Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 271057

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
557 AM CDT Thu Apr 27 2017

.updated for 12z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 407 AM CDT Thu Apr 27 2017

The short term concerns are P-type and temperatures the next 24

Latest radar showing drizzle across the metro with some patchy light
rain. Various surface obs showing there may be some drizzle or
flurries farther to the west as well.  We will mention the drizzle
over the eastern cwa this morning along with the threat of freezing
drizzle with temperatures flirting with 32. Not expecting
significant problems with surface/road temperatures still above
freezing to the southeast. Also...we have the trough over the
central US lifting northeast. Satellite showing some enhanced clouds
lifting north ahead of the trough extension over northwest MN. This
was likely enough to generate the drizzle over the region. Radar is
showing rapid north movement to the rain shield associated with the
Missouri trough. Models indicate this will clip the far eastern
portion of the cwa of west central Wisconsin...mainly through the
morning. With cooling boundary layer temperatures...we expect this
to be a mix bag of p-type.  We may see a light glaze on some roads
or elevated surfaces along with a dusting of snow. Clouds are
expected to remain over the area today and will limit any real
warming. Temperatures will remain in the upper 30s to lower 40s.

A surface ridge is progged to move into southwest Minnesota later
tonight and this should provide some clearing. We expect slow
clearing to the northeast through 12z Thu. Wind will be lightest to
the southwest and guidance suggests there will be some wind
remaining much of the night elsewhere. This may limit widespread
frost formation...but air temperatures are expected to drop below
freezing across the cwa. Readings below 28F may linger a few hours
after midnight as well...promoting a hard freeze...especially across
central areas.

.LONG TERM...(Friday through Wednesday)
Issued at 407 AM CDT Thu Apr 27 2017

The focus of the long term centers around a storm system that
will move northeast across our area from Sunday into Tuesday.
Model solutions have less spread than they did 24 hours ago with
the GFS and Canadian having slowed down some. Unfortunately, just
when they look like the ECMWF from 24 hours ago, the ECMWF has
slowed some more and is now a western/southern outlier for a
time. Looking upstairs helps shed some light on why this is
occurring. First, the downstream ridging north and east of the H25
low on the ECMWF is much sharper versus the GFS and Canadian.
This results in the jet being much closer to us with the low/mid
level features moving more NNE across MN instead of WI. Another
feature seen is that the ECMWF has a closed H5 low dropping SE
across southern Alberta and Saskatchewan from Sunday into Monday.
This is non existent on the GFS while the GEM has the feature but
somewhat weaker. This second upper low tries to merge in with the
upper low over us, ending up slowing the movement and elongating
the low to the NW. This would not be too much of a problem if we
were looking at all rain with the system. However, that`s not the
case and accumulating snow is likely looking at the GFS/GEFS and

Hence, given the preponderance of solutions that would favor snow
from late Sunday through Monday, we and surrounding offices took
a preemptive strike against the Forecast Builder grids and went
much colder which made it easier to have the forecast indicate snow
instead of rain and snow. We cut 50s back into the 40s for Sunday
and then to around 40 for Monday. This is still some 5 degrees
above what the GFS and Canadian guidance would say. This is a
severe cut and if the ECMWF ends up being right, then we are too
cold. In fact, with the movement that the ECMWF has with this
storm system, it has virtually no snow in MN. However, we do not
want to underestimate the potential for the snow during the
aforementioned periods. Sampling the GFS in Bufkit shows the
potential for 6 inches or more for much of our MN CWA. It
certainly could be much higher as this system has it all, coupled
upper jet, PV boot, 12 hour 200-300M H5 height falls, favorable
track of the H85/H7 low and thermal profile along with 0-1km Layer
Max Wet-Bulb Temps less than 1 degree C. Looking at previous May
snowfalls in the Twin Cities, the greatest amount has been 3
inches of three occasions, May 20th 1892, May 1st 1935 and May
11-12th 1946. There is certainly potential to break this. The axis
of best 24 hour probability of snowfall greater than 3 inches
from the GEFS is now over 60 percent from Hutchinson to Cambridge
and northwest WI for Monday. The CIPS analogs also have
accumulating snow in 3 of the top 4 analogs. Two of the analogs
are more west central into northeast MN while the other is right
across the Twin Cities. Also, the Twin Cities just missed a big snow
back in the May of 2013. The heaviest snow of over a foot fell
across portions of southeast MN and west central WI.

Finally, even if the snow forecast does not pan out, all
solutions indicate widespread 1.5 to nearly 2 inches of rain
across southern and eastern MN and much of WI which would
certainly increase hydro concerns next week.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 555 AM CDT Thu Apr 27 2017

MVFR to occasional IFR cigs in -fzdz moving across the eastern
area this morning. Enough lift from the Iowa/Illinois region for
some light precipitation. May fluctuate between the drizzle and
snow flurries during the morning before ending. KEAU may be
clipped by the upper trough as well...with some more meaningful
vsbys and -sn. Expect cigs to erode to the northeast overnight
and become vfr most ares by 12z Fri.

KMSP...Areas of drizzle.freezing drizzle and flurries early should
give way to mvfr cigs through the remainder of the day. Expect
CIGS to erode overnight and become vfr after midnight. Nw winds a
bit gusty through the day...and becoming light wnw into tonight.

Fri night...VFR. Winds N 5-10 kts.
Sat...VFR. Winds NE 5-10 kts.
Sun...MVFR/IFR with -RA/SN. Winds NE 10-15G20-25 kts.




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