previous WorkCompare Eta, MM5, and WRF forecasts to observations
– Models initialized with EDAS
at 0000 UTC 25 Dec 2002
– 36/12/4 km one-way nest
for MM5/WRF
Model SST Convection PBL Micro-physics
Eta Eta BMJ MYJ Ferrier
MM5 v3.4.0
Navy Grell MRF Simple Ice (3 class)
WRF v2.0.3
Navy Grell–Devenyi MRF WSM-3
MSLP Time Series
MSLP Time Series
960
965
970
975
980
985
990
995
1000
12Z 15Z 18Z 21Z 00Z 03Z 06Z
Time (UTC)
MS
LP
(m
b) Obs
Eta
MM5
WRF
12 km MM5 12 km WRF
•Simulated Radar Reflectivity (shaded, dBZ)
•700-hPa height (thick solid, m)
•700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)
1800 UTC
12 km MM5 12 km WRF
•Simulated Radar Reflectivity (shaded, dBZ)
•700-hPa height (thick solid, m)
•700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)
2000 UTC
12 km MM5 12 km WRF
•Simulated Radar Reflectivity (shaded, dBZ)
•700-hPa height (thick solid, m)
•700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)
2200 UTC
12 km MM5 12 km WRF
•Simulated Radar Reflectivity (shaded, dBZ)
•700-hPa height (thick solid, m)
•700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)
0000 UTC
4 km MM5 4 km WRF
•700-hPa 2D Miller Frontogenesis (shaded, °C 100 km -1 h-1)
•700-hPa temperature (thick solid, C)
•700-hPa wind barbs
2000 UTC
Motivation• Why did the MM5 and WRF models forecast the
band too far to the southeast?– Is the deformation/frontogenesis farther northwest?
• Can the modeled sharp 700-hPa trough and attendant intense frontogenesis be verified?
• What accounts for the different band evolution forecasts in the WRF and MM5?– MM5: one single band that dissipates early– WRF: correct event length but two separate bands
Analyses and Observations
• RUC and EDAS used for analysis, with supplemental tropospheric observations
Datasource Variables Instrument Error
NOAA Profiles Wind 1 kt; 3 degrees
WSR-88D VAD Wind Situationally dependent
MDCRS Wind, Temp 3–5 kt, 5 degrees
Analysis Resolution Technique
RUC 20 km OI
EDAS 12 km 3-D VAR
Analyses and Observations18 UTC
RUC
700 mb Height (red, 15 m)
700 mb Temp (shaded, 2°C)
Analysis Winds (white barb)
Observed Winds (black barb)
RUC vs. EDAS18 UTC
RUCEDAS
Analyses and Observations19 UTC
RUC
700 mb Frontogenesis (red, °C 100 km-1 h-1)
700 mb Temp (shaded, 2°C)
Analysis Winds (white barb)
Observed Winds (black barb)
Analyses and Observations22 UTC
RUC
700 mb Frontogenesis (red, °C 100 km-1 h-1)
700 mb Temp (shaded, 2°C)
Analysis Winds (white barb)
Observed Winds (black barb)
Analyses and Observations00 UTC
RUC
700 mb Frontogenesis (red, °C 100 km-1 h-1)
700 mb Temp (shaded, 2°C)
Analysis Winds (white barb)
Observed Winds (black barb)
RUC vs. EDAS00 UTC
RUCEDAS
MM5 and WRF19 UTC
WRFMM5
MM5 and WRF22 UTC
WRFMM5
MM5 and WRF01 UTC
WRFMM5
Features of Note
• Sharp 700-hPa trough, attendant winds and frontogenesis can be verified
• Trough and associated frontogenesis farther northwest than models forecast
• Easterly flow forecast in WRF run over CT was not observed
p
fgPV )(
Potential Vorticity
• High values of PV associated with– Cyclonic flow
– High static stability
– Low tropopause
– Upper trough
• Low values of PV associated with– Anticyclonic flow
– Low static stability
– High tropopause
– Upper ridge
• PV is the product of the – Absolute vorticity
– Static stability
Figures from Thorpe (1985) for Northern Hemisphere
Slide courtesy Dr. Mike Brennen (NCSU)
Dynamic Tropopause12 UTC
MM5 WRF
Pressure and winds on the PV=2 PVU surface (shaded)
Dynamic Tropopause15 UTC
MM5 WRF
Dynamic Tropopause16 UTC
MM5 WRF
Dynamic Tropopause17 UTC
MM5 WRF
Dynamic Tropopause18 UTC
MM5 WRF
Dynamic Tropopause19 UTC
MM5 WRF
Dynamic Tropopause20 UTC
MM5 WRF
Dynamic Tropopause21 UTC
MM5 WRF
Dynamic Tropopause22 UTC
MM5 WRF
Dynamic Tropopause23 UTC
MM5 WRF
Dynamic Tropopause00 UTC
MM5 WRF
Dynamic Tropopause01 UTC
MM5 WRF
Dynamic Tropopause02 UTC
MM5 WRF
• PV generated below level of maximum heating – Warming increases static stability– Pressure falls convergence increases absolute vorticity
PV+PV+
PV-PV-
PV and Latent HeatingPV and Latent Heating
• Opposite occurs above level of maximum heating where PV is reduced
• PV growth rate determined by vertical gradient of LHR
Slide courtesy Dr. Mike Brennen (NCSU)
12 UTCModel PV - Reflectivity Comparison
MM5 WRF
Pressure/winds on the DT (shaded) and reflectivity contoured > 32 dBZ
15 UTCModel PV - Reflectivity Comparison
MM5 WRF
16 UTCModel PV - Reflectivity Comparison
MM5 WRF
17 UTCModel PV - Reflectivity Comparison
MM5 WRF
18 UTCModel PV - Reflectivity Comparison
MM5 WRF
19 UTCModel PV - Reflectivity Comparison
MM5 WRF
20 UTCModel PV - Reflectivity Comparison
MM5 WRF
21 UTCModel PV - Reflectivity Comparison
MM5 WRF
22 UTCModel PV - Reflectivity Comparison
MM5 WRF
23 UTCModel PV - Reflectivity Comparison
MM5 WRF
00 UTCModel PV - Reflectivity Comparison
MM5 WRF
PV Cross Sections21 UTC
MM5 WRF
800-600 mb PV21 UTC
MM5 WRF
PV Findings• Model-simulated bands appear downwind of
PV filaments
• PV filaments appear to be created by diabatic processes occurring in southeast sector of cyclone
• Simulated band evolution was particularly sensitive to diabatically-generated lower-tropospheric PV anomaly over Long Island
Conclusions and Implications
•Southeast band position error appears to be due to a misplacement of the sharp 700-hPa trough and associated frontogenesis
•Although both the MM5 and WRF successfully predicted band formation, respective band evolution appears to be sensitive to convection occurring in the southeast sector of the cyclone
• Suggests the likelihood of banding may be more predictable than exact timing, location, and evolution
18 UTCRadar Observations
19 UTCRadar Observations
20 UTCRadar Observations
21 UTCRadar Observations
22 UTCRadar Observations