Weather Forecasting

Weather Forecasting
4 Major Methods;
1.) Climatogical – uses long-term averages, or climatic data.
2.) Persistence – assumes either current conditions will continue or trends in current
conditions will continue.
3.) Analog – assumes likes between current conditions and similar well-studied patterns
from past experience.
4.) Numerical – (latest approach) uses computer models to predict future events.
3 Types of Forecasting Methods; (RESULTS or PRODUCTS of FORECAST METHODS)
1.)
2.)
3.)

Quantitative – amount of a forecast variable is specified.
Qualitative – provides a categorical value for the predicted variable.
Probability – states the chance of an occurrence of a certain event.
Quality – agreement between forecast and observed weather.

Value – the usefulness of the forecast.
(WMO) – World Meteorological Organization
Numerical Three-Dimensional Models (Phases); - form basis
1.) Analysis Phase – observations are used to supply values for the variables used in the
models (i.e. the current conditions).
2.) Prediction Phase – The data supplied during analysis is then run through the models,
which supply the governing equations that describe atmospheric behavior.
3.) Post Processing – Forecasted conditions are represented at various regular time periods
or intervals on maps. Forecasts for secondary variables, called model output statistics
(MOS) are also produced.
4.) Final Forecasting – Weather forecasters then use the models to construct a single final
forecast, weighting each model according to its own particular strengths and weaknesses
in given situations as well adding guidance from other observations.


Medium-Range Forecasts (MRFs) - Forecasts that are for beyond 72 hours,
typically covering something like a week or two.

Long Range Forecasts - Forecasts that range from a week to the limits of technical
feasibility, which is usually a season or sometimes an entire year.
o Seasonal Outlooks -compare to normal conditions (above, below, near)
o Sea surface temperatures (SST) for up to a year in advance.
Ensemble Forecast – more than one forecast is made.
SURFACE MAPS
Large-scale features are easily interpreted from the surface maps, including relative wind
direction and speed, conditions favoring clear or cloudy skies, etc.
Station Models indicate current temperature, pressure, dew point, wind speed, wind direction,ect.
UPPER LEVEL MAPS
Produced by the NCEP (National Center for Environmental Prediction)
850 MB
700 MB
500 MB
300 & 200 MB
850 MB – Averages a little less than a mile (1.5 KM), Gradient Flow over sea level but
mountains could change wind role, 27oF in Summer, 16oF in Winter, 22oF in Spring/Fall, Warm &
Cold air convection may take place.
700 MB – Averages 2 miles (3 KM), Used to monitor short ripples in a Rossby Wave, Useful to
predict the movement of air mass thunderstorms.
500 MB – Averages 18,000 feet (5.6 KM), represents conditions in the middle atmosphere, Good
for showing Rossby Waves
300 & 200 MB – 300 MB = 9 KM while 200 MB = 12 KM, Shows areas of higher wind speeds
called “JET STREAKS”
TYPES of STATLLITE IMAGERY used in METEOROLOGY
1.) Visible Images – radiation of the electromagnetic spectrum.
2.) Infrared Images (IR) – difference in temp. results from emitted long wave radiation.
3.) Water Vapor Images – strong returns in RH above 50%.
Radar Images – transmitting radar waves and measuring
strength and speed of return of signal, covers 250 miles,
composite images by combining stations.
DOPPLER RADAR – track movements of weather phenomena.
CLIMATE CLASSIFICATION
Climate – long-term weather of a place, the expected conditions, the statistical properties of the
atmosphere for a given location.
Climatology – scientific study of climates. (attempts to simplify and understand the complex
natural systems of weather).
Koppen System
Developed by Vladimir Koppen between 1918-1936, later modified by Glen Trewarth (German
that worked for Russia) & others.
6 Major categories and many subdivisions (20ish)
Based on mean monthly values of ‘precipitation’ & ‘temperature’, which are keyed to major
plant boundaries.
