Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 121156
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
556 AM CST Thu Jan 12 2017
.SHORT TERM...(Today and tonight)
Issued at 403 AM CST Thu Jan 12 2017
Overnight, we had another shortwave go across southern MN/IA.
However, at the surface, we have seen a 1021mb surface high drift
over southern MN. So even though we have ample forcing/moisture in
he 8-10k foot range, the air below this has been too dry to support
snow down to the surface, so it has been nothing but virga in the MPX
cwa. Not anticipating any precip this period, with snow this morning
remaining to our south, while any snow associated with the
approaching arctic front remaining to the north later today as the
surface low driving this front will remain up in Canada.
Said arctic boundary is beginning to plunge into ND and has some
rather impressive winds associated with it, with the 815z ob out of
Crosby (KD50) showing a sustained wind of 45 kts with a gust of 54
kts. The bad news, is this arctic boundary is coming through here
this afternoon, which will send our temperatures on a free fall. The
good news though is the type of winds we are seeing at Crosby will
remain north of us as the brunt of the isallobaric high goes along
the international border. For us, forecast soundings show the
greatest gust potential up in central MN and currently expect gusts
in the wake of the front to be 25-30 kts in central MN, with 20-25kts
elsewhere. So not enough wind to warrant a winter weather advisory
for blowing snow.
For tonight, high pressure coming in behind the arctic boundary will
be strengthening, with a nearly 1050mb high expected to be centered
over central MN by 12z Friday. For lows tonight, kept things pretty
similar to what we had last night, though did warm south central MN
lows a few degrees. The complicating factor for lows tonight is the
fact that we will see clouds clear out this afternoon, but tonight,
a dense CI/CS shield will be building back north out of IA. Greatest
cold potential exists in central MN and along the US-8 corridor in
WI as this is where skies will remain clear the longest. Still have
some lows pushing -30F up toward Staples in northern Todd county.
Also still expect winds to decouple, with winds under 5 mph through
the night. If we were to do an advisory, it would have to run from
about 21z to 06z in western/central MN. After 6z, we lose the wind
part of a wind chill advisory.
.LONG TERM...(Friday through Wednesday)
Issued at 403 AM CST Thu Jan 12 2017
There are two concerns in the long term. The first is the threat
for light snow on Friday with the second being a more significant
threat for wintry precipitation in the Monday-Wednesday period.
After a cold start Friday morning, mid/upper level forcing will
quickly spread in from the southwest. Southern MN is initially in
the right entrance region of a 130+ knot jet at 250mb with good
differential divergence indicated. The entrance region moves
basically eastward during the day. Looking at the deterministic
models, the ECMWF and GEM would take snow development over
southwest MN Friday morning and move it almost due east along the
I-90 corridor during the day. This seems plausible given the
orientation of the upper jet. On the other hand, the NAM and GFS
would expand the snow northeast, passing across the Twin Cities
and western WI during the afternoon and evening with up a half
inch of accumulation. The CAMS are split as well on what happens
with the ARW more like the ECMWF/GEM with the NMM like the
NAM/GFS. Our own MPX ARWWRF is more like the ARW. Therefore, the
highest pops and some small snow accumulation were confined to far
south central MN. However, due to the spread in the various
solutions, slight chance pops were allowed to spread northeast for
the afternoon and evening hours.
At least the weekend is looking dry with weak high pressure
overhead. Highs will be warming from Friday through Sunday, going
from the single digits to lower 20s respectively.
Next week remains a debacle. The problem is how the various models
handle an upper over Baja on Saturday that eventually reaches
Texas late Sunday and then makes its way northward to the Upper
Mississippi Valley by Tue. There are speed and location
differences, with the GFS/GEM faster and colder than the ECMWF. In
addition, there are also continuity concerns as well. When looking
at the past 12 runs of the GFS, only 3 really had this system in
our CWA. The others were to the east and south of us. So,
confidence on the outcome is low. Certainly the trend is that this
system is coming our way. With that in mind, we kept the likely to
categorical pops spreading from south central MN through west
central WI from Monday into Tuesday. At this point, we kept most
of the precipitation type as snow with the exception of the far
southeast CWA. This is based on the GFS and GEM. However, if the
ECMWF ends up being more correct, then we will have a more
substantial elevated mixed layer and an increased chance for
freezing rain and sleet.
On a side note, to add more spread to the situation, looking at
the GEFS spatial plots indicates that the best chance for
accumulating snow (>3") being across eastern NE and northern IA.
The CIPS analogs point to the highest probability of accumulation
(>60 percent chance of 4" or more) from southwest MN through the
Twin Cities to northern WI. Finally, the Global HopWRF keeps the
whole system south of us. One thing for sure, it will be warmer
next week with highs in the 25 to 35 degree range with lows in
the teens and 20s.
.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 556 AM CST Thu Jan 12 2017
Winds are the only concern this period, with an arctic front still
progged to move through late morning through the afternoon. Not
much was changed with going TAFs and confidence is high in these
TAFs, with airmass behind the front too cold to support much more
than a FEW stratocu clouds in the cold advection behind the front.
KMSP...confidence is high in all aspects of the TAF, with the
biggest impact coming on the human side of things, with those that
have to work outside having to deal with dangerous cold Friday
/OUTLOOK FOR KMSP/
Fri...VFR. Chc MVFR/-sn. Wind vrb 5 kt or less.
Sat-Sun...VFR. Wind S 5 kt.