Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
324 PM CST Wednesday Nov 25 2015
issued at 325 PM CST Wednesday Nov 25 2015
Main issues for tonight are front and associated precipitation. Front now
from northestern to southwestern Minnesota and it should be east of Ladysmith and Eau
Claire by midnight. Moisture has been quite shallow...generally
in the lowest mile. There has not been that much in the way
of higher level moisture this afternoon...and that persists through
most of the night. Have cut down on probability of precipitation a bit...but still have
some possible light rain in south central Minnesota into wisc. Influx of
colder air doesn't really allow for mixed precipitation until 09z or so...
which is when winds turn more north-northwest in conjunction with better
Long term...(thursday through wednesday)
issued at 325 PM CST Wednesday Nov 25 2015
Complicated forecast Thursday/Thursday evening as a storm system
moves out of The Rockies and into the plains with forcing in the
middle/upper levels...but weak near the surface. P-type is also a concern
initially...but not as overwhelming as previously had in the
First...initially dry air mass overhead...especially north of I-90
will hold off on any measurable precipitation until mid-morning.
Middle/upper level forcing initially is well north into
central/northern Minnesota and the eastern Dakotas. This has been well
advertised from the models in the past two days. However...initial
dry atmoshpere has played havoc on when snow begins once the
atmosphere saturates. Soundings across mpx County Warning Area indicated a top-down
type of saturation scenario which leads to some freezing
precipitation during the onset Thursday morning as the snow growth
area /ice crystals/ are non-existent. Once the atmosphere
saturates...the dendritic zone/-15 c Omega field/ will be maximized
in a 3-6 hours time frame /9 am to 3 PM/ from SW to ec Minnesota...and into
wc WI. In addition...along the Iowa/Minnesota border...NE to near Keau has an
elevated warm layer which will lead to a mixture of sleet/freezing
rain/freezing drizzle during the morning/afternoon before the depth of
the colder air arrives.
As previously stated...the middle/upper level forcing is well north/northwest
of mpx County Warning Area. There is a significant 250-300mb jet streak which is
likely the main forcing for a short period of light/moderate
snowfall across mostly the 1/3 southeast of mpx County Warning Area Thursday. Based on
thermal fields/best chance of higher snowfall rates...a quick 1-2
inches of snow will fall...with locally higher amts along the Minnesota/Iowa
border...NE to Red Wing where moisture depth is greater and a longer
duration of snow occurs. There is also a brief period during the
late afternoon/early evening where light freezing drizzle may occur as
the dendritic zone is gone but some low level forcing remains in a
weak warm air advection regime. Any ice or freezing drizzle that falls should be
minimal. As with any forecast with large scale forcing upstream from
a frontal boundary...any deviation north or south of the main
forcing bands can lead to large adjustment in snowfall amts.
Past Thursday night...a dry period is forecast for
Friday/Saturday/Sunday with a moderating trend. However...30s for
highs are near normal for late November. The mean flow next week
will keep the upper Midwest in an unsettled period with a chance of
snow Mon/Tue/Wed. No major cold periods are forecast through early
December...with climate models indicating much above normal temperatures
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1227 PM CST Wednesday Nov 25 2015
Two areas of concern this afternoon and evening with MVFR and
IFR. Front and trough making their way through western Minnesota...and
ceilings and visibilities have dropped to low MVFR and in some
cases...low IFR ceilings in far west central and SW Minnesota. IFR
ceilings appear to be on the doorstep of kaxn...which should
move in to kaxn for a few hours.
Other area is MVFR in east central and south central Minnesota into
wisc...ahead of trough/front. As front approaches this area...
ceilings will lower...and may even go IFR in a few spots in
eastern Minnesota this evening. As cold advection takes hold tonight...
expect mostly MVFR ceilings.
Thursday morning...precipitation moves into south central Minnesota and spreads
into west central wisc. The northwest edge of this will be snow...and
likely some IFR visibilities. Farther south/east...a mix appears
likely before transitioning to snow near 18z.
Kmsp...higher MVFR ceilings will dominate early this afternoon
before lower MVFR arrives later in the afternoon with trough and
front. There is a small chance of IFR ceilings from 23z-03z with
front and in its wake. MVFR ceilings likely to remain overnight
amidst cold advection. Next wave of precipitation should arrive around
14z. There may be a brief period of mixed precipitation...but even if
there is...it should transition to snow quickly. There will also
be a small chance of LIFR visibility at times during midday
/Outlook for kmsp/
Thursday night...MVFR. Snow ending. Winds north 10-20 kts.
Friday...VFR. Winds north-northwest 5-10 kts.
Sat...VFR. Winds SW 5 kts.
Sun...VFR. Winds northwest 5 kts.
WI...Winter Weather Advisory from 6 am to 9 PM CST Thursday for
Minnesota...Winter Weather Advisory from 6 am to 9 PM CST Thursday for