Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 240906

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
406 AM CDT Mon Apr 24 2017

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Mon Apr 24 2017

Today and tonight...Surface analysis early this morning shows the
quasi-stationary front still lingering over southern MN through far
SW WI, with ENE winds and temperatures in the 30s to the N 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 MN will push
northward today in response to slightly increasing H7-H5 heights,
allowing for decent warming for much of the WFO 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 MN while lows in western MN 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 QPF 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. QPF amounts should be heaviest during this
period as well...with 0.50 to 0.80 inch amounts 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 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 inbetween 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 do to the strenght of ther eastern
ridge. The 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
CWA. This would take us to the first of May.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 1001 CDT Sun Apr 23 2017

Made few changes to previous forecast, with things still looking
mostly on track. VFR conditions will predominate, with some MVFR
possible toward the end of the period as a cold front works
through the area. Some rain is also possible, but looks most
likely at the eastern sites (more widespread rain during the day
looks to stay to the north).

KMSP...Only real uncertainty at this point looks to be at the end
of the period when some lower ceilings will arrive along with
perhaps a few showers. For now, it still looks like things should
remain VFR through the period.

Tuesday...MVFR expected, IFR possible. Rain likely in the
afternoon. Northwest wind 5 to 15 kt becoming northeast 15 to 25
Tuesday night...MVFR expected, IFR possible. Rain likely.
Northeast wind 10 to 20 kt.
Wednesday...MVFR expected in the morning. Rain likely in the
morning. Northeast wind 10 to 20 kt.
Wednesday night...MVFR possible. Chance of rain and snow showers.
North wind 5 to 15 kt.
Thursday...MVFR possible early. Chance of rain and snow showers
early. North wind 5 to 15 kt becoming variable less than 10 kt.




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