Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 160935
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
435 AM CDT Thu Mar 16 2017

.SHORT TERM...(Today through Friday)
Issued at 403 AM CDT Thu Mar 16 2017

The main driver of the weather this period will be the low pressure
system currently positioned in southwestern Saskatchewan.  This low
is expected to deepen some today and push eastward, well north of
the USA/Canada border.  It`s the frontal boundary associated with
this low that is of our primary concern as guidance is in good
agreement that precipitation will form out ahead of the front (which
will be oriented in a north to south direction and extend into
southern Minnesota) as it moves through our forecast area.

Really fine-tuned our thinking this shift with hourly POPs and
Weather type.  Eliminated POPs from the morning period today as the
dry air will not be overcome until later based on forecast
soundings.  In fact, looking at numerous soundings in this area
indicates a struggle to saturate the low levels today into tonight.
Essentially what looks more likely in much of southern MN
(especially western) is that as the front approaches from our west,
the mid level saturation will out-pace low level saturation.  The
deep moisture saturation looks to come together in across near far
eastern MN/western WI this afternoon into the evening.  Only
included likely POPs in western WI for this reason as confidence
that widespread precip occurs in eastern MN is quite a bit lower.

In terms of p-type, it`s a bit of a mess.  Rain should be
predominant this afternoon into the early evening, but forecast
soundings indicate accumulating snow is possible across northwest WI
where surface temps could cool rapidly at the onset of precip thanks
to dry air in the low levels.  Could see 1-2" of snowfall in the
Rice Lake to Ladysmith, WI areas.

The other thing to keep an eye on is potential ice accumulation.
With warm southerly flow ahead of the front, the 800-900mb layer
looks to warm above freezing and with surface dew points this
afternoon and evening in the low to mid 20s, this could lead to
periods of freezing rain or freezing drizzle tonight.  Would not be
at all surprised to see an area of freezing drizzle behind the main
precip band tonight as mid level dry air causes loss of ice in the
cloud layer aloft.  We don`t expect significant icing with this,
only brief periods and light amounts most likely, but it is worth
noting.

.LONG TERM...(Friday night through Wednesday)
Issued at 403 AM CDT Thu Mar 16 2017

Friday night through Sunday...The occluded frontal system will
exit the region Friday night, bringing any and all precipitation
with it away from the WFO MPX coverage area. In conjunction with
the surface feature departure Friday night will be the eastward
shift of a deepening upper level low over the Great Lakes. This
will be replaced by a large dome of high pressure moving east from
the Rockies. Preceding the ridge will be surface high pressure,
thus allowing for clearing skies on Saturday along with the start
of a warming trend over the weekend. A few more clouds are
expected on Sunday as the ridge departs and deep southerly flow
brings additional moisture from the Deep South into the region.
Highs in the 40s on Saturday will climb to the 50s and lower 60s
on Sunday. There is an outside shot at a few rain showers in
west- central Wisconsin Sunday evening as a weak cold front
approaches but these will be of little consequence. Any rain/snow
mix will remain in northern Minnesota and northwest Wisconsin from
this system.

Monday through Wednesday...A rather benign pattern is expected for
the first half of next week as surface high pressure, arriving
from western Canada, regains control while another ridge of high
pressure arrives from the western CONUS. This will mean a dry
forecast for the start of the week with slightly cooler
temperatures due to the origin of the surface high. What is still
grabbing attention is pretty good model agreement of a fairly
well organized mid- latitude cyclonic system for the latter half
of next week. Still too early for specific localized details but
the fact that both the GFS and ECMWF both show the development of
the system within 1-2 states of one another with a fairly similar
Colorado low track should raise some eyebrows. Given the
temperatures associated with this system, at this point it looks
to be a rain/snow mixture. Will need to see how this evolves over
the next week before being able to discern sensible weather
details and their associated impacts.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1115 PM CDT Wed Mar 15 2017

MVFR cigs moving into the Twin Cities now have held firm this
evening, so followed the idea of the RAP/NAM in taking these
clouds all the way into EAU by 12z. Outside of western WI, precip
potential looks to be on a downward trend, with dry low level air
looking to be a limiter. CAMS are pretty uniform in showing a
band of warm advective precip forming near the MN/WI border around
20/21z and moving east, clearing EAU shortly after 00z. Precip
mentions in TAFs are tied to what the CAMs are showing and think
the LAMP is too late in starting precip and overdoing it as well.
Low confidence on what will happen with cigs behind this precip
band. We`ll certainly be moistening up the low levels ahead of a
cold front that will be near an AXN/RWF line at the end of the
period. Followed a more optimistic NAM route for bringing low
ceilings in. Again, the concern is the models are just overdoing
the amount of low level moisture coming in and with the low going
across southern Canada, the threat for low cigs will be better in
northern MN.

KMSP...MVFR cigs just moving in have lasted 2-3 hours at airports
to the west, so they will be long gone by the time the morning
push starts, though around 4k foot cigs are expanding to the west
of them, so we may go from MVFR to lower end VFR cigs this
morning. Precip chances look much better east of MSP today, but
left the VCSH mention in there for when the warm advective band
comes through, may end up as just virga. Low confidence on cigs
tonight, but as the front approaches (early Friday morning
FROPA), the low levels should moisten, with low cigs developing
again.

/OUTLOOK FOR KMSP/
Fri...MVFR/-SHRA possible early, then VFR. Wind NW at 10g25kt.
Sat...VFR. Wind NW at 10kt.
Sun...VFR with MVFR possible. Wind S at 15g25kt.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...SPD
LONG TERM...JPC
AVIATION...MPG



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