Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 081724

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1124 AM CST Thu Dec 8 2016

.SHORT TERM...(Today and tonight)
Issued at 400 AM CST Thu Dec 8 2016

Occasional light snow continues early this morning with visibilities
in some cases briefly falling below 2 miles. The main wave of snow
pushing south across the region early this morning is being driven
by warm air advection from the north in the low to mid levels and a
weak disturbance. Think the steadiest snow will begin to wane
following the passage of this disturbance and as the depth of the
DGZ decreases with low level temps warming into the 20s. Cyclonic
flow persisting through the day may keep flurries going, but drier
air will eventually put an end to those as well by early evening.
Highs today will be warmest across western WI with mid 20s. Teens
will continue across most of Minnesota.

Clouds will linger tonight, but will be on a gradual decline. Winds
will also remain elevated. These are two reasons we aren`t expecting
to get very cold. It will still be the coldest night of the season
though with single digits and lower teens.

.LONG TERM...(Friday through Wednesday)
Issued at 400 AM CST Thu Dec 8 2016

Forecast issues ahead remain the weekend snow event and the Arctic
cold settling over us early next week.

More divergence has developed in the past 24 hours with regards to
the snow event this weekend which has resulted in a low confidence
forecast. It`s starting to turn into a foreign versus domestic
event with the models. Something we have certainly seen in past
winters. The NAM and GFS remain gung-ho on spreading accumulating
snow across the forecast area for Saturday and Saturday night with
the NAM showing upwards of 0.51 inches of QPF just southwest of
the Twin Cities for the event. The ECMWF and Canadian are saying
not so fast and not so much. This is especially true with the
ECMWF which has just a minor WAA snow event over southern MN on
Saturday with more accumulating snow coming back for the area
Sunday afternoon into Monday, which neither the NAM or GFS have.

There really isn`t much of a difference in the jet pattern between
the solutions mentioned, but the ECMWF and Canadian just don`t
want to deepen a short wave coming in from the Pacific Northwest
like the NAM and GFS do. In fact, run to run continuity between
the ECMWF and Canadian show the short wave actually weakening. The
00z GEFS was not available for this discussion to see what kind of
spread it showed. A check of the CIPS analogs is not very
encouraging as the top analogs don`t have much snow accumulation.
This was something I noted the previous night which seemed rather
odd for such a potent system on the GFS.

With the NAM and GFS remaining on course with regards to their
previous runs, the forecast reflects much more snow over what the
ECMWF or Canadian show. We have seen these divergences go down to
within 12 to 24 hours of an event before agreement was reached, so
even the upcoming runs today may not instill confidence. For now,
we have between 4 and 7 inches of snow forecast from Saturday
morning to Sunday morning from north to south respectively. This
could be way overdone if the other solutions verify with only a
couple of inches in far southern MN and adjoining areas of WI.

As for the late weekend and early next week, we did agree with
surrounding offices to add chance pops to the forecast in the
event the ECMWF is correct about a second wave emanating from the
Central Plains ahead of the approaching front. The ECMWF shows
that the snow Sunday night and early Monday could be significant
across far southern MN, northern IA and adjoining areas of western

Finally, an arctic front is still posed to move through early on
Tuesday with single digits highs and sub zero lows settling in for
much of the remainder of the week. Wind chills in the minus 15 to
minus 25 degree range are likely. Adjustments were made to lower
the highs and lows a few degrees from Tuesday night onward.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1115 AM CST Thu Dec 8 2016

No major changes for the 18z tafs with MVFR ceilings through most
of the period, with only a small chance of VFR at times this
afternoon and evening. Any snowfall will be light and briefly
lowering visibilities to 5SM. Blowing snow is still possible at
KAXN this afternoon. Winds will remain gusty, but light winds and
backing to a more westerly direction is expected tonight.


Similar scenario with high end MVFR, or low end VFR conditions
through most of the taf period. Best chance of VFR will occur
Friday afternoon. Gusty winds this afternoon will back and drop to
around 5-8 knots by Friday.


Sat...MVFR, then IFR in SN. SE wind 5-10 kts.
Sun...IFR/MVFR in SN early. MVFR/VFR possible late. N wind 5-10 kts.
Mon...MVFR/VFR with -sn possible. WNW wind 5-10 kts.




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