Terms and Abbreviations used in the Forecast
- Alberta Clipper - An area of low
pressure that originates from the Canadian Prairie Province of
Alberta. The low usually tracks MN, WI and into far northern sections
of IL, IN, OH and southern lower MI. Light snows on the order of
1-4" usually fall with these systems. There is usually arctic air
in place when the storm arrives and thus the snows are usually light and
- Canadian High - Area of high pressure
that moves in from Canada. These generally produce clear weather and
- Cat (x) Storm
- A snow storm where (x) is used to describe the intensity level (1-6) using
the Dee Snowstorm Scale.
- Clipper low - see Alberta Clipper
- Colorado low - An area of low pressure that forms on the east side of the
Rockies in the vicinity of eastern CO and then tracks almost due east
through the central Plains and central/northern Midwest. These low
pressures generally bring light to moderate snows on the order of 3-8"
to the northern 1/2 of the Midwest.
- Cross Polar Flow - The atmospheric
setup when the jetstream crosses the north pole and continues nearly
straight south into the US. This setup generally produces the coldest
air outbreak possible for the central US.
- Cut off Low - An area of low pressure
in the upper atmosphere that is cut off from the main jetstream flow.
Cut off lows can be very slow to move and thus produce a prolonged
precipitation event over the area where it is sitting.
- Ensemble - Long term forecast model,
going out to 360 hours with global coverage. The Ensemble is actually
just what it says it is, an ensemble of different runs of the GFS.
Each version of the GFS has been tweaked to "force" an error into
the forecast. They then take the averages of all these models to try
and hone in on the strong points of the forecast and eliminate as many
errors as possible.
- NAM - Short term forecast model, going
out to 84 hours covering North America Only
- GFS - Long term forecast model, going
out to 360 hours with global coverage
- Jetstream - A corridor of stronger
winds in the higher levels of the atmosphere- typically 20-30 thousand feet
above the surface of the earth. There can be as many as three
different jetsream branches going over the US at any particular time.
The sub tropical jet rides along the southern US and separates the cool air
of the mid latitudes from the warmer and more humid air of the tropics or
sub tropics. The polar jet is the main weather making jet in the US
and separates the cool air of the mid latitudes from the cold air of the
higher latitude regions. The arctic jet occasionally visits the lower
48 in the cold months. It separates the cold air of the higher
latitudes from the bitterly cold air of the arctic.
- LES - Lake Effect Snow
- LES Belts - The areas downwind of the
Great Lakes that are favored for Lake Effect snow. (see
- Low Level Jet - A corridor of stronger
winds in the lower levels of the atmosphere (1000-7000 feet above the earths
- Midwest - The states including the
Dakotas, MN, IA, WI, IL, MI, IN and OH.
- Northwest Flow - The atmospheric setup
when the jetstream is aligned from western Canada into the central and
southeast US. Known to bring below average temperatures to the Midwest
along with below average precipitation.
- Northwoods - Opinions my differ, but
my description of the Northwoods of the Midwest is areas generally to the
north of a line from about Fargo ND to Brainerd MN to Wausau WI to Houghton
- NWL - Northwest lower MI. Area
of MI running roughly from about Frankfort to Grayling to Cheboygan
- OH River Valley - Area of land around
100 miles either side of the OH River from it's juncture with the MS River
to the south eastern corner of OH
- Panhandle Hooker - An area of low
pressure that forms in the vicinity of the TX/OK panhandle region. It
then tracks to the east and northeast into the Midwest. These storms
are known to bring heavy snows to the Midwest on their northwest side of the
- Phasing or Jet Stream Phasing - A
situation when the troughs of one or more of the jetstreams phase up or
become aligned. This usually results in the combining of the energies
contained in the different jetstreams and forms a powerful area of low
- Split Flow - Nearly the opposite of
phasing. It is when the different branches of the jetstream are
misaligned or separated from each other. This setup usually causes the
polar jet to be displaced to the north and puts the northern US in above
average temps. Storms can still form, but are usually not big snow
producers because of the mild temps.
- SWL - Southwest Lower MI. An
area of MI running from the IN border north to near Holland.