Synoptic Analysis of Heavy
Snowfalls over Central New
England, 1996-2007
Daniel Michaud
Jared Rennie
Norman Shippee
Introduction and Objectives
• Forecasting Snowfall can be a tricky task
– Synoptic changes and topographic features can
enhance precipitation, as well as inhibit it.
• This research concerns itself with the synoptic
differences between:
– Cases where Plymouth, NH receives significant
snowfall
– Cases where little or no snowfall was recorded in
Plymouth, yet surrounding cities received significant
accumulations
Data and Methodology
• F6 Climatological Data
– Winter seasons of 1996 through 2007
– Looked at three cities:
• Plymouth, NH
• Concord, NH
• St. Johnsbury, VT
– Defined an “event” as when any one of the above three
cities received significant snowfall during a single storm
• Determining “Significant Snowfall”
– Local NWS definition of a winter storm warning
• Area receiving at least seven inches from a single storm (NOAA
2005)
Data and Methodology (con’t)
• Surface Maps
– Determined to classify storm evolution
• Lee side cyclogenesis off the Rocky Mountains
• Coastal Redevelopment (most cases were this)
– Multiple cases were eliminated
• Data was split into two groups
– Criteria (Plymouth receiving 7”)
• 25 cases
– Non-Criteria (Plymouth not receiving 7”)
• 19 cases
Data and Methodology (con’t)
• Using local Metars and archived surface maps
– Time of snowfall initialization was calculated and
inserted into NCEP/NCAR composites
• 12 hourly composites were created for the following
three cases
– All 44 cases (used as a control)
– 25 Criteria Cases
– 19 Non-Criteria Cases
• Generated maps of 250-hPa winds, 500-hPa heights,
700-hPa omega, 850-hPa vector
winds/temperatures, sea level pressure and surface
winds
Results
All Data
Fig. 1. NCEP/NCAR Composite analysis 24 hours prior to event onset (T-24) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
a.
b.
c.
d.
0°C
Fig. 1. NCEP/NCAR Composite analysis 24 hours prior to event onset (T-24) for a) 250-hPa vector
wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
a.
b.
c.
d.
0°C
Fig. 2. NCEP/NCAR Composite analysis 12 hours prior to event onset (T-12) for a) 250-hPa vector
wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
a.
b.
c.
d.
0°C
Fig. 3. NCEP/NCAR Composite analysis at event onset (T-0) for a) 250-hPa vector wind, b) 500-hPa
geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
a.
b.
c.
d.
0°C
Fig. 4. NCEP/NCAR Composite analysis 12 hours after event onset (T+12) for a) 250-hPa vector
wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
a.
b.
c.
d.
0°C
Fig. 5. NCEP/NCAR Composite analysis 24 hours after event onset (T+24) for a) 250-hPa vector
wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level pressure.
Criteria cases vs. Non-criteria cases
a.
b.
c.
d.
Fig. 6. NCEP/NCAR Composite analysis of criteria events for Plymouth, NH 24 hours prior to event
onset (T-24) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature,
and d) sea-level pressure.
a.
b.
c.
d.
Fig. 7. NCEP/NCAR Composite analysis of non-criteria events for Plymouth, NH 24 hours prior to
event onset (T-24) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa
temperature, and d) sea-level pressure.
a.
b.
c.
d.
Fig. 8. NCEP/NCAR Composite analysis of criteria events for Plymouth, NH 12 hours prior to event
onset (T-12) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature,
and d) sea-level pressure.
a.
b.
c.
d.
Fig. 9. NCEP/NCAR Composite analysis of non-criteria events for Plymouth, NH 12 hours prior to
event onset (T-12) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa
temperature, and d) sea-level pressure.
a.
b.
c.
d.
Fig. 10. NCEP/NCAR Composite analysis of criteria events for Plymouth, NH at event onset (T-0) for
a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d) sea-level
pressure.
a.
b.
c.
d.
