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500hPa chart parameters

-18000ft, 5500m.
-contours are at 6 decameter intervals.
522, 546,570,594 contours are accentuated
-Height centers are black L or H as appropriate
-Two charts, 500hPa vorticity (early)
500hPa thickness (complete)tx


500hPa Vorticity

-twice daily, based on 00z and 12z data
-tx 2 hours after obs
- 500 hPa contours and isopleths
-+ signs are maximum absolute vorticity
- - signs are minimum absolute vorticity
-dashed lines are isopleths of absolute vorticity at regular intervals labelled 0,4,8...


500 hPa Thickness

-twice daily, based on 00z and 12z data
-tx 3.5 hours after obs
-dashed lines are 1000-500 hPa thickness isopleths analyzed at 6 decameter intervals, labelled in decameters
-+ indicates high thickness,- indicates low thickness, labelled in decameters


500 hPa vorticity enhancements

-Vorticity centers- Max -red C or plus sign
Min - blue A or minus sign
Shortwave trough- red line
ridge - blue line
Vorticity advection
area - PVA- red shading
- NVA - blue shading



-the transport of an atmospheric property solely by the mass motion of the atmosphere
-the smaller the quadrilateral the stronger the advection
-when isopleths are parallel to the contour lines there is no advection.



Positive Vorticity Advection
-found in advance of disturbances aloft (shortwave)
-enhances the potential for thunderstorms.
-excellent indicator of where instability may develop



Negative Vorticity Advection
-Movement of negative vorticity towards an area of higher vorticity
-convergence at upper levels


500 hPa thickness enhancements

-Height centers - black H or L
-Thickness centres- Warm - red W
Cold - blue C
trough -dashed blue lines
ridge - dashed red line
- Thickness advection -PthA red shading
-NthA blue shading
-540 dm contour - dashed yellow



Positive Thickness Advection
-A thicker layer moves over a point
-supports cyclogenesis
-fronts usually located in the ridges (warm tongue)of the thickness field
-area between 534 and 540 dm indicate chnge of phase zone.


Prog SFC-400 mb

-low and mid level weather
-pressure centers, surface frontal positions
-surface position of tropical storms
-significant cloud
-turbulence, freezing level, icing
-prepared twice daily, valid 00z and 12z, issued 11 hours before validity


Comox Prog

- forecasst issued for a period of 12,24,36 hours
-west coast and pacific
-ground to upper levels


CMC Sig Wx Prog

-700mb - 400mb
-composite of forecasts from across canada
-produced 4 times daily, issued 1 hour after GFA.
-essentially a GFA, but for mid level flight
-Surface pressure centers, fronts, tropical storms
-sig cloud, turb, icing , freezing level


Upper winds forecast

-winds and temps for FL240,340, 450


Mid-level prog chart features

-H and L are in colour, as it is a prog chart
-standard met markings for fronts etc
-showery precipitation - green outline, hatched
-Cont or INTMT shown as solid green, stipled
-clouds are scalloped brown
-icing is solid blue outline, stipled
-turb is solid red, hatched
-freezing level-freezing levels, 5000ft intervals, labled in 100s of feet.



-the estimation of values between known values
-accuracy dependent on density of grid points
-topography and local effect must be taken into consideration



-Isodrosotherms - equal dewpoint
-isalobars - pressure over time
-isohyets - equal rainfall
-isochrones - occurance at the same time


Factors of interpolation

-Recognizing the chart
-understand the plotting model
-topography/local effects
-proportional distance


Local effects and 3 elements that contribute to

-Localized weather due to interaction between atmosphere and topography


Local effects near water bodies

-Moisture source
-Thermal lows
-Moderated temperature extremes
-land/sea breezes
-Convergence zones
-fog and stratus - advection fog
-steam fog


Local effects of higher terrain

-orographic cloud/weather
-persistent radiation fog
-persistent freezing rain


Procedures to follow when discrepancies exist between current weather and forecast conditions

-Identify discrepancy
-Determine manair requirements
-apply local procedures


Numerical chart codes

-TB - significant and mandatory levels
-TA - mandatory levels and 12 hr changes
-AN analyzed tephigram data
-PB - all pilot winds
-PA - significant, fixed pilot winds
-UP - upair


Stability codes

-STB - stable
-POT - potential convection
-CVT - convective
INV - inversion
UNS - unstable
-NUT - nuetral layer