Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 180816
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
316 AM CDT Tue Jul 18 2017

.SHORT TERM...(Today and tonight)
Issued at 315 AM CDT Tue Jul 18 2017

Surface analysis shows a NE-SW oriented cold front from a low
pressure center over Hudson Bay, extending through NW Minnesota into
western South Dakotas into SE Wyoming. Outflow boundaries from
earlier convection are scattered across the area (which will
contribute to additional convection later today). Aloft, broad upper
level ridging remains centered from the Four Corners region into the
Deep South with zonal flow across the northern tier states from the
northern Rockies through to the Great Lakes. With pronounced south
to southwest flow in place in advance of the cold front, a deep
plume of moisture continues to surge into the upper Midwest from the
deep South, contributing to PWATs around 2 inches for much of the
area and expected to last through to this evening. Also of note are
dewpoints around 70 even in the overnight hours for much of central
MN while the rest of the WFO MPX coverage area has dewpoints in the
60s. These dewpoints will only increase today while the front out
west takes its time moving through the region. Given the presence of
multiple outflow boundaries and the approach of the cold front, it
will not take much for more widespread convection to once again
develop later on today. MUCAPEs will again climb to 3000-4000 j/kg
while bulk shear hits the 30-35kt range. The deeply moist
environment with little-to-no capping will result in clusters of
storms developing by late morning in western and central MN which
will slowly but steadily progress southeast. In terms of severe
weather, nothing overly organized is expected but some storms could
contain strong/severe winds in a downburst fashion and potentially
marginally severe large hail. The cold front is expected to drop
into southern MN and western WI by late this afternoon then drop
south of the WFO MPX coverage area altogether overnight tonight,
bringing an end to the precipitation across the area. QPF totals
through this evening may commonly range between 1.0-1.5 inches with
locally higher amounts certainly possible. Have added heavy rain
mention into the grids as there remains the Slight Risk for
Excessive Rainfall. As for temperatures, the added cloud cover will
hold back highs from the 90s experienced yesterday for much of the
MN portion of the coverage area. Max temps today will remain in the
low-mid 80s but there is a shot that highs could hit the upper 80s
close to the Iowa border. Lows tonight will run about 5-10 degrees
cooler, mainly due to the passage of the cold front, resulting in
slight cold air advection and incoming drier low level air.

.LONG TERM...(Wednesday through Monday)
Issued at 315 AM CDT Tue Jul 18 2017

The longer term remains active through the end of the week with
the area remaining on the edge of the mid level cap/surface front.
Periodic bouts of thunderstorms will continue with severe weather
possible along with torrential rain, mainly Wednesday night,
thursday night into possibly Friday night.

Much of Wednesday will remained capped for convective development
with mid level temperatures warming to +14c into the southwest.
An 100kt upper 300mb level jet rides across northern MN and the
right entrance region will move into MN Wednesday evening. Very
unstable airmass will be in place along with PW`s over 2 inches.
The GFS has been consistent in developing an MCS and moving it
along the instability gradient and mid level cap the last several
runs. This continues to favor about the southern third of MN. WPC
paints a slight risk of excessive rainfall during this period
which is definitely possible. We should see rainfall rates of 2-3
inches an hour once convection matures into the late
evening/overnight. The convection should be moving however/forward
propagating with damaging winds the main severe weather threat.

The area continues to remain in the favored region for convective
development again later Thursday, Thursday night into Friday. The
southern third, perhaps a bit farther south if Wednesday nights
convection moves the surface boundary farther south, looks like
the area of concern. Again torrential rain and severe storms will
be possible. Large hail and damaging winds being the main
threats.

Finally, the deterministic models drive a cold front through the
area Saturday and should end the convective threat lasting into
early next week. Temperatures and dewpoints will drop off as well
as high pressure builds south over the Great Lakes.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1220 AM CDT Tue Jul 18 2017

There are three main concerns for the next 24 hours. The first is
how long current shower and thunderstorm activity stretching from
north of RWF to MSP/RNH/EAU will last tonight. A few models show
it going most of the night, but others taper it off quickly.
Maintained some shower mention for the next couple hours. The
second concern is whether IFR cigs will develop to the north of
the showers overnight into early Tuesday. There are hints of that
between STC and AXN at taf issuance time, but it doesn`t show much
sign of expanding yet. The third concern is when and how widespread
showers and thunderstorms will become late Tuesday morning and
Tuesday afternoon. Models are indicating a band of torrential
rainfall totals from RWF eastward to MSP and EAU.

KMSP...MVFR conditions may persist for a couple more hours before
VFR conditions prevail into Tuesday. There is an outside chance of
IFR cigs overnight, but it appears the best chance will be to the
north.

/OUTLOOK FOR KMSP/
Wed...VFR. Chc MVFR/TSRA. Winds SE 5-10 kts.
Thu...VFR. Chc MVFR/TSRA late. Winds lgt and vrb.
Fri...VFR. CHc MVFR/TSRA. Winds SE 5-10 kts.


&&

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

$$

SHORT TERM...JPC
LONG TERM...DWE
AVIATION...BORGHOFF



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