(A) Tropical Humid;
(B) Dry;
(C) Mild Mid-latitude;
(D) Severe Mid-latitude;
(E) Polar;
(F) Highland;
Af, Am, Aw
Bwh, Bsh, Bwk, Bsk
Cfa, Cwa, Cwb, Cfb, Cfc, Csa, Csb
Dfa, Dfb, Dwa, Dwb, Dfc, Dfd, Dwc, Dwd
Et, Ef
H
TROPICAL CLIMATES
-Mean temperature of the coldest month is atleast 64oF
-Between the Tropics of Capricorn & Cancer
-Types;
- Tropical Wet
(Af)
- Tropical Monsoonal
(Am)
- Tropical Wet & Dry
(Aw)
(A)
TROPICAL WET (Af)
FUECHT/WET
-Driest month has a mean precipitation of atleast 2.4 inches.
-Found between 10oN – 10oS
-Relatively even monthly precipitation
-Temperature values yearly under a 5oF range change
-ITCZ dominates throughout the year
(Amazon Basin, Central America, Congo, Indonesia, Hawaii)
TROPICAL MONSOONAL (Am)
-Excessively heavy precipitation in some months, which makes
up for the months with less than 2.4 inches of precipitation.
-Commonly found in Coastal areas
-Seasonal reversals in wind make drastic precipitation changes.
- 4-6 month wet season
- Cherrapunji, India 1,000 inches in a year (6 months)
(India, Caribbean, western southeast Asia, Philippines, French Guyana)
TROPICAL WET & DRY (Aw)
-Winter dry period, driest month less than 2.4 inches mean
-Savanna vegetation, fire, drought is common
-Poleward margins of Tropics
-Moderate changes in temperature
(Southern Brazil, Southern Mexico, Surrounding the Congo,
Northern Australia & India)
DRY CLIMATES
(B)
-Potential evaporation exceeds precipitation, no temperature limitation
-Occupies 30% of land area on the Planet. (more than any other type)
-Types;
-Subtropical Desert
(Bwh)
-Subtropical Steppe
(Bsh)
-Mid-latitude Desert
(Bwk)
-Mid-latitude Steppe
(Bsk)
SUBTROPICAL DESERTS (Bwh)
HOT
-Less than 10 inches of precipitation a year
-Annual temperature 64oF or more
-Extensive dry climates in vast belts from the
Western sides of continents into the interiors
-Occur due to STH’s (discourages uplift & cloud formation)
-Libya = 136oF
(U.S. southwest/Mexico, Sahara, Saudi Arabia, Central Australia, Namibia)
SUBTROPICAL STEPPE (Bsh)
-Less than 20 inches of precipitation a year
-Annual temperature 64oF or more
-Transitional Subtropical desert / Tropical Wet
-Strong STH influence
-Rainshadow!
-Grasses / Shrubs
(Mexico, Surrounding Sahara, Central Asia, Surrounding Central Australia)
MIDLATITUDE DESERT (Bwk)
COLD
-Under 10 inches of precipitation a year
-Annual temperatures below 64oF
-Occur due to extreme distance from moisture (rainshadow)
-Prone to Snow
(Caspian/Ariel Sea area, Western China, Nevada/Arizona, Chile)
MIDLATITUDE STEPPE (Bsk)
-Under 20 inches a year/annual mean temperature below 64oF
-Marginal between mid-latitude deserts/humid climates
-Occurs because of distance to ocean (rainshadow)
-Short grasses, prairie grass
(New Mexico/Colorado/Wyoming/Montana,
Argentina, Mongolia/Kazakhstan, Turkey)
MILD MIDLATITUDE CLIMATES
-Mesothermal (middle/intermediate heat)
-One or more months below 64oF
-No month below 27oF average
-One month above 50oF
-Humid, Mild Winter temperatures, Summers harsh
-Types’
-Humid Subtropical
(Cfa,Cwa,Cwb)
-Mediterranean
(Csa,Csb)
-Marine West Coast
(Cfb,Cfc)
(C)
HUMID SUB-TROPICAL (Cfa) North America (Cwa) (Cwb) Asia – (Wet)
