Newton's Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first.

Basic Upper Air Analysis

Upper level charts for 00 UTC Nov. 10, 1998, showing geopotential height (black contours), temperature (red contours), and observed winds. Contour interval 30 m for 850- and 700-hPa height, 60 m for 150-hPa height, 120 m for 250- and 200-hPa, and 60 m for 100-hPa height. The contour interval for temperature is 4 degrees celsius in the left panels and 2 degrees celsius in the right panels. The shading in the 250-hPa chart are isotachs defining the position of the jet stream. [Wallace and Hobbs 329]

Synoptic charts at 00, 09, and 18 UTC Nov 10, 1998. (Left) The 500-hPa height (contours at 60-m intervals; labels in dkm) and relative vorticity (blue shading; scale on color bar in units of 10^(-4) s^(-1)). (Right) Sea-level pressure (contours at 4-hPa intervals) and 1000- to 500-hPa thickness (colored shading: contour interval 60-m; labels in dkm). Surface frontal positions, as defined by a skilled human analyst, are overlaid. [Wallace and Hobbs 315]

1000-500 mb / SLP Chart

• Includes SLP and 1000-500 mb thickness
• Given distribution of geopotential height on any two pressure surfaces we can determine the distribution of thickness for the intervening layer.
• The "thickness" chart reveals temperature advection through the lower half of the troposphere.
• Frontal location: A cold front is usually placed at the leading edge of the greatest thickness packing (cold air advection) and a warm front is placed at the trailing edge (warm air advection
• 540 line: meaning 5400 meters between the 1000mb and the 500mb level.
• Often used to delineate the rain/snow line with snow expected on the cold side of that line and rain on the warm side (this is a rule of thumb, not a hard fast law)

800-mb Chart (~1,500 m)

• The 850-mb pressure surface is closest to the surface Through examination some differences should be mentioned:
• Solid lines are height contours (gpm).
• Dashed lines are isotherms (ºC).
• Closed lows at surface may appear as troughs @ 850 (in this case the winds stronger than at surface why? Less friction.
• Winds generally more parallel to height contours.
• Tilt of the cold front westward (backward) into the cold air as one goes up from the surface.
• Warm front is more clearly defined and farther poleward at 850.

[Wallace and Hobbs 329]

• Warm Air Advection
• Typically the greatest dynamically caused lifting mechanism over the large scale.
• Related to QG Theory.
• To be detailed in Synoptic Meteorology.

http://atsc.uga.edu/wx/ncep_loops.htm

700-mb Chart (3,000 m)

• Typically, the trough associated with surface lows are more difficult to identify and are displaced upstream (in this exceptional case, the low is still closed at 700 mb!)
• Further increase in wind speed
• Cold front located even farther west
• Warm front located much farther poleward and coincides with the location of the precipitation reaching ground.
• Frontal zones less clearly defined than at lower levels. (often difficult to detect equator-ward end of cold front).

[Wallace and Hobbs 329]

500-mb Chart (~5,000 m)

• Further upstream displacement of troughs.
• Strengthening of winds.
• Sloping of the frontal zones toward the cold air.
• Frontal zones hard to detect but thermal contrasts exist.

[Wallace and Hobbs 329]

250-mb Chart (~10,366 m)

• Near the climatological position of the polar jet stream.
• Warmest air (-44ºC) located north of jet stream near the  trough (over 4-Corners).
• Little to no advection as you go south.

[Wallace and Hobbs 329]

100-mb Chart (~16,000 m)

• Located well above the tropopause and jet stream.
• In stratosphere there is a marked decrease in wind speed when compared to 250-mb.
• Only planetary scale features present at 100 mb (not the synoptic scale).
• Temperature field reverses -- colder air as one goes toward the equator, warmer towards the poles.

[Wallace and Hobbs 329]

Three-Stage Model

• The three-stage model of an idealized mid-latitude (N.H.) cyclone with 1000-mb heights, 500-mb heights and 1000-500 mb thicknesses shows the development of the cyclone.
• Early Stage - surface low just beginning to form as wave along front on the warm side of the region of strong thickness contrast.
• Mature Stage - cold air starts streaming southward behind the surface low pressure area and warm air advances northward in advance of the cyclone.
• These distortions in the temp. field are reflected in the growing amplitude of the wave in the thickness pattern.The thickness pattern is closely related to the position of the warm and cold fronts.
• Surface low is in the process of passing under the jet stream, from the warm to cold side.
• Late Stage - the occlusion process has begun:
• The surface low moves across the thickness contours towards lower values as it deepens progressively farther back into the cold air.
• Junction of the warm and cold fronts remains on the warm side of the region of strong thickness contrast
• Occluded front coincides with a warm ridge in the thickness field.
• As the disturbance continues to amplify, the positions of the surface low and the 500-mb trough (or closed low) gradually begin to come into vertical alignment (stacked).
• In fully developed systems the vertical tilt completely disappears and all three sets of contours become mutually parallel.

