Forecasting weather elements and phenomena Flashcards
Maximum temperatures usually occur at about
2 P.M. or 3 P.M
while minimum temperatures occur
around sunrise or just after sunrise. (6 A.M.)
To determine tomorrow’s maximum temperature
examine today’s 2 P.M. or 3 P.M. surface map. Calculate, using ½ the speed of the 500 MB winds the parcel of air that will be influencing your area 24 hours later. The temperatures in that parcel will very closely resemble tomorrow’s maximum temperature in your area.
To determine tomorrow’s maximum temperature, examine today’s 2 P.M. or 3 P.M. surface map. Calculate, using ½ the speed of the 500 MB winds the parcel of air that will be influencing your area 24 hours later. The temperatures in that parcel will very closely resemble tomorrow’s maximum temperature in your area. …………………….. must be studied and then introduced into each forecast.
Local variations
Since the 500 MB winds are from the
southwest at 50 kts
Since the 500 MB winds are from the southwest at 50 kts. weather which is now ………………………….. will influence our area tomorrow at ………
600 miles (1/2 50 X 24 hours) to our southwest
3 p.m.
Since the 500 MB winds are from the southwest at 50 kts. weather which is now 600 miles (1/2 50 X 24 hours) to our southwest will influence our area tomorrow at 3 p.m. Since most of the upstream temperatures are in
the upper 60’s, temperatures in the upper 60’s are likely for the forecast area the next day.
The procedure for minimum temperatures is
exactly the same as for maximum temperatures with one exception. Instead of using a 3 P.M. surface map, the 6 A.M. or 7 A.M. surface map should be used. Employ the same upstream procedures and introduce the local variations experienced in your area.
If an increase in clouds, moisture or wind is expected in the parcel of air being transported into your area,
certain modifications must be made.
If an increase in clouds, moisture or wind is expected in the parcel of air being transported into your area, certain modifications must be made. Generally speaking, any or all of these will tend to
to lower the maximum temperature expected as well as raise the minimum temperature expected
Morning cloud cover can be very
misleading
Morning cloud cover can be very misleading. For example,
“upstream” weather may indicate overcast skies at all reporting Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures.
Morning cloud cover can be very misleading. For example, “upstream” weather may indicate overcast skies at all reporting
Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures. However, upon investigation,
the forecaster may notice that the HEIGHT of these clouds is below 1000 feet
Morning cloud cover can be very misleading. For example, “upstream” weather may indicate overcast skies at all reporting
Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures. However, upon investigation, the forecaster may notice that the HEIGHT of these clouds is below 1000 feet. These ………. clouds, probably ………….
low clouds, probably stratus, will most likely “burn off” by mid morning, thus not preventing temperatures from reaching the expected maximum.
These low clouds, probably stratus, will most likely “burn off” by mid morning, thus not preventing temperatures from reaching the expected maximum. However,
, if these low clouds have a higher deck of clouds above them (two or more decks) the sun will probably not be able to penetrate. Overcast skies will persist all day. Lower maximum temperatures can thus be expected.
The above factors, yes or no, when and how much can usually be determined very accurately for the
next 12 hours by using the surface map along with the 500 mb
the figure indicates that
the 500 MB. winds indicate the rain area will effect station “A”. In fact, light rain (..) should move into the area in approximately six 6 hours. (150 miles divided by 25 MPH). However, the rain should become moderate (…) and heavy (….) after about four (4) hours. (100 miles divided by 25kts) of light rain. Moderate and heavy rain should continue for about 4 hours, tapering off to very light rain showers, then ending.
Station “B” would not be affected by this rain pattern, since all the rain would be passing to the north of the area.
RAIN, YES OR NO, WHEN AND HOW MUCH?
Here are some factors that may complicate matters:
1.A MOVING 500 MB. TROUGH
2.A “LIFTING OUT” TROUGH
3.A “DIGGING” TROUGH
4.A DEVELOPING STORM
this will work if
the trough is stationary
The example given above works well if the trough is stationary. However, if
the trough is moving, modifications must be introduced.
