CWS 10B - 1
EXTRATROPICAL CYCLONE TRACK
WEATHER
1. As directed by your instructor, complete this activity with its associated images. Also print
any other Summary or Supplemental files designated.
2. Reference: Chapter 10 in the Weather Studies textbook. Complete the Investigations in the
Weather Studies Investigations Manual as directed by your instructor.
There have been a few episodes of wintry weather already this autumn for residents in the
western mountains and northern states. A recent case of significant snow and copious rainfall
accompanying a passing storm system occurred on November 5th and 6th. According to the
Wednesday, 6 November 2013, Daily Weather Summary: “The counterclockwise circulation of
air around this low was bringing warm and humid air northward across the Mississippi Valley on
the eastern flank of the low, while cold air was being carried southward to the west of the low.
While rain fell ahead of the advancing low across sections of the Midwest, a transition to snow
occurred where the air became sufficiently cold to support snow. A narrow band of locally
heavy snow extended across the central Plains and into the upper Midwest to the northwest of the
track of the low pressure center. Snowfall totals ranged from two to at least ten inches. As of
late Tuesday afternoon, 10 inches of snow had fallen at Gordon in northwestern Nebraska. By
late evening, an observer near Pipestone in southwestern Minnesota reported 10 inches of snow.
A daily maximum snowfall record for the date was set at Rapid City, SD (3.1 inches). For some
areas, this snowfall was the first snow of the upcoming winter snow season.”
The Summary also noted that, “While the locally heavy snowfall was occurring across the
central Plains and the upper Midwest, heavy rain from showers and thunderstorms was falling
farther to the south along the front. According to 24-hour radar estimates, between one and two
inches of rain had fallen across sections of Kansas, Oklahoma, Missouri and Arkansas. Daily
maximum precipitation records were set on Tuesday at Concordia, KS (1.09 inches); St. Joseph,
MO (0.61 inches); and Borger, TX (0.38 inches).”
Image 1 is the surface weather map for 12Z 05 NOV 2013. At map time, the low-pressure center
of the storm was still developing in New Mexico. This development occurred along a
meandering frontal system that stretched between Canada and extreme southern California.
1. Temperatures at stations to the north and northwest of the low-pressure center were generally
in the [(20s and 30s)(50s and 60s)].
2. Rapid City, in western South Dakota, was reporting a present weather condition of two stars
or asterisks. Therefore, in this area on the “cold” side of the low-pressure area and northwest
of the warm front, at least some [(liquid)(solid)] precipitation was occurring.
CWS 10B - 2
3. To the southeast of the low-pressure center, temperatures were generally in the
[(20s and 30s)(50s and 60s)].
4. Radar shadings indicated that a broad shield of precipitation [(did)(did not)] exist generally
east and northeast of the developing Low and on both sides of the warm front in that region.
5. Image 2 is the 500-mb constant-pressure map for 12Z 05 NOV 2013, the same time as the
Image 1 surface map. Mark the approximate center of the storm’s surface circulation with a
bold L on the 500-mb map. The surface low-pressure center was positioned generally to the
[(east)(west)] side of the trough that was located over the western states.
6. As suggested by the pattern of contour lines and the 500-mb wind directions in the area of
the surface low-pressure center, this developing storm was likely to move generally toward
the [(northeast)(southeast)(northwest)(southwest)].
Image 3 is a composite of views from the NWS National Operational Hydrologic Remote
Sensing Center of total amounts for various types of precipitation over the coterminous U.S. for
two successive twenty-four hour periods. The top two views are reported snow precipitation
while the bottom maps show non-snow precipitation (essentially rain) for the twenty-four hours
ending at 06Z on each day. The left panels are the twenty-four hour period ending 06Z on
06 NOV 2013. The right two panels are for 07 NOV 2013. The respective shaded scale for each
panel in inches and millimeters is below the maps.
Bold yellow Ls with the UTC times have been placed on the top sequence of snow precipitation
maps to denote the low-pressure center’s general positions at six-hourly intervals of each period.