(Top) Fields of 500-hPa height (thick black contours), 1000-hPa height (thin black contours), and 1000- to 500-hPa thickness (dashed red) at 00, 09, and 18 UTC Nov 10, 1998; contour interval 60-m for all three fields. Arrows indicate the sense of the geostrophic wind. (Bottom) Idealized depictions for a baroclinic wave and its attendant tropical extratropical cyclone its early (left), developing (center), and mature (right) stages. [Wallace and Hobbs 317]

Vertical Soundings

• Vertical soundings (found through radiosondes) show how the temp changes vertically with height, generally up to 100-mb or so.
• Backing -- counterclockwise winds; CAA.
• Veering -- clockwise winds; WAA.

Soundings of wind, temperature (red lines), and dew point (green lines) at 00 UTC Nov. 10, 1998 at Amarillo, Texas (left) in the cold frontal zone and Davenport, Iowa (right) in the warm frontal zone. [Wallace and Hobbs 331]

Sea-level pressure, surface winds, and frontal positions at 00, 09, and 18 UTC Nov. 10, 1998. Frontal symbols and wind symbols are plotted. The dashed blue line denotes the secondary cold front. The frontal positions are defined by a human analyst. [Wallace and Hobbs 319]

Vertical Cross Sections

• It is important to know the vertical structure of the atmosphere near a cold front.
• The forthcoming cross section was constructed using temps and wind soundings at locations between Riverton, WY, and Lake Charles, LA.
• Temps in ºC are solid red lines.
• Solid blue lines are isotachs (lines of constant wind speed) for the wind component normal to the section (positive into the section, negative out of the section).
• The section is oriented normal to the front and to the jet stream.

[Wallace and Hobbs 329]

Locations of the stations and vertical cross sections shown in this section. From north to south, KMQT is the station identifier for Marquette, Michigan; KRIW for Riverton, Wyoming; KLBF for North Platte, Nebraska; KSUX for Sioux Falls, South Dakota; KGAG for Gage, Oklahoma; KSGF for Springfield, Missouri; KBWG for Bowling Green, Kentucky; KCAE for Columbia, South Carolina; KJAN for Jackson, Mississippi; and KLCH for Lake Charles, Louisiana. [Wallace and Hobbs 339]

Screen capture from a PDF version of a powerpoint. Images from Wallace and Hobbs 319, 333, and 339.

Characteristics of Cross Section

• Well defined frontal zone in the lower troposphere, sloping toward the cold air with increasing height.
• Within the frontal zone the isotachs are sloping and very close together, wind component into the section is increasing very rapidly with height. This represents an area of strong vertical wind shear.
• Middle-latitude tropospheric jet stream is located within the gap in the tropopause where winds are the greatest (80 m/s)
• Reversal in the horizontal temp gradient between troposphere and stratosphere.

Isentropic Analysis

• Sometimes we use potential temp rather than temp in these cross section analysis.  We like isentropic analysis because:
• Under adiabatic conditions the isentropes in sections can be closely identified with air motion.
• In the figure the stability stratification is directly related to the vertical spacing of the isentropes.
• Regions of close spacing (i.e. the stratosphere and frontal zone) are characterized by strong static stability.

http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/pot_vort.html

Screen capture from a PDF version of a powerpoint. Images from Wallace and Hobbs 319, 333, and 339.

Upper-Level Structure

• Understanding how cyclonic disturbances change over time requires a keen understanding of cyclones at various heights within the entire troposphere.
• Often we think of 500-mb winds as steering winds for features at the surface.
• The upper level patterns also act to influence the rates of intensification and weakening of surface cyclones and anticyclones, as well as the amounts of precip. associated with them.

Convergence and Divergence in a Column

• Convergence (divergence) within an air column is associated with increasing (decreasing) surface pressure, since the weight of the air column will increase (decrease) with time.
• Vertical motions in the atmosphere are related to divergence and convergence fields.

