Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
424 am CDT Wednesday Jun 3 2015
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 06z tafs through 06z Wednesday night)
issued at 1256 am CDT Wednesday Jun 3 2015
Feature of concern this taf period is the mesoscale convective vortex that has developed
along the Nebraska/South Dakota border. Majority of lead mesoscale convective system over Nebraska should dive
south into Iowa...but like the idea of the 3&4z runs of the hrrr
with a band of showers working across Minnesota and into WI during the
morning hours with the arrival elevated instability plume. After
that...also like the idea of the hrrr/nmm/arw and a couple of the
hopwrf members of showers/storm expanding in western Minnesota around 18z as
the mesoscale convective vortex arrives. In the tafs...mentioned a rain showers or vcsh for when
morning activity could impact tafs...while thunderstorms in the vicinity was used in the
afternoon to account for potential mesoscale convective vortex precipitation. Also tried
to back track some on the MVFR potential in the morning. Right
now...sub VFR ceilings are confined to the northwest of the front and think
we need to start getting into that Post frontal environment before
MVFR or lower ceilings become a big concern...but the front will not
get into the northwest mpx area until the afternoon.
Kmsp...confidence in precipitation forecast is low...hence the long
periods of vcsh/vcts. Afraid the hrrr may be overdone on how much
precipitation we see this morning...but the hrrr has support from a
couple of hopwrf members for some morning showers...so left that
mention in. Afternoon has lower confidence as well as it is still
to early to pin down exactly where/when rain showers/thunderstorms and rain will develop
late this morning/early afternoon beneath the mesoscale convective vortex. Tonight...we
will have a baggy pressure gradient with a moist boundary
layer...so that is likely when the threat for MVFR or lower ceilings
will be greatest...per sref probabilities.
/Outlook for kmsp/
Thursday...MVFR ceiling/visible in morning. Wind north-northeast 5 kts.
Friday...VFR. Wind east 10 kts.
Sat...VFR. Wind southeast 10 kts.