Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230914

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
414 AM CDT TUE AUG 23 2016

.SHORT TERM...(Today and tonight)
Issued at 414 AM CDT Tue Aug 23 2016

The main concern for the short term is convective trends this
afternoon and tonight which will determine where the best potential
for heavy rainfall will set up.

A relatively small cluster of thunderstorms over southern Nebraska
is associated with a mid level disturbance which appears well
initialized in many of the CAMs. This wave will lift northeast
quickly this morning, reaching northwest Iowa by early this
afternoon. CAMs are not showing much weakening of this cluster as it
heads northeast and it may reach the southwestern CWA or the
counties south of the MN river by 2-4 PM and toward the metro as
early as 6-8 PM. By that time, the mid level disturbance will weaken
as it heads into WI, with thunderstorms likely refocusing on
outflows left behind from the original cluster, and on the leading
edge of the moisture boundary pushing north into MN. This should
generate additional clusters, with one possibly organizing into a
sizable MCS as the LLJ strengthens this evening over Iowa. The MCS
would then track southeast but a meso low with the MCS could send
stratiform rain/isolated TS northeast into Wisconsin. During the
transition period between the disturbance today and the LLJ-fed MCS
tonight, slow moving cells could produce very heavy rainfall with
some CAMs showing several inches in spots -although that is not all
that unusual with hi-res models. Because moisture quality increases
markedly with the wave and there is some potential for slow moving
cells, introduced heavy rainfall to the grids across southern MN
this afternoon and evening.

The faster the initial wave reaches our area, the more likely it is
the next round sets up closer to home. The ECMWF QPF bullseye over
southern MN closely resembles some of the hi-res guidance,
particularly the WRFARW, WRFNMM, and the four members of the 06Z
HopWRF. A Flash Flood Watch may be eventually be needed if it
becomes evident this solution is panning out.

Further north from west central MN into northwest WI, confidence is
low with respect to convective coverage. Some storms may fire along
the cold front late this afternoon near the Dakotas/MN border, but
large scale dynamics don`t favor widespread activity. Kept chance
pops going in these areas.

.LONG TERM...(Wednesday through Monday)
Issued at 414 AM CDT Tue Aug 23 2016

Picking up the forecast at 12Z tomorrow, a cold front will be
draped from north to south through the middle of MN with
lingering precipitation in eastern MN and west central WI. Surface
dew points of near 70 will be seen along and east of the frontal
boundary along with a pool on instability and showers and storms
moving through from the overnight period. The front will continue
advancing east fairly progressively tomorrow, clearing the Twin
Cities around midday and west central WI including Eau Claire by
tomorrow evening. Winds will turn northwesterly and skies will
scatter out, while dew points fall into the 50s behind the front.

The strong upper level low in southern Canada will remain to our
north while it works its way directly east through the day
Thursday, while surface high pressure builds into the upper
Midwest. A secondary cold front will push through early Thursday
and 850mb temps will fall below 10C. Highs Thursday look to fall
into the lower 70s thanks to this cold air advection from the

The high pressure ridge will work through on Friday, with
southwesterly flow developing toward the evening. With this wind
shift, warm air and moisture advection will increase Friday night
through Saturday ahead of a decent shortwave that will eventually
pivot through the upper midwest from Saturday through Sunday.
Saturday and Saturday night look to be the most likely time for
Thunderstorm activity across the region.

The weekend trough will move off to the east and a warming trend
is forecast for early next week as the thermal ridge behind the
departing trough leans over to the east early next week, allowing
our daytime highs to return to the lower and mid 80s.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1042 PM CDT Mon Aug 22 2016

VFR conditions are expected into Tuesday evening...and then
showers and thunderstorms are expected to spread north and east
from SD/IA across the area Tuesday night into Wednesday.
The main focus this TAF period remains on wind. Gusts will
continue to slowly subside late this evening, and then the main
concern becomes low level wind shear. Still expect to see 2000ft
winds around 45-50kts developing between 06-08z...from a 210-230
directional component. Surface gusts return around 15z Tuesday,
with sustained 15-20kt speeds gusting into the mid/upper 20s
(knots). Mostly sunny conditions are expected on Tuesday, but
mid/high clouds will be on the increase toward the evening as
convection develops over IA/SD. Have included a Prob30 for SHRA/TS
after 03z at KRWF and 09z at KMSP.

Low level wind shear looks to be developing at the start of the
period, persisting until around or shortly after 14z when surface
gusts return. The threat for thunder looks to return
overnight...primarily after 09z Wed.

Wed...VFR with -TSRA/MVFR possible. Wind SW 5-10 kts becoming W.
Thu...VFR. Wind NW 7-10 kts.
Fri...VFR. Wind SSW 5-10 kts.


.MPX Watches/Warnings/Advisories...


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