LAB 1: Association Forecast Method
Name:
FALL 2010
1. In this lab we will use the ASSOCIATION technique to make a 12-hr forecast of
where it will be precipitating. The forecast is valid at 06Z Dec. 9th and we will use
the 700mb RH and 700mb Omega products to assist us in our endeavor.
a. Before we embark on our journey, begin by drawing any synoptic-scale
fronts onto the 1000-500mb/SLP panel of Fig. 1 valid at 18Z Dec. 8th
Fig.1 -> http://www.meteo.psu.edu/~jps33/m415/1207f30.gif
b. On the lower right panel of Fig. 1, trace the 700mb Omega -2 ubs-1 isoline
(only over the contiguous U.S.)
c. Re-trace your isoline from 1b. onto the 700mb RH panel of Fig. 1
d. Re-trace onto the observed precipitation of Fig. 2 the intersection of where
both the 700mb Omega is < -2 ubs-1 and the 700mb RH is > 90%.
Fig.2 ->
http://www.meteo.psu.edu/~jps33/m415/rad2007120818.gif
e. How well does the observed precipitation correlate to this intersection?
Circle below:
VERY WELL
WELL
SO-SO
POOR
f. Explain why there is a relationship between where it is precipitating and
what the 700mb omega and RH values are at the location of precipitation.
.
g. What might be a reason why this relationship (as shown in question 1e.)
may not be perfect? Explain.
.
h. Based on the relationship/matching-up of the 700mb RH/Omega fields and
observed precipitation from Question 1d., we will make a prediction of
where it will be precipitating at 06Z December 9th. Go ahead and make
your wonderful prediction by outlining (in green on the 1000-500mb thk/slp
panel of Fig. 3) where you think it will be precipitating.
Fig.3 -> http://www.meteo.psu.edu/~jps33/m415/20071207f42.gif
i. Shade in red where you think the precipitation is freezing rain (FZRA) or
ice pellets (PE); and shade in blue where you think the precipitation is snow.
2. In this question we will make a max temperature forecast for UNV on Sep. 17,
2008 using two techniques.
a. First, let’s try the 850mb skew-T method. Using the WRF sounding valid at
12z on Sep. 17 (Fig. 4), locate the 850mb temperature on the sounding and
go down the dry adiabat to the surface (assume the surface is 1000mb).
Fig4-> http://www.meteo.psu.edu/~jps33/m415/sounding091700z12hr.png
Your 850mb “down dry” prediction:
.
b. Do you think that this method will work well? At what times of year would
the method tend to underestimate the max temp and at what times of year
would it tend to overestimate the max temp? Explain:
.
3. Using the same skew-T, what would you expect the approximate peak wind gusts to
be at UNV on this day and from what direction?
4. In this problem we will use the “delta method” to make a temperature and
maximum wind speed forecast for Sep. 19th of 2009 using the NAM tabular
guidance for UNV and actual UNV observations. (Figs. 5, 6)
Fig5-> http://www.meteo.psu.edu/~miner/m415/unvnam2009SEP18.txt
Fig6-> http://www.meteo.psu.edu/~miner/m415/unvobsSEP18.txt
a. Predict the maximum temperature at u-park airport on Sat. Sep. 19th using
the “delta method”.
i. Highest NAM 2m temp (F) at UNV from previous day [12Z 9/18 to
00Z 9/19] (Fig.5)
ii. Highest NAM 2m temp (F) at UNV from 12Z 9/19 to 00Z 9/20
(Fig. 5)
iii Calculate Delta (temp difference from above 2 values)
iv Find the highest hourly temp observed temp (F) at UNV on the 18th
using the observations from Fig. 6:
iii. Based on the above answers, your delta temp forecast:
iv. Now determine how well this technique actually worked by looking
at the hourly UNV obs from the 19th (Fig. 6). What was the actual
highest hourly temp on the 19th?
v. By how many degrees was the forecast off?
vi. In what type of situations would this max temp forecast technique
tend to work best?
b. Predict the highest hourly sustained wind at u-park during the day of Sep.
19th using the “delta method”.
i. Highest NAM 10m wind at UNV from previous day [12Z 9/18 to
00Z 9/19] (Fig.5)
ii. Highest NAM 10m wind at UNV from 12Z 9/19 to 00Z 9/20
(Fig. 5)
iii Calculate Delta (10m-wind diff. from above 2 values)
iv Find the highest hourly sustained wind speed (not gust!) at UNV on
the 18th using the observations from Fig. 6:
iii. Based on the above answers, your max sustained wind forecast:
iv. Now determine how well this technique actually worked by looking
at the hourly UNV obs from the 19th (Fig. 6). What was the actual
highest hourly sustained wind on the 19th?
v. By how many knots was the forecast off?
vi. In what type of situations would this wind forecast technique tend to
work best?