Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
346 am CDT Tuesday Mar 11 2014
Short term...(today and tonight)
issued at 345 am CDT Tuesday Mar 11 2014
Most significant precipitation over the next 7 days will fall within
the next 12 hours of this discussion as an impressive frontgenetically
driven band of precipitation blossoms across the southern half of the County Warning Area
this morning. Hires models continue to be too cool with the low
level thermal fields...and thus their ptype algorithms are likely
overdoing the snowfall across the region during the initial
development early this morning. However...bufr forecast soundings
show tremendous lift along the low/middle level front as inferred from
the sharp wind shift within the h850-700 layer. Aside from the
lowest few hundred meters the entire sounding is below freezing...so
anticipating that the rain will change over to a rain snow mix
around 6-7am...and then quickly over to heavy wet snow around middle
morning across southern Minnesota.
Snow ratios will be in the middle-single digits...but quantitative precipitation forecast should easily
manage around 0.20 to 0.30 yielding snowfall totals of 1-2 inches
under the heaviest band of snow. At this point the rap 11.07 places
this heavy band from Canby Minnesota eastward through the southern
metropolitan...and therefore all the hires models that use the rap for
their initial boundary conditions are subconsciously drawn to this
conclusion. However...the h850-700mb fgen...which as of early this
morning matches up nicely with the ongoing precipitation...shifts southeast
from Canby to Mankato and Owatonna. Based on that diagnostic
tool...expect the precipitation to fall toward the southern side of the
current model generated quantitative precipitation forecast field. At this point not anticipating
any advisory criteria snowfall amounts...but expect heavy wet snow
with 1/2 to 1/4 Michigan visibility possible at times.
Long term...(wednesday through monday)
issued at 345 am CDT Tuesday Mar 11 2014
Looking ahead...cold air will surge southward behind this system as
it strengthens into a major storm over New England. Closer to home
temperatures will fall below freezing tonight and remain there until
Thursday when the next shot of Lee-side warm air spreads across the
region. This will bring temperatures into the 40s once again...with
50s in western Minnesota. There is a chance for some light precipitation ahead of
this warm air advection...mainly along the St Croix River Valley.
This warmup will be short lived as cold air spreads southward and
lasts into next week. No significant precipitation is expected until
the next storm system arrives on Tuesday.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1045 PM CDT Monday Mar 10 2014
A narrow band of light rain will enter west central Minnesota near the
start of the tafs and work east-southeast into the Twin Cities before
daybreak and into Keau around daybreak. It still looks like
kaxn...kstc and krnh are going to be on the northern edge of the
precipitation shield. Kmsp and Keau are a little more in line to
receive a few hours of rain and snow. Krwf remains the site for
a few inches of snow accumulation Tuesday morning as the band of
precipitation sinks into southern Minnesota. Ceilings are expected
to become MVFR in the rain/snow mix with MVFR or lower visibility. The
back edge of the precipitation will move southeast of the taf sites early
in the afternoon with ceilings forecast back to VFR. Light winds
overnight becoming north to northwest at 12-15 knots by Tuesday afternoon
with gusts from 20 to 25 knots. Winds diminishing Tuesday evening.
Kmsp...light rain still expected to begin in the 09z-10z period
and then mix with snow around 12z with a period of light snow
during the morning. Accumulations will be light and less than an
inch. Improved ceilings to VFR in the wake of the snow for Tuesday
afternoon. Northwest winds will be on the increase as well during
the afternoon with gusts to around 20 knots.
/Outlook for kmsp/
Wednesday...VFR. North wind 8 kts becoming west.
Thursday...VFR. SW wind 5-10 kts.
Friday...VFR. West 10-15 kts.