Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182109

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
409 PM CDT SUN SEP 18 2016

.SHORT TERM...(This evening through Monday)
Issued at 400 PM CDT Sun Sep 18 2016

A warm front lifted across the area today and the result was a
switch to southwest surface winds and temperatures that climbed
into the lower 80s this afternoon. The 1000-500mb thickness ridge
is moving across MN and thickness diffluence will gradually move
across the northern half of MN this evening and tonight. The
result should be scattered showers/storms across northern MN and
perhaps east central and northwest WI. Farther south, the high
clouds are moving in, but the chance for precipitation isn`t
looking as good. A light shower or two can not be ruled out.
Tomorrow morning, central MN will get a quick shot of mid-level
FGEN which could shake out a few showers or sprinkles between
6am-11am. The operational guidance and now the CAMS are in pretty
good agreement on this scenario. Nothing heavy, and overall
tomorrow will be dry and slightly cooler than today despite the
isolated to scattered showers in the forecast.

.LONG TERM...(Monday night through Sunday)
Issued at 400 PM CDT Sun Sep 18 2016

...Heavy rainfall will increase flooding risk by next weekend...

The summer pattern of 2016 does not want to let up with multiple
rounds of heavy rainfall likely throughout most of the long term.
This will raise the likelihood of river and flash flooding
into next weekend.

High pressure will slide east across Iowa and Illinois Monday
night and Tuesday. A warm front from South Dakota into
southwestern Minnesota may spark a couple light showers across
west central Minnesota Tuesday as the initial round of moisture
advection begins reaching the area. Most models display light QPF
in this area. What does develop should not produce much with the
boundary layer rather dry and stable.

A much better surge of moisture with pwats of 1.5-1.75 inches will
arrive Tuesday evening on the nose of a 40 kt LLJ. Although the
jet is not particularly strong, the quality of moisture
accompanying it will contribute to a rapid development of showers
and thunderstorms by mid evening across southwestern Minnesota. It
is not entirely certain how far north and east this activity will
build through the night, but given a weaker LLJ and stronger winds
aloft, potential for an anchored MCS - or one that reshapes the
warm front/dives southward is lower than in previous events. The
thinking is this MCS should build eastward across southern
Minnesota and into western Wisconsin by Wednesday morning. Local
training is still likely on the southwestern flank of this
activity near where the surface warm front resides and excessive
rainfall would result.

Conditions are not expected to change appreciably Wednesday,
except to shift the heavy rain threat northeastward a bit into
central MN/western WI. The LLJ is expected to maintain itself into
Wednesday with pwats as high as 1.75-2 inches - or near record
values this time of year. In addition, a mid level disturbance
will lift northeast across the Plains and provide another trigger
for convection. Increased PoPs into the categorical range along
and north of I-94.

The top analog for Tuesday and Wednesday continues to be Sept
23, 2010 where over 5 inches of rain fell over a large portion of
southern Minnesota and central Wisconsin. As mentioned in previous
discussions, there are several other analogs where multiple inches
fell in or very nearby the area. CIPS analogs prog a 50% chance of
greater than 2 inches and a 10-20% chance of greater than 5 inches
from south central to east central MN and west central WI through

The LLJ should begin veering eastward Wednesday evening with
showers and thunderstorms winding down from west to east. A cold
front will push southeast overnight and into Thursday as high
pressure builds across the northern Great Lakes and Upper Midwest.
This should be a dry period, but kept PoPs across portions of
south central MN and west central WI where the front may not clear
if it slows any further.

The front will lift back north Friday. The good news is models are
progressive with this warm front and most of the CWA will be in
the warm sector Friday night and Saturday morning following
another round of storms Friday. The threat for convection in
advance of the front may slow it from what synoptic scale models
show at this range, so kept chance PoPs going Friday night and
temperatures cooler Saturday than what a convection-free
atmosphere would yield.

Cold front will slowly push east Saturday afternoon through
Sunday, with the ECMWF all but stalling it across Minnesota as
low pressure centers lift north along it. Yet more repeated
rounds of heavy rain would exacerbate any ongoing flooding.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1250 PM CDT Sun Sep 18 2016

VFR is expected through the TAF period. A few more high clouds and drier
southwest winds at the surface should keep morning fog out of the
area tonight and tomorrow morning. There is a front passing
through this evening and a few showers (possibly a rumble of
thunder) can not be completely ruled out, but we think the chance
of these impacting the TAF sites in Minnesota are pretty low - a
little better chance in western Wisconsin.

A stray vicinity shower can`t completely be ruled out this
evening, but the airport is looking at dry weather for the most
part with VFR conditions. Winds will gradually veer from south to
west this evening through tomorrow morning - becoming lighter with

Tue...VFR. SW winds 5 kt.
Wed...VFR/Chc MVFR. TSRA likely. SE wind 5-15 kts.
Thu...MVFR/IFR. Chc of TSRA. NE wind 5-10 kts.


.MPX Watches/Warnings/Advisories...


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