Classic Alberta Weather Situations -- some Examples

Slow-moving closed upper low produces cool, wet summer weather

8-9 July, 2011

Freezing Rain

29 Dec., 2011

Surface
- 12Z 29 Dec
850 hPa level
- MSC 850 hPa analysis, 12Z 29 Dec
- vert moisture flux, from 0hr GEM prog valid 12Z 29 Dec (spots of large upward flux in C. Alberta; Edmonton lat 53.53N, long -114.10)
700 hPa level
- vert moisture flux, from 0hr GEM prog valid 12Z 29 Dec (spots of large upward flux in C. Alberta)
Sounding
- 12Z 29 Dec
Observed weather
- Hourly obsv. at Edmntn 29 Dec
- MSC forecasters' informal discussions

Extreme Winter Cold

Typically the cause is a sustained northerly upper flow due to a low in NE Canada, e.g. 1 Feb. 2007 (note that we are on the cold side of an Omega block). Typically when an "arctic vortex" in NE Canada sweeps cold air down, we escape the worst of it, e.g. note here the isotherms at 850 hPa on 5 Feb. 2007.

9 Dec. 2009

500 hPa analysis 12Z 11 Dec. A flow from the N.
700 hPa analysis 12Z 11 Dec
850 hPa analysis 12Z 11 Dec. Cold air moving south at low level.
850 hPa analysis 12Z 12 Dec
surface analysis 06Z 13 Dec. The arctic ridge.
surface analysis 12Z 13 Dec
sounding 12Z 12 Dec

17 Jan. 2012

Observed weather at CYEG
700 hPa flow 12Z today (and 12Z 16th and 12Z 14th). Note the switch from a flow off the Pacific (which had dominated the fall and early winter of 2011) to a northerly flow
850 hPa flow. Cold air over Ab with a sharp temperature rise across the Rockies.
surface. An arctic high in residence.
sounding. Much milder air aloft.
forecasters' discussion
backward trajectory ending at ground level at Edmonton 12Z Jan 17.
NOMADS 700 hPa (i.e. regenerated at NOMADS Nat'l Op'l Model Archive & Distrib'n System).
Cross-section of temperature and potential temperature along a line NW-SE from Fort Smith (NWT) to Wilmington Illinois (prepared using RAOB).

Late fall mild spell -- courtesy of lee trough

16 Nov. 2009

700 hPa analysis 12Z 16 Nov. SW flow over Rockies.
850 hPa analysis 12Z 16 Nov. Strong ageostrophic flow. Lee trough. Trowal.
surface analysis 06Z 16 Nov. Lee trough seen in sfc isobars.
GOES IR showing dry slot in lee of Rockies (14Z 16 Nov.)
View from campus
Hourly weather at Edmonton Int'l Airport (CYEG). Nov. normal daily maximum is -0.4

Often it is the SW flow that makes temperatures much, much warmer in Alberta than further to our east, e.g. 4 Mar. 2007.

22 Nov. 2011

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