Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 172029

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
329 PM CDT MON OCT 17 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 325 PM CDT Mon Oct 17 2016

Tonight and Tuesday...Surface analysis this afternoon depicts a wavy
cold front extending SW from a surface low in the middle of Lake
Superior, draped over northern WI and SE MN into eastern Nebraska.
The front transitions to a warm front in the vicinity of the NE/IA
border, east of the surface low in that area. Aloft, a generalized
SW flow will persist but there are some noticeable features within
the broad flow. A potent jet streak over Rockies will shift into the
Great Lakes region by the overnight hours, essentially helping to
shunt the NE/IA surface low northeast along the draped front. Plenty
of low level moisture is resident over the area, to the tune of low-
mid 60s dewpoints over much of the central-southern MN into western
WI portions of the coverage area. KMPX radar already showing plenty
of echoes across the coverage area, with the strongest ones in the
vicinity of and south of the aforementioned front where convection
has been expected to break out this afternoon. Said convection is
expected to last through the evening hours for much of the coverage
area as MLCAPE values have climbed to around 1500 j/kg and shear
will continue to increase with the approach of the mid-to-upper
level jet streak. Should storms have enough growth near the front,
enough convergence could produce an isolated tornado. However, the
main hazards look to be damaging straight-line winds and large hail,
especially with freezing levels only in the mid-12 kft range. Storms
will persist for only a few hours, dissipating with loss of max
heating/instability, but precipitation will continue into the early
morning hours in conjunction with an upper level trough axis
trailing the surface front. Both the surface front and the upper
level trough will be east of the coverage area by daybreak Tuesday
morning, leading to a dry Tuesday but with clouds through at least
the first half of the day.

Mild temperatures will persist through tonight in advance of the
cold front, followed by noticeably cooler and drier conditions
tomorrow behind the front. Lows tonight will bottom out in the mid
40s to lower 50s while highs on Tuesday only climb to the upper 50s
to mid 60s.

.LONG TERM...(Tuesday night through Monday)
Issued at 325 PM CDT Mon Oct 17 2016

Very quiet weather Tuesday night through Monday as no precipitation
is expected during this time period. That makes for a short and
simple forecast discussion.

Early afternoon water vapor imagery identified a broad longwave
trough over the western Conus, with a few embedded shortwaves. The
first one was just crossing the High Plains and will cause a cyclone
to rapidly intensify over the Great Lakes into Quebec. A second one
was located off the coast of California, and the other was just south
of the Allucian Islands. On Tuesday the second and third shortwaves
will arrive and dig a trough over the Great Plains, with a surface
low developing over the Ohio River Valley. This should keep the
precipitation well to the south and east of MN/WI as high pressure
builds over the region. The 17.12 ECMWF has and area of rain across
southern MN Wednesday night, but for now kept the forecast dry.

Upper level ridging will continue through the end of the week, which
means more dry weather for the Upper Midwest. The 17.12 ECMWF has
some warm advection precipitation Friday night across the region,
but for now kept the forecast dry. Meanwhile the 17.12 GFS shows a
shortwave forecast to move along the International border Saturday
night, but as of now all the precipitation with this system will
fall north of the forecast area.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1235 PM CDT Mon Oct 17 2016

VFR conditions expected for all TAF sites early this afternoon
(including EAU which is initialized at MVFR but the lower ceilings
there will lift, as they did for the remaining TAF sites).
However, a stalled cold front wobbling over NW WI through SE MN
will become the focusing mechanism for convective development late
this afternoon through this evening. Scattered to numerous
-SHRA/TSRA can be expected, mainly after 22z, lasting through
02z-04z this evening. For now, have capped flight condition
degradation into MVFR range but IFR visibilities surely cannot be
ruled out should a heavy shower move atop any terminal. That said,
the terminals most likely affected by convection look to be KRWF-
KMSP-KRNH-KEAU while KAXN-KSTC look to be too far displaced to the
NW from the stalled front to have much of an influence. Once the
precipitation ends, which will be during the pre-dawn hours, drier
air moving in from the NW will help scour out low level moisture,
leaving mid-to-high clouds for the first half of tomorrow,
followed by clearing skies late tomorrow.

KMSP...Am generally expecting MVFR conditions with the
thunderstorms but a few periods of IFR cannot be ruled out. In
addition, the earliest TSTMs look to impact KMSP is 22z while the
latest timing is about 02z, so there is a good possibility the
duration may well be less than the 4-hours currently advertised.
Some gusty winds may accompany the TSTMs while additional gusts
from the NW may develop in the wake of the front during the pre-
dawn hours.

Wed...VFR. Wind NW 5-10 kts.
Thu...VFR. Wind NW 5-10 kts.
Fri...VFR. Wind SE 5 kts.


.MPX Watches/Warnings/Advisories...


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