The relationship between divergence, convergence, and vertical motions in air columns. Black portions of arrows are outside the columns, while gray portions are inside. [Robert et al. 139]

Works Cited

Rauber, Robert M., et al. Severe and Hazardous Weather: An Introduction to High Impact Meteorology. 4th ed., Kendall Hunt, 2014.

Wallace, John, and Peter Hobbs. Atmospheric Science: An Introductory Survey. 2nd ed., Academic Press, 2006.

Surface Weather Elements

Station Plots

• Station "plots" or "model" are used to spatially display the current conditions in a particular region.

Current Plots

Test Yourself

Isoplething

• The analysis process represents only one step in the production of an analysis chart. The construction of isopleths can entail either subjective or objective analysis schemes.

• Subjective analysis refers to a hand-drawn product, where a meteorologist draws isopleths based upon visual interpolation between the irregularly distributed data points, coupled with continuity from previous charts, experience and intuition.

• Objective analysis typically refers to computer generated products, where the isopleths are generated by numerical interpolation schemes involving an organized grid representation of the given field.

• On the surface map there are many more stations to provide information and the following information is given to you:
• Wind speed and wind direction (wind barb at each station)
• Isobars drawn at 4-mb intervals
• Areas of relatively High (H) and Low (L) pressure.

• As one studies the sequence of the three surface maps one sees how both the surface fronts and the areas of low and high pressure move. These features are:
• Transient
• Linked to what's going on at 500-mb! Dynamic!

• Matter of fact, the activity associated with upper-level troughs (movement, location, development) dictates the movement, location and development of the surface low- and high-pressure systems!

• One thing to do in any sequence is pick a location, let's say St. Louis and examine how the surface characteristics change with time. 

Sea-level pressure, surface winds, and frontal positions at 00, 09, and 18 UTC 10 Nov 1998. The dashed blue line denotes the cold front. The contour interval for sea-level pressure is 4 hPa. [Atmospheric Science, Wallace & Hobbs]

Surface air temperature (in degrees celsius) and frontal positions at 00, 09, and 18 UTC 10 Nov 1998.  [Atmospheric Science, Wallace & Hobbs] 

Winds and Pressure

• Wind is plotted vectorially, showing the direction from which the wind is coming from.

• It tends to blow across the isobars going from higher pressure to lower pressure at and near the surface.
• This flow across the isobars is due to friction.

• As you examine the maps you will see that areas of high pressure are separated by troughs of lower pressure.

• A surface trough represents an area of convergence or a line of confluence where air is flowing together in the wind field. The confluence line is generally represented by some type of front.

• Areas of surface low-pressure develop along the confluence line.

• Generally ahead (or to the east) of the surface low pressure the confluence line moves northward (with southerly winds) while behind (or to the west) of the surface low pressure the confluence line moves southward (with northerly winds).

• Counterclockwise (cyclonic) circulation develops around the surface low

Station Models. Wind entries. [Aguado and Burt 411]

Temperature and Fronts

• Surface temps can be plotted.  Once plotted these values represent an excellent way to define frontal location.

• As one can clearly see the temp. north of the convergence or confluence line are much cooler than those south of it.  This is typically the case in the N.H. (weaker differences in the summer than winter).
• Gulf air (warm, moist) -- mT
• Canadian air (cool, dry) -- cP

• If we compare temps to where the wind is blowing from, the relationship between temps and wind direction can be drawn.

• In the warm air region south of the confluence line the temps appear horizontally homogeneous. This is expected in a air mass.

Idealized cross sections through frontal zones showing air motions relative to the ground in the plane transverse to the front. Colored shading indicates the departure of the local temperature from the mean temperature of the air at the same level. (a) Warm front. (b) Stationary front. (c) Cold front. Heavy arrows at the bottom indicate the sense of the frontal movements. [Wallace and Hobbs 321]

Surface air temperature (in degrees celsius) and frontal positions at 00, 09, and 18 UTC 10 Nov 1998.  [Wallace and Hobbs 324] 

Fronts

• Because the confluence line, a boundary, separates relatively cool air from warm air we call it a front.

• The region of strong thermal contrast on the "cold air side (poleward)" of the confluence line is called a frontal zone or baroclinic zone.
• It is the zone, not the front, that separate the cool and warm air masses.  The front represents the warm air boundary of the frontal zone and coincides with the line of confluence in the wind field.

