Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210900

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
400 AM CDT Wed Jun 21 2017

.SHORT TERM...(Today and tonight)
Issued at 355 AM CDT Wed Jun 21 2017

Surface analysis early this morning shows a low pressure center over
southern Saskatchewan province. From this low pressure center, a
leading warm front extends southeast through eastern MT and the
western Dakotas through Nebraska into northern MO while a trailing
cold front meanders through western MT into southern ID and northern
NV. Aloft, a modest upper level ridge extends north from the central
Plains through Manitoba province while a northern-stream trough
moves across Alberta province and the CONUS Rockies. The upper level
trough is expected to continue shifting southeast and deepen,
forming an upper level low over southern Manitoba by daybreak
Thursday morning. The associated shortwave trough axes rounding this
system will help drag the surface low and its associated fronts
eastward. The key will be when and how much north the warm front of
this system moves. The consensus and current thinking is that the
warm front will generally remain to the south and west of MN through
much of the day, possibly nudging northward into far southwestern MN
by late afternoon (which would help push highs temperatures in that
corner of the state to the mid-upper 80s). By late afternoon into
early evening, as the upper low drops south and helps enhance low-to-
mid level jetting, the warm front will lift north into southern MN
while the cold front enters western MN. The cold front will then
continue to sweep through the state overnight, exiting all but far
southeastern MN by daybreak.

There are several factors at play which may allow for strong/severe
convective development today. First is the arrival of the warm front
which will act as a low level convergence boundary. Secondly, the
stronger low-mid level jetting will enhance shear. Third, depending
on how far north the warm front pushes, instability will increase
over far southern MN. Lastly, the incoming cold front will again
provide increased low level lift. All things being equal, within a
fairly deeply moist atmosphere, these would contribute to a somewhat
robust period of convective development. However, there are some key
mitigating factors. Primarily, deep moisture will be lacking which,
although that would contribute to an enhanced hail threat, will
overall limit the coverage of any strong/severe storms. Secondly,
most models are indicating fairly good capping over much of the area
which will inhibit convective development. Third, much of the
concern will surround the northward progression of the warm front
which looks to be fairly late today into this evening which would
not be diurnally optimal for capturing available instability and
also which looks to be subject to the zonal flow developing aloft
and not have much punch to lift north. There still will be a large
hail threat due to the strong lapse rates and even isolated elevated
convection with the warm front, while any damaging wind threat will
be confined to southwestern MN due to diurnally driven convection
which could take the form of strong/severe clusters in advance of
the cold front.

Adding all this forecast thinking together leads to scaling back
pops to the low-chance category and only for far southern portions
of MN for much of the day today. As the warm front moves east and
nudges north later this afternoon and evening, chances for precip
increase into the mid-high end chance category for southeastern
portions of the WFO MPX coverage area, but duration will be limited
as the cold front will be in close proximity behind which will close
down precip chances through the overnight hours.

Because of the uncertainty of how far north the warm front will
lift, this will create the potential for a large northeast-southwest
gradient in high temperatures today. There may also be some variance
with there the warmest air may reside. At this point, highs looks to
range from the mid-70s north and east to the upper 80s far west and
southwest. Lows tonight will not be subject to ideal cold air
advection in the wake of the cold front (better tomorrow), so will
look for lows ranging from the mid 50s to mid 60s north-to-south.

.LONG TERM...(Thursday through Tuesday)
Issued at 355 AM CDT Wed Jun 21 2017

The longer term concerns remain the thunder/rain chances into
Thursday night and overall development of the eastern CONUS trough
through the weekend.

The surface front is progged along the MN/IA border Thursday
morning. There may be at least some left over scattered
convection over the eastern and southern areas Thursday morning.
The western trough is forecast to move east and attendant height
falls/forcing and F-gen along and north of the boundary...any
capping potential will be eroded quickly. We expect a good shot
of rain/thunder especially across the southern third of the area
Thursday afternoon...and then shift east with the upper trough
into Thursday evening. There will be some elevated showers/isolated
thunder into central MN especially during the morning/early
afternoon as the trough and forcing arrive. The severe weather
threat should be limited to the vicinity of the frontal boundary
with mainly elevated hail and wind threat. This matches SPC Day2

Following this front...cooler and drier conditions should envelop
the region as the eastern conus trough digs south and east. THis
draws in very cool canadian air with the GFS bringing in +4 to +8c
850mb temepratures for the weekend...with the ECMWF even a little
cooler. The deterministic models differ somewhat on how they
handle the short wave that moves into the region in the northwest
flow pattern for Saturday/Sunday. We will retain the small chance
PoPs and follow the GFS for now which has been most consistent
with this feature. Still looks cool into early next week as well.
There is some indication of the western ridge moving east into the
northern plains region as the eastern CONUS trough propagates
farther to the east. This should bring in warmer condition along
with another threat of showers/storms to the area by midweek.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1038 PM CDT Tue Jun 20 2017

Benign weather is expected to start the period, and other than
the potential for some light fog in west central WI, no
restrictions are expected overnight. Mid/high clouds will be on
the increase Wednesday, with widely scattered showers possibly
spreading eastward across the area (while decaying) during the
morning. The more widespread activity with thunder potential as
well will arrive after 00z Thursday, when ceilings will likely
become bkn-ovc low-end VFR. Winds shift to south/southeast on
Wednesday morning, with gusts up to 20 knots possible during the

High confidence in VFR through sunrise Wednesday. Could see a few
showers Wednesday morning, but the more organized activity (with
the potential for thunder) is expected to hold off until Wednesday

Thu...Mainly VFR. Slight chc -TSRA/MVFR. Wind WNW 5-10 kts.
Fri...VFR. Wind NW 10 kts.
Sat...Mainly VFR. Slight chc -TSRA/MVFR. Wind NW 5-10 kts.




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