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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
652 am CDT Sat Sep 5 2015

Short term...(today and tonight)
issued at 420 am CDT Sat Sep 5 2015

Hot and humid weather will be the main story today...with a heat
advisory for Hennepin/Ramsey counties where effects of
urbanization will add some impact to the hot weather that will
obviously be across the entire region today. One concern is temperatures
this past night have not cooled down very much...and the effects
of heat are more likely to be felt if it does not cool down very
much at night. Main concern of course is during the afternoon and
early evening. Incoming clouds and a few storms will move through
the metropolitan the next few hours. Residual cloudiness will gradually
thin out and there should be plenty of sun this afternoon.

Next short wave to affect the area will arrive later this
afternoon and mostly affect west central into central Minnesota. There
is some potential most of this will remain west of Minnesota...but
certainly there is a better chance of it spreading or developing
into western and central Minnesota by late afternoon. Instability is such
that it will not take much to set off a few storms. More
impressive wave arrives tonight...and this is when heavy rain
could be a threat to much of our area. Precipitable water values
may exceed 2 inches according to a couple models.

Long term...(sunday through friday)
issued at 420 am CDT Sat Sep 5 2015

Sunday-Monday...sun will start out with a negatively-tilted trough
axis over the northern rockies extending south-southeastward from a cutoff low over
southern Alberta province with pronounced SW-NE upper level flow over the
northern plains into the upper miss River Valley. At the surface...a large
surface low will be centered over the Dakotas with a southward-sagging
cold front. The upper low is expected to swing a poignant trough axis
northeastward...helping kick the surface low and associated cold front also to the east
and NE. In advance of this fnt...lingering/ongoing showers and thunderstorms
in the morning look to diminish and shift off to the east...allowing for
some midday insolation to help heighten afternoon instability which
will already be of concern due to precipitable waters likely in excess of 1.75
inches. Scattered to numerous showers/thunderstorms are expected to re-
develop during the afternoon and evening hours on sun and the concern is for
strong to severe thunderstorms to develop due to MLCAPES around 2500 j/kg
and bulk shear around 30 knots. Though upper level support may not entirely
phase surface features to create ideal supercellular traits for
thunderstorms...the instability in place and steeper lapse rates look to
be conducive to the creation of multicellular storms capable of
large hail and/or damaging winds Sun afternoon and evening in advance of
the cold front. The upper low will rotate itself into Saskatchewan
province sun evening...quickly dragging the surface low into S-central
Canada in the process. High pressure steadily moving in behind the
cold front Sun night into Monday morning will push the cold front into the Great
Lakes...allowing for a drying out period on Monday with a much
cooler/drier airmass originating from The Rockies to settle into
the upper miss River Valley region. The difference will certainly be
felt in terms of temperatures and humidity levels on either side
of the front...meaning from Sunday to Monday. Highs on sun hitting
the middle 80s /with heat index values into the lower 90s/ will drop to
the middle- upper 70s with much lower humidity levels.

Tuesday-Friday...the cooling trend will continue through the
upcoming Post-Labor Day week as upper level flow remains progressively
E-W...not allowing any southerly warm air surges to reach the upper miss
River Valley. In fact...models indicate a few weak systems will
enable cooler Canadian air to drop into the region in small
pieces...making for high temperatures only into the 60s by the end
of the week. As for any potential precipitation...the best chances
look to be Monday night into Tuesday...owing to the western parts of the
weekend cold front lifting slightly north to bring isolated/scattered showers...and
then Wednesday night into a clipper-type low pressure center drifts
through the region originating from western Canada. Neither system
looks to bring any significant amount of rain nor strong/severe
thunderstorms...just passing showers with possibly isolated thunderstorms.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 652 am CDT Sat Sep 5 2015

Scattered early morning rain showers/thunderstorms and rain are weakening a bit as they
move east...but should reach krnh before fading out. Some fog
surrounding have continued the forecast of bringing in
some fog this morning...but not as dense as what we are seeing in
eastern Wisconsin. A little more MVFR visibility fog in far west central
Minnesota in wake of storms...and some of this could sneak into kaxn for
a couple hours this morning.

Once we get to 15z or so...storms should have weakened and fog
dissipated...leaving scattered to broken clouds and strengthening
S-southeast winds. May be some gusts over 20 kts by midday or early
afternoon...especially in Minnesota.

The next rain showers/thunderstorms and rain chances return to western Minnesota late Saturday
afternoon with incoming short wave from the SW. Have tried to
narrow timing down with thunder beginning around 21z in the
southwest and sprwading it to the north-northeast. Even better thunderstorms and rain chance
will be late tonight. Confidence is medium on this.

Kmsp...the airfield will get some thunder through 13z but may not
be for very long as storms seem to be weakening. Thereafter...
looks like short wave this evening may graze kmsp early this
evening but the better chance will be later tonight. The most
significant wind remains this afternoon with gusts around 22

/Outlook for kmsp/
sun...VFR with MVFR/thunderstorms and rain likely at times. Wind south-southwest at 15g20kt.
Monday...VFR. Wind northwest at 5-10kt.
Tuesday...VFR. Wind north-northwest at 10kt.


Mpx watches/warnings/advisories...
Minnesota...heat advisory from 10 am this morning to 7 PM CDT this evening
for mnz060-062.



long term...jpc

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