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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
613 PM CST Friday Dec 19 2014

Update...for 00z aviation discussion


Short term...(this evening through saturday)
issued at 354 PM CST Friday Dec 19 2014

Like last weekend...we are back into a weather pattern favorable for
endless stratus this weekend as warm air advection in the 900 to 700 mb layer
results in another strong inversion developing...though nowhere near
as warm as the warm nose we were dealing with a week ago. This
inversion will keep moisture trapped beneath it...and persistent
srly low level winds will only help reinforce the moisture and keep
the clouds in place. Only hope in the short term for seeing some
clearing is Sat afternoon out in western Minnesota depending on how far east
the clearing currently across the central Dakotas makes it. For
now...we have the stratus staying.

For precipitation...there will be three shortwaves impacting the area
during just the short term. The first one is out over NE Minnesota into northern
WI and has brought the occasional snow report to the US-8 corridor
in WI...but this will be out of the Ladysmith area pretty quick this
afternoon. Wave two is already moving into western Minnesota per cooler cloud
tops moving in. Although there will be some pv advection with this
feature...Omega plots show very little vertical motion getting
induced by the not thinking we will see much precipitation
overnight. In addition...this wave looks to bring enough moisture
back into the dgz that the primary p-type would be snow as we get a
seeder-feeder scenario setting up. For drizzle...lift down in the
stratus layer looks weak as do not think we will see much
drizzle either. Short term hi-res support the limited precipitation idea
tonight...with nothing really generating much in the way of quantitative precipitation forecast.
Given the still low confidence in seeing any precipitation tonight...kept
precipitation mention to a slight chance for snow with patchy fzdz. The
third wave is now moving across wash/Oregon and will be getting near
western Minnesota by the end of the short term...but any potential precipitation with
it looks to hold off until Saturday night.

On the fog threat...the probability for dense fog tonight looks very
low as dew points look to remain in the 20s. Will likely see dense
fog develop along the west edge of the stratus deck...but the edge
of the stratus deck is far enough west to keep the dense fog across
the Dakotas. Instead...expect fairly widespread visibilities between
1 and 3 miles in haze and br to develop across most of the Minnesota area

Finally...the clouds and continued srly winds will really limit the
temperature drop tonight. In fact...temperatures will likely
continue to slowly rise this entire period...finishing in the upper
20s/lower 30s by sunset Saturday. Boosted lows a few degrees tonight
as result...with lows tonight basically a degree or two colder than
the temperatures we are seeing this afternoon.

Long term...(saturday night through friday)
issued at 354 PM CST Friday Dec 19 2014

A warming trend will continue in the early portion of the long
term (saturday night through monday) as southerly flow increases
ahead of an approaching low pressure system arriving from the
Dakotas. All of the deterministic solutions were similar with this
idea today with a surface low pushing into west central Minnesota Monday
afternoon. Initially...small amounts of precipitation will develop
Saturday night and early Sunday across eastern Minnesota and western WI in
the best low level warm air advection along with weak forcing aloft. The ptype
will be a wintry mix but again amounts look to be very light. A
lull in the forcing and deep layer moisture is forecast on Sunday
before the main impulse arrives later Sunday night and Monday.
This latter feature will bring a period of rain to the Twin well as points to the east and south on Monday. Areas
of central Minnesota could see a few inches of snow depending on how the
thermal profile ends up. A changeover to snow is expected across
all of the region Monday night as the upper level impulse deepens
over the region and becomes a closed low. It is here that
differences begin to show up that last through the remainder of
the long term. Although the GFS and European model (ecmwf) would place much of our
forecast area in accumulating snow from Tuesday through
Wednesday...they do it in different ways. The GFS would bring a
surface low from Chicago to the western tip of Upper Michigan
during this period. There is a considerable dry slot that pushes
northward across eastern Minnesota and western WI as well which cuts down
on the accumulating snow potential. The European model (ecmwf) on the other hand
has a rapidly deepening surface low moving northward across Ohio
and into the central Great Lakes on Wednesday. The low deepens 29
millibars in 24 hours with 10 millibars prognosticated as the low moves
northward across Ohio from 12z-18z on Wednesday. Because of the
low being farther east...the dry slow it farther east and the forecast area
is in a much better deformation zone with accumulating snow
likely. The Gem looks to be an outlier with little to no
precipitation. Continuity over the past two days has been quite
good with the European model (ecmwf). The GFS has been bouncing around and this has
also been seen in the parallel run as well. Hence...if the European model (ecmwf)
holds...higher probability of precipitation will be needed from Tuesday through Wednesday
with a white Christmas in store.

Yet another potential accumulating snow event is shown by the
European model (ecmwf) from Friday into Saturday. This event could be well underway
by daybreak Friday in the Twin Cities. The GFS is starting to hint
at this idea while the 12z parallel run of the GFS is similar to
the European model (ecmwf) but a little farther south. Overall...we could end up
with quite a bit of snow accumulation by next weekend if the European model (ecmwf)
forecast remains on track for these two events.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 615 PM CST Friday Dec 19 2014

IFR conditions will become the Standard tonight across the entire
forecast area...with sub-1000ft ceilings and visibilities in the 1sm-4sm
range due to the fog. Freezing drizzle and/or light snow may also
be an artifact of the stratus...but at this point
coverage/probability is too low to include it in the tafs. Not
much improvement expected for Saturday...except the stratus deck
should lift slightly to around 1500 feet during the late morning and
early afternoon hours...with visibilities beoming VFR. Winds will hang
in the 150-180 degree direction through the speeds of
5-10 kts.

high confidence in IFR ceilings prevailing overnight...with visibilities in
the 3-5sm range. Will also be monitoring the freezing drizzle
potential very closely...but at this time do not see it being an
issue. Minor improvement to a ceiling circa 1400 feet and VFR visibilities is
expected by Saturday afternoon.

/Outlook for kmsp/
sun...MVFR/IFR. Chance -fzdz/-ra/-sn. Winds south-southeast 7-10kts.
Monday...IFR. -Ra with -ra/snow mix late. Winds southeast 7-10kts.
Tuesday...MVFR/IFR. Rain/snow mix changing to all snow late. Winds northwest 12 kts.


Mpx watches/warnings/advisories...


Short term...mpg
long term...rah

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