This page contains the text from the handout for the Forecasting the Weather Class that I teach. The pictures from the slides shown during
the class follow the text. Reference material that was used in preparing the text for the class appears near the bottom of the class text under tools
and on-line references.
The windvane above is mounted outside the house on a long pole. I made it a few years ago, for more information
on the metalworking see the Metal Working Page on this site.
This picture is of the sky when a very strong cold front passed through near home one afternoon this summer. The boundary between the weather system was quite dramatic and clearly visible in the sky. The temperature dropped about 20 degrees F in 30 minutes with the passage of the front.
I have also been working on some temperature data logging. It has enabled me to track the outdoor temperature for days at a time. It has allowed a close look over time of some sharp cold fronts that have passed through the area. More information on data logging can be found on this site at the Temperature Data Logging page.
See the links page on this website as well.
Introduction- Weather can be predicted to a degree by simple observation of the sky. This can be enhanced by keeping track of the barometric pressure. With a little effort in noticing what is going on in the sky and observing the trends, good predictions can be made. Comparing guesses against what is reported by the weather services is a way to help refine predictions. Knowledge of the climate itself, in general and the local effects helps to connect a person with the cycles of the earth and how they are coupled with the weather.
In the end all weather is caused by the sun ( also much of the energy we use came from the sun, think about it). Weather is modified by the earth's rotation, land masses, mountains, ocean current and ground temperatures.
Global air circulation-
The basic idea is that warm air rises and cold air falls. One
would expect that the warm air from the tropics would rise there and move
northward to fall back down at the poles. And the cold air at low altitudes
would go back toward the equator. This is the simple one cell (Hadley Cell) model.
that the earth is spinning adds yet another modification to this. The spinning
earth twists the movement of air from a north-south circulation to a prevailing
movement of easterlies and westerlies. For our temperate region a general
westerly flow prevails, for the
The earths spin also modifies the local wind
direction around high and low pressure systems. This is caused once again, by the Coriolis
Effect. It causes wind at high altitude to circulate clockwise around high pressure systems and
counterclockwise around low pressure systems. Near the ground wind direction is modified slightly
by the drag caused by the Earth's surface and other objects. It is modified in such a way that wind
points slightly away from the high pressure center and slightly towards the low pressure center.
Pressure Trends and Weather
High Pressure - Typically cooler, dryer, fair skies. Winds rotate clockwise around high pressure centers. Wind speed depends on how 'steep' the slope is between high and low. The air is sinking within areas of high pressure; causing it to be denser.
Approaching High - Bad weather breaking up. Pressure rising, winds shift to the North or Northwest. Cooler/ Drier.
Arrived High - Clear skies, possible fair weather puffy clouds. Low Humidity, calm winds. West if the High is to the south, east if to the north. Stable temperatures, cool nights, clear. Pressure High and stable. Contrails dissipate quickly during the day. Crisp stars and moon.
Leaving High - Warmer, winds shifting the South or Southeast. Warmest temperatures. High thin clouds make an appearance, contrails stay in the sky. Moon appears surrounded by a ring or blurry.
Low Pressure - Warmer, wetter. The air is generally rising within areas of low pressure. Winds rotate counterclockwise around low pressure centers. Wind speeds once again depend on steepness of pressure difference between high and low. Low pressure areas form between areas of high pressure and tend to form along weather fronts. Sometimes several of them will be located along a front that covers a large distance.
Approaching Low- Warmer, winds any where from NE to S, typically S or SE. Increasing is speed for a while then settling down. High clouds thickening, ground glass sky. Finally lowering and thickening to obscure sky.
Arrived Low- Calmer winds, rain starts lightly at first then steady.
Leaving Low- Spotty precipitation winds shift to the North or Northwest. Cooler/ Drier. Going back into approaching high.
The cycle of High to Low and back is approximately 5-7 days. This roughly coincides but is not related to the moons phases.
Fronts form along boundaries between weather systems of different temperature and humidity. Fronts separate two different types of weather.
The winds are generally going in different directions on each side of a frontal boundary. The following is a basic rundown of the most common fronts that occur in our area.
Cold Front - Cold air displaces warm by wedging underneath. This forces air higher and higher generating tall clouds associated with thunderstorms and snow squalls in the winter. The higher the altitude, the cooler the air is. More and more moisture that is present in the air condenses at high altitudes. Water and ice particles eventually can reach a size that will fall as precipitation.