• Fronts are named based on the direction of movement:
• Cold air advancing → cold front (triangles on front)
• Cold air retreating → warm front (semi-circles on front)

• The direction of the front movement is based on the side of the front the symbols are located and direction they are pointing.

• Stationary fronts are denoted by alternating cold and warm front symbols on different sides.

• A transition zone between two air masses of different densities (temp) and humidities.

• They are important not only for temp. and humidity changes they bring but also for the uplift they cause (frontal “wedging”).

• Four primary types:
• Cold
• Warm
• Stationary
• Occluded

Frontal symbols used on surface weather maps. [Robert et al. 166]

• Identifying Fronts:
• Sharp horizontal temperature change
• Sharp horizontal dewpoint/humidity temperature change
• Shift in the wind direction
• Presence of clouds & precipitation
• Change in pressure

• Frontal Characteristics
• Why do fronts move?  Examine the vertical cross sections normal to the fronts which are moving.
• Air within the frontal zone is "trapped" in the shallow wedge beneath the frontal surface and thus can not move relative to the front, or conversely, the front can not move relative to it.
• The direction and speed of movement of the front is determined by the winds within the frontal zone.
• In warm front situation -- cold air retreats poleward and warm air tied to southerly winds tries to push up the frontal surface -- providing for the development of layered clouds (aka stratus).
• In cold front situation -- cold air (associated with northerly winds) advances southeastward forcing the warm air to rise vertically -- giving way to vertically developed clouds.

• Temperatures and Fronts
• Role of fronts in mediating surface temps is important, but other factors influence surface temps including: time of day, sky cover, altitude of the station, and proximity to water
• These can exert an equally important role of influencing temps

• Fronts are often difficult to locate because...
• Over oceans, temps are strongly influenced by underlying water (sea surface temps do not change much over a short distance)
• In mountainous terrain, large difference in station elevation mask the temp gradients
• Terrain effects, nocturnal inversions, convection, and UHI can all affect temps.

Moisture and Dew Point

• Similar to the steep temp. gradients located along lines of confluence, we see horizontal gradients of dew point.
• Steep gradient (continental vs. maritime air)
• Weak gradient (cool maritime vs. warm maritime air)

• In some situations the dew point gradient is a more reliable indicator; especially in summer when temp. differences near fronts are small.

• Dryline is the boundary between  marine and continental air masses.
• Forms due to land-sea geometry and terrain features.
• Typically form during warm season and are situated meridionally across the southern and central Great Plains.

Precipitation

• The distribution of fog and precip. is very much related to the location of the front.

• Early on, the precip. is located north of the stationary front because the warm air overruns the sloping frontal surface.  The snow continues along the front-range of the Rockies as easterly surface winds push the air up the mountain range, lifting mechanism.

• Eventually, the precip will become of greater intensity and will increase in areal coverage due to the surface low and upper air trough deepening causing more surface convergence.

• Fog exists along the warm front and north of the stationary front. Fog is common when warm, moist air passes over a colder, underlying surface.

• The band of precip. associated with the cold front is generally more intense but in narrow bands.  Often t-storms will occur along the cold front

Precipitation Tendency

• Passage of warm front is associated with a leveling off of the pressure (warm, moist air).

• Passage of cold front triggers a rise in the surface pressure.

• Pressure rises after a cold front are usually greater than the pressure falls which occur prior to the passage of a warm front.

• In surface analysis, lines connecting points at which the same pressure tendency occurs are called isallobars.

• The pressure falling in the vicinity of the low pressure indicates that the low is deepening as it moves.  With this comes stronger winds in the circulation around the low.

• When interpreting small changes in pressure, the diurnal cycle in solar heating produces small but noticeable pressure fluctuations that have nothing to do with synoptic situation.  These are referred to as tidal fluctuations and should be removed before a true synoptic assessment.

Works Cited

Aguado, Edward, and James E. Burt. Understanding Weather and Climate. 7th ed., Pearson, 2014.

Rauber, Robert M., et al. Severe and Hazardous Weather: An Introduction to High Impact Meteorology. 4th ed., Kendall Hunt, 2014.

Wallace, John, and Peter Hobbs. Atmospheric Science: An Introductory Survey. 2nd ed., Academic Press, 2006.

Upper-Level Troughs and Ridges

• We plot upper-level maps with contours, which are curves that connect places with the same heights (isoheights / isohypse).

