Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181200

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
700 AM CDT Wed Apr 18 2018

Issued at 612 AM CDT Wed Apr 18 2018

Updated to include 12z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 251 AM CDT Wed Apr 18 2018

Surface analysis early this morning shows a fairly well-organized
low pressure system centered over eastern KS with a warm front
extending eastward through the southern tip of IL and a trailing
cold front extending SW through the TX/OK Panhandles into NM.
Aloft, a narrow negatively-tilted upper level trough, emanating
from a larger trough over western Canada, remains offset to the
northwest of the surface low while ridging builds into the CONUS
Intermountain West.

Over the next 24 hours, the trough near the surface low will
become cutoff, with this new low being dragged eastward by
another large upper trough over the northern Atlantic. The surface
low will then also be similarly ushered along eastward, centering
itself into central IL by midday today then moving through the
Ohio Valley tonight and to the Mid-Atlantic region by daybreak
Thursday. This system still looks to have plenty of moisture with
it but the system is overall shifted a bit south again, as was
shown yesterday. There are still multiple dynamic factors at play
which may well produce nearly 1 in/hr rates in far southern MN
later this morning but with the better forcing further south and
weaker upper level support, snowfall amounts are again expected to
be not quite as high. Have lowered amounts such that the winter
storm warning will be confined to the southern-most 3 counties in
south-central Minnesota with the advisory only one row of counties
north then nothing beyond that. The snowfall will mainly take
place during the day today and the forcing from the snowfall
should keep highs only in the 33-34 degree range in far southern
MN with higher temperatures going north.

With the system quickly pulling away this evening and tonight, the
snowfall will end late this afternoon into the evening with little
to no additional accumulation by sunset. Skies will then partially
clear out overnight as lows drop into the mid-20s area-wide.

.LONG TERM...(Thursday through Tuesday)
Issued at 251 AM CDT Wed Apr 18 2018

Long term concerns will trend warmer with focus turning toward
hydro as snow melts in earnest this period. Some timing differences
in the frontal passage early next week.

Following Wednesday storm system, high pressure follows in its
wake  leaving mainly dry conditions during the first part of the
period. Upper flow pattern continues to be split with the main
moisture and energy for the next frontal in the southern stream.
Some moisture tries to work north into the Dakotas and may clip
far western MN later Friday night or early Saturday but it looks
like the surface ridge in place will preclude any significant
precipitation threat. Temperatures over the first part of the
period will be modulated somewhat by snowcover and possible fog
development as the snow melt continues. Greatest fog threat would
be found under the surface ridge. We wont warm it as fast as
models currently do, shade a degree or two through the weekend.

Question comes how much of a snowpack will there be by next
Monday. We could be nearly snow free again. If this happens,
warming ahead of the next cold front could be realized, with some
lower 60s possible. There are some timing differences in the front
with the GFS a bit faster and holding more moisture than the
ECWMF. We will temper the highs some and mention a small chance of
rain with its passage.

Rivers will continue to be on the rise with the snow melt, and several
rivers and streams will reach minor flood stage through the
weekend and into early next week. Consult the latest river summary
concerning the latest river forecast trends.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 542 AM CDT Wed Apr 18 2018

Wintry storm system coming out of KS will shift east across MO/IL
through tonight. Clouds will increase from the south and the -SN
shield will spread over southern MN into central MN. Intensities
will be highest at the southern TAF sites, producing visibilities
as low as 1-2SM, with intensities dropping off going north to just
MVFR range. Main timing of snow will be late this morning through
mid-afternoon then snow will diminish this evening followed by
clearing overnight. Winds will be out of the N to NE in the
10-15kt range before dropping off this evening.

KMSP...Mid-level VFR ceilings will drop into MVFR range later this
morning then remain in VFR range through this afternoon. While IFR
ceilings are not expected, they will likely be not too far off to
the south this afternoon. Ceilings below 1700ft certainly cannot
be ruled out and may well impact MSP late this afternoon as -SN
moves in. Intensities are expected to be light so have kept
visibility in MVFR range. Conditions quickly improve this evening
to VFR with no ceilings expected overnight.

Fri...VFR. Wind S less than 5 kts.
Sat...VFR. Wind SE less than 5 kts.
Sun...VFR. Wind S around 5 kts.


MN...Winter Weather Advisory until 7 PM CDT this evening for MNZ082.

     Winter Weather Advisory until 1 AM CDT Thursday for MNZ083>085.

     Winter Storm Warning until 1 AM CDT Thursday for MNZ092-093.

     Winter Storm Warning until 7 PM CDT this evening for MNZ091.



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