11 Inches of Snow from an Alberta Clipper?! Post-Analysis of an Unlikely Heavy Snow EventScott M. Rochette1 and Thomas A. Niziol2
1Department of the Earth Sciences, SUNY College at Brockport 2NOAA/NWSFO Buffalo, NY
Summary• Cool-sector MCS
– cool side of sfcboundary– cool side of 850-hPa e
• Strong LLJ– moisture transport– destabilization– coupled to ULJ?
• MCS in region of positive LL e advection
• Stable boundary layer– elevated CI– MCS not rooted to
boundary layer
• High moisture content– PW 230-270% of normal
• Diagnosis of UVM– Cross-sections – surfaces
• Isentropic MT vectors very illustrative– MCS forms downstream
of max MT vectors
11
8108
8
106
6
26
2
94
5
1 6
3”
6”
6”
6”
3”
3”
3”
9”
9”
6”
24-h snowfall amounts (in.) ending at 1200 UTC 12 January 2004
1800 UTC 11 January 2004 (f06) 0000 UTC 12 January 2004 (f12)
0600 UTC 12 January 2004 (f18)
1200 UTC 12 January 2004 (f24)Eta MSLP (blue, hPa) and 500-hPa heights (pink, dkm)
Eta 400-hPa heights (pink, dkm)/divergence (blue, 10-5 s-1)/isotachs (colors
60 kt)(f00/1200 UTC 11 January 2004)
Summary• Coupled UL jet streaks
– modest (each ~100 kt)– phased quickly over
Great Lakes area (< 24 h)– enhanced UL divergence
around time/location of +TSSN
• Eta performance– coupling signal present
but not obvious– QPF suggested potential
for +SN
• Cross-sections– strong UVM beneath
divergence max– linked secondary
circulations evident– LL max (ageo WAA) – Deep moisture/mid-level
conditional instability
• Moral– evaluate potentially
strong forcing for significant model QPF
– (it might be on target!)
Introduction• Fast-moving clipper
– weak low (~1005 hPa)– MN to ON in 24 h
• Limited expectations– modest snow amounts– main concern: wind
• Eta forecast– 0.5 in. liquid (6 in. snow)– from a clipper?– should (would) you
believe this?
• What happened…– narrow band of +SN over
western NY state– 1 in. h-1 snowfall rate at
times– lightning/thunder (!)– up to 11 inches of snow!
• Questions (be honest): – would you think +TSSN
with a clipper?– how well do you trust
model QPF?
Eta 400-hPa heights (pink, dkm)/divergence (blue, 10-5 s-1)/isotachs (colors
60 kt)(f06/1800 UTC 11 January 2004)
Eta 400-hPa heights (red, dkm)/divergence (blue, 10-5 s-
1)/400-hPa isotachs (colors 60 kt)/
850-hPa isotachs (dashed pink, kt) (f18/0600 UTC 12 January 2004)
Eta 400-hPa heights (red, dkm)/divergence (blue, 10-5 s-1)/isotachs (colors 60 kt)
(f12/0000 UTC 12 January 2004)
Eta cross-section of ageostrophic circulation (red arrows)/
isotachs (white, kt)/divergence (blue, 10-5 s-1)/ (cool colors < 0 b s-1)
(f12/0000 UTC 12 January 2004)
Eta cross-section of lapse rate (pink, C km-1)/RH (colors 30% or 70%)
(f12/0000 UTC 12 January 2004)
Eta cross-section of ageostrophic circulation (blue arrows)/
along-section ageostrophic isotachs (red, kt)/frontogenesis (cool colors > 0)(f12/0000 UTC 12 January 2004)
1145 UTC 11 January 2004 IR satellite (colors T -30C)/
Eta 400-hPa heights (blue, dkm)/isotachs (black, kt) (f00/1200 UTC 11 January 2004)
1815 UTC 11 January 2004 IR satellite (colors T -30C)/
Eta 400-hPa heights (blue, dkm)/isotachs (black, kt) (f06/1800 UTC 11 January 2004)
0015 UTC 12 January 2004 IR satellite (colors T -30C)/
Eta 400-hPa heights (blue, dkm)/isotachs (black, kt) (f00/0000 UTC 12 January 2004)
0301 UTC 12 January 2004 0.5 reflectivity (dBZ)/0300 UTC 12 January 2004 METAR observations
