Download The most cammon way in which air cools to form clouds is in th e

The most cammon way in which air cools to form clouds is in the upward
movement of a stream of air. It is at this point that the variation of
temperature with height becomes so linportunt. Consider two cuses, the first
when temperature falls off slowly with height, say 20F per 1000 feet, and
the second when temperaturG falls off rapidly with height, say 6 or 70F per
1000 feet.
In the first case any upward moving current of dry air will cool
by expansion at 5.40F per 1000feet coming into contact with air progressively
warmer than the upward moving current. As the current of cold air will have
a greater density than the surrounding warm air there is a general force to
stop the cold air from rising and eventually to force it to sink back earthward. This condition, when the decrease of temperature with height is small
and all vertical currents dampened, is known as atmospheric stability.
The opposite, or atmospheric instability results when the decrease
of temperature with height in the atmosphere is rapid. Any upward moving
current of dry air cooling at 5.4~ per 1000 feet will be surrounded by
progressively colder air and the current being warmer and less dense will
accelerate its upward motion. If the air is cooled beyond the dew point the
latent heat of condensation is added and the instability increased.
Coming back to the original point, that clouds form most frequently
by the cooling of air in rising currents, it becomes obvious that unstable air
will always favor bad weather and stable air good weather.
Thunderstorms are caused by the release of energy in the atmosphere
which exists under conditions of extreme instability. There are two types
of thunderstorms, first those set off by frontal activity when warm unstable
air is forced aloft by lifting over cold air, and second, those set off by
connective activity within an air mass.
The frontal thunderstorms tend to be general along the line of a
front, whether warm, cold or occlusion front. General cloudiness with
extensive rain and occasionally hail accompany these thunderstorms.
A cold front may have an almost solid line of thunderstorms along its length,
and these will move along with the front. Warm front thunderstorms extend
over a large area ahead of the front. Usually the storms are at high levels
and heavy rain and sheet lighting occur. Occlusion fronts cause infrequent
thunderstorms in generally rainy conditions.
Frontal thunderstorms occur ar intervals along the coast throughout the year but are seldom a fire hazard as the accompaning precipitation
usually is heavy. The thunderstorms may persist as the fronts move eastward
over the province but mainly they die out at the orest of the coastal range.
Air mass thunderstorms are the fire setters. They occur most
frequently over the southern interior becoming less frequent over the
northern interior and rare along the coast. They form in hot, dry, summer
weather when the air aloft is cool and moist. During the afternoons the
surface heating sets off the storms which may last till after sundmln but
rarely after midnight. Their motion is erratic but tends to follow the speed
tind direction of the winds at ten thousand feet.
The individual storms are not large, in fact seldom more than a few miles in
diameter, and they may move as far as 60 to 80 miles before dissipating.
They do vary in concentration over a given area but are most numerous when
instability and surface heating are extreme.
Air mass thunderstorms give showers of rain or hail of variable
intensity depending on the density of the clouds, on the strength and
distribution of the rising currents of air, and on the dryness of the air in
the layer next to the earth. The rising currents may be so strong and
persistan~ that the rain is accumulated in the central portion of the cloud
for the considerable time during which little or no rain reaches the ground.
When the rising currents do break down the resulting rain may be so heavy as
to warrant the name of Ilcloud burst". In the case when the air in the lower
levels is very dry a considerable amount of rain will evaporate into the air
through which it is falling. The precipitation from anyone storm may vary
between the limits of no rain to rain of cloud burst proportions. The
deciding factors will be the height, size and intensity of the storm, the
dryness of the air in the lm1er levels, and the air currents within the
thunderstorm cloud. However, even so-called Ildrythunderstorms" must have
rain drops present to generate the necessary static electric charges.
Hail frequently forms in the more intense thunderstorms when the
rising currents are strong enough to sweep falling rain drops back upwards
above the freezing level. The frozen droplets or hailstones so formed may
fall into the lower portion of the cloud and then be swept up again
becoming progressively larger.
Thunderstorms need the following factors for their development:
1. A layer of air at least six thousand feet thick with a lapse rate in
excess of 4 degrees F. per thousand feet.
2. The air must contain an adequate supply of moisture for heavy cloud
formation.
3. The winds aloft must not be too strong, othenvise the central core of
the thunderstorm cloud will be broken.