-East sides of continents in lower mid-latitudes
-Summers nearly Tropical (hot & humid)
-Warm ocean currents
-Winters very mild & dry (high pressure ‘Asia’)
-Broadleaf, deciduous, evergreen, tall grass prairie
-Types;
- Cfa - long hot summers (a), mild winters, all months moist (f)
- Cwa – long moist summers (a), mild dry winters (w)
- Cwb – long but not as moist or hot summers (b), mild dry winters (w)
Cfa = (U.S. southwest, eastern China, southern Brazil, eastern Australia)
Cwa= (Himalaya’s, Mid-China)
Cwb= (South Africa)
MEDITERRANEAN (Csa) (Csb)
-Dry summers / moist winters
-West coasts in lower mid-latitudes (maritime influence)
-Dry summers are result of STH blocking precipitation and
stifling uplift, while winter moisture occurs due to MLWC’s
on shore winds (westerlies)
-Types;
- Csa – mild moist winters, long hot dry summers (inland)
- Csb – mild moist winters, short warm dry summers (coast)
Csa= (California, Mediterranean)
Csb= (Cape Town, South Africa, Chile, California, Mediterranean)
MARINE WEST COAST (Cfb) (Cfc)
-Precipitation well distributed throughout the year
-Poleward from the Mediterranean
-Wet, humid, cool, temperature ranges are small (Mp air)
-May reach high amounts of rain (ocean controlled)
-Temperate rainforest (may have been cleared)
-Types;
- Cfb – short warm summers (b), mild winters, all months moist
- Cfc – short cool summers (c), mild winters, all months moist
Cfb= (New Zeland, U.S. Northwest, Eastern Australia, Southern Chile, Western Europe)
Cfc= (southern Alaska)
SEVERE MIDLATITUDE CLIMATES
(D)
-Microthermal (little heat) one or more months with mean temp. above 64oF
-Atleast one month lower than 50oF, coldest month mean 27oF
-Found only in NH in upper midlatitudes (40oN – 70oN)
-Strong continentality and large annual temperature ranges
-Very cold snowy winters (may be dry)
-Somewhat short summers that vary from cool to warm (long day’s but lower sun angles)
-Precipitation peaks in summer (MLWC’s in westerlies)
-Types;
-Humid Continental
(Dfa) (Dfb) (Dwa) (Dwb)
-Subarctic
(Dfc) ( Dfd) (Dwc) (Dwd)
HUMID CONTINENTAL (Dfa) (Dfb) (Dwa) (Dwb)
-Found on NE sides of NH continents (40oN – 55oN)
-Annual ranges of temperature are significant
-Precipitation between 20-40 inches, decreasing towards the west
-Deciduous forest (south), mixed with needle leaf (north),
tall grass prairie (west)
-Subtypes based on precipitation distribution
-Dfa – cold winters, hot summer (a), all months moist (f)
-Dfb – cold winters, warm summers (b), all months moist (f)
-Dwa – cold/dry winters (w), hot moist summers (a)
-Dwb – cold/dry winters (w), warm moist summers (b)
Dfa= (lower Northeast U.S., Romania)
Dfb= (upper Northeast U.S./Northern Plains, Southern Russia, Southern Scandinavia)
Dwa= (Northeast China)
Dwb= (Southeast Russia/Northeast China)
“EXAM” – Marquette = Dfb
SUBARTIC (Dfc) (Dfd) (Dwc) (Dwd)
-Occupies Northernmost mid-latitudes
-Cold snowy winters, short cool summers, vast annual temperatures
-Verkhoyansk, Russia = greatest temperature range 183oF
-Precipitation peaks in summer (cyclonic activity), winters dominated
By continental polar air masses (polar highs).
