Lab 7-G109-1
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Indiana University, Bloomington *
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Course
109
Subject
Geography
Date
Dec 6, 2023
Type
Pages
7
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G109 Weather and Climate Lab Manual
Lab 7-1
Lab 7: Weather Forecasting
Background Material on Model Output Statistics
Background Material on MOS
The standard four-panel progs are generated using data from the GFS and NAM dynamic
models. By "dynamic", we mean that these models solve mathematical equations in order
to predict how the atmosphere will evolve with time (these equations include variables such
as temperature, moisture and wind).
On average, the dynamic models don't predict surface temperatures very accurately (we can say
the same thing about surface dew-point temperatures and surface winds).
To give you a sense
for why the NAM and GFS dynamic models don't predict surface temperatures very well, we
point out that physical processes near the earth's surface (such as the cooling and heating of the
ground by radiation gains and losses) are just too complicated to mathematically model very
accurately. Instead, meteorologists use oversimplified mathematical parameters and schemes to
model complicated physical and radiative processes near the ground. Not surprisingly, these
"oversimplifications" lead to forecasting errors.
Why, then, are forecasts for daytime high and low temperatures generally pretty accurate? Good
question. As it turns out, weather forecasters use statistical models to more accurately
predict surface air temperatures, dew points and winds. Here's the scoop. Over a relatively long
period of time, meteorologists kept statistics of observed surface temperatures (for example)
and the corresponding data from the dynamic models that helped to predict surface
temperatures. These data, called predictors, included 850-mb temperatures, wind direction, wind
speed and a couple of other variables (these are some of the parameters that govern surface
temperatures).
At each airport or weather station, meteorologists developed statistical equations that expressed
surface temperatures as a function of these predictors. To ground these statistical equations in
reality, meteorologists also incorporated climatological values into the statistical schemes.
They
also developed similar statistical equations for dew points, wind direction, wind speed,
probability of precipitation, visibility, cloud coverage, cloud ceilings, etc. In the final analysis,
forecasts based on statistical equations turned out to be a more accurate way to predict surface
temperatures, surface dew points, surface winds, etc. at a given airport or weather
station (compared to the raw output from the dynamic models).
Collectively, all the forecasts from the statistical equations are called Model Output
Statistics (MOS, for short; pronounced "moss"). For the record, the GFS MOS is run four times
per day (at 00Z, 06Z, 12Z and 18Z), while the NAM MOS is run twice daily at 00Z and 12Z.
Additionally, we retrieved these MOS data from the
interactive Web site at the University of
Wyoming
.
To interpret the NAM MOS and GFS MOS for University Park, please carefully read the
Description of the NAM MOS
and the
Description of the GFS MOS
. The row labeled "N/X"
G109 Weather and Climate Lab Manual
Lab 7-2
lists the mi
N
imum and ma
X
imum temperatures for the nighttime and daytime cycles during the
specific forecast period (
refer to this site
). Once you feel comfortable with how to
interpret NAM MOS and GFS MOS, you'll be ready to tackle Laboratory Exercise.
G109 Weather and Climate Lab Manual
Lab 7-3
Name:
___________________
Lab Date & Time:_______________
Exercise 9: Weather Forecasting 100points
Exercise
You are given the NAM MOS (ETA MOS) and GFS MOS for St. Louis, MO (KSTL), from the
12Z runs on December 6, 2009
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G109 Weather and Climate Lab Manual
Lab 7-4
(a)
What were the high temperature forecasts from the GFS MOS and NAM MOS for
December 7 and December 8?
Provide a brief comparison. (5)
The highest temperature on December 7th on the GFS was 41degrees and on the NAM
MOS was also 41 degrees. On December 8
th
GFS said the highest temperature was at
9pm at 41 degrees and on the NAM MOS was also 41 degrees at 9pm. All the
temperatures where the same between the two graphs at the same time. There was no
difference.
(b)
What were the low temperature forecasts from the GFS MOS and NAM MOS for both
December 7 and December 8?
Provide a brief comparison. (5)
The lowest temperature on December 7
th
on NAM MOS graph was 29 degrees and on the
GFS graph it says the lowest temperature was 32 degrees. On December 8
th
on the NAM
MOS graph the lowest temperature was 30 degrees and on the GFS graph 28 degrees.
This time the lower temperatures were different between the two, but they all were pretty
close in range to each other.
(c)
What were the NAM MOS and GFS MOS predicted temperatures for 21Z on December
8? (5)
On the NAM graph the temperature was 41 degrees and on the GFS graph the
temperature was also 41 degrees.