4. The realization of the potential energy within the layer of unstable
air, leading to the development of a thunderstorm, must be started by lifting
at a front or by radiational convection.
1. Unstable moist air is started off as a rising current and commences to
cool by expansion, eventually reaching the dew point. The cloud base forms
and the current of saturated air will continue to rise at an increased
rate with the development of a towering cloud.
2. Once the cloud is sufficiently dense the cloud droplets will group
together to form rain drops, which will then commence to fall as rain through
the rising air currents. If the air currents have an upward velocity greater
than 25 feet per second they will strip th~ outer layer charged with negative
static electricity from the rain drops, carrying this cha~ge to the top
portion of the cloud. The bottom portion of the'cloud will be left with a
positive static charge,which in turn will induce a negative static charge
in the earth below.
At this point electrical discharges may occur between the top and bottom
of the same cloud giving rise to sheet lightni~g; or between cloud and
ground or cloud to cloud giving rise to chain lightning. Both are fundementally the same.
3. The flashes of lightning will stike between the maximum negative and
positive potentials of static electricity along the line of least electrical
resistance once the pent up forces become sufficiently large to overcome the
resistance of the air. Strikes tend to take the shortest possible distance
between concentrations of opposite charges. The intensity of the flashes
will vary with the build up of the static charges and will be least when the
flashes are short and greatest when the flashes are long.
4. Thunder is the audible wave set up by the rapid expansion of the violently
heated air along the length of the flash. The sound wave travels roughly one
mile in five seconds which is useful when estimating the approximate distance
from the observer to the lightning strikes.
British Col~nbia situated between the 49th and 60th degrees of
latitude and facing westward on the Pacific Ocean has a maritime climate
along its entire coastline. Inland the weather is conditioned by high north
and south mountain ranges. Only in the northeast corner of the province
adjacent to the Peace River Block is the climate continental in nature.
The mild temperatures along the coast are due to the moderating
influence of the air blowing in from over the ocean. Both the annual
variation between winter and summer and the daily variation bet~een night
and day are kept to a minimum.
East of the coast range the effect of the sea becomes less apparent and the summer temperatures soar. Fortunately the winter temperatures
seldom fall drastically as the l~fty Rockies ~vard off the really cold air
of northern Canada and the prairies allowing the moderate ocean air to reach
inland. Occasionally, though, the cold air musses from the north build
sufficiently to pass over the Rockies, then the northern portion of the
province becomes gripped in really cold weather. Intense polar high pressure
systems may send the cold air as far south as Seattle and Victoria with cold
clear weather general over the entire region. Such polar outbreaks seldom
reach the coast more than once or twice each winter.
Rainfall is due mainly to frequent cyclones or low pressure
systems which move onshore from over the Pacific. These lows supply a warm
moist flow of air from the south and the lifting effect of convergence in
the frontal lows and ascendance over the mountains along the coast preeipitates much of the available moisture on the Coast Range. As the air moves
inland it tends to subside and warm by compression with a corresponding fall
in relative humidity. The result is that the rainfall slackens sharply as
the air from the Pacific moves into and over the main north and south valleys
of the interior often resulting in near arid conditions. When the Pacific
air encounters other main ranges such as the Selkirks and Rockies the air is
again forced aloft with further loss of moisture in the form of rain or snow.
This accounts for the extensive wet belts found on the western slopes and
tops of the interior mountain chains. A further small amount of rain is
supplied by the shower activity of convective clouds.
This type of precipitation is erratic in nature with a maximum incidence over
the mountains.
The annual distribution of rain and snow is dependent on the
passage of the cyclones. These are most common in winter often two or
three per week becoming less common in fall and spring usually one or more
per week and generally rare in summer.
During the summer months a large semi-permanent high pressure
system known as the Pacific high moves northward over the coast of Washington,
Oregon and British Columbia, effectively blocking the path of moving lows.
A similiar condition occurs occasionally during the winter months when a
polar high pressure system moves southward over the Province giving periods
of clear cold weather of up to three weeks in duration.
Prevailing winds along the coast tend to blow either fram the
southeast or northwest. Approaching lmv pressure systems give the southeast winds which turn to intense gales when the lows are active storm
centers. The other common situation is when a high pressure system moves
over the Gulf of Alaska. At such times the winds will blow from the northwest quite strongly, usually with clear, cool weather associated.
