Scientific Forecaster Discussion
fxus63 kmpx 081120
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
520 am CST sun Dec 8 2019
Update...for 12z aviation discussion below
Short term...(today through monday)
issued at 313 am CST sun Dec 8 2019
Surface analysis shows the trough has entered northeastern
Minnesota early this morning. Brisk south/southwest winds will
continue to gradually shift to the northwest across the forecast
area today as the trough shifts to the Great Lakes. Ensuant low
level cold air advection will mean surface temperatures will reach
their daily Max's at daybreak, with a nearly steady to slowly
declining trend through the day.
Tonight we expect snow to Blossom across the area as a burst of
700-600mb frontogenesis sweeps eastward across central Minnesota toward
northern/central WI. 08.00z models stayed fairly consistent with
the favored heavy snow axis aligned along and north of a Morris to
Bethel to Chetek & Ladysmith Wisconsin line, where 3-6 inch
(isolated 7 inch) totals look likely. What has changed ever so
slightly, is timing. This could spare the Twin Cities Metro and
points eastward into west central WI from having much in the way
of accumulations at the start of the morning commute. However,
snow will be falling throughout it, so impacts are still likely.
Envision the Winter Weather Advisory will quite possibly need to
be extended a tad farther south to include another row of counties
(including the remainder of the tc metro). However, given the
storm total amounts are borderline for an advisory south of where
it currently resides, the trends for any shifts have been
northward, and even another timing shift of a couple hours could
spare the bulk of the commute from notable impacts, will hold off
for now (given we still are 24 hours out). That all being said,
right now we expect locations north and west of the Twin Cities to
have 2-5 inches on the ground by 6 am Monday, with a dusting to
half inch in the Metro by that time. The remainder of storm
accumulations would primarily occur prior to 1 PM, with the
exception of eastern parts of the forecast area (ie. Eau Claire
and ladysmith), where accumulating snow is likely through the
afternoon. One other item of note is that thermal profiles
indicate the potential for a brief period of freezing drizzle at
event onset over southern Minnesota into west central WI as weak lift
develops ahead of the main forcing. If this indeed occurs, it
would most likely be short in duration and of little significance.
The other potentially impactful factor to consider for Monday is
the wind. Northwest winds will increase to 25-35 mph with gusts up
to 40mph, primarily from west into south central Minnesota. Therefore
even areas that don't pick up more than a couple inches of
snow could possibly still need an advisory given this will be the
light-fluffy type of snow that doesn't take much to cause issued
with blowing snow.
Long term...(monday night through saturday)
issued at 313 am CST sun Dec 8 2019
The longer term still looks fairly quiet weatherwise. The large
scale pattern will be amplified at the start of the period, and
trend toward zonal flow as the eastern upper trough lifts out and
the western ridge flattens. Longer range guidance shows things re-
amplifying after the current 7-day forecast period, so we may see a
return of colder temperatures after next weekend depending on where
the large scale trough sets up. In terms of forecast specifics,
things look dry from Monday night through Wednesday as Arctic high
pressure settles over the region. Return flow will bring chances for
some light snow back into the area late Wednesday night into
Thursday, with some lingering precipitation chances into the weekend
as we see several weak shortwave troughs move east with the zonal
flow. We may see a weak surface low intensity a bit as it moves
through the region next weekend, but it's far too early to have any
confidence in timing, location, or intensity of things. Given the
generally quiet pattern and increasing spread in the ensemble
guidance beyond midweek, see no reason to stray from the consensus
nbm guidance at this point (other than some minor tweaks to
temperatures Tuesday through thursday).
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 520 am CST sun Dec 8 2019
IFR ceilings are on the doorstep at taf issuance, and will
overspread the area this morning, signaling the end of VFR for the
remainder of the period. Brief improvement in ceiling heights to
MVFR is possible this afternoon after the main Post-frontal IFR
surge, but a return to IFR will occur after sunset. Snow will
develop at western Minnesota sites between 02z and 08z, with attendant
LIFR conditions becoming possible. Models are hinting at the
potential for minor visibility reductions (br) over east/south
central Minnesota into west central WI this evening; will need to
monitor the potential for a brief period of freezing drizzle as
shallow lift develops ahead of the main area of snow/forcing.
Winds will shift to the north/northwest today behind the front,
but the notable gusts aren't expected until Monday.
Kmsp...IFR ceilings expected around 15z, with brief improvement up
to 1500 feet possible during the afternoon. IFR returns in the
evening with snow arriving around 09z.
/Outlook for kmsp/
Mon...IFR/sn likely, mainly in the morning. 2-4 inches expected. Wind
north-northeast bcmg north-northwest 10-15g25 kts.
Tue...VFR. Wind northwest 5-15 kts.
Wed...VFR. Wind west 5 kts.
WI...Winter Weather Advisory from midnight tonight to 6 PM CST Monday
Minnesota...Winter Weather Advisory from 9 PM this evening to noon CST
Monday for mnz041>045-047>053-055.
Winter Weather Advisory from midnight tonight to noon CST Monday