In a thunderstorm a chimney effect causes more and more warm air to rise quickly, condensing rapidly, resulting in heavy precipitation. The cold front passage is marked with a line of energetic weather and gusty winds that shift direction as the front passes. In the more energetic systems hail can form as the back edge of the thunderstorm passes through a region. The temperature will also drop rapidly. Gusting winds will occur and change direction as the front passes.
Warm Front - It is more difficult for warm air to displace cold. It tends to ride up over the cooler air and it displaces it gradually over a period of days. The progressions of clouds signaling an approaching warm front are as follows. High thin stratus (layer) to thicker and lowering stratus from which precipitation finally falls. The initial approach of the warm front can be detected by observation of clouds. First high thin clouds and/or high herringbone (cumulo-stratus) clouds will appear, contrails will begin to stay in the sky. This is a sign of upper level moisture in the atmosphere. The clouds that follow will lower and thicken as the warm air displaces the cold air. The temperature will rise slowly and when the clouds cover the sky fully (nimbostratus) precipitation will fall.
Weak Fronts - A weak cold front may pass causing a slight drop in temperature, with some wind and clouds that move fast through the sky. This would normally end in clearing skies. Typically associated with high clouds. Very high clouds that are high enough exhibit curvature.
A weak warm front may produce days of cloudiness with no rain.
Stationary - Produces the same weather, good or bad for an extended period of time, sometimes days. The fronts stay put, therefore the weather stays the same.
Occluded - Cold fronts generally move faster than warm fronts. Therefore they can overrun a warm front. The cold front can drive itself under a warm front wedging it aloft. This forms a triple point where both fronts converge. Occluded fronts can occur in the vicinity of mature low pressure systems.
Sun angle and its effects - The position of the sun moves from the equator at the vernal equinox to 23.5 degrees North on the summer solstice back to the equator on the autumnal equinox, to 23.5 degrees South on the Winter solstice.
The noon peak sun angle in degrees is related as follows, assuming we are at 42 degrees North is as follows. Equinoxes, 90 - 42 = 48, Summer solstice 48 + 23.5 = 71.5 Winter Solstice 48 - 23.5 = 24.5. This coupled with the length of day at 9:05 hrs Winter Solstice, 12:11 at the Equinoxes, 15:15 at the Summer Solstice, gives the amount of solar energy reach the face of the earth.
The sun angle and length of day combine to influence heating of the earth, ocean and atmosphere. This heat is uneven from place to place and tends to make the air want to move around the earth as discussed earlier with reference to global air circulation.
Many times when the sun goes down the winds calm as the air is no longer driven by convective heating. At night the cool air tends to fall and will travel downhill, in the morning this trend reverses.
Inertia - Average temperatures lag the seasons by about 36 days. The lowest average temperature for the winter season here will occur Jan 27, 2007. The maximum average summer temperature will occur July 27, 2007. The maximum rate of change up will be Apr 25 and down will be Oct 29 respective to the equinoxes. This lag is due to the fact that the ground and water bodies retain heat and that the atmosphere being a giant ocean of air cannot respond immediately to changes either. On a daily basis there is a lag also, it warmer somewhat later in the afternoon rather than at noon when the solar radiation reach the earth is the most powerful. This lag is present in most large scale natural systems.
Average Temperatures (Deg F.) for
Seasons - The length of the seasons are not equal, 3/20-6/21 = 93 days, 6/21-9/23 = 94 days, 9/23 - 12/22 = 90 days, 12/22 - 3/20 = 89 days. This is due to the sun being further away in winter, peaking in distance at about January 5th. It takes it longer to cover the same distance in space over the winter, lengthening winter with respect to summer.
Using a computer program to obtain the rise and set time for Binghamton NY and Asheville NC, I derived the following chart. It compares the two locations and shows the difference in sun rise/set and length of day between them.
Asheville (82.57 deg W) lies West of Binghamton (75.75 deg W) So the day is shifted to favor the sun rising and setting later by an average 33 minutes. Clearly the greatest difference is near the Winter solstice where it sets almost an hour later. The length of day is not as short in Asheville as it is in Binghamton at the Winter solstice. Good news for solar heating and Seasonal Affective Disorder sufferers!
At the equinoxes, only Spring is shown, Fall would be identical, the length of day for both is nearly equal.
The data shows that at the Summer solstice there is little difference as well. In my mind I would have expected more spread in the rise/set times and length of day between the two cities in the summer as well, with Binghamton winning the day length competition. But the data reveals otherwise.
