Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210834

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
334 AM CDT Mon Aug 21 2017

.SHORT TERM...(Today and tonight)
Issued at 334 AM CDT Mon Aug 21 2017

The short term concerns are convective potential early and again
later this afternoon along frontal boundary.

Initially, the Iowa/Nebraska complex appears to impeding flow with
the LLJ and as of 08z nary a shower has developed into south central
MN. The 06Z HRRR did try and develop some showers after 10z so we
will continue to mention small chance into the southern metro south
through much of the morning. Another forecast challenge is the
convective band across South Dakota. The FGEN induced convection is
forecast to move into central MN late morning/afternoon and
gradually weaken as the trough translates east and forcing is
redirected along frontal boundary further southeast. The GFS
indicated fairly strong mid level FGEN but produced little in the
way of QPF with this feature. The HRRR moves the band east into
central MN late morning/afternoon and does produce some light QPF.
We will have to hold onto small chance PoP into west central MN for
this potential.

Instability increases with MUCAPE to 2500 J/kg, best LI`s to minus 8
over the southeast area and deep layer shear around 40kts along the
surface front. The FGEN may be enough to generate at least some
widely scattered convection along the boundary as it drops southeast
during the evening. The exiting MCV associated with this mornings
complex may retard development some. If anything does develop it
could be severe. Due to the somewhat conditional nature of the
threat, the DAY1 outlook of marginal risk over the far south appears
reasonable at this time.

The front sags south this evening and we will continue to hold PoPs
along and south of the boundary. Some of the HIRES models were
indicating a possible increase in convection late tonight mainly
along and south of I90.

.LONG TERM...(Tuesday through Sunday)
Issued at 334 AM CDT Mon Aug 21 2017

Troughing aloft over the eastern half of the CONUS with high
pressure at the surface regionally will yield continued cool
temperatures during the long term forecast period. With respect to
precipitation, chances will be low/limited into next Friday given
the dominance of surface high pressure, but then the arrival of a
surface trough next weekend brings increased shower and
thunderstorm chances.

The period starts out cool and dry, with highs in the upper 60s to
mid 70s on Tuesday and Wednesday. Wednesday afternoon into
Thursday weak ripples on the western periphery of the
aforementioned eastern trough could spawn a few showers, but
precip amounts and coverage would be very light.

By Friday evening there is relatively decent agreement amongst the
models that a surface trough will be bisecting the central
Dakotas, with a shortwave trough approaching from the northwest on
the heels of the eastern trough. As spokes of energy associated
with the trough to the northwest pivot across the area over the
weekend along with the surface trough, more widespread shower and
thunderstorm activity is expected. For now have kept precip
chances around 40 percent for the weekend, but will most likely be
able to bump those up once timing details are more certain with
subsequent model runs.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1120 PM CDT Sun Aug 20 2017

Conditional threat of storms across southern MN and western WI
overnight and lingering in the morning for western WI. Added
vicinity mention at a few taf sites. Then the main concern is for
thunderstorms again tomorrow afternoon and evening, included
PROB30 wording at several sites for those.

KMSP...Added VCTS to the taf as HRRR and RAP maintain consistency
in bringing storms in overnight.

TUE...VFR. Wind NW 10 kts.
WED...VFR. Wind N 5 kts.
THU...VFR. Wind SE 5 kts.




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