The example given above works well if the trough is stationary. However, if the trough is moving, modifications must be introduced. We must use
vectors
The example given above works well if the trough is stationary. However, if the trough is moving, modifications must be introduced. We must use vectors.
The rain pattern will move according to the
“resultant of the two vectors, the vectors being 1) direction of the upper air winds plus 2) the eastward movement of the trough
The faster the trough is moving, the
greater the eastward component will be in the resultant vector showing the actual movement of precipitation, taking the trough movement into account
The STRONGEST WINDS are
“digging” down the western side of the trough.
. The STRONGEST WINDS are “digging” down the western side of the trough. Since the winds are weak at the “bottom” of the trough, this trough will
DEEPEN AND MOVE SOUTH-EASTWARD VERY SLOWLY, IF IT MOVES AT ALL. WE CALL THIS A “DIGGING TROUGH”.
the trough in the central part of the United States with the STRONGEST WINDS AT THE BOTTOM OF THE TROUGH. This trough will REMAIN ABOUT THE SAME IN INTENSITY BUT WILL MOVE EASTWARD
shows the trough in the center of the United States with the STRONGEST WINDS MOVING UP THE EASTERN SIDE OF THE TROUGH**. This trough will **weaken and move rapidly towards the NORTHEAST.
A “LIFTING OUT” TROUGH
When a trough is lifting out, the area of precipitation, along with the intensity of the precipitation, generally DECREASES
When a trough is lifting out, the area of precipitation, along with the intensity of the precipitation, generally DECREASES. This should be taken into account when determining
when precipitation will start,
how much will fall, and
when it will end.
.A “DIGGING” TROUGH
When a trough is “digging”
the area of precipitation, along with the intensity of the precipitation generally INCREASES. This again must be considered when making a forecast.
A DEVELOPING STORM
If rapid storm development (cyclogenesis) is expected, the size of the precipitation area, as well as the precipitation intensities, will increase significantly
If rapid storm development (cyclogenesis) is expected, the size of the precipitation area, as well as the precipitation intensities, will increase significantly. This data should then be
utilized in modifying amounts and duration of precipitation expected.
.STORM INTENSIFICATION:
Certain conditions favor rapid storm intensification. A few are given below:
- COLD AIR AT THE 500 MB. LEVEL
- VORTICITY:
- COLD AIR ADVECTION AT THE 700 MB. & 500 MB. LEVEL
- THE “DIGGING” TROUGH ->
- DIVERGENCE AT THE 200 MB. LEVEL >
- BAROCLINICITY AT THE SURFACE
- THE JET STREAM AND ITS INFLUENCE ON STORM DEVELOPMENT
COLD AIR AT THE 500 MB. LEVEL:
Storms intensify rapidly if
the trough (short wave or long wave) possesses cold air.
A storm developing near station “A” would
deepen rapidly.
A storm developing near station “A” would deepen rapidly. 500 MB. wind speeds to the east of “A” are ->
100 Kts
while to the west of “A” near the center of the trough, they are
only 25 Kts
A storm developing near station “A” would deepen rapidly. 500 MB. wind speeds to the east of “A” are 100 Kts. while to the west of “A” near the center of the trough, they are only 25 Kts. This creates a
counterclockwise (cyclonic) wind shear
The air at “A” in Figure 34 is located in an area of
wind shear and is being induced to circulateCOUNTERCLOCKWISE.
Generally, storms develop and intensify in
AREA I is most favorable because it possesses CYCLONIC WIND SHEAR and alsoCYCLONIC CURVATURE,
AREA III,
possesses CYCLONIC CURVATURE, favorable for storm development, BUT it also exhibits ANTICYCLONIC WIND SHEAR, unfavorable for storm development, therefore, strong storm development in AREA III would not be expected.
AREA II
is also not a favored area for storm development because although it has CYCLONIC WIND** **SHEAR**, it also has **ANTICYCLONIC CURVATURE.
AREA IV
the least likely area for storm development.