• Ridges = areas on upper-level maps with greater heights, representing warmer columns of air.

• Troughs = areas on upper-level maps with lower heights, representing cooler, shorter columns of air.

• Generally, colder, shorter columns are found in the polar regions and the warmer, taller columns are found in the tropical and subtropical regions.

• On upper-level maps, the air is accelerated from the region of greater heights toward the region of lower heights (from high to low pressure).

• Warm air tends to rise ahead of the trough axis, while cold air tends to sink behind the trough axis.

• The rising, warmer air may generate clouds and precipitation ahead of the trough axis, while the sinking, colder air may generate clearing skies behind the trough axis.

• The upper-atmosphere dictates what happens at the surface!

• Wind speed is inversely proportional to the spacing between the height contours (isobars).
• Close height contours = faster wind speeds.
• Far apart height contours = slower wind speeds.

• The upper-level flow is dominated by the location of very large amplitude, synoptic-scale disturbances (troughs and ridges), which generally change in intensity and position from day-to-day.

• Generally, ridges and troughs cancel each other out when averaged for a month, season, or year, providing a more zonal appearance!

http://mp1.met.psu.edu/~fxg1/HEMI500/5dayloop.html

Longwaves

(aka Rossby / Planetary Waves)

• Longwaves have wavelengths of thousands of kilometers and represent the large scale, global flow.

• Generally, move slowly from west to east, but may become stationary or retrogress slowly from east to west.


• In the northern hemisphere, we see 3-7 long waves with wavelengths of 50-120°, with the wave number changing over days or weeks, and through the long waves move the faster short waves.

• Influence the locations of large regions of warm versus cold temperatures, wet versus dry conditions, the position of the jet streams and storm tracks.

• Longwaves are barotropic (in which pressure depends only on density).

Advection

• Advection = horizontal movement of air.

• Warm Advection occurs when the wind blows across the gradient of temperature from higher toward lower temperature / thickness.

• Cold Advection occurs when wind blows across the gradient of temperature from lower to higher temperature / thickness.

Shortwaves

• Shortwaves tend to have wavelengths of less than 3,000 km.

• They move rapidly from west to east, around or through longwaves.

• Represent smaller pools of cold and warm air aloft.
• Shortwaves are baroclinic

• Pools of cold air aloft may lead to instability, outbreaks or rain/snow showers, or thunderstorms (in extreme cases).
• Significant "weather-makers"

• Dry channels ahead, moist channel behind.

Extratropical / Midlatitude Cyclones

• Cyclone = any circulation around low-pressure.

• Extratropical Cyclone = large low-pressure system that often form in the mid-latitudes.

• Day-to-day weather in the mid- and high-latitudes is closely related to the location, development, and movement of cyclonic storms.

• Cyclones are responsible for:
• Changing air masses (temperature, dew point, wind, etc)
• Bringing precipitation opportunities

• Most weather is linked to extratropical cyclones, rather than being discrete weather events.

• Vertically speaking, they're found in the tropopause.

• Needed to balance temperature differences between the poles and equator (between the cold upper troposphere and the warm lower troposphere).

• Most intense in the late fall, winter and spring due to the temperature gradient between the tropics and the north pole being the strongest during that time.

• Winds blow counterclockwise (cyclonically) in the northern hemisphere and clockwise (cyclonically) in the southern hemisphere.

• It forms at intersecting fronts:
• Cold front is typically south and west, to east of the low.
• Cold air is "behind" the low, while warm air is "ahead" (lows and highs both move in the direction of the jet stream winds).
• Thunderstorms are often ahead of the cold front.
• Steady precipitation is often ahead of the warm front.

• Cloud Sequence: cirrus, cirrostratus, altostratus, nimbostratus

Norwegian / Bergen Cyclone Model

• During WWI, Vilhelm Bjerknes identified that midlatitude cyclones formed along the boundary separating polar air from the warmer air to the south.

• Widely used by weather forecasters to intercept and anticipate changes in the surface synoptic chart.

• Most real cyclonic disturbances do not fit the model perfectly.

•  Things that are difficult to identify:
• Warm fronts
• Problems with topography distorting / obscuring fronts.
• Some storms develop away from the stationary front.
• Fronts sometimes develop by themselves.

