Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1104 PM CST Thursday Nov 27 2014
Short term...(this evening through friday)
issued at 327 PM CST Thursday Nov 27 2014
Main concern is timing of snow and the attendant headline over the
northeast County Warning Area.
Models trend a burst of warm air advection snow across the County Warning Area developing over
west and central Minnesota this evening...and spreading into west
central Wisconsin mainly after midnight. With clouds
increasing...should see temperatures stop their decline...which will
likely be rapid to the east this evening.
Best isentropic lift moves into eastern Minnesota by 06z and the remainder
of the night over western Wisconsin. Snow amounts in the 2 to 3
inch range are expected for the most part along and north of i94 and
along and north of Highway 8 in Wisconsin. This should gradually end
over the northeast portion of the County Warning Area Friday morning...perhaps
lingering a bit into northwest Wisconsin into the afternoon. Added
another County east/Rusk County/in Wisconsin for now...beginning
after midnight. The remainder of the advisory looks good. There may
be a bout of freezing drizzle on the back side of the warm air advection Wing of
snow and elevated warm layer moves through. Continued to mention
that possibility as well. Models also generated a small chance of
sleet...which could be possible if the water droplets refreeze in
the cooler air near the ground. Again...this would occur on the west
end of the snow area...as it moves east into Wisconsin Friday
Fridays high temperatures will remain in the 20s for the most
part...perhaps some readings around 30 in the far southwest County Warning Area.
Expect clouds to remain however.
Long term...(friday night through thursday)
issued at 327 PM CST Thursday Nov 27 2014
Friday night and Saturday...the strongest warm air advection and associated lift
will be north of the forecast area by Friday night. Some weak warm air advection aloft still
expected through the night...however 900-700h drying will inhibit any
very light precipitation that may try to reach the ground. Closer to the
surface...saturated soundings with increasing dew point temperatures
still introduce the concern for fog...at least in southern Minnesota
overnight through Saturday morning. 850h temperatures should warm to +8 to
+12c by early Saturday morning.
Saturday through Saturday night...warm advection will continue over
the entire County Warning Area Saturday morning. Decent isentropic lift with
relatively moist air moving over the snowpack should promote the
development of a stratus deck especially in northern
locations...which could persist much of the day. The GFS and NAM
also develop some spotty, very light precipitation over parts of our
region during this time...but the European model (ecmwf) has nothing. With the best
forcing to the north of our region...will not introduce precipitation into
the grids. Cloud cover will likely suppress warming...especially in
northern and eastern parts of the County Warning Area. However...enough breaks in
the cloud deck and continued warm advection should lift some
southern areas into the 40s during the afternoon...especially in
locations that did not receive significant snow from wednesday's
storm. A cold front will then move through the area from northwest
to southeast Saturday evening through the overnight hours.
Measurable precipitation is once again unlikely with the frontal
passage...but temperatures will drop significantly behind the front,
with some gusty northwest winds possible in western Minnesota.
Sunday and beyond...the see-saw of temperatures will continue
through early Sunday morning as strong cold air advection continues
from the overnight frontal passage mentioned above. Temperatures will hardly
recover Sunday and be a solid 20 degrees colder than Saturday at
least. Good agreement on a very strong high pressure area moving in
from the northwest will make for a very cold start to the work
week. Significantly lowered the high temperatures for Monday to the lower
teens across the region. That type of cold wont last long though as
increasing southerly winds on the back side of the high deliver some
modification to the region Tuesday.
The GFS has been advertising a large cyclone moving through the
Midwest during the middle of next week. It has been sporadic with
its overall evolution of the pattern and the European model (ecmwf) indicates dry
with a ridge over the Midwest at the same time. So confidence is so
low in any precipitation occurring for our area...decided to keep
the forecast dry until at least some agreement or consistency is
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1103 PM CST Thursday Nov 27 2014
A band of warm air advection snow will push across eastern Minnesota and western WI
early this morning. Ceilings and visibilities will drop to IFR for
a several hour period. In the wake of the band of snow...a loss of
middle level clouds/ice crystals is still seen in short term
guidance. This may lead to some light freezing drizzle Friday
morning. Confidence is not real high on occurrence and a probability
group was used at most of the taf sites. Another weak weather
disturbance will move across central Minnesota and west central WI Friday
evening. Profile data indicates a rather significant warm layer
aloft with sleet being the precipitation type. Confidence is not
high on this occurring as it has recently begun to show up in model
data this evening. Again...used a probability group from kstc through
Keau. Southeast winds 6-12 knots overnight becoming east-southeast 4-6 knots Friday
afternoon and evening.
Kmsp...a band of IFR snow will move through in the 06z-08z time
frame with MVFR conditions/-sn through daybreak. Snow accumulation
overnight up to an inch. A threat remains Friday morning/early
afternoon for some freezing drizzle. Moved the occurrence to a probability
group due to lower confidence. Pushed ceilings to VFR Friday
evening as the warm front moves east of the airfield.
/Outlook for kmsp/
Sat...MVFR ceilings. Winds S at 5-10 kts.
Sun...VFR. Winds northwest at 15g20 kts.
Monday...VFR. Winds northwest at 5-10kts...becoming S late
Minnesota...Winter Weather Advisory until 4 PM CST Friday for mnz042>045-050-
WI...Winter Weather Advisory until 4 PM CST Friday for wiz014-015.
Winter Weather Advisory until 4 PM CST Friday for wiz016.