In the interior prevailing winds are southerly in the main
valleys during the winter as frontal lows move inland but change to northerly
when cold air moves southward over the province. Summer winds in general
are light and variable with erratic winds near the mountains due to uneven
surface heating and cooling.
Strong local winds blow up or down the main valleys connecting the
coast and the interior when the barometric pressures vary markedly. The
air then funnels from the high to the low pressure area.
In general the winds over the entire province tend to have many
local peculiarities always associated with mountainous country. The air has
few chances to flow in accordance with baromertric pattenns and follows the
line of least resistance which is normally up or down the steep valleys.
Air that lies stagnant for some time over the surface of the
earth will absorb the properties of the underlying surface and spread these
properties upwards. At the s~e time a general increase in pressure takes
place till there exists a well developed anticyclone or high pressure system.
These processes happen more readily in certain areas and the air masses
mainly come from so-called source regions.
Northern Canada and the Pacific Ocean are the source regions of
the air masses which influence British Columbia. The air which forms over
northern Canada is known as Polar Continental air. It has the property of
being exceedingly cold and dry in winter and cool and dry in summer. This
air causes extended cold periods in the Peace River Block and over the
northern portion of the Province during the winter. Large outbreaks
occasionally cross the Rockies moving as far south as the Cariboo, and on
rare occasions wven the coast range may be crossed, with general cold,
clear weather over the entire Province.
The Pacific Ocean provides the bulk of the air masses which affect
the coast and central and southern portions of the Province. This type of
air is known as Polar Maritime Air and is subject to very large variations
in temperature and humidity depending over which portion of the ocean the
air has passed. Polar maritime air in winter invariably has s surface
temperature somewhat above the freezing point. The decfease of temperature
with height is rapid if the air comes from the northwest and less rapid if
from the west or southwest. Humidity is always high in the lower levels and
moderatley high aloft. In summer the surface t~aperature remains relatively
cool with moist air in the lower levels. Frequently there is a marked
inversion in the lower few thousand feet with moderately warm dry air aloft.
When two anticyclones fram different regions come together in
their movements over the earth, there will exist between the biO a well
marked surface of discontinuity called a front; and characterized by a
contrast in temperature and humidity associated with a change in wind
direction. The greater the difference in temperature, humidity and winds,
the more marked will be the front.
At first the front may lie in a straight line as depicted below,
with a minimum amount of weather associated.
wind
~
warm air
At some point along the front an indentation into the cold air,
linked with a rapid fall in pressure, developes. The winds no longer flow
parallel to the front but swing in towards the front.
cold air
/ ,._-
~
wind
,
The process of barometric deepening continues with the winds
conforming into a sharp anti-clock wise circulation. The front, now hinged,
at the center of low pressure, has one portion moving northward into the
cold air and another portion moving southward into the warm air.
wo,().
f/~t1
tJf Ct'nley- (£ NE)
c) O~/;7;:~
Cold
All"
Cr;/t;!
of
A
II
"rti?!
"Arm
yA/;!7
.
jll/q
v I'll
A If"-
,411"
,A
These are the warm and cold front with weather and cold front
with weather as shmvn on the cross section.
</;-
/51
/ t)
r
~
\ '
ff~~
/
Sr
t/
(
S
-
1//.
II/.=;//;r
I
1
-
II;::
-
~tJ"Y
/
_/~
__
,-J-y-
RA
0,~~
_·__'
__
-_.
.s h 0"'/ II
I
(>"
r
1/ / ~ III::::: 111-=/1/
t
In
: 1// :::./ / /.:: 1//
-.
-
••••
-
_
=- / /
I ::
t
.o~
700
IdtJo
/;1. ~()()
The next stage cames when the cold front (travelling at a rate
usually twice that of the warm front) ca.tches up to the warm front and
begins to out under it. This produces yet another front kno~vn as an
occlusion.
~
;"0
7d~
centre
~p~~_
'\-
Co
u-
~d
New
tow
~
.~
?
WYW
4YYYl
Cl!ntt-y
()f
IJ~ Vt!-/lII/?j
q;h,
rJ-()~
7-
.;n
Alr~
Croes section BB through as occlusion.
207
T
~/
1S
ItYT
.5
r
t ~I J A, r
11I"i:111~ III
,
.;? a I "'.
