RECORD SNOWFALL in UPPER MIDWEST- DEC
|Bob Rabin1,2 and Scott Bachmeier2
NOAA/National Severe Storms Laboratory,
Cooperative Institute for Meteorological
Satellite Studies, University of Wisconsin-Madison2
After several mild
winters, the upper Midwest experienced near record low temperatures and
high snowfall during the month of December 2000.
First cold December in years
the mean temperature in Madison was 11.2 F as compared to the December
average of 21.7 F. This was 0.4 F above the record low of 10.8 F.
was subfreezing continuously except for 2 brief periods on the 3rd and
4th when high temperatures reached 34 and 35 F respectively.
The mean minimum
temperature was 2.0 F. The temperature fell below zero (-18 C) on 13 days
with -21 F (-29.5 C) the coldest on the 25th.
Waterloo IA set
a monthly minimum record with -29 F on 25 December..
snow fell on 20 days giving a record total of 35" for the month.
was 8.2" on the 18th, followed by 5.0" on the 11th, 4.6" on the 20th.
equivalent for the month was only 1.39" giving an average snow/liquid ratio
of almost 30 to 1.
occured when the temperature was between 5-15 F. In some cases the snow/liquid
ratio was as high as 40 to 1.
Madison snow depth of 17" tied for the greatest December snow depth.
set a new snowfall record of 49.5" in December. This broke the previous
record of 27.9" by almost 22"!
in Milwaukee was occasionally enhanced by northeasterly flow over Lake
on the 11th was the greatest December single-day snowfall
as much as 32" of snow on the ground at MKE late in the month.
data from Wisconsin are available from the NWS MKE
(Milwaukee/Sullivan) Web page.
the 21st, the average snowfall from all stations across the state was 19.8"
- already a new record for December
depth reached 31" across northeast Iowa (29 December at Tripoli).
record Midwest snowfall for December:
59.2 " *
8.2" (.8" short of record)
* - record snowfall for any month (see link from NWS
The abnormally cold
snowy December was due to the frequent delivery of arctic air and passage
of perturbations in northwesterly flow aloft. A high latitude blocking
pattern was accompanied a persistent high amplitude central/eastern trough,
western ridge at mid latitudes. Fig.
1 and Fig.
2 show the geopotential height (m) mean and anomaly patterns
at 500 mb for December 2000 (obtained from the NOAA Climate Diagnostics
Center interactive website).
Note the closed high just south of Greenland and the ridge stretching from
the west coast of Canada north through Alaska to another closed high north
Highly amplified northwesterly flow pattern
This is similar
to the general pattern described in the winter outlook (issued this December)
by the Climate
Prediction Center. As described in their winter outlook, the pattern
is characteristic of the low index phase of the arctic oscillation (Fig.
3) where high pressure is dominant near the north pole and the negative
phase of the North Atlantic Oscillation (Fig.
4) where blocking is observed near southern Greenland. Note that most
of the winters in the 1990's were dominated by the high index phase of
the arctic oscillation (lower pressure near the pole) and a positive phase
of the North Atlantic Oscillation (low pressure near Greenland). The arctic
oscillation appears to have a connection with stratospheric temperature
changes, for example see the Annular
Modes Website . This December 2000 pattern finally broke down during
the first week in January 2001 with the onset of more zonal flow preventing
the southerly penetration of arctic air into the U.S.
Winter outlook: Arctic and North Atlantic oscillations
Photos of the landscape
in Madison WI taken by the author on the morning of 21 December can be
viewed by clicking here.
These were taken along the bicycle route to work near the University of
Wisconsin-Madison campus. The temperature was 0 F (-18 C), skies were clear,
and winds were gusting from the west in the wake of a departing clipper
system. Some interesting satellite and ground scenes of the ground blizzard
in Iowa that day can be found here.
Winter scenes from Wisconsin
For a view of the snowcover as viewed from Scott's deck on 20
December click here.