Transcript Slide 1

Lecture 4: Map Discussion
In Wednesday’s class I noted the
weather office comment that “A
COLOSSAL WEATHER
PATTERN CHANGE IS
UNDERWAY OVER THE
PRAIRIES”….
… with a switch to a flow
from the far north, and
formation of a closed
upper low over BC
SIGNIFICANT WEATHER DISCUSSION FOR THE CANADIAN PRAIRIES
ISSUED BY THE PRAIRIE AND ARCTIC STORM PREDICTION CENTRE OF
ENVIRONMENT CANADA AT 7:00 AM CDT THURSDAY SEPTEMBER 14
2006… SNOWFALL WARNING IN EFFECT FOR THE MOUNTAIN PARKS.
DISCUSSION...THE PATTERN CHANGE IS UNDERWAY OVER AB, WITH
PLENTY OF COLD AIR FLOODING INTO THE PROVINCE. THIS IS
DESTABILIZING THE AIRMASS OVER ALBERTA AND TIGHTENING THE
BAROCLINIC ZONE LOCATED OVER THE EASTERN PRAIRIES. THUS,
THERE WILL BE MANY CONCERNS OVER THE NEXT FEW DAYS.
AB...UPPER TROF CONTINUES TO DIG OVER WESTERN CANADA WITH
BROAD CLOSED CIRCULATION DEVELOPING. RAIN WILL CONTINUE
FOR THE REST OF THE WEEK WITH TOTAL VALUES NEAR 60MM.
…PRECIP TYPE IS STILL THE MAIN CONCERN AS THE FIRST SNOWFALL
WARNINGS OF THE SEASON HAVE BEEN ISSUED. END/CARLSEN/MARK
(The forecaster David Carlsen is an EAS graduate)
Received the following bulletin at Thu Sep 14 08:55:15 2006 GMT
… FCST PRBLM IS HOW FAR TO THE E AWAY FROM THE FOOTHILLS
MIGHT SOME OF THIS SNOW CREEP. REG GEM** BRINGS EDGE ABT
AS FAR E AS A PEACE RIVER-EDSON-CALGARY LINE BY ABT 3036HRS..AS SFC LOW HEADS FOR ND..ALLOWING FOR MORE ARCTIC
AIR TO PUSH SWD & SEWD..A TRICKY SITN..AS THE FIRST SIG
SNOWFALL OF THE SEASON USUALLY IS.
(** Regional GEM, Regional run of the CMC Global Environmental
Model)
• closed low
• coastal ridge
• wind // height
• weak prairie winds
•T=?
• Td = ?
CMC 500 mb analysis, Thurs 14 Sept 2006, 12Z
• upslope C. Ab
• ovc entire W. Cda
• steady rain, Edm, Cgry
Surface
Convergence?
• upslope Ab wind
• how high is 850 mb sfc
over Edmonton?
• baroclinic zone (strong
temperature gradient,
“T”)
height
CMC 850 mb analysis, Thurs 14 Sept 2006, 12Z
- - - 0oC isotherm
Low cloud
over Ab
uppr lo +
sfc cnvgnc
Correlates with the 500 mb
current around base of
closed low
absence of deep cloud
consistent with the rain
proving light and
intermittent Thursday am
• wind profile consistent
with analysis charts
• entire troposphere
saturated (or nearly)
Light, upslope