Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 240017 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
717 PM CDT SUN OCT 23 2016

.SHORT TERM...(This evening through Monday)
Issued at 415 PM CDT Sun Oct 23 2016

Cloudy, cool and breezy conditions were the norm today across
Minnesota and western Wisconsin in the wake of a cold front that
passed across the area this morning. The front was just entering
eastern Minnesota around sunrise, but strong northwest flow has
pushed the front into southern Wisconsin and Illinois this
afternoon. As the front and weak surface low exited the area, high
pressure has continued to build across the Northern Plains this
afternoon. The high pressure will slide overhead late tonight,
which should make for a very chilly Monday morning - as we expect
the wind to become light and the clouds to eventually clear late
this evening or tonight. This is especially true in west central
and central MN where winds should drop off late this evening. It
looks like widespread low to mid 30s are likely outside the core
Twin Cities metro with even mid to upper 20s possible in low
lying areas. Even though heights build slowly tomorrow, a cool day
is expected after a chilly start. There is little temperature
advection and weak boundary layer flow to promote mixing tomorrow
afternoon. There may also be a cirrus deck overhead. There is
pretty good model guidance consensus of low to mid 50s for highs

.LONG TERM...(Monday night through Sunday)
Issued at 415 PM CDT Sun Oct 23 2016

Biggest weather feature for the week ahead continues to be the
rainmaker for Tuesday afternoon into Wednesday morning. Beyond
Thursday, confidence in the forecast is very low, with the ECMWF and
GFS about 180 degrees out of phase when it comes to placement of
surface features this weekend.

Our storm for Tuesday is currently moving on to the central
California coast as it is rounding the base of a deep low off the
Washington coast. This wave is pretty well forecast by the models to
strengthen as it is going across Iowa Tuesday night. This system
will have two phases. During the day Tuesday, isentropically forced
precip will break out from west central MN toward northeast Iowa,
with a more dynamically forced heavy burst of rain expected Tuesday
night into Wednesday morning down along the MN/IA border into
central WI as the main upper wave moves through.

One trend we have seen with the models is for a little less QPF
overall, with the 3.5" total amounts we had been seeing with the
NCEP models now down closer to 2.75", with the ECMWF showing a half
inch lower trend in QPF as well. This makes sense given how quickly
the most intense forcing and associated high precip rates come
through. In addition, the ECMWF shifted south some, with it`s
heaviest rain down in northeast IA into southwest WI. Fortunately,
this is an all rain event as we should see a pretty good gradient in
amounts across the metro from south to north. The 23.12 GEFS QPF
plumes show the gradient peril well at MSP, with amounts ranging
from 0.1" to almost 2", the spread is an indication of the gradient
being nearby.

Based on 12z guidance, a couple of changes were made to the forecast
for this system. One, we continue to reduce pops in WI Tuesday
afternoon, with dry air from a surface high north of Lake Superior
looking to put a pretty hard stop over central and eastern MN to the
isentropic rainfall Tuesday afternoon. QPF was not changed much with
the blended forecast used being a pretty good split between the
ECMWF/GFS. Biggest change with QPF was a reduction in amounts with
rainfall during the day Tuesday as initial dry airmass looks to take
a bite out of the isentropic precip.

Behind this system, an upper ridge will build across the Plains,
being downstream of the ridge, we will dry out for Thursday, but
once again, cold air behind this system is non existent, so we will
continue to run near to above normal for highs on Thursday.

After Thursday, models diverge significantly and confidence with the
forecast from Friday into the weekend is very low. The differences
stem with the handling of a couple of troughs out in the Pacific.
The first will come ashore in the Pac NW Thursday, with a stronger
wave following into California Friday.  The ECMWF deamplifies the
first wave pretty quick and has the second wave coming through here
over the weekend. The GFS plays up the first wave more, which delays
wave two locally to after the weekend. The differences they create
are kind of staggering, with the GFS bringing a warm sector in on
Friday with highs possibly pushing into the 70s. As the GFS brings a
front through, the ECMWF has a cool and dry surface high working
across MN. The discrepancies continue into the weekend, with the
ECMWF showing wave two spreading rainfall across the area Saturday
night, with the GFS keeping us dry through the weekend. Given the
spread in the guidance, stuck with with blended guidance for Friday
through the weekend, though this is likely to change, possibly quite
a bit as we work through the week.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 717 PM CDT Sun Oct 23 2016

VFR conditions are expected through the period. Cigs are beginning
to break up across the region which will continue through the
evening. High clouds will stream overhead through tomorrow. Winds
will remain light.

KMSP...No additional concerns.

Tue...Becoming MVFR with -RA. Chc IFR late. Wind SE at 10G20kt.
Wed...MVFR/IFR with -RA early. Wind ENE at 5-10kt.
Thu...VFR. Wind W 5-10kt.


.MPX Watches/Warnings/Advisories...


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