Weather Footnotes
This page explains what the terms in the Insect Migration Risk Forecasts and associated risk map figures mean. If you have any questions, please contact Mike Sandstrom, IMRF author, at wxtrw44@yahoo.com .
1) Insect Pump: area indicated by arrow where pests have potentially lifted into the lower atmosphere and are now being transported northward by speed indicated beside arrow (see #2 below).
2) Wind Speeds: < 10mph equals weak, 10-25 mph equals moderate, 25-40mph equals strong, and 40mph+ is dangerous/exceptional.
3) Drop Zone: area either along a frontal boundary (most likely) or area of precipitation where, if conditions warrant downward motion for the specific pest, it will have a high probability of dropping out of the sky to the ground.
4) Arrow: the base of the arrow indicates the area where the winds transporting the pests in the insect pump will originate. This same area also indicates a potential insect source region where, if pests are present, have a higher probability of being transported by weather patterns. The tip of the arrow indicates the area where pests have the highest probability to be transported before they will have the potential to drop out of the sky in great numbers.
5) Frontal Boundary:
a. Cold: colder air is advancing from north to south behind (usually to the north or west) of the boundary. Winds ahead of a cold front are usually south or southwest, and behind the cold front are north or northwest. Indicated by a blue line with blue triangles pointing in the direction the front is moving.
b. Warm: warm air is advancing from south to north to the south of the boundary. Winds ahead of an advancing warm front are usually east or southeast, while to the south of the warm front they are usually south or southwest, with an increase in atmospheric moisture and temperature after the frontal passage. Indicated by a red line with red half-circles pointing in the direction the front is moving.
c. Stationary: as the name suggests, the front is not moving or is moving very little. This pattern is frequently observed in the late summer when weather patterns are more stagnant due to less drastic temperature changes are present when compared to spring or early summer. Temperatures and moisture can vary quite dramatically on either side of the front and precipitation is frequently observed especially from late afternoon into the overnight hours along and to the north of the front. Indicated by a combination of cold and warm fronts with blue triangles pointing down and red half-circles pointing up.
6) Winds with a cardinal direction (i.e. a southerly wind or south wind) indicate winds blowing from south to north. Winds are blowing FROM the direction indicated.
7) Low pressure indicates an area where wind flow is blowing in a counter-clockwise fashion around the low. Winds to the east of a low, therefore, are southerly. Clouds and precipitation are common around lows.
8) High pressure indicates an area where wind flow is blowing away from the high in a clockwise fashion. Winds to the east of a high are from the north and to the west of a high are south. Clear/calm weather is normally associated with high pressure systems. Return flow indicates a resumption of southerly wind flow to the west of a departing high pressure system.
9) Lower levels of the atmosphere indicates the lowest 1500 meters (5000 feet) of the atmosphere where insects are most likely being transported.
10) The risk of insect migration in the outlined risk region (indicated by none, very low, low, moderate, and high) indicates the threat of insect migration into the specified area. Each written term means the following:
a. None: Insect migration is not a concern in the area. Most likely, this area is under the influence of high pressure, indicating calm or winds with a northerly component. Indicates a 0% risk of a location being affected by insects.
b. Very Low: Insect migration is only a minor concern in this area, or uncertainty in the forecast (especially several days ahead) justifies at least a very low risk with potential for either no risk or a higher risk to be assigned to the specified area in later forecasts, depending on changes in the weather pattern. Usually associated with a 2-5% probability risk, or a 1 in 25/50 chance that a location in the specified area will be affected with insects.
c. Low: Insect migration is an increased concern but not on a widespread or significant basis. The weather pattern does indicate a favorable pattern for insect migration, but less-than-ideal weather conditions may be present or forecasted (weak southerly wind flow or low chances of precipitation). Usually associated with a 5-15% probability risk, or a 1 to 3 in 20 chance that a location in the specified area will be affected with insects.
d. Moderate: Insect migration is a real threat and conditions should be monitored closely for a higher probability of insect “drop-out” at a given location. The weather pattern is favorable, and given the time of year, insects are more likely to affect fields in the specified area. Usually associated with a 15-30% probability risk, or a 3 in 10/20 chance that a location in the Moderate risk area will be affected by insects.
e. High: Insect migration is likely on a widespread basis in the specified area for a given forecast period. Not only is the weather pattern favorable, but insects are known to be affecting areas in the source region, and weather patterns show a very good chance of the insects traveling from the source region to the high risk area. Usually associated with a 30-50% probability risk, or a 3 in 10 to 1 to 2 chance of a location being affected by insects.