Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201037
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
537 AM CDT Sun Aug 20 2017

.updated for 12z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Sun Aug 20 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...(Monday through Saturday)
Issued at 335 AM CDT Sun Aug 20 2017

The long term forecast is bookended with active weather periods,
with thunderstorm chances on Monday/Monday night and again
Friday night/Saturday.

The period starts off with the cold front of recent interest
having stalled from northern Iowa across central Wisconsin Monday
morning. The front should be the continued focus for showers and
thunderstorms, especially during Monday afternoon when surface
heating is forecast to allow for decent destabilization along the
Iowa border and south. The shortwave trough sinking south out of
Canada will also supply sufficient ascent for storm development,
possibly severe along/south of I-90.

Tuesday through Thursday surface high pressure broadens across
the Upper Midwest. This will bring dry weather and temperatures
generally in the 70 to 75 degree range for highs.

Medium range models are in pretty decent agreement that the next
trough will move in on Friday evening, then gradually work across
the area through the weekend. It looks to be a fairly stormy
weekend if these progs hold.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 530 AM CDT Sun Aug 20 2017

Sfc cold front to drop southeast across the area today. Small
chance of -shra/-tsra with fropa mainly to the east and south
this afternoon/evening. Will mention VCSH at KMSP/KEAU for now.
Expect fair amount of mid/high level clouds until this evening as
high pressure builds over the northern areas. Winds becoming NW-N
and eventually N-NE into Monday as front settle over northern
Iowa.

KMSP...Still looks like fropa around 21z. Some threat for -tsra
with passage. Will mention VCSH for now. Otherwise VFR trend to
continue with fair amount of mid/high level clouds around.

/OUTLOOK FOR KMSP/
MON night...Chc MVFR/-TSRA. Wind SE 5 kts.
TUE...VFR. Wind NW 10 kts.
WED...VFR. Wind N 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...DWE
LONG TERM...LS
AVIATION...DWE


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