Weather Forecasting

Dr. Adel Awad

What is synoptic Meteorology?

Historical Background

The adjective synoptic comes from the

Greek word synoptikos , meaning “

affording a general view of a whole”

Synoptic in context refers to horizontal

dimensions and length of time of

atmospheric phenomena ; such as

Extra-tropical cyclones and Anti-cyclones,

Troughs and Ridges and extent to Frontal

zones and Jets.

Horizontal-length scales and time scales for the following

atmospheric phenomena: A, dust devils; B, tornadoes and

waterspouts; C, cumulus clouds; D, downbursts; E, gust fronts; F,

meso-cyclones; G, thunderstorms; H sea/land/lake breezes,

mountain-valley circulations, and meso-highs and meso-lows; I,

precipitation bands; J, coastal fronts; K, meso-scale convective

systems; L, the low-level jets; M, dryline; N, “bombs” and

tropical cyclone; O, upper level jet; P, surface fronts; Q, extra-

tropical cyclones and anti-cyclones; and R, troughs and ridges in

the barclinic westerlies.

Classification of atmospheric phenomena

The atmospheric phenomena classified

by two factors, their horizontal dimensions

and time scales.

Time scale means; the time it takes air

to travel completely across the feature.

For example; an intense extra-tropical

cyclone may form over a 1-2 day period, not in 3

hours, 10 minutes or a month.

There are several common

classification schemes for phenomena:

Isidoro Orlanski sub-divides phenomena

according to the order of magnitude of the

horizontal extent of each phenomena, using

Greek letters and the prefixes ;

“micro” , “ meso “ , and “ macro “

Ted Fujita sub-divides phenomena

according to the order of magnitude of the

horizontal extent of each phenomena relative

to the circumference of the earth at the

equator.

The width of synotic-scale features such

as: troughs ( R ) and ridges ( R ) in the

baroclinic westerlies and large extra-tropical

cyclones ( Q ) and anticyclones ( Q ) is much

grater than their depth;

the Dynamics of these features is

Hydrostatic.

Although Fronts ( P ) and Jets ( L )

associated with the synoptic scale features

are as long as the Troughs ( R ) and Ridges

( R ) in the baroclinic westerlies and have

similar time scales , they are much narrower.

Intense Oceanic extra-tropical cyclones,

tropical cyclones ( N ) , meso-scale convective

systems ( MCSs) ( K ) , drylines ( M ) , and the low-

level jet ( L ) are of sub-synoptic scale.

With the exception of squall lines, sub-synoptic

scale features are Hydrostatic, but with horizontal

scale and time scale slight shorter than synoptic

phenomena.

Meso-scale features include the

following: coastal fronts ( J ) , outflow

boundaries ( J ), precipitation bands in extra-

tropical cyclones ( I ) , gravity waves ( H ) ,

sea/land/lake breeze fronts ( H ) , mountain-

valley circulations ( H ) , meso-highs ( H ) , and

meso-lows ( H ) .

Meso-scale features have time scales

roughly identical the period of a pendulum day,

and horizontal dimension less than the sub-

synoptic scale phenomena.

Precipitation bands ( J ) and dry-lines ( M ) ,

which are deeper, are not hydrostatic, while the

other meso-scale features are.

Thunderstorms ( G ) , meso-cyclones ( F )

, gust fronts ( E ) and large downbursts ( D )

are storm scale, they have horizontal

dimensions on the order of convective storms

and time scales larger than that of the Brunt-

vaisala period, N-1 ( usually around minutes).

cumulus clouds ( C ) , tornadoes ( B ) ,

and waterspouts ( B ) are sub-storm scale.

They are contained within the area bounded by

convective storms.

Their time scale range from 10 minutes to

nearly an hour.

These features are markedly non-hydrostatic.

finally, sub-vortices within tornadoes ( B )

and waterspouts ( B ) and dust devils ( A ) are

micro-scale.

They are markedly non-hydrostatic , and have

time scales on the order of the typical Brunt-

vaisala period and horizontal dimensions

smaller than these of the sub-storm scale.

In summery, meteorological features

occur over a wide range of space and time

scales.

It is interesting that phenomena having long

space scales have long time scales, and vies

versa, with ration between horizontal space and

time scale is roughly of the same order of

magnitude for all features ( i,.e. 10 ms-1)

As a postscript we note that, if a

feature’s width is much greater than its

depth it is Hydrostatic.