What matters for climate as well as the length of day is the solar angle which connects to the actual amount of solar radiation energy that reaches the surface of the earth and the atmosphere as discussed above.
Climate Regions on
the East Coast - The northeast is a humid continental region, south of NJ
and PA the region transitions into humid subtropical. The Appalachian Mountains
are high enough to still be a transition region all the way to
Temperate climates extend from the tropics of Cancer and Capricorn, north or south to the arctic circles experience the four seasons. Tropical regions experience a cooler dry "winter" and a warm hot wet "summer". Some tropical regions can have three levels, cool, hot, followed by wet.
Lake effects - After bad weather clears out in the winter, winds shift to the W/NW. The Great Lakes being warmer than the land and large bodies of water liberate significant moisture into the air. This condenses causing trails of clouds, think of smokestacks. The cloud trails cross this region, snow eventually falls from them as they cool and are driven over elevated land. As a typical one-two punch in the winter for our area is that, we get snow and just as it clears out, lake effect snow starts up for a period of days. Lake effect typically happens early in the winter before the lakes are not frozen. It also contributes to winter cloudiness. If the lakes were not there we would more clear days and less snow in the winter. Lake effect can cause confusion in weather prediction. The confusion is that the barometer is rising (fair weather) but it is cloudy, blowy and snowing.
Cloudiness - This area has the 2nd lowest rate of insolation
(amount of solar radiation reaching the earths surface), bad for solar heating!
The average amount of sun per day is 3.16 for
... which shows this off clearly. It has to do part with the prevailing westerly flow of air
across the lakes and the basin formed over the
during the spring and fall it is possible to go a short distance away from
42nd Parallel -
Folklore has is that the 42nd parallel separates different kinds of weather in
our region. This is the line between PA and NY nearby us. This roughly
correlates with the aforementioned perpetual cloudiness, lake effect possibly
also starting the trail off at this distance. Another factor is the river
changing direction at
There are actually two jet streams that form at very high altitudes. One of them,the Polar Jet Stream,rides
along the boundary between the Polar Cell and the Ferrel Cell.
The Polar cold front would lie below and to the South of it.
I have read somewhere( I can't remember where ) that the jet stream certain amount of loops in it; they have to be a whole number. Sometimes it will snap to a different number, repositioning where the loop lands in the continental US. This can lead to different weather patterns. I have noticed that sometimes weather changes will happen mid-season, so that you may get a hot/dry start of summer followed by cooler/wet or the other way around. This can happen in winter as well. I have not paid a lot of attention to what the jet stream was doing at those times. It is something I will have to look for in the future.
The following link shows graphical representations of the jet stream, both current and
forecast winds. The graphs are shaded to show wind speeds above 60KMH. There are also
graphs of the jet stream winds superimposed on satelite images.
I have observed a pattern.There is a distinct 2 year pattern; generally bad winters come 2 in a row. This might be related to the jet stream or El Nino/La Nina. Certain winter/summer patterns can couple in this way as well, extreme winter/summer, 2nd half of summer extreme, 1st half of winter extreme or just the opposite. I would like to know more about this myself, I am as always open to ideas.
Noreaster - A
coastal storm where the low pressure is off of the east coast of the
Floods - Floods are the biggest natural disaster threat in our area. Most deaths occur from floods in this area than from any other natural disaster. Floods can occur at any elevation when a quick heavy storm occurs. Culverts overflow and cause water to take paths that it normally would not. Flooding is compounded in poor drainage areas and when the ground is saturated.
Main stem and river flooding typically involves low lying flood plains. Rain over many days, snow melt and a saturated ground all set up the potential for this type of flooding.
Things to look for
If contrails stay in the sky there is upper level moisture forming. Precipitation will generally be arriving in 2-3 days. This will sometimes be followed by herringbone clouds and a ground glass look to the sun or moon which is further evidence of bad weather approaching.
If smoke from chimneys stays low and birds fly low, precipitation is approaching soon.
Winds from North to Southwest mean fair weather, South to Northeast fowl weather.
A clear night and fog in the morning generally mean a rain free day.
The air in front of a thunderstorm or an isolated heavy rain cloud is generally sinking and calm, when it starts to gust there is only a minute or two to take cover.