Life Cycle of a Midlatitude Cyclone. (a) According to the Norwegian model, the stationary polar front separates opposing masses of cold air and warm air. (b) Cyclogenesis first appears as a disruption of the linear frontal boundary. (c) The cyclone becomes mature; distinct warm and cold fronts extend from a low-pressure center. (d) Occlusion begins as the cold front catches up to the warm front. (e) Occlusion intensifies as more of the cold front catches up to the warm front. [Aguado and Burt 291]

Aguado, Edward, and James E. Burt. Understanding Weather and Climate. 7th ed.,  Pearson, 2014.

Types of Relative Vorticity

Radar Reflectivity: March 1, 2017 Severe Weather Event

March 1, 2017 Severe Weather Event

Strong linear storms, sparked by an incoming cold front, swept across most of the eastern united states. There was also strong forcing along the impending cold front, as shown in figure 1. Due to the very warm temperatures prior to the cold front with steep mid-level lapse rates and some wind shear, that encouraged the storms to become severe. However, the Georgia area had enough instability for convective development which gave way to the watches and warnings which were issued throughout the day from 11:50 AM to about 9:00 PM, as you can see in figure 2. Strong winds downed many trees and power lines, leaving roughly 32,000 people without power. Meanwhile, further north, the great smoky mountains national park, straddling Tennessee and North Carolina, closed all roads due to the high wind danger. Many reports of hail were also recorded and even one brief tornado in northern Georgia. The QLCS (quasi-linear convective system) tornado had 90 MPH winds, the EF-1 tornado touched down near Chatsworth, GA, tracking three miles west of Chatsworth. As you can see in figure 3, the cell to the northeast of the red point (Chatsworth, GA) seems to be the one from which produced a tornado. Unfortunately, the closest radar, KHTC in Hunstville/Hytop, AL, was down due to the power outages thus the next closest radar was used, KFFC in Atlanta, GA. The NWS (national weather service), from KFFC, provided figure 4 which shows the storm when it produced the EF-1 tornado over Chatsworth, GA at about 4:30 PM. This system also produced up to golfball sized hail and peeled back roofs. However, as the system continued to move southeast into central Georgia, the storms weakened substantially. Nonetheless, before dying out, this system produced roughly five dozen tornadoes, over 600 high wind reports, and over 100 large hail reports as it tore through parts of the Midwest, South and East United Stated from February 28 to March 1, 2017, making it the largest severe weather outbreak since late spring 2011.

Figure 1

Figure 2

Figure 3

Figure 4

Velocity Radar: November 5, 2017 KBUF

November 6, 2017—Buffalo, NY

A storm system moved through the area of Buffalo, New York on November 6, 2017 between 0029Z and 0200Z. A cold front was prominent near Saint Catharines, Ontario, Canada to Erie, Pennsylvania and crossed the region from west to east between 0100Z and sunrise. In advance of this cold front, there was moderately strong south-southwest low-level flow with surface gusts up to 30 MPH (fig.1). In radar imagery from GIF1 and GIF2, there seems to be a mesoscale convective vortex (MCV) present over northwest Pennsylvania. Towards the beginning of GIF1, there was actually an EF-1 tornado reported at 23:22 UTC (6:05 PM EST) by the National Weather Service (NWS) storm survey team, just four miles southwest of the town of Erie in the Millcreek Township. The tornado track was roughly 2.4 miles in length by 100 yards in width, with maximum winds estimated to be 90 MPH. Fortunately, no one was killed or injured during this event that brought nearly three inches of rain to the area. However, there was not really any indication on radar that there was a tornado. Next to the green inbound winds, there was no red outbound winds near the area, instead there was purple haze, indicating that the radar was unable to determine the wind’s velocity, which is referred to as range folding (RF) or velocity folding. Depending on the radar’s operation mode and PRF (pulse repetition frequency), the range folded data may occasionally obscure large portions of the radar’s image. As you may notice in GIF3, there seems to be a decent amount of range folding near the southern end of this storm system. At any rate, another reason I would not have thought there was a tornado just from radar alone was due to the lack of intensity of the inbound winds. Generally, intense circulations with diameter of one mile or less are tornadic, while large couplets are associated with mesocyclones. There is no specific value of diameter and magnitude that differentiates between the two due to the variety of circulations that may occur and due to gates having a variety of volumes and height, which depend on range and beam width. However, in this case, I suspect that the radar probably overshot the tornado circulation completely, given that the tornado occurred roughly 8,351 feet from the radar.

Figure 1

GIF 1

GIF 2

Figure 2

GIF 3