Fig. 11. NCEP/NCAR Composite analysis of non-criteria events for Plymouth, NH at event onset
(T-0) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature, and d)
sea-level pressure.
NonCriteria
Criteria
Fig. 12. Topographical Map of
New Hampshire. Arrows depict
surface wind direction.
(Image courtesy Color Landform
Atlas of the United States)
a.
b.
c.
d.
Fig. 13. NCEP/NCAR Composite analysis of criteria events for Plymouth, NH 12 hours after event
onset (T+12) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature,
and d) sea-level pressure.
a.
b.
c.
d.
Fig. 14. NCEP/NCAR Composite analysis of non-criteria events for Plymouth, NH 12 hours after
event onset (T+12) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa
temperature, and d) sea-level pressure.
a.
b.
c.
d.
Fig. 15. NCEP/NCAR Composite analysis of events for Plymouth, NH 12 hours after event onset
(T+12) for a) criteria surface temperature, b) non-criteria surface temperature, c) criteria surface
vector wind, and d) non-criteria surface vector wind.
a.
b.
c.
d.
Fig. 16. NCEP/NCAR Composite analysis of criteria events for Plymouth, NH 24 hours after event
onset (T+24) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa temperature,
and d) sea-level pressure.
a.
b.
c.
d.
Fig. 17. NCEP/NCAR Composite analysis of non-criteria events for Plymouth, NH 24 hours after
event onset (T+24) for a) 250-hPa vector wind, b) 500-hPa geopotential height, c) 850-hPa
temperature, and d) sea-level pressure.
a.
b.
c.
d.
Fig. 18. NCEP/NCAR Composite analysis of events for Plymouth, NH 24 hours after event onset
(T+24) for a) criteria surface temperature, b) non-criteria surface temperature, c) criteria surface
vector wind, and d) non-criteria surface vector wind.
Fig. 19. Topographical Map of
New Hampshire.
(Image courtesy Color Landform
Atlas of the United States)
Conclusions
• There are several crucial differences in storm evolution within
the 24 hours surrounding event onset
– Cases meeting criteria in Plymouth are generally colder at low
levels
– The cyclone in these cases develops slower, deepens rapidly around
T+12, takes a track further offshore
– Non-criteria cases develop faster due to better mid- and upperlevel dynamics, create more WAA downstream over New England
• Low level flow and topographical influences can make or break
a large snowfall event in Plymouth
– Cases meeting criteria in Plymouth tend to have a period of
easterly surface winds at event onset whereas non-criteria cases
tend to have northeasterly flow (terrain blocking)
– Non-criteria cases tend to have stronger cold advection soon after
(T+24) event onset on a west-northwesterly flow (a dry,
downsloping direction)
– Criteria cases have north to northeasterly flow at this time period,
allowing for continued access to Atlantic moisture and the
possibility of wrap-around precipitation to continue across the area
Works Cited
• HPC, cited 2007: Surface Analysis Archive. [available online at
http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml]
• Kocin, Paul J and Uccellini, Louis W, 2004: Northeast Snowstorm: Volume I:
Overview, Volume II: The Cases. Meteorological Monograph Series, 818
pp.
• NCDC, cited 2007: Unedited Local Climatological Data. [available online at
http://cdo.ncdc.noaa.gov/ulcd/ULCD]
• NCEP/NCAR, cited 2006: 6-Hourly Reanalysis Data Composites. [available
online at http://www.cdc.noaa.gov/Composites/Hour/]
• NWS Gray, Maine Climate Data, cited 2007: Monthly F6 Climate Statistics.
[available online at http://www.erh.noaa.gov/er/gyx/climate_f6.shtml]
• PSU Vortex, cited 2007: Product Generator for Archive Data. [available online
at http://vortex.plymouth.edu]
• Unisys Weather, cited 2007: Image and Map Archive. [available online at
http://weather.unisys.com/archive/index.html]
QUESTIONS???
GO BILLS!!! …next year