-Boreal Forest, Taiga, some deciduous larch forests (eastern Russia)
-Subtypes based on winter severity, summer temperatures, precipitation
Dfc - Very cold winters (c); short, cool summers; all months moist (f)
Dfd - Excessively cold winters (d); short, cool summer; all months moist (f)
Dwc - Very cold (c), dry winters (w); short, cool, and moist summers
Dwd - Excessively cold (d), dry winters (w); short, cool, and moist summers
Dfc= (Southern-Mid Canada, Mid Russia, Mid Scandinavia)
Dfd= (Mid-East Russia)
Dwc= (Southern-East Russia)
Dwd= (Northern-East Russia)
POLAR CLIMATES
-Arctic, warmest mean temperature month below 50oF
(E)
(NO TREES)
-Found in high latitudes in NH/SH 70o – Poleward
-Dry and extremely cold!
-Types;
- Tundra
(ET)
- Ice Cap
(EF)
TUNDRA (ET)
-Plant growth possible, one month above 32oF
-Low growing mosses, lichens, herbaceous plants
-Found in the NH more than the SH
-Harsh winters, short cool growing season, low sun angles
-Temperature ranges do not range much, land doesn’t heat up much
-Permafrost very common
(Northern Canada & Russia, Coastal Greenland, tip of South America)
ICE CAP (EF)
-Frozen, no plant life
-No month above 32oF
-Extremely brutal winters, very short summers
-Worlds maximum low temperature @ Vostok, Antarctica -129oF
-Extremely dry, Precipitation = Snow, doesn’t melt = Glaciers
-Dominated by polar highs & Katabatic Winds (Year Long)
(Greenland Ice Cap, Antarctica, Himalayas?)
HIGHLAND CLIMATES
(H)
-Governed by topography rather than precipitation & temperature
-Rapid changes in climates that occur over short horizontal distances in high elevation areas
-Decreasing temperatures with the increasing elevation
-Local modifications, due to slope angle & aspect
-Vertical changes eventually lead to alpine Tundra and Ice Cap conditions at the top
(Rocky Mountains, Andie Mountains, Alp’s, Himalaya’s,
Ethiopian Highlands, Indonesia Highlands)
CLIMATE CHANGE
Climate Change – the magnitude & timing of major climate changes in earth’s history.
-A change in any statistical property of the atmosphere;
-Temperature
-Precipitation
-Seasonality
-Annual Totals
-Year to year fluctuations
TIME SCALES of CLIMATIC CHANGE
-Millions of Years
-Hundreds of Thousands of Years
-Thousands of Years
-Hundreds of Years
-Tens of Years
Climate changes change from place to place (Spatial Scale), Changes do not occur everywhere in
the same manner. Tropical latitudes change ‘slower’ than polar latitudes.
CLIMATIC RESEARCH UNIT (CRU)
“EAST ANGLIA” United Kingdom
Russians hacked sent e-mails and discovered a conspiracy, collusion, exaggeration warming
data, illegal destruction of information, manipulation of data.
EARTH HISTORY
Divided into eras, periods, and epochs
-QUATERNARY PERIOD – (last 1.8 million years)
PLEISTOCENE & HOLOCENE EPOCHS
-PLEISTOCENE (last 1.8 million to 10-15 thousand years ago)
-Includes glacial & interglacial periods
-HOLOCENE (last 10-15 thousand years)
-Most recent interglacial period.
ICE AGES – Punctuated by relatively short periods of
colder climates. (Ice ages that lasted 10’s of millions of years)
-‘Seven’ major ice ages occurred over the last 2.3 billion years.
CURRENT ICE AGE
-Began 55 Million years ago
-Fully established about 5 million years
(Greenland/Antarctic)
-30 glacial/interglacial cycles occurred through Quaternary.
-Slow glacial buildup (100,000 years), followed by rapid
warming (10,000 years)
-Significant ice volume changes (TWO MAIN PULSES)
-ILLINOISAN GLACIATION (75,000 years ago)
-WISCONSINAN GLACIATION (20,000 years ago)
-Large amounts of ice cover in North America & Europe
-Sea levels drop ‘100 meters’, exposing areas of the
continental shelf. (‘Beringia’ (landbridge) formed
between North America & Asia)
PreIllinoian
-‘ISOSTATIC DEPRESSION’ – caused the land to sink because of heavy glaciers.
-‘DRIFTLESS AREA’ – area where no glaciers covered the Wisconsin River area.
