The southern Alberta snowstorm of October 27, 2013

What happened

A cold front passed through Alberta on the morning of October 27, 2013, ushering in a deep upslope flow and air much colder than the previous day, where temperatures had reached into the 20s. As the cold air deepened, the rain changed over to snow. The RADAR presentation of this changeover is presented here.

The beginning of the animation shows a bright band. A bright band is a region of higher reflectivity embedded within a relatively lower-reflectivity synoptic precipitation shield. The bright band signifies where relatively low-reflectivity snow is melting, changing over to much higher-reflectivity wet snow or rain. When you see a bright band on the RADAR, it's a strong signal that melting is likely occurring at that level. On the morning of October 27, 2013, the bright band can be seen as a ring of higher reflectivity around the RADAR, and this ring moves steadily closer and closer to the centre of the RADAR until, at 13:50Z (7:50 AM MDT), the ring disappears--indicating that the changeover from rain to snow at the surface is complete.

RADAR images

0.5° PPI

Observations

Here are the Calgary observations, showing that the changeover to snow finished there (about 40 km away from the RADAR site) at 14:34Z (8:34 AM MDT).

CYYC 270900Z 01011G16KT 15SM VCSH OVC045TCU 06/03 A2993 RMK TCU8 SLP146
CYYC 270906Z 02011KT 14SM -SHRA OVC045TCU 06/03 A2993 RMK TCU8 SLP145
CYYC 271000Z 04012KT 14SM -SHRA FEW025 OVC040 05/03 A2994 RMK CU1SC7 TCU EMBD SLP153
CYYC 271033Z 07008KT 9SM -SHRA OVC020 04/03 A2993 RMK SC8 DIST BR / TCU EMBD SLP151
CYYC 271100Z CCA 07006KT 9SM -SHRA FEW007 OVC020 04/03 A2993 RMK CF1SC7 DIST BR / TCU EMBD SLP155
CYYC 271139Z 06010KT 8SM -SHRA BKN005 OVC020 04/03 A2994 RMK SC6SC2 VRY LO CIG / DIST BR / TCU EMBD SLP157
CYYC 271200Z 06006KT 7SM -SHRA FEW004 BKN005 OVC020 03/03 A2994 RMK CF1SC7SC1 CF TR LO CIG / DIST BR / TCU EMBD SLP160
CYYC 271300Z 07006KT 8SM -RA OVC006 03/02 A2996 RMK SC8 LO CIG SLP168
CYYC 271328Z 07008KT 5SM RA BR OVC010 03/02 A2997 RMK SC8 SLP173
CYYC 271347Z 07010KT 5SM RA BR OVC014 02/01 A2999 RMK SC8 T / 2C SLP179
CYYC 271349Z 06009KT 5SM RA BR SCT007 OVC014 02/01 A2999 RMK SC3SC5 VIS VRB 4-6 PRESRR SLP180
CYYC 271400Z 05011KT 5SM RASN BR BKN006 OVC012 02/01 A3000 RMK SC5SC3 PRESRR SLP187
CYYC 271415Z 05011KT 2 1/2SM -RASN BR FEW002 BKN006 OVC015 00/M00 A3002 RERA RMK SC1SC6SC1 PRESRR SLP196
CYYC 271434Z 05011KT 3/4SM SN BR FEW003 BKN005 OVC015 00/M00 A3004 RERA RMK ST1SC5SC2 PRESRR SLP203
CYYC 271500Z 04011KT 3/4SM SN BR BKN005 OVC013 M00/M00 A3007 RERA RMK SC5SC3 PRESRR SLP216
CYYC 271551Z 04019KT 5/8SM SN BLSN BKN005 OVC016 M01/M01 A3012 RMK SC6SC2 PRESRR SLP235
CYYC 271600Z 04026KT 5/8SM SN BLSN BKN005 OVC016 M01/M02 A3013 RMK SC6SC2 /S03/ PRESRR SLP242
CYYC 271624Z 04019G25KT 5/8SM -SN BLSN OVC008 M01/M02 A3016 RESN RMK SC8 PRESRR SLP252
CYYC 271700Z CCA 04021G29KT 5/8SM -SN BLSN OVC009 M02/M03 A3021 RESN RMK SC8 PRESRR SLP273
CYYC 271717Z 03020G26KT 3/4SM -SN DRSN BR BKN011 OVC022 M02/M03 A3023 RMK SC6SC2 PRESRR SLP279
CYYC 271743Z 03021KT 1SM -SN DRSN BR BKN006 OVC020 M02/M03 A3026 RMK SC5SC3 PRESRR SLP289
CYYC 271800Z 02019G24KT 1SM -SN DRSN BR BKN007 OVC015 M02/M03 A3028 RMK SC6SC2 PRESRR / S04/ SLP293
CYYC 271839Z 02019G25KT 3/4SM -SN DRSN BR OVC012 M02/M03 A3031 RMK SC8 SLP302
CYYC 271900Z 36019G25KT 3/4SM -SN DRSN BR FEW005 BKN008 OVC016 M02/M03 A3031 RMK ST2SC4SC2 SLP306
CYYC 271945Z 02018G25KT 5/8SM -SN BLSN BR BKN007 OVC015 M02/M03 A3033 RMK SC6SC2 /S01/ SLP310
CYYC 272000Z 02020G28KT 5/8SM -SN BLSN BR BKN006 OVC016 M03/M04 A3033 RMK SC6SC2 SLP315

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