EO 317.1 Given 500 hPa upper air analysis charts,
identify the source, content and availability
of the products.
name the 2 charts
500 hPa vorticity (early)
* 500 hPa thickness (complete)
The 500 hPa chart represents an altitude of approximately 18 000 feet
(5500 metres) in the atmosphere.
There are two types of analysis done at this level, a thickness chart and a
vorticity chart. For aviation weather briefing purposes, only the pattern of
height contours (with highs and lows shown) and winds are useful
Contours are represented by a solid line and are indicated at intervals of ______
six
decameters. . The 522, 546, 570 and 594 decameter lines are accentuated by
a dark bold line. Height centres are marked L or H, as applicable.
most stuff above and measurng angles you dont need to know
Components of vorticity
Vorticity on the weather charts is comprised of three components that are
added together:
- Coriolis component
- Shear component
- Curvature component
Negative vorticity advection (NVA) refers to areas of convergence (where
spin is increasing).
Positive vorticity advection (PVA) refers to
PVA is on the test
areas of convergence (where
spin is increasing). (NVA)
areas of divergence (where spin is
decreasing). (PVA)
(sidenote) On a 500 hPa chart, dotted isopleths depict lines of equal vorticity.
A vorticity maximum represents the point in that region of the atmosphere
where the flow creates the greatest spin. As an air parcel approaches a
vorticity maximum, its spin increases. As its spin increases, the air parcel
must converge on itself (contract) to maintain its angular momentum.
Vorticity minimum
The opposite happens as an air parcel approaches and moves through a
vorticity minimum (local area of least spin). As the parcel approaches the
minimum it will spin slower and diverge (expand). After it passes the
minimum its spin will increase and the air parcel will converge (contract).
500 hPa THICKNESS (COMPLETE)
Prepared twice a day at 0000Z and 1200Z
› Transmitted approximately 3 ½ hours after observation
In
Canada, the 570 and 546 decameter lines are the bold lines. A rule of
thumb:
.
* The geographical area south of the 570 line has warm and sunny weather
* The geographical area north of the 546 line has cold and clear winter
weather
* The area between the 570 and 546 lines is the geographical area where
you will encounter weather
EO 317.2 Analyze standard features on 500 hPa charts
LOCATE AND ENHANCE THE FOLLOWING FEATURES ON THE 500 hPa
VORTICITY (EARLY) CHART: - dont need to memorize
- Height centre
- Vorticity centre
- Short wave
- Advection analysis
- Vorticity advection
Ahead of the maximum, spin is :
Behind a maximum, spin is:
Ahead of the maximum, spin is increasing; this is an area of positive vorticity
advection (PVA). Behind a maximum, spin is decreasing; this is an area of
negative vorticity advection (NVA).
an isopleth is a line of equal or constant
value of a given quantity with respect to either space or time; same as
isogram. More specifically, it is a line drawn through points on a graph at
which a given quantity has a specified constant value. - not importatnt
Advection is occurring when the isopleth of the property being considered
crosses the contour lines. The degree of advection is determined by the size
of the quadrilateral formed by two different isopleths crossing two different
contours. The smaller the quadrilateral, the stronger the advection.
Advection decreases as the angle made by the two sets of isopleths
decreases. When the isopleths are parallel to the contour lines, there is no
advection - not important
If PVA represents high levels of vorticity moving towards lower levels of
vorticity, then negative vorticity advection (NVA) represents lower levels of
vorticity moving towards higher levels of vorticity. NVA is associated with
convergence in the upper levels, while PVA is associated with divergence in
the upper levels.
The divergence associated with PVA is significant because it creates forced
lift in the atmosphere. This forced lift, in the presence of conditions
favourable for atmospheric convection, can cause clouds or precipitation.
PVA represented on a 500 hPa chart is an
excellent indicator of where instability may develop in the future. NVA, on
the other hand, is indicative of a stable atmosphere.
Height centre
Centres are marked L or H, as applicable, and central values are labelled in
decameters.
Thickness centre
A low (cold) thickness centre, depicted by a (-) sign, is labelled with a blue
C.
A high (warm) thickness centre, depicted by a (+) sign, is labelled
with a red W.
The area between the 534 and 540 decameter dashed lines
(1000 to 500 hPa thickness) is
stippled to indicate a change-of-phase zone
from liquid to freezing precipitation (at the Earth’s surface). - used upstIrs alot
EO 317.3 Given low and mid-level prognostic charts,
identify the source, content and availability
of the product.
Low to mid-level significant weather
PROG SFC-400 hPa
DND PROGS
Mid-level significant weather - one we use the most
Forecast wind for FL240
EO 317.4 Analyze standard features on mid-level
prognostic charts.
xx indicates that the cloud base is below the lower level considered for
that chart. For example, if the base of the cloud is at 8000 feet, and you
are using the 700-400 hPa chart, then the base will be depicted as XX.
TCU and CB indicate mod-sev icing without icing symbol.
CB clouds are indicated in the area where they are forecast to occur. They
are enhanced in the same manner as other clouds, except that the type,
base and tops of the clouds are enhanced in red
EO 317.5 Interpolate weather conditions at a specific
location given an analyzed weather chart. - will be asked to interpolate, dont worry about chart
INTERPOLATION
Between locations
› Surface (in the horizontal)
› Aloft (in the vertical)
› Between times
› Analysis / forecast valid times
› Different GFA valid times
(T00 / T06)
47
› Regular interpolation procedures
› Motion
› Development
› Take local effects into account
› Specific areas
› Surface charts only
› Possible TAF amendments
Other lines that give interpolated values are:
* Isodrosotherms: lines connecting points of equal or constant dew point
* Isallobars: lines connecting points of equal change in atmospheric
pressure
* Isohyets: lines connecting points of equal rainfall
LIST THE STEPS NECESSARY FOR INTERPOLATING CONDITIONS
BETWEEN TWO REPORTING POINTS ON AN ANALYZED WEATHER
CHART - COULD ASK ON EXAM
Recognizing the chart
› Understanding the plotting model
› Topography / local effects (Surface charts only)
› Proportional distance
EO 317.6 Explain the impact that local effects have on
forecast weather conditions.
A local effect may be defined___
as localized weather caused by the interaction
between the atmosphere and the Earth’s topography
SIGNIFICANT FACTORS FOR LOCAL EFFECTS
Moisture
› Stability
› Circulation
When looking at local effects, take the following into consideration:
- Moisture and stability
o Open water versus land
o Snow and ice cover versus bare ground
o Vegetation versus soil and rock - Circulation
o Onshore versus offshore
o Upslope versus downslope