(Western Wisconsin, Eastern Iowa, Southeastern Minnesota)
-The ‘Solutream’ (French People) could have been the ‘Clovis’ (Eastern Canada Indians)
They share archaeological data, maybe linking them by crossing the Atlantic during the
Wisconsinan Glaciation.
HOLOCENE EPOCH
-Began 15,000 years ago (10,000 for everywhere)
-RAPID WARMING
-Colder phase ‘Younger Dryas’ (13-12,000 years ago)
-The final glaciation of ‘Marquette Advance’ (10,000 years ago)
-‘Altithermal Period’ slightly warmer conditions (7-9,000 years ago)
-Only in Northern Hemisphere (Plains went to Lake Superior)
-‘Neoglacial Period’ slight cooling (5,000 years ago) (Great Lakes start forming)
- ‘Medieval Warm Period’ (AD 900 – 1200 ) (Norse Expansion)
-‘Little Ice Age’ (AD 1450-1850) (Western Europe Suffers)
L’anse Aux Meadow – area in ‘Newfoundland’ where
Norse people were discovered settling.
Last Century Trends Recognized
+ 1900 – 1936, temperatures were below climatic normal. (Tail end of the Little Ice Age)
+ 1936 – Late 1970’s, temperatures fluctuated above the normal, some years below normal
+ Late 1970’s – Present, mostly above normal temperatures
FACTORS INVOLVED IN CLIMATE CHANGE
-
Variations in Solar Output
Changes in Earth’s Orbit
Land Surface Changes
Variations in Atmospheric & Aerosol Composition
SOLAR OUTPUT
-Varies from 0.1 to 0.2% due to sunspot activity
-‘Sunspots’- cold regions on the solar photosphere
-Follows an 11 year cycle
-Increase in sunspots = Increase in solar output
-Synchronicity with the cycle
- Great Plain droughts every 22 years
- ‘Maunder Minimum’ – minimal sunspots = Little Ice age
- Nile River flows seem to fluctuate on an 11 year cycle
CHANGES IN EARTH’s ORBIT (Milankovitch Cycle)
-Three astronomical factors;
1.) Eccentricity – 100,000 year cycle, earth’s distance varies as much as 11% around the sun.
2.) Obliquity – 41,000 year cycle, tilt of earth’s axis varies from 22.1o – 24.5o
(influences the severity of seasons)
3.)Precession – 27,000 year old cycle, changes the direction of the earth’s axis.
(changes aphelion & perihelion)
Eccentricity
Obliquity
Precession
CHANGES IN LAND & SURFACE CHARACTERISTICS
-Plate Tectonics play a likely role (over long periods in time)
-‘Pangaea’ – Super Continent
-Mountain building (orogenesis)
-Alters Rossby wave configurations
-Human land use, deforestation, overgrazing by cattle
- Changes ‘albedo’ & ‘evapotranspiration rates’
CHANGES IN ATMOSPHERIC TURBIDITY
-Amount of suspended solid & liquid material in the air (aerosols)
-Affects transmission, absorption, and reflection
-Tropospheric Aerosols continue to reductions in surface heating
-Startosphereic Aerosols have a longer residence and acts to
decrease surface temperatures much longer
CHANGES IN RADIATION-ABSORBING GASES
(Carbon Dioxide, Methane, Nitrous Oxide, and CFCs)
-Anthropogenic contributions of CO2
-Since the mid-19th century, CO2 has increased exponentially
-Result of burning fossil fuels
-Over 5 billion tons of carbon in the atmosphere
-Troposphere warms through terrestrial radiation
-Exchange of CO2 between atmosphere and Ocean, CO2 is removed by marine organisms
FEEDBACK MECHANISMS
NEGATIVE FEEDBACK – feedback tends to inhibit further changes in the system.
(Self Regulating System)
POSITIVE FEEDBACK – feedback amplifies changes in the first variable.
(Snowballs, Domino Effect)
ICE ALBEDO FEEDBACK – climatic cooling may
cause ice surfaces (ice sheets & sea ice) to expand,
while warming causes them to contact.