For example, the top left snow panel shows the positions of the Low centers at 06Z, 12Z, 18Z
05 NOV and 00Z and 06Z 06 NOV, respectively. The right panel contains the 06Z, 12Z, 18Z
times for 06 NOV and ending at 00Z 07 NOV.
7. On the top left total snow precipitation panel, note the position of the L at 12Z 05 NOV.
This was the same time as the Image 1 map, which was six hours into the 24-hour period
covered by the total time period. The precipitation type reported in the Rapid City station
model [(was)(was not)] consistent with the response for question 2.
8. Precipitation in the top and bottom left panels [(does)(does not)] generally cover the region
of the central U.S. as shown by the Image 1 map’s radar echoes of the advancing general
path of the storm center’s positions.
9. The rain, during the time period of the lower left map, [(was)(was not)] consistent with the
report of heavy rainfall amounts in the introduction above from the Daily Weather Summary.
10. During this same time period, the frozen precipitation (snow) [(was)(was not)] restricted
generally to the north of the low-pressure centers.
11. On both of the top snow panels, draw a broad arrow from the beginning to the final Low
positions going through the center of each L. Add an arrowhead to the eastern end of each
CWS 10B - 3
curve to clearly mark the direction of the storm track. The areas that experienced snow were
located generally to the [(north)(south)] of the storm track.
12. Looking along the storm track arrows you placed on the snow precipitation maps, during the
storm’s passage, the “cold” side would be to the [(left)(right)] of the storm track.
13. In the bottom, non-snow precipitation maps, copy the bold arrow positions representing the
storm’s track. The rain area across the south-central to eastern U.S. was located broadly
along the frontal system and ahead of the respective Low centers. In general, rain would be
expected to be found trending [(north)(south)] of the storm track.
14. Looking along the storm track arrow you placed on the non-snow precipitation map, during
the storm’s passage, the “warm” side would be to the [(left)(right)] of the track.
15. These relative positions of the respective precipitation types in this actual storm [(are)
(are not)] consistent with the model presented in Investigation 10B.
Figure 1 is the surface weather map of frontal positions and pressure centers at
12Z 06 NOV 2013 from NOAA’s Weather Prediction Center surface analysis archive
(http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml). These maps formed the basis of
locations for the low-pressure centers shown on Image 3.
Figure 1. Surface weather map features from NOAA WPC at 12Z 06 NOV 2013.
16. The approximate position of the Low center in Figure 1 [(did)(did not)] track as expected
from the Image 2 500-mb wind directions.
Complicating factors exist in actual storms. In many cases, the temperature patterns involved
with the cyclonic circulation bring warm air northward ahead of the Low center and cold air
CWS 10B - 4
southward behind it. Also, as Lows approach the East Coast, warmer Atlantic air is brought into
the mix. Temperatures are crucial to the types of precipitation, while snow does not accompany
every storm, there are warm and cold portions of the track with or without their frontal passages.
Many surface map products can be found from the course website’s Surface section, “NWS
Surface Analyses” link. Links further down the WPC Analysis page provide surface maps for
regions in a variety of formats as well as animations for the past day at three-hourly intervals.
There is also a link at the bottom of the NWS Surface Analyses page to the official how-to
book, NWS Unified Surface Analysis Manual.
Another valuable map resource is available from the NOAA Daily Weather Maps series
(http://www.hpc.ncep.noaa.gov/dwm/dwm.shtml). Go to this site. To get a particular day’s set
of maps, click on the image of the map page. (The most recent map available is one or two days
prior to the current day.) Then, from the left menu, select the date and click Get Map. Maps are
available from the webpage for each day at 7:00 A.M. E.S.T. (12Z) since September 1, 2002 and
in paper form prior to that. The maps for each day include the analyzed surface map, maximum
and minimum temperatures, 24-hour precipitation, and 500 mb. Clicking on any of these images
brings up a detailed view of the data. Navigation links also allow easy perusal of a sequence of
maps for a storm system.
If directed by your instructor, place the answers to Investigation 10B and Current Weather
Studies 10B on the B Answer Form linked from the AMS Weather Studies website.
Return to AMS Weather Studies website
©Copyright 2013, American Meteorological Society