The total maximum points were 100 for Part #5.1 and 50 points for Part #5.2.
The attached map contains the surface weather features observed over the upper Midwest at 6:00 AM CST on Friday, 1 November 1991.
At each station the following abbreviated surface station model has been utilized:
Wind arrows fly with the wind. Each full barb equals 10 knot wind speed. [Sample station reports a 15 knot wind from the southeast (SE)]. Missing values are indicated by an " M".
What were the conditions reported at Madison, WI at map time? (Include units)
Temperature: = 52 degrees F
Dewpoint: = 50 degrees F
Pressure: = 1002 mb
Sky cover: = Overcast (completely cloud covered)
Wind Speed: 15 knots Wind Direction: Southeast
Precipitation type or significant weather phenomenon: Rain showers
Remember that isobars portray the sea-level corrected pressure field. Analyze the sea-level pressure field by drawing isobars spaced every 4 mb, centered upon 1000 mb (i.e., ..., 992, 996, 1000, 1004, 1008, ..., etc.). The reported values may not necessarily equal the desired values. Therefore, you would have to interpolate between those stations with pressures within + 4 mb of the desired value. When performing your analysis make a light sketch of the isobars with a pencil initially; then smooth the isobars. After smoothing and checking your analysis, isobars may then be inked with a black pen and each labeled neatly.
Points to consider during your isobar analysis:
1. Where is the low or high pressure center(s) located?
(Identify the pressure feature and state or province)
The surface low was in southeast Iowa, near Cedar Rapids.
The surface high was in the Prairie Provinces - off the map
Hint: you should look for the regions with a distinct, closed wind circulation. Locate the center of the low or high pressure system and mark with a large red block "L" (for the low) or a large blue "H" (for the high). Give an estimate of the value of the central pressure.
The central pressure of the low over Iowa was approximately 995 mb.
2. Since the atmosphere is a continuous fluid, no discontinuities nor sharp kinks should appear in your isobar analysis. The spacing between isobars should suggest a smooth horizontal pressure gradient, if possible. Some kinks in the isobars should be expected, especially near wind shift lines and fronts.
3. The isobars are usually spaced closer in regions where the wind speed is greatest.
4. Does your smoothed analysis conform to the above items ?
Yes it worked for me!
Analyze the surface temperature field by drawing isotherms every 10°F (e.g., 10°, 20°, 30°,...). Some smoothing may be necessary. Attempt to follow the same rules as for drawing isobars noted above; however, the temperature field is usually more variable than the pressure field. The finished isotherm analysis should be drawn in dashed red lines and each isotherm should be labeled accordingly.
Points to consider during your isotherm analysis:
1. Where are the warmest and coldest regions (by state) found?
a. Warmest Southern Indiana, Illinois or central Kentucky and Tennessee.
b. Coldest Nonwestern North Dakota, extending into Manitoba and Saskatchewan.
2. Where are the sharpest horizontal temperature contrasts located?
Along the Mississippi River, extending from Eastern Iowa (near the low) to Missouri.
Answer the following questions using your analyzed Midwest map.
1. Where are the regions of a) highest and b) lowest dewpoints?
a) Highest (humid) Kentucky, Tennessee and southern Illinois
b) Lowest (dry) Western South Dakota, into Wyoming and Montana
2. What type of precipitation is found in:
a) Illinois Steady Rain
b) Nebraska Steady Snow
c) Northcentral Iowa - Southeast Minnesota Freezing rain
3. What is the prevailing wind direction that is observed in the following locales?
a) North Dakota = Northwest winds
b) Central Illinois = Southeast winds
4. In what region do you find the strongestwinds on the map?
Kansas
Are the isobars closer or farther apart in this area? Yes, they are closer in Kansas.
5. What region(s) is experiencing warm advection , where winds are transporting warm air toward colder regions?
Illinois and South-central Wisconsin
What region(s) is experiencing cold advection, where winds are transporting cold air toward warmer regions?
Missouri and essentially most of the states in the region that are west of the Mississippi River.
With the aid of your isotherm analysis, the distribution of dewpoint temperatures and the wind field through the regions of distinct wind shifts, can you identify a cold front? A warm front? Using the conventional frontal symbols (see page 479 of your text), draw the appropriate surface fronts on your analysis.
96205/EJH
For each of the weather elements listed, describe the time sequence that you would expect to observe at your "weather station" during:
1. A warm frontal passage in autumn resulting when an idealized cyclone passes from south to north, while staying west of you:
PRE-FRONTAL FRONTAL POST-FRONTAL
CLOUDS (type) Cirrus/Cirrostratus
to Altostratus
to Nimbostratus & stratus to Fog to Clear
PRECIPITATION
(type) Steady rain to drizzle till front None
TEMPERATURE
(trend) Cool to Warm
WINDS (direction) Northeast East, Southeast and South
PRESSURE TENDENCY Falling Unsteady Steady to slow rise
2. A cold frontal passage in the spring of the year when an idealized cyclone moving eastward passes from the northwest to the northeast of you:
PRE-FRONTAL FRONTAL POST-FRONTAL
CLOUDS (type) Clear to Cumulus to Cumulonimbus to clear and stratocumulus
PRECIPITATION
(type) Rain (snow) Showers Thunderstorms Snow (rain) showers
TEMPERATURE
(trend) Warm to Cold
WINDS (direction) South Southwest West Gusty Northwest
PRESSURE TENDENCY Falling Unsteady Rapid rise
3. The passage of an idealized snow producing cyclone (and attendant trough line) in winter traveling from southwest to northeast, but remaining just south of you:
BEFORE TROUGH TROUGH PASSAGE AFTER TROUGH
CLOUDS (type) Cirrus/cirrostratus
to altostratus to nimbostratus to stratocumulus
PRECIPITATION
(type) light to heavy snow snow showers
TEMPERATURE
(trend) Cool to Cold
WINDS (direction) Northeast North Northwest
PRESSURE TENDENCY Falling Steady Rising
Last revision 7 August 1996
Produced by Edward J. Hopkins, Ph.D. Department of Atmospheric and Oceanic Sciences University of Wisconsin-Madison Madison, WI 53706 hopkins@meteor.wisc.eduATM OCN 100 Homework Instruction Page / ATM OCN 100 Home Page /AOS Dept. Home Page