Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 202007

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
307 PM CDT Thu Apr 20 2017

.SHORT TERM...(This evening through Friday)
Issued at 306 PM CDT Thu Apr 20 2017

This afternoon, the departing surface low was centered over the
Great Lakes at the surface, but the large upper level trough
enveloped most of the upper midwest with the trough axis over
eastern MN/western WI.  The widespread stratocu shield will
gradually begin to erode this evening, with diminishing cloud cover
expected from west to east overnight.  Some scattered low clouds may
linger into tomorrow morning.  But, ultimately as the upper trough
shifts east tonight, a ridge will push in from the west, leading to
widespread subsidence across the region, and clearing skies.

Meanwhile, surface high pressure will strengthen overnight across,
centered across western MN.  With the lack of wind and clearing
skies there, have included fog overnight and into tomorrow morning.
Farther east, thinking that the scattered clouds and more wind will
prevent much fog from developing tonight.  For tomorrow, the high
will slowly push across north central MN to the east.  We will see
mostly sunny skies and generally north winds of 5 to 10 MPH.  Highs
will be in the upper 50s to near 60.

.LONG TERM...(Friday night through Thursday)
Issued at 306 PM CDT Thu Apr 20 2017

The weather this upcoming weekend continues to look great for being
outdoors. However a much more active weather pattern will develop
early next week with several strong storm systems expected to move
across the Midwest. Confidence is fairly high that this active
weather pattern will come to fruition since it will be driven by
strong Pacific jet upstream that will come crashing on shore and
break down into several shortwave troughs.

In the meantime, a cool dry Canadian air mass will remain across
Minnesota and Wisconsin in the wake of the cold front that pushed
through the region overnight. This seasonably dry air mass will make
for a sunny weekend, but it will also have implications on the
weather for Monday. The first of a series of PV Anomalies will
develop a surface low over Minnesota and Wisconsin. The wind shear
profile favors organized storms and severe weather, but the boundary
layer is very dry and is not able to recover ahead of the cold
front. For that reason there is not instability, and may see the
cold front pass through dry on Monday. Areas across northern
Minnesota and Wisconsin will have a much higher chance of seeing
precipitation than areas to the south.

Looking ahead, the is a tremendous amount of energy associated with
the aforementioned upper level jet. The models show considerable
disagreement on how they handle this energy. For example, the GFS
and EMCWF 20.12 bring another shortwave and surface low across the
region, and this one is further south which would mean a better
chance of precipitation. Later next week a stronger system should
develop across the Midwest, but at this point it is beyond our
forecast period.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1246 PM CDT Thu Apr 20 2017

Low pressure at the surface is over the Great Lakes at this time,
but the upper level trough axis is moving through, with a very
broad cloud shield encompassing most of Minnesota and across the
Dakotas. The ceiling heights across the area are gradually lifting
with increased boundary layer mixing. The HRRR is quite optimistic
that the cloud cover in most of MN and through the Dakotas will
begin eroding later this afternoon. Other guidance is much slower
with this, and I tended toward the pessimistic side as well due
to the thickness and western extent of the cloud cover. There will
also be some gust northwest winds today that become calm tonight
as high pressure develops at the surface as the upper ridge pushes
into the eastern Dakotas. This could lead to the development of
some patchy fog, primarily across central MN where the precip
lingered the longest. Introduced some fog at KAXN but not
condiment enough at any other site to add it at this time. That
can be done during future issuances if confidence increases.

KMSP...Looks like we have already risen above the 017 critical
level, and we should stay above that level for the remainder of
the day. We leaned toward the pessimistic side of the guidance,
but some models indicate a rapid erosion of the cloud cover late
this afternoon could lead to a SCT ceiling prior to 00Z. Doubtful,
but a possibility.

Fri...VFR. Wind NNE 5 kts.
Sat...VFR. Wind light and variable.
Sun...VFR. Wind light and variable, bcmg SE 5 kts late.




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