(d)
What were the NAM MOS and GFS MOS predicted wind direction and wind speed for
00Z on December 9? Express wind direction in degrees. Proper units on wind speed are
a must!
Provide a brief comparison. (10)
On the NAM MOS graph the wind direction on December 9
th
was 100, 200 and 260
degrees and the speed were 11.5 mph and 17.2 mph. On the GFS graph, the wind
direction was 120, 150, and 280 degrees and the wind speed were 18.4 mph, 11.5 mph
and 25.3 mph. Between the two graphs the GFS graph had a higher wind speed and the
direction was more towards west. While the MOS graph highest speed was 17.2mph and
the wind was going between east and west.
G109 Weather and Climate Lab Manual
Lab 7-5
(e)
Give the time and date when the NAM MOS and GFS MOS predicted the lowest cloud
ceilings. At what altitude were the ceilings predicted to be? Proper units are a must. (5)
On the NAM graph the lowest cloud ceiling was 2( 200-400 feet) and on the GFS graph
the lowest cloud ceiling was 1 (< 200 feet.)
(f)
Referring to part (e), did the NAM MOS and/or the GFS MOS predict any obstructions
to visibility? If so, provide the specific obstruction to visibility. Please explain,
incorporating your answer in part (d) where it's appropriate. (10)
On the NAM graph it showed that there was HZ which is haze, smoke and dust. It also
showed that there was BR which is mist. On the GFS graph it only showed that there was
BR which is again mist.
Go to the following link:
http://weather.uwyo.edu/cities/usnorth.shtml
and select the weather
station that is labeled “BMG Bloomington/Monroe, Indiana.”
For consistency,
select
“American Units.”
(a)
Provide screenshots of your GFS MOS and NAM MOS results. (5)
G109 Weather and Climate Lab Manual
Lab 7-6
(b)
What are the high temperature forecasts from the GFS MOS and NAM MOS for the next
two days?
Please provide the day and time at which you accessed the models. Provide a
brief comparison. (5)
On the GFS graph it says that the highest temperature Is 62 degrees at 9 pm on November
3
rd
. On the NAM graph the highest temperature was 57 degrees at 9pm on Nov 3
rd
as well.
Between the two graphs they both had different high temperatures, but both were on the same
day at the same time
(c)
What are the low temperature forecasts from the GFS MOS and NAM MOS for the next
two days?
Provide a brief comparison. (10)
On the GFS graph the lowest temperature was 31 degrees at 12pm on November 2
nd
. On
the NAM graph the lowest temperature was 30 degrees at 6am and 9am on November
2
nd
. Between both graphs the both were on the same days but this time different
temperatures and different times.
(d)
What are the NAM MOS and GFS MOS predicted dewpoint temperatures for 00Z on for
the next two days? (10)
On the days of November 3
rd
and 4
th
the dew point for the GFS was 26 on November 3
rd
and 29 on November 4
th
. On the NAM the dew point was 25 on November 3
rd
and 31 on
November 4
th
.
(e)
What day and time are the dewpoint and surface temperature the closest? What does this
mean for the relative humidity of the air? (10)
On both the GFS graph and the NAM graph both the dewpoint temps and surface
temperatures we at the same day and time. On the GFS the surface temperature was 31
degrees and the dew point was 23 degrees. On the NAM graph the surface temperature
was 29 degrees and the dewpoint was 22 degrees. Both happening on November 2
nd
at
12pm. When this happens the air means that the air is being saturated.
(f)
What were the NAM MOS and GFS MOS predicted wind direction and wind speed for
00Z For the next two days? Express wind direction in both degrees. Proper units on wind
speed are a must!
Provide a brief comparison. (10)
over the next two days (November 3
rd
and 4
th
) the wind speed on November 3
rd
is 180
degrees going south at 4.3 MPH and on November 4
th
190 degrees also going south at 5.2
MPH all on the GFS graph. On the NAM graph on November 3
rd
the wind is 200 degrees
going south and little southwest at 5.2 MPH and on November 4
th
190 degrees south at
6.1 mph. between the two graphs both winds are going the same direction and around the
same speed.
(g) Based on this information and what you have learned in class. What would be your forecast
for Bloomington for the next two days? (Looking for a qualitative textual answer) (10)
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G109 Weather and Climate Lab Manual
Lab 7-7
Over the next two days (November 3
rd
and November 4
th
) the low temperature would be 40
degrees and the high would be 57 degrees. There will be no vision categorical forecast at the
hour so it would be sunny both days
. The wind for both days won’t be that bad as the highest
mph wind will be 6.1 mph and the lowest being 4.3 mph.