Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
658 am CDT sun Aug 2 2015
Short term...(today and tonight)
issued at 400 am CDT sun Aug 2 2015
Today and tonight...surface analysis depicts a surface low over eastern South Dakota this
morning with a warm front extending southeastward and a cold front extending southwestward from
this center. Isolated convection overnight due to convergence in vicinity of the
warm front and a localized midlvl jet evident on WV imagery has shifted
off to the east and weakened...resulting in a mainly dry start to the
day. Kmpx radar shows a few strong storms within mostly weak
echoes driving southeastward from northestern ND and northern Minnesota. Aside from the
stronger storms...much of this is not reaching the ground within
the weather forecast office mpx County warning forecast area. However...as the day progresses...deep mixing
will still promote 30-40 knots of bulk shear highlighted over far eastern
Minnesota into western WI this afternoon and evening. Best instability and forcing
aloft will be well southeast of the County warning forecast area...but still being in the warm
sector of this system will allow for some SBCAPE to develop which
will make for some isolated- scattered thunderstorm development later today. Have
maintained slight-low chance probability of precipitation in eastern portions of the County warning forecast area to
account for this. As the cold front sweeps southeastward across the region
today...this will bring an end to any and all precipitation by this evening.
Cooler/drier high pressure will then begin to make inroads to the
region tonight...starting a drying out period for the region going
into the first half of the week.
Temperatures will still run warm in advance of the cold front today. Highs
will generally range 80-90 degrees north-to-south across the County warning forecast area today.
With late afternoon timing of the cold frontal passage...this will start cold air advection that
will be felt for tonight. Lows tonight into early Monday morning will fall to
the 50s across the County warning forecast area...which will be about 10 degrees cooler than
lows experienced this morning.
Long term...(monday through saturday)
issued at 400 am CDT sun Aug 2 2015
The main feature of note in the long term period continues to be
the large upper low over Hudson Bay. By tomorrow morning...this
feature will begin sagging south toward the upper Great Lakes
region. The longwave trough associated with the low will be in
place into at least Wednesday...meaning Monday and Tuesday we will
remain in relatively cool northwest flow...with little cloud cover
owing to the dry air mass coming in from Canada. High temperatures
will generally be in the middle to upper 70s all week...slightly
cooler than normal for this time of year.
It looks like we have one decent chance of precipitation in the
long term period...and that comes on Wednesday into Wednesday
night. The aforementioned upper low will begin drifting very
slowly east by Wednesday as a shortwave trough advances east over
the along the longwave ridge over the western Continental U.S.. at this
time...this feature looks to have the ingredients for a decent
rainfall maker. As the trough pushed into Minnesota...a cyclonically
curved jet streak around the long wave trough to our northeast
will place the upper Midwest in a favorable area of upper level
divergence. In addition...strong Theta-E advection is forecast
Wednesday- Wednesday night as low level winds turn southerly on
the leading edge of the wave...and we make a Gulf moisture
connection with precipitable water values increasing to greater
than 1.5 inches. At the surface...a frontal boundary will lift
north into the upper Midwest with increasing surface dew points as
well. Best Li values become negative for most of southern Minnesota by
Wednesday afternoon...so there is some instability to work with as
well. Being 4 days away however...confidence in the placement of
potential rainfall is not high...especially given the various
solutions offered by the deterministic guidance...and the fact
that the Hudson Bay upper low could wreak havoc on the entire
upper air pattern. So...decided to stick with the allblend
guidance for this period which for now suggests chance probability of precipitation.
Slight chance probability of precipitation litter the forecast late in the week as a weak
frontal boundary pushes into western Minnesota...but at this time there
is little agreement in seeing organized precipitation during that
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 650 am CDT sun Aug 2 2015
Warm front to remain north of all weather forecast office mpx terminals today with its associated
cold front in the Dakotas expected to gradually sag east-southeast across the area.
Isolated to scattered convection...mainly north of I-94 this morning and east of
I-35 this afternoon...to be expeceted today. Thus...the only terminal that
may possibly have impactful precipitation looks to be Keau so have
included a thunderstorms in the vicinity for only that location. Precipitation chances are too low
for inclusion at any other terminal...but will monitor and amend as
needed. As such...have kept all terminals as VFR with the
potential for MVFR conds should showers/thunderstorms affect the terminal.
The cold front looks to move through the area by this evening...resulting
in sky clear conds overnight through tmrw morning. Winds will swing around from
SW to northwest by this afternoon and become gusty this afternoon into this evening
before settling down tonight.
Kmsp...no significant weather impacts are expeceted as any convection is
expeceted to remain north and east of msp.
/Outlook for kmsp/
Tuesday...VFR. Wind northwest 5-10 kts.
Wednesday...VFR. Wind east 5-10 kts.
Thursday...mainly VFR. Chance MVFR shra/tsra. Wind east 5-10 kts.