The Raymond, AB tornado of April 18, 2004

What happened?

At approximately 6:10 PM on the evening of April 18, 2004 (0010Z April 19 2004), a tornado touched down in a field near Raymond, AB. No damage was reported from this tornado. Raymond is in the south end of the province, about 30 km southeast of Lethbridge. The tornado was on the ground for approximately 20 minutes, and was photographed many times. Dime to quarter sized (18 to 25 mm) hail was associated with this thunderstorm, falling at approximately the same time as the tornado was seen.

Location

Click here to see maps of where, exactly, the tornado touched down

Photographs

Pictures of the tornado and other associated pictures, courtesy of Bob Schefter

Meteorological setup

note: the upper air fields are based on the 12-hour GEM prog; the surface-based fields are derived from a combination of actual surface conditions and the 12-hour GEM prog

250 mb - there was a reative lull in the jet level winds with 10 knots progged over the area; the base of a trough was approaching
500 mb - the 15 knot southwest wind at this level was advecting in cooler (-28° C) air, promoting destabilisation
700 mb - the 10 knot west wind at this level was also advecting in cooler (-8° C) air
850 mb - with the approach of a subtle trough and its associated thermal ridge, the stage was set for some upward motion
Surface - with the approach of a subtle trough, surface convergence was likely
Surface-based CAPE - there are fairly low values here, in the 200 J/kg range
Helicity - very little 0-3 km helicity here - YQL (Lethbridge) is showing 12 m²/s²
Energy-helicity index - with the relative lack of CAPE and helicity, this dimensionless parameter's values were nil
850 mb to 500 mb lapse rate - a strong area of destabilisation was approaching from the west, with values of up to 35° C
Lifted index - weak instability is apparent here, with LI values in the -1° C range
Lethbridge progged tephigram - the tephigram shows the fairly dry low levels and modest lapse rates, including a superadiabatic lapse rate from the surface to about 750 mb
Lethbridge progged hodograph - this clearly shows very little low-level wind shear

RADAR images

Strathmore RADAR 2200Z to 0200Z 1.5 km CAPPI animation - the storm of interest is near the south (bottom) end of the image, around the 5th range ring
Schuler RADAR long-range radial velocity at 0010Z - the area of interest here is the far southwest corner of the image, near the outer (red) range ring
Strathmore RADAR long-range radial velocity at 0010Z - the area of interest is near the south (bottom) end of the image, around the 5th range ring
Cross-section of the storm from Schuler RADAR at 0010Z - left to right here is southwest to northeast through the storm; the storm is so far away from the RADAR that the lowest beam angle is almost up at 6 km above ground level
Cross-section of the storm from Strathmore RADAR at 0010Z - left to right here is south to north through the storm; once again, the storm is so far away from the RADAR that the lowest beam angle is almost up at 6 km above ground level
Strathmore RADAR 6-hour precipitation accumulation up to 0200Z - notice the relative maximum in the precipitation accumulation at the south end of the image, just south of YQL

Satellite animation

GOES-12 animation from 2202Z to 0202Z

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