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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
553 am CDT Thursday Jul 10 2014

Updated for 12z aviation discussion...
issued at 537 am CDT Thursday Jul 10 2014


Short term...(today and tonight)
issued at 537 am CDT Thursday Jul 10 2014

Warm and Summer-like weather with periods of sun and thunderstorms
will give way to cool...cloudy...and downright Fall-like weather for
the beginning of next week. Warmer and drier weather will follow the
near record cool temperatures.

Early morning water vapor with 500mb heights and winds showed a
shortwave located across western Montana. This shortwave will
continue eastward and draw up warm moist air ahead of it. Still some
uncertainty with the timing of the precipitation...whether it will be late
Thursday night or more toward Friday morning. Given the consistency
of the upper level wave being located over the Minnesota/WI border by 06z
Friday...and central WI by 12z...have sped up the timing of the probability of precipitation
even though the best low level moisture lags this upper level
feature. The NAM 10.00 is the most progressive with the quantitative precipitation forecast...and in
the past has done better with the timing of warm air advection
precipitation. Given the 925mb mass fields are fairly consistent between
the GFS/ECMWF/NAM feel comfortable with leaning towards the quicker

Long term...(friday through wednesday)
issued at 537 am CDT Thursday Jul 10 2014

Once this precipitation exits the region boundary layer destabilization
will occur behind it across western reintroduced probability of precipitation late
Friday afternoon. The chance of precipitation lingers through
Sunday...but the highest probability is across Iowa where the
boundary becomes more east/west oriented setting the stage for
heavy rain down there. However...cant rule out thunderstorms at
anytime over the weekend across MN/ continue with slight
chance of precipitation although most of the period should be dry.

Looking ahead...aside from Thursday night...the highest confidence
in precipitation will be on Monday as a powerful upper level wave
strengthens across central Canada and drops southward across the
upper Midwest. The GFS/Gem/ECMWF are in remarkable agreement with
the location of this pv anomaly...and the heightfalls that precede
it. Cold air advection will keep boundary layer lapse rates
steep...and deep low level moisture means overcast skies and periods
of light rain showers. This pattern is similar to July 17 2009...or
July 27 2013 which set record low maximum temperatures of 65 and 64
respectively. Therefore hedged temperatures closer to the
GFS...which has highs only in the 60s for both Monday and Tuesday.
Also increased cloud cover considerably since forecast soundings
show overcast skies for both Monday and Tuesday afternoon.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 537 am CDT Thursday Jul 10 2014

Southerly winds will develop this afternoon ahead of the next
upper level disturbance. Showers and thunderstorms will develop
toward the end of the period. Timing differs between the faster
large scale models...and the slower hires models. Trended toward
the faster have the precipitation moving in quick. There
are 3 parts to the precipitation. The first is warm air advection later
today...followed by upper level lift tonight...and finally low
level moisture transport Friday morning. As a result...have
extended period of vcsh in the tafs to portray this long duration
chance for precipitation.

in addition to the general looks like out of the 3
possible forcing mechanisms for precipitation...the best chance at msp
will come late tonight into Friday morning.

/Outlook for kmsp/
Sat...VFR with MVFR/shra/tsra possible. Wind northwest at 5kts.
Sun...VFR with MVFR/shra/tsra possible. Winds west at 5g10kts.
Monday...VFR with MVFR ceilings/rain showers possible. Wind northwest at 15g20kts.


Mpx watches/warnings/advisories...


Short term...jrb
long term...jrb

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