### Tips for Forecasting

#### Meteorology

- Station map plot info:
- Low cloud height in station plot: square the number x 100 =
height of cloud base in feet.
- Visibility code in station plot: for code numbers under 50, the
code is the visibility in 100's of meters (e.g. 30 = 3.0 km); for code
numbers between 50 and 80, subtract 50 from the number and this is the
visibility in km (e.g. 62 = 12 km). For numbers above 80, no one
really cares! (Table found by googling "navcanada visibility code")

- A 2 dm increase or decrease in the 1000-500 hPa thickness is
equivalent to warming or cooling by 1 C.
- An estimate of the temperature in F is 12 plus the last two
digits of the 1000-500 hPa thickness
- An estimate of the RH for RH values greater than 50% - for every
degree C in the dewpoint depression, the RH decreases by 5%:

RH = 100 - 5(T-Td)

where T, Td are Temp and Dewpoint in Celcius.
- Geostrophic Wind estimate: 5 times the number of hPa across a
distance of 4 degrees of longitude at the latitude of interest
measured perpendicular to the isobars.
- Isallobaric Wind estimate: same as Geostrophic above when applied
to 3 hour isallobars. This is correct at 43 N latitude and within 20%
plus or minus 10 degrees from 43 N latitude.
- speed in degrees latitude per 12h times 5 = speed in knots
- Marine stratus push on the inner south coast: look for gales
through Juan de Fuca the evening before as a precursor to stratus
forming/advecting just after sunrise. "In thick before 8:00, out after
2:00"
- Radar Beam Height versus horizontal range:
range \ angle (deg) |
0.5 |
1.5 |
3.5 |

20 km |
0.2 km |
0.6 km |
1.3 km |

40 km |
0.5 km |
1.2 km |
2.6 km |

60 km |
0.8 km |
1.8 km |
3.9 km |

80 km |
1.1 km |
2.5 km |
5.3 km |

100 km |
1.5 km |
3.2 km |
6.7 km |

snow forecasting in Vancouver: 500-1000 thickness less than 522
dam, and 850 mb temperature less than -6 C.

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