A wake low, or wake depression, is a mesoscale low-pressure area which trails the mesoscale high following a squall line.[.] Due to the subsiding warm air associated with the system's formation, clearing skies are associated with the wake low. Once difficult to detect in surface weather observations due to their broad spacing, the formation of mesoscale weather station networks, or , has increased their detection.[Mark R. Conder, Steven R. Cobb, and Gary D. Skwira (2006). West Texas Mesonet Observations of Wake Lows and Heat Bursts Across Northwest Texas. American Meteorological Society. Retrieved on 2009-04-24.] Severe weather, in the form of high , can be generated by the wake low when the pressure difference between the mesohigh preceding it and the wake low is intense enough.[.] When the squall line is in the process of decay, can be generated near the wake low. Once new thunderstorm activity along the squall line concludes, the wake low associated with it weakens in tandem.
Formation
Wake lows form due to adiabatic warming in the wake of mature squall lines at the back edge of their rain shields, where
evaporation cooling is unable to offset warming due to atmospheric
subsidence, or downward motion. They can be caused by
which duct through boundary layers which are deep and cold to the north of a
weather front. As with mesoscale high-pressure areas behind a squall line, when new
thunderstorm development stops along the squall line, the wake low will weaken as well. Clearing conditions will accompany the wake low, due to the descending warm air mass associated with the feature.
Within the
United States, these systems have been observed to form in the Mississippi River valley,
Southeast,
[National Weather Service Office Huntsville, Alabama (2009). April 12-13, 2009 Wake Low Event. Retrieved on 2009-04-23.] Florida, and
Great Plains.
[Robert R. Handel and Pablo Santos (2005). P4.6 Observations From the 13 April 2004 Wake Low Damaging Wind Event In South Florida. American Meteorological Society. Retrieved on 2009-04-24.] A wake low producing strong northeasterly winds of and very rough seas was determined to be responsible for the capsizing of the
Seacor Power lift boat (according to the National Weather Service) with 13 mariners drowned or missing.
Detection
Both direct and indirect ways have been found to indicate the presence of a wake depression. The most direct is through the use of surface observations. Prior to the development of mesoscale weather station networks, or mesonets, it was difficult to locate wake lows. With the advent of mesoscale networks, wake lows have become easier to detect. On weather satellite and
weather radar imagery, wake lows and heat bursts normally occur on the rear side of a precipitation area. However, within larger precipitation areas, they can be located within the area showing a minimum of returns.
When using velocity data from a WSR-88D doppler radar, high winds on the back edge of reflectivity data can give away the location of a wake low.
Association with heat bursts
Heat bursts are rare atmospheric phenomenon characterized by gusty winds and a rapid increase in
temperature and decrease in
dew point (moisture). Heat bursts typically occur during night-time and are associated with decaying
thunderstorms.
In association with wake lows, heat bursts are caused when rain evaporates (
virga) into a parcel of cold dry air high in the atmosphere making the air denser than its surroundings.
The parcel descends rapidly, warming due to compression, overshoots its equilibrium level and reaches the surface, similar to a
downburst.
Recorded temperatures during heat bursts have reached well above , sometimes rising by 20 °F (11 °C) or more within only a few minutes.
See also
-
Mesoscale convective vortex (MCV)