=-11Ii:"IIF=IIJ-;:::/II=III:-II/=-
•
I
I
ltJO
IfIJ()
~()O
/I/~I//=III
I
7()()
/I()()
The f1nal process is for the occlusion to disintegrate into a
whirl ot cold air in the lower levels with warm air trapped aloft. A
maximUlllamount or mixing, see back of last page,has resulted and a new
center wi11 form at the ~unction of the Warm and cold fronts in a further
effort to neutralize the temperature difference bet~een the wurm and cold
air.
1;
CoLd
AIY
The semi-permanent Pacific anticyclone, ~hich lies off the coast
of California during the winter, moves northward over the coast of Oregon,
Washington, and British Columbia during the summer. This high pressure
system acts as an effective barrier to the majority of low pressure
systems moving across the Pacific deflecting them northeastward towards the
Panhandle and southern Alaska. The southern high frequently ~inks forces
with a weaker high pressure over northern Canada and the whole Province
eomes under the influence of a ridge of high pressure whose axis lies northeast - southwest slightly off the coast of Vancouver Island.
The air aloft in the antict-c1one has a definite tendency to
subside earthward. This subsidence is accompanied by warming by compression
at the rate of 5.4 degrees F per 1000 feet of earthward movement. As the
temperature of the air rises there"is a oorresponding lowering of the
relative humidity. Under these influences the air aloft is warm and dry
with general fine weather.
In the interior of the Province the surface heating during the
day often is so intense that an abnormally high lapse rate is set up in the
lower levels of the atmosphere leading to widespread shower or thunderstorm
activity.
On the coast the surface heating is moderated by cooling ocean
breezes and thunderstorms seldom occur in periods of fire ueather. In fact
the warming aloft by subsidence and cooling near the ocean surface by
proximating with the cold water results in a sharp inversion. The top of the
inversion varies from about one thousand to five thousand feet, and above
that height the normal decrease of temperature with height resumes. At
night the inversion is intensified by radiational cooling of the ground;
and this cooling is passed to the air in the lower few hundred feet. Air
cooled along mountain slopes sinks slowly to the valley bottoms where
humidities may reach quite high proportions in this cool air. Air above
the effects of surface cooling will remain warm and dry with practically no
variation between night and day. In the air layer next to the ground the
day time beating reduces the inversion, and may, at points remote from the
sea shore, destroy the inversion completely.
One of the results of this co~stal inversion is the wide spread
swarner fogs of the west coast of Vancouver Island. The inversion traps the
air in the levels next to the water where it becomes progressively more
moist and eventually a dense bank of fog a few hundred feet thick forms.
At nignt the fog moves over the coast and up the inlets and low valleys;
during the day the fog over the land and along the coast is dissapated by
surface heating and the main fog bank remains offshore. Under these conditions
the fire hazard in the valley bottoms is quite low but along the side hills
above five hundred of one thousand feet the air remeins warm and dry both
night and day often with high fire hazard.
The pressure pattern which produces long spells of fine summer
weather also gives light variable northerly winds. Along the coast there is
a decided land and sea breeze effect; during the day the breeze blows from
the water towards the land and at night from the land towards the water.
A further influence is the draft up and down the main mountain valleys.
During the warm afternoons a decided breeze up the valleys developes and at
night the cooling produces an opposite effect and the wind blows down the
valleys. All these winds, whether due to pressure patteun, land and sea
breezes) or valley breezes interact, but the resultant winds still remain
light.
In general the winds at the five and ten thousand foot levels will
be light to moderate northerly. Forest fires as in the case of thunderstorms
probably drift slowly with the prevailing winds aloft.
This discussion of the winds associated with fire weather does not
take into account the very local winds which individual fires set up.
These winds blow towards the fire and are due to the movement of the air at
ground level to replace the column of air rising above the fire
Notes:
The biscuit mixes, muffin mixes, and pancake mixes are ~ll very easily prepared, and
if prepared in sraall amounts will not go stale. t cup of pancake mix with t cup of
water or milk will make enough for one.
The hot roll mixes are not too difficult to handle, and will solve the fresh bread
problem.
Stele bread can be freshened by immersing in cold water then placing in a
wet paper bag, which is put in a moderately hot oven for 20 minutes, approximately.
The ne\olcake mixes are quite fool proof, and if the liquid added is less than called
for vety good cookies can be made. Baking might prove a diversion as well as variety
to the 111enu.
