Scientific Forecaster Discussion
fxus63 kmpx 241719
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1219 PM CDT Mon Apr 24 2017
Short term...(today and tonight)
issued at 350 am CDT Mon Apr 24 2017
Surface analysis early this morning shows the quasi-stationary
front still lingering over southern Minnesota through far SW WI, with east-northeast
winds and temperatures in the 30s to the north of the front and S
winds with temperatures in the 50s S of the front. The front waves
back west to a low pressure center over western South Dakota and
western Nebraska. Aloft, flow continues to be generally zonal over
Minnesota and Wisconsin while a modest longwave trough axis sits
in the Lee of the northern-central rockies. With this trough set
to progress eastward, this will then nudge the developing low
pressure center eastward, through South Dakota today and through
central Minnesota tonight and into Lake Superior by daybreak
Tuesday morning. The surface front sitting over southern Minnesota will
push northward today in response to slightly increasing 700 mb-500 mb
heights, allowing for decent warming for much of the weather forecast office mpx
coverage area. Warming will not be maximized due to the increased
cloud cover expected across the area today. In addition, some
scattered rain showers are expected over mainly the northern half
of the area through this evening in response to the northward
progression of the front and deeper moisture being advected into
the region in advance of the surface low. Not looking for much at
all in the way of qpf, generally a few hundredths north of the
I-94 corridor. The precipitation will gradually diminish and shift
off to the east late tonight into tomorrow morning then resume by
around daybreak on the backside of the surface low. As for
temperatures, the large temperature gradient this morning will
become tempered by this afternoon with the northward progression
of the front. This will resulting in a more uniform southerly flow
over the entire mpx coverage area. Highs will range from the
lower 60s near Lake Mille lacs to the upper 60s by the Iowa
border. With the low pressure center crossing the area tonight,
cold air advection will commence with its passage, resulting in a
west-to-east temperature gradient instead of the north-to-south
gradient. Lows tonight will drop to the upper 30s in western Minnesota
while lows in western Minnesota hold in the upper 40s.
Long term...(tuesday through sunday)
issued at 350 am CDT Mon Apr 24 2017
The longer term concerns are overall development/movement of the
western conus trough with embedded short waves and timing of which
will determine overall p-type and quantitative precipitation forecast amounts Tue into Thu. Then
potential of a significant storm to affect the area into the
weekend. Overall...favoring a cool and wet period.
The front associated with the initial short wave should be exiting
into western Wisconsin Tuesday. This will lead to strong forcing
along the baroclinic zone producing strong f-gen into the eastern
cwa later Tuesday into Tuesday night. This should spread rain
across this region during the afternoon and have opted to mention
categorical pops. Quantitative precipitation forecast amounts should be heaviest during this
period as well...with 0.50 to 0.80 inch amounts common...as the
main trough lifts northeast. With the passage of the
trough the thermal structure of lower boundary begins to favor at
least a rain/snow mix developing Tuesday night into Wednesday
morning over the western cwa. We could see some light
accumulations over that region...less than one inch however.
Then the models diverge somewhat on overall movement of the trough
to the northeast Wednesday into Wednesday night. The GFS weakens
the wave as it lifts northeast and redevelops the front/wave
further to the east into Wednesday night. This splits the
precipitation to the northeast and farther southeast by Thursday.
The European model (ecmwf) is slower and a bit deeper with the trough and lifts a
wave farther north into Wisconsin Thursday. This would leave much
of the cwa vulnerable to some wet snow later Wed night into
Thursday morning. Best potential would be over west central
Wisconsin where we could see an inch or so of wet snow accumulate.
Following this we should see a general decrease in overall
precipitation as we are in between significant systems. There is
a small threat of showers affecting the area Friday/Friday as a
weak wave lifts northeast ahead of the deeper western conus
trough. This stronger system is forecast to eject north and east
over the weekend. This should provide an increasing threat of rain
over the weekend. The deterministic models diverge on when this
does take place...with the GFS holding off more widespread rain
until later Sunday into Monday due to the strength of the eastern
ridge. The European model (ecmwf) is faster lifting the system over the area later
Saturday and Sunday. Still have time to resolve these model
differences. Also...dynamic lift associated with the trough could
cool the boundary layer enough to generate more wet snow for the
County Warning Area. This would take US to the first of may.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1215 PM CDT Mon Apr 24 2017
No aviation concerns through the next 6-12 hrs with gusty winds
remain from the south, with the highest gusts in south central
Minnesota until 00z. A few showers will be possible this afternoon
but coverage remains scattered at best. MVFR/IFR cigs are still
expected across west central Minnesota later this evening, and
across most of central to southwest Minnesota by 6-9z tonight.
Confidence is high on cigs lowering overnight, but timing is low.
Once the winds shift to the northwest, lower cigs will start. Most
of the measurable precipitation will hold off until after 18z
Still confident that MVFR cigs will develop late tonight, early
Tuesday morning once the front nears the area. Higher confidence
that IFR cigs/vsbys will hold off until after 18z Tuesday, and
most likely after 21z. Gusty winds this afternoon will decrease
and veer to the northwest by Tuesday morning, then northeast by
the afternoon. There remains some elevated instability late this
afternoon, and again Tuesday afternoon, but not enough to warrant
thunderstorms in the vicinity at this time.
/Outlook for kmsp/
Tue ngt...MVFR, IFR possible. -Ra likely.
Winds NE 10-20 kts.
Wed...MVFR, IFR possible. -Ra likely early, mixed with -sn late.
Winds NE 10-20 kts.
Thu...MVFR, IFR possible. Chc -ra/-sn early.
Winds north 5-15 kt bcmg light & variable.