Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 281715
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1215 PM CDT Fri Apr 28 2017

.UPDATE...
Issued at 1207 PM CDT Fri Apr 28 2017

Updated to include 18z aviation discussion below.

&&

.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
weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1207 PM CDT Fri Apr 28 2017

High pressure dropping in from the northwest will keep the frontal
system and associated precipitation to the south of all TAF sites
through tomorrow. High clouds from the system will be the main
impact, keeping ceilings in place. Though there are some isolated
pockets of MVFR-level clouds (such as KRWF at initialization
time), those instances are expected to be few and far between to
impact any other sites. Thus, have maintained VFR conditions at
all sites through tomorrow. N winds around 10 knots with
occasional higher gusts will persist through this evening then
diminish closer to 5 knots while veering to NNE then to NE by
daybreak tomorrow.

KMSP...VFR conditions expected throughout this set with high
ceilings later this afternoon into the early morning hours. There
may be a few occasional periods of FEW-SCT clouds at 2-3 kft
through this evening but no lower ceilings are expected.

/OUTLOOK FOR KMSP/
Sun...MVFR/IFR with RA. Winds NE 15-20G30kts.
Mon...IFR/RA mixing with SN AFTN/EVE. Winds N 15-20g30kts.
Tue...MVFR ceilings possible. NW 10-15 kts.

&&

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

$$

UPDATE...JPC
SHORT TERM...JRB
LONG TERM...RAH
AVIATION...JPC


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