Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 281120

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
620 AM CDT Fri Apr 28 2017

.SHORT TERM...(Today and tonight)
Issued at 425 AM CDT Fri Apr 28 2017

Early morning water vapor imagery together with GFS 500mb heights
and winds showed a positively tilted trough with a very strong upper
level jet ready to manifest itself in a powerful synoptic cyclone
that will bring extensive heavy rain and flooding across the central
Conus this weekend. In the mean time expect surface high pressure to
build across the Upper Midwest a bring a brief window of dry
conditions over Minnesota and Wisconsin. Winds will be light and
temperatures will remain cool with Friday`s highs 10 to 15 degrees
below the seasonal average for late April.

From a pure meteorological standpoint, one has to appreciate the
weather that will begin to unfold over the next 36 hours. A powerful
super-positioned upper level jet crashing on shore the west coast is
already showing its hand with the precipitation developing over the
Central Plains. Downstream a residual artifact in the form of a low
level thermal gradient draped east/west along I-70 was left over
from the cyclone currently in Ontario CA. This thermal gradient will
be the catalyst for training thunderstorms which will likely cause
significant flooding across Missouri and Illinois. By the time
Saturday morning rolls around should see a line of convection from
central Kansas up through the Illinois and Ohio River Valleys.
Meanwhile the Upper Midwest will have high clouds and northeast
winds Saturday morning

.LONG TERM...(Saturday through Thursday)
Issued at 425 AM CDT Fri Apr 28 2017

The focus in the long term remains a storm system that will move
northeast across the region from Sunday through Monday.
Deterministic guidance for the most part is now in great agreement
with the location and timing of this system. Even the GEFS is
practically on top of the ECMWF/GFS solutions. The one outlier is
the Canadian, which is further north and west. This seems tied to
a secondary upper low trying to phase in on Monday from southern
Saskatchewan. The ECMWF has had this idea as well the past few
runs, but not as deep on tonights run.

Rain will begin spreading into far southern Minnesota ahead of the
storm system by late in the day Saturday and then continue
expanding north and east on Sunday. This is a long duration event
with likely to categorical pops from Sunday through Monday. It`s a
very dynamic system with plenty of moisture to work with. There
are two concerns with this precipitation event. The first is how
much rain and the second is where and how much snow. Confidence
remains high on widespread rain amounts in the 1.25 to 1.75 inch
range, with the high end amounts across southern MN into east
central MN (Twin Cities). Fortunately it`s spread out over two
days, but some hydro issues are certainly possible with the wet
soil conditions in place along with standing water being reported
here and there.

The other issue is the potential for accumulating snow.
Confidence has increased on this with regards to the location.
However amounts could get out of hand late Sunday night and early
Monday. With the agreement in the model solutions, temperature
profiles are best for snow from southwest through central into
northeast MN and northwest WI. For our area, this would be Canby
and Redwood Falls on northeast through Alexandria, Staples, St.
Cloud, Little Falls and Cambridge. Right now, we have 2 to 4
inches of snow accumulation for these areas. The GFS would suggest
6 to 10 inches of snow possible in this area. The GEFS
probabilities for 2-4 inches are in the likely category for
basically this same area. We`ll certainly need to keep an eye on
this for potential headlines as we head forward. Main changes
again overnight to the FB grids were to lower high temperatures
across southern MN on Sunday and across all of MN on Monday with
upper 30s in place for the snow area. This may still be too warm
with some solutions suggesting only middle 30s. We ended up with a
nice temperature gradient from west to east on Monday from the
upper 30s in western MN to 50 at Eau Claire. Other changes
included more widespread categorical pops along with increasing
the north winds on Monday.

This system will exit the region on Tuesday. Two minor short waves
will move through in the northwest flow for Wednesday and Thursday
with some small chances for showers. After that, the pattern
begins to change with massive ridging aloft spreading into the
center of the country, bring a big warm up heading into next


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 620 AM CDT Fri Apr 28 2017

VFR through the period as high pressure noses in from the Dakotas.
BKN-OVC035-040 will SCT early this morning across east central MN
and west central WI. WNW winds 10 knots or less this morning
becoming NNE this afternoon and tonight.

KMSP...VFR. Winds similar to those described above.

Sat...VFR. Winds NE 10-15 kts.
Sun...MVFR/IFR with RA. Winds NE 15-20G30kts.
Mon...IFR/RA mixing with SN AFTN/EVE. Winds N 15-20g30kts.




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