-Expansion of ice = higher surface albedo
-Contraction of ice = decrease of surface albedo
EVAPORATION of WATER VAPOR
-If the climate warms, evaporation will occur, which adds
to more water vapor in the air.
-More water vapor to absorb terrestrial radiation, which
results in warmer temperatures.
-This leads to more evaporation and so on and so forth.
-This positive feedback mechanism is thought to contribute
about ‘half of the warming’ associated with increases in
greenhouse gases.
OCEAN – ATMOSPHERE INTERACTIONS
-Warming can raise sea levels through thermal expansion and melting glaciers
-Major changes in sea levels ‘5-30 meter rise’
-THERMOHALINE CIRCULATION – moves energy in deep ocean currents, also a parta of the
climate puzzle (millennial scale)
ATMOSPHERE BIOTA INTERACTIONS
-Climate determines vegetation, but vegetation influences climate
-Increases in CO2 may cause some plants to increase, which may decrease CO2
(Negative Feedback)
-May cause some plants to die
(Positive Feedback)
PALEOCLIMATE – clues used to reconstruct past climates.
PROXY INDICATORS – paleoclimate clues…..
-Relict landforms
-Paleoflora/Faunal Evidence
-Deep sea Cores, Ice Cores
-Ect.
REMNANT LANDFORMS CREATED UNDER PAST CLIAMATIC CONDITIONS
+Features associated with Ice & Water
-Glacial landforms (marks of passage/moving ice)
-Fluvial landforms (are evidence of flowing water)
-Paleolakes (are evidence of former bodies of water)
+Coral Reefs
-Formed in layers by colonies of coral in tropical near shore ocean waters
UPPER GREAT LAKES LAKE-LEVEL CHRONOLOGY
-High ice-marginal Algonquin levels (Lake Michigan/Lake Huron Basins)
-Chippewa/Stanley Lows (Lake Michigan/Lake Huron Basins) 10-9,000 years ago
-Ice-marginal Minong Highs (Lake Superior Basin, associated with the retreat of
Marquette Advance Ice) 9.5 thousand years ago
-Followed by Houghton Low, 8,000 thousand years ago
-Rising Lake Nipissing after 8,000 thousand years (all 3 lakes)
-Lake Nipissing maximum 4.5 thousand years ago, (one giant lake)
-Algoma High, 3,000 thousand years ago, later basins separate
-Post Algoma Highs 2.5, 2, 1.5, 1, 0.5 thousand years ago
PAST VEGETATION (PALEOFLORA)
Palgnology – (pollen) allows reconstructions of past vegetation communities
-Small cores are taken from ponds
-Radiocarbon dating of sediments
Dendroclimatology – (tree rings) uses the width of annual tree rings
as an indicator of temperate & precipitation.
-‘INCREMENT BORER’ – is used to extract cores.
REFLECTED or BURIED SOILS (PALEOSOLS)
-Soil development is heavily influenced by climate/vegetation
-Some soil types have strong correlations with certain
climatic conditions/vegetation communities
-‘Spodosols’ – cool, humid climates, acidic vegetation (Marquette)
-‘Mollisols’ – semi-arid, sub-humid, grassland vegetation
-‘Histosols’ – very wet, saturated conditions, wetland plants
-Soils become buried & preserved in stratigraphic sequences, allowing researchers a glimpse of
past conditions. (Pictured Rocks –Grand Sable Dunes & Yellow Dog Basin)
OCEAN DEPOSITS
-Deep sea cores taken from the bottom of the ocean
-Layers of sediments, primarily calcium carbonate (CaCO3) from once living material,
Are analyzed for oxygen isotope ratio (016 and 018)
-High ratios of 018 to 016 means more evaporation, losses of water from the oceans,
glaciation coverages.
ICE CORES
-Deep ice cores from Greenland, Antarctica, and Alpine Glaciers allow climate reconstruction.
-Water in the cores examined for oxygen isotope ratios
-Provides information on atmosphere chemistry & volcanic eruptions from trapped air bubbles.
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