Cereals and rice. swell when cooked, about 3 to 4 times, so for 1 cup start with only
to 1/3 cup dry cereal. The same is true of macaroni or noodles.
t
Pudding powders can be made with
made for One serving at a time.
Jello powders can also be divided
and use
cup of water. Be sure
from the air and will go lumpy.
t
just water or with reconstituted milk and can be
All packages have directions.
and made into single servings.
Divide them into 4
to rewrap the jello tightly as it absorbs moisture
Reconstitute a pint or quart of milk each morning and set it to keep cool. The flavor
improves on standing, but if not sufficiently then chocolate syrup can be added to it
for drinking purposes.
Try and have one fresh fruit a day. Citrus fruit will not dry up if kept in a large
jar and the fruit covered with cold water. Keep the \iater fresh. Edible wild berries
e.g. huckleberries have a good vitamin C content so are good in this regard also.
Each time you get food supplies order some carrots, celery, (tomatoes if feasible)
and check the number of days they keep fresh. Use them raw with the lunches.
Use
canned tomatoes in their place when the supply rlIDS out.
The new Minute Potatoes are very good and can be made a serving at a time.
They are a dehydrated product.
Prem, Speef, Spork etc. can be baked in loaf form in the oven for variety.
Spread
marmalade, catsup, or brown sugar and mustard made to a paste over the meat, and
place in a moderate oven for 20 minutes to t an hOl~.
Canned soups, especially cream of mushroom, cream of celery, cream of tomato, cream
of chicken, and vegetable soup make excellent casserole dishes with canned fish, diced
canned meats.
Rice and noodles can be added. This is one way to get some variety
when confinod to foods that are so similar in flavor.
The cake ffi1dgingergread mixes can also be used as desserts with sauces as mars~~allow,
and the syrup from canned fruit heated with some lemon juice added.
Sund~;y:
Fresh fruit juice
Package cereal
Bacon
Toast
Jam
Reconstituted
Milk or Coffee
Casserole of canned spaghetti
with canned meat or fish
(Salmon or Tuna)
Fresh celery, carrot sticks,
or tomatoes. See Notes.
Canned or dried cooked
fruit
Reconstituted milk
Tea
Nonda,y;
As above
Tuesd&
Fresh fruit juice
Package cereal
Scrambled eggs made from
Dried eggs
Toasted biscuits
As above
Biscuits and jam for
dessert
Corned beef hash
Raw vegetables as above
Canned or dried cooked
fruit
Milk or tea
Canned solid mel:l.ts
as
Canned hronburgers
Canned sausages
Prem etc.
Dehydrated potatoes
Canned vegetables
Jello
Tea or coffee
Corned beef hash
Cold Canned Tomatoes
Canned fruit
Hilk or tea
As above
Pudding from mix for
dessert
Canned soup
Sandwiches
Peanut-butter
Cheese
Cold canned tomatoes
Canned fruit
Milk or tea
As above
Jello dessert
Sliced canned meat
Lunch tongue
Chicken
Cold canned tomatoes
Canned or dried fruit
Hilk or tea
As above
Boiled rice with canned
fruit
Casserole of Cream soup
and canned meat or fish
with rice or noodles
As above
As above
Muffins and honey for
dessert
Jam
Hilk or coffee
l.[ednesday
Fresh fruit
Pancakes
Honey or syrup
1viilkor coffee
Thursd§Y
Fresh fruit
Package cereal
Bacon
Toast
Jam
Milk or coffee
Frida;y:
Fresh fruit Ju~ce
Package cereal
Scrambled eggs
Hot rolls or toast
Jam or honey
Milk or coffee
Saturda;y:
Fresh fruit
Pancakes
As above
Fresh meat, {Steak or chops)
Dehydrated potatoes
Canned or dehydrated
vegetables
Pudding made from a mix
Cake or cookies made from
a mix
Tea or Coffee
./
-Notes:
above is planned to give a few ideas of what can be accomplished, but it may be more
,aborate than many of the boys wish to make. Under the lunches we have tried to give
Lrious types of lunches quickly and easily made, and a change from sandwiches.
We feel
1St the dinners will be more satisfying if the solid type of canned meats ~re used
lthor than the mixtures with vegetables.
More variety can be achieved with them aDd the
lavor therefore does not get as monotonous.
he TI1CnUis planned starting with fresh supplies arriving on the Sunday.
;I