Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
100 PM CDT Wednesday Jun 3 2015
Update...for 18z aviation discussion below
Short term...(today and tonight)
issued at 423 PM CDT Wednesday Jun 3 2015
Key feature today that will be playing the primary roll in what
happens with precipitation potential is the well defined mesoscale convective vortex that was over
the eastern sodak/Nebraska border at 3 am. The mesoscale convective system that generated this mesoscale convective vortex is
racing to the southeast...following the trend of the low level jet which has split as
it entered the mpx area...with one enhanced are of moisture
transport going across northern Minnesota and the southern branch now nosing
into SW Iowa...this explains why most of US ended up dry overnight
with one batch of storms remaining north and the other batch going
To say the initialization of the mesoscale convective vortex in the models was poor would
been an understatement...with plenty of spread in the deterministic
models and even the cams for really the whole short term period.
Looking through the weeds though...there were a couple of models
that looked to have caught on to some idea of the mesoscale convective vortex this morning
at that would be the rap/hrrr along with the hires arw. From the
deterministic models...the European model (ecmwf) looks to have gotten closest to
initializing this wave...though think it is underdone with the
amount of quantitative precipitation forecast it generates through tonight. If there are any issues
with what the rap/hrrr are showing for the evolution of the mesoscale convective vortex...it
is that they are probably a bit slow and possibly sending it to far
What we are currently anticipating is that we will not see much
precipitation in the mpx County Warning Area until the mesoscale convective vortex arrives...which will be around
12z in our SW counties. As the mesoscale convective vortex moves east-northeast through the
morning...it should be accompanied by a shield of rain with embedded
thunderstorms. Think this mesoscale convective vortex will bring with it a 4-6 hour period
where folks see a good soaking rain with a few rumbles of thunder.
Because of that...our severe threat will be pretty low today given
the extensive cloud cover/rain expected. If we were to see any
severe weather...think where the Storm Prediction Center has their marginal risk is a
pretty good estimate...is this would be toward the south end of the
mesoscale convective vortex where there is a little better chance of some more enhanced
Going into tonight...given the timing of the mesoscale convective vortex across Minnesota in the
morning/afternoon...expect greatest precipitation potential between 8pm and
midnight over western WI before this wave continues on its way toward
the western u.P. Of Michigan.
For temperatures...expectation of extensive cloud cover means we
will not be achieving our potential given 925-850 temperatures are very
similar to what we saw yesterday in Minnesota...where highs topped out in
the middle 70s to lower 80s. Instead favored the cooler end of the
model envelop for highs today...going with mainly low/middle 70s.
Tonight...we did slow down the eastern progression of the front...so
warmed lows a few degrees as well for all but western and central Minnesota.
Long term...(thursday through tuesday)
issued at 432 am CDT Wednesday Jun 3 2015
The aforementioned cold frontal movement discussed in the short
term discussion will be a slow process and even by Thursday
morning...the front should be near the southern and eastern edge
of the forecast area. The frontal position is the reason for the
small chances of showers/storms through Friday. At this point the
best thunderstorm coverage will be just to the south across
Iowa...although areas along I-90 in southern Minnesota and locations in
western WI are close enough to the boundary to warrant slight
chance or chance of precipitation. Eventually the boundary slides farther
southeast of the area as a weak surface high builds across the
upper Mississippi River valley...so there should be a 12-24 hour
window heading into the weekend where the weather will remain dry.
Minnesota/WI does remain on the northern edge of the 830-300mb thickness
ridge with pieces of shortwave energy rotating through every so
often and thus the reason for the multiple periods of 20%-40%
through the extended. Eventually a trough that originates in the
Gulf of Alaska takes a trip across the interior of Canada and into
the Great Lakes and upper Mississippi Monday night into Tuesday.
This will cool temperatures down early in the work week with moderating
temperatures expected due to the arrival of return flow by
Wednesday. Highs will push /or surpass/ 80 degrees late next week.
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1 PM CDT Wednesday Jun 3 2015
Showers and thunderstorms will plague the sites at times into the
evening hours. LIFR visibilities and IFR ceilings are possible at
times...with prevalent MVFR ceilings. By sunset...the majority of the
activity should be in WI...with all sites dry by 09z. Southerly
winds will gradually shift to the northwest as the front passes.
Br and stratus development expected overnight...with MVFR
cigs/vsbys. Scattering of the low clouds should commence between
15z and 18z.
after the initial surge of thunderstorms rolls through at taf
time...will see a brief break until the next batch of showers and
thunderstorms move through between 21z and 01z. MVFR ceilings will
develop...dropping below 1700ft between 05z and 09z. Should see
ceilings improve to VFR between 15z and 18z Thursday.
/Outlook for kmsp/
Thursday night...VFR. Wind north-northeast 5 kts.
Friday...VFR. Wind east 10 kts.
Sat...VFR. Chance MVFR -tsra late. Wind southeast 10 kts.
Sun...VFR. Chance MVFR -tsra. Wind SW 7-10 kts becoming northwest 7-10 kts.