- Many models are available relatively inexpensively today. Digital ones
are available from many sources for under $100. Local sources include Radio
Cloud Identification and Weather Book
Cloud Chart 17 inches X 22 inches
Weather Radio & Warnings - Inexpensive ones can be bought that have programmable alerts. These alerts only sound when threatening weather is moving into your county. Some are built to trigger different levels of alert depending on the severity of the approaching weather.
Watch - Conditions are favorable for ________.
Warning - _______ is occurring, imminent or highly likely.
Advisory - Hazardous weather conditions are occurring, imminent or likely. Conditions will cause a significant inconvenience and if caution is not exercised...(Advisory is not as urgent as a warning.)
Short term map forecast for 0000 and 1200 UTC, 8AM and 8PM EDT.
Shows High & Low Pressures, precipitation, fronts and pressure isobars for continental US.
Good to use to compare reading the clouds against what is happening on the weather map.
Text based forecast for our zone.
Zone Forecast for
State Forecast for
Area Conditions for
Nearby Cities- Sky, weather conditions, temp, dew point, relative humidity, wind speed and direction, barometric pressure and remarks.
Climate data from the entire US.
One file is a PDF the others are the same data broken down by category in a text file format. The text files are suitable for import into spreadsheets.
Quick one page summaries with bar graphs for many cities.
Some further climate information, details these climates around the world.
This one has all of the symbols for the fronts.
Radar images of the
Severe Weather: Warning, Watches and Advisories Defined
Hazardous weather risks: repeated here
The various weather conditions described above have different levels of risk. The NWS uses a multi-tier system of weather statements to notify the public of threatening weather conditions. These statements are used in conjunction with specific weather phenomena to convey different levels of risk. In order of increasing risk, these statements are:
Outlook - A hazardous weather outlook is issued daily to indicate that a hazardous weather or hydrologic event may occur in the next several days. The outlook will include information about potential severe thunderstorms , heavy rain or flooding, winter weather, extremes of heat or cold, etc., that may develop over the next 7 days with an emphasis on the first 24 hours of the forecast. It is intended to provide information to those who need considerable lead time to prepare for the event.
Advisory - An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. Advisories are for less serious conditions than warnings, that cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life or property. NWS may activate weather spotters in areas effected by advisories to help them better track and analyze the event.
Watch - A watch is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location or timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so. A watch means that hazardous weather is possible. People should have a plan of action in case a storm threatens and they should listen for later information and possible warnings especially when planning travel or outdoor activities. NWS may activate weather spotters in areas affected by watches to help them better track and analyze the event.
Warning - A warning is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. A warning means weather conditions pose a threat to life or property. People in the path of the storm need to take protective action. NWS may activate weather spotters in areas effected by warnings to help them better track and analyze the event.
Weather Pictures for Class
The following are the NOAA weather forecasts of fronts pressure and weather, with a picture of the current weather outside at the time and
a picture taken of the barometer/thermometer placed on them.
Weather/Climate Data for Class
The image above shows the relationships between the Sun's position relative to the equator on a unit scale, the rate of change of the Sun's position (1st derivative) and the curve representing the daily average temperature for out area. The daily average temperature has a 'phase shift' of 36 days from the Sun's position relative to the equator.
The following images are screenshots of an MS Excel document that compares the climate across 12 months for 4 locations. The raw
data was obtained from the NCDC data files. A link to this directory appears on the links page of this web site. The data files contain
data by category such as Average Snowfall and so on, for some 102 locations across the US and its territories. I followed the categories
and naming conventions of those data files.
The links below are by category and compare the statistics graphically for 4 locations. They are as follows.
Series 1 - Dark Blue Line - Gainesville,FL - Near where my Mom lives. The warmest place I have visited.
Series 2 - Fuchsia Line - Binghamton,NY - Near where I currently live, and are familiar with since 1997.
Series 3 - Yellow Line - Islip,NY - Near where I grew up and familiar with.
Series 4 - Light Blue Line - Asheville,NC- I visited this city twice, it seems like a great place to live.
As an interesting sidenote, I composed the four city comparision 'study' above upon returning from Asheville, NC in April 2007.
I thought to myself, I would like a deeper look after viewing on-line the brief average temperature chart on CityRating.com.
Well I went on-line followed some links to the NCDC website and produced the Excel sheet comparing the four locations.
Sometime after I did this I went back to the NCDC site for a more in depth look, there are some good global warming studies going on there.
To my big surprise I found out that the NCDC is located in Asheville!
Original Build Date:11-02-2007
Last updated 11-07-2007