Storm Track Monitoring and Research at the Climate Prediction Center (CPC)

1
Storm Track Monitoring and Research at the
Climate Prediction Center (CPC)
(a)
(c)
J. Gottschalck, W. Higgins, and V. Kousky
1. MONITORING
a. Algorithm
Storms are tracked using a method originally
developed at the Climate Diagnostics Center (CDC)
(Serreze, 1995, Atmos.-Ocean Serreze et al,
1997, J. Climate). The algorithm locates sea
level pressure minima using a threshold of 1 mb
as criteria for storm identification and storms
are tracked by analyzing the position of systems
between time steps and applying a maximum
distance threshold between candidate pairings
(800 km). The maximum distance moved north,
south, or west for a particular storm between
time steps is restricted. Currently, Global Data
Assimilation System (GDAS) six-hourly, 2.5º x
2.5º data are used for monitoring purposes. The
sea level pressure fields are converted to an
equal area projection before tracking is
conducted.
Measure of Storm Days
Active and shifting storm track in the Pacific
Ocean during the period
(b)
Southern California storminess in early to mid
February
Split flow in the eastern Rockies/western Plains
from late February to mid-March. Alberta clippers
and southern Plains cyclones
(d)
Figure 3 Latitude-time plots of storm days per
pentad the number of closed circulations (6-hr
data) divided by 4 in a 10 x 10 degree region
for selected cross sections in the northern
hemisphere. A three pentad running mean is
applied to the data.
Figure 5 (a,b) Storm tracks and CAI for
September, October, and November 2004, (c) CAI
seasonal climatology, (d) map of specific areas
for the time series shown in (e), (f), and (g)
which show the monthly climatological CAI for the
twelve regions.
(f)
(e)
(g)
Heavy precipitation, high winds, and strong wave
action in the Pacific Ocean with an expected
strong Pacific storm track during a weekly
forecast period.
Figure 1 Example storm tracks for the period
from February 14 March 15, 2005 using the
algorithm described above.
b. CPC Web Page Products
http//www.cpc.ncep.noaa.gov/products/precip/CWlin
k/stormtracks/strack.shtml
21APR2005 - 30APR2005
Figure 4 Example storm tracks web page product
of the week 1 operational GFS forecast for May
15, 2005. Figures show the same variables as that
described in Figure 2. Storm tracks from the GFS
ensemble mean forecast data are also available on
the web page.
Storms affected by blocking pattern
Storms beginning to undercut Alaska ridge
Strong anomalous meridional flow along the west
coast of Alaska Enhancement into the central
California coast
21APR2005 - 30APR2005
Figure 7 The histograms of seasonal CAI for the
twelve regions depicted in Figure 6a show
considerable variation in the distribution of
seasonal CAI.
2. RESEARCH
Elevated wave action in the central Pacific
a. Background and Cyclone Activity Index (CAI)
21APR2005 - 30APR2005
Alaska storminess has received increasing
attention as communities along the Alaskan coasts
have documented severe social and economic
impacts. The multi-disciplinary Pacific Region
Integrated Data Enterprise (PRIDE) wind/wave
coastal workshop in Anchorage, Alaska in August
2005 recommended research to better characterize
possible trends/changes in storm
frequency/intensity in the Alaska domain.
Attributes of an initial choice of storminess
index are presented here (Zhang et al, 2004, J.
Climate). An index of storminess is important as
it allows not only a consistent and easily
interpretable measure of storm activity but also
allows other disciplines (geology, ecology, etc.)
to relate their findings with variations in storm
frequency and intensity.
21APR2005 - 30APR2005
Figure 8 Normalized time series of monthly CAI
for AREA 2 and AREA 6 as outlined in Figure 6a
for the period 1950-2004. Running means of three
months, thirteen months, six years, and eleven
years have been applied for top, top-center,
bottom-center, and bottom respectively.
3. ONGOING WORK
Figure 2 Example storm tracks web page product
for the ten day period from April 21 April 30,
2005. Storm tracks and total ten day
precipitation (mm) (top), mean ten day 925 mb
anomalous wind vectors and magnitude (m/s,
shaded) (middle) and mean ten day significant
wave heights (m) from NCEP EMC (bottom). The 500
mb mean height and anomalies for the same period
(bottom right) illustrating the strong blocking
pattern across Alaska that played a major role in
the evolution of the storm tracks shown.
i N,6hr CAI sigma SLP (x, y,
t) SLPclim (x, y, month) i
1 N Number of six-hourly cyclone centers
SLP Sea level pressure of six-hourly cyclone
center SLPclim Monthly climatological sea
level pressure

• Realtime verification of GFS/CFS storm tracks on
  web page
• Alaska storm track theme page (wave heights, sea
  ice, extreme events)
• Identify/develop and evaluate other measures of
  storminess
• Identify extremes in storminess in the Alaska
  region and document precursors
• Relation of interannual variability and leading
  modes of climate variability