----- Original Message ----- 
From: "Janet Millenson" <>
To: "Ed Boyd" <>
Sent: Wednesday, April 09, 2008 10:24 AM
Subject: Re: [MDOSPREY] Weather questions about BWI


> Ed,
>
> Thanks for providing links to these phone numbers. As you say, it's useful
> to be able to get weather info for other parts of the state when you don't
> have access to the internet. However, after calling two of the numbers, I
> realized that the units used can be confusing to those of us who aren't
> pilots.
>
> Converting Celsius to Fahrenheit is easy enough, and I understand that the
> altimeter number represents current barometric pressure at ground level. 
> But
> when the Hagerstown recording says the wind is "one eight zero at zero
> seven" -- does that mean 18 mph? From what direction? Going to the
> Hagerstown ASOS website, I don't see any windspeed readings over 8 mph.
>
> I'd be grateful if you could explain how to interpret this information.
>
> -Janet Millenson
> 
>

Ah yes, translations for those that don't speak the language. As someone 
that has been doing this for more than 26 years, I forget that this can be 
confusing to those that aren't in the aviation field. Sorry about that.

The weather will be reported in Greenwich time (Zulu time) EVERYWHERE. 
You'll need to know the time zones that you are in to translate the actual 
time, but for MD Greenwich is 4 hours later during daylight savings time and 
5 hours during standard time (1100Z is 07:00 a.m. local right now). Time is 
reported via the military clock in 24-hour format. After noon subtract 12 
from the time to get the p.m. time (1700Z = 5:00 p.m.).

When ceilings are reported as clear, that pretty obvious, scattered layers 
means the cloud obscure less than 50% of the sky, a broken layer means that 
the breaks in the clouds are less than 50% of the sky or the clouds block 
more than 50% of the sky, an overcast layer means the sky is completely 
overcst with no sun breaking through. Visibility will be reported in Statute 
miles (1 mile = 5280 feet). Below 3 miles it will be reported using 
fractions of miles will smaller fractions being used at lower visibilities. 
The obscurations (what is reducing the visibility) will be reported in the 
order of relavance, with any precipitation being reported first. If there is 
more than one type of precipitation listed, it will be in the order of most 
prevelent. If snow is changing to rain, it will list snow then rain. As the 
transition goes farther and rain becomes the more common precipitiation, 
rain will be listed first, then snow.

The temperature is reported in celcius. 0 celcius is equal to 32 fehrenheit 
(the temperature at which water freezes). To convert it, take the celcius 
temperature (let's say 20), double it (20x2=40), subtract 10% 
(40-10%[4]=36), then add 32 (36+32=68). This works when the temperature in 
below 32 (0 celcius) as well. (-4 x 2 = -8, -10%[+.8]= -7.2 + 32 = -24.8). 
Too complicated? Use the chart at the bottom of this email.

Wind is reported via the 360 degree compass in 10 degree increments and the 
speed is in knots (Nautical miles - 6000 feet to a nautical mile). 360 is 
due north, 090 is due east, 180 is due south and 270 is due west. Thus, 
040-050 is northeast, 130-140 is southeast, 220-230 is southwest and 310-320 
is northwest. A wind of 180 at 08 means the winds are out of the south at 8 
knots. Knots are roughly 1.15 times MPH. So 8 knots equates out to about 9 
MPH, 15 knots equalt 17 MPH, 35 knots = 40 MPH, etc.

The rest of the observation will contain any remarks like towering cumulous 
(developing thunderstorms) and the direction, lighting in the area and the 
direction, lower/higher quadrants of visibility that differ from the 
reported, etc. you'll mostly be interested in the sky conditions, 
visibility, temperature and wind.

For anyone that hasn't had enough already, you can find pretty much 
everything that you wanted to know about reading a weather observation 
(METAR) here:

http://www.wikihow.com/Read-an-Aviation-Routine-Weather-Report-(METAR)

For an easy celcius to fehrenheit chart, click here.

http://www.ncdc.noaa.gov/oa/climate/conversion/tempconvert.html

Here's a chart to convert knots to miles-per-hour:

http://www.disastercenter.com/convert.htm

That's you weather lesson for the day.

Good birding,

Ed Boyd
Westminster, MD