Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 160853
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
353 AM CDT Wed Aug 16 2017

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Wed Aug 16 2017

Surface analysis early this morning shows a low pressure center over
northwest Kansas/southwest Nebraska with a warm front extending
nearly due east to southern Ohio and a trailing cold front extending
southwest through the TX/OK Panhandles into central New Mexico.
Aloft, the Upper Mississippi River Valley is caught between a ridge
axis extending south southeast from western Hudson Bay into the
southeast CONUS and a longwave trough over the lee of the Rockies. A
poignant shortwave axis curls from west-central Saskatchewan
province into eastern North Dakota then into eastern Wyoming. In
advance of the surface features, the deep southwesterly flow aloft
is tapping moisture from the subtropical jet, pushing PWATs to
between 1.50-2.00 inches over the WFO MPX coverage area this
morning. A band of light-moderate showers associated with a smaller
shortwave aloft will continue to push northeast through eastern MN
into western WI. These showers will be only the beginning of what
will be a rather wet 30 hours over the coverage area. The larger
trough axis aloft will help drag the surface low east northeast,
taking a path that will bring it to near KFSD by midday today then
over far southern MN tonight to around KMSP by daybreak Thursday
morning. This is a slower progression than models have depicted in
previous days so have adjusted the precip chances as such. After the
showers this morning, there will be a relative break in the action
for eastern MN into western WI through early afternoon while western
MN sees an increase in rain coverage in advance of the surface low.
In the meantime, the trough features to the west will pivot and
allow a cutoff low to develop within in, offset to the west of the
surface low. As this scenario develops, precipitation coverage
should increase steadily this afternoon through this evening, with
rainfall potentially heavy at times over central MN. With the deep
moisture remaining in place as the surface low moves across,
rainfall totals of 1-2" will be commonplace with amounts as high as
3" not unreasonable. Given the recent rainfall over portions of
western and central MN recently, isolated flooding issues are
possible but the progressive nature of the storm system is not
expected to be conducive to training storms. There is also a small
risk of severe storms given the enhanced jetting but instability
will be meager at best and with little insolation expected and warm
sectoring to remain to the south of the area, the risk for severe
weather is quite low. The threat for heavy rain will continue into
tonight with the slow progression of the surface low but rain
coverage and intensity is expected to diminish during the early
morning hours into daybreak Thursday.

As for temperatures, have continued the trend of advertising
slightly cooler temperatures from the previous forecast. As such,
will look for highs in the lower 70s in central MN and in the mid
70s in southern MN into western WI. Lows tonight will be similar to
this morning, ranging from the upper 50s to mid 60s.

.LONG TERM...(Thursday through Tuesday)
Issued at 350 AM CDT Wed Aug 16 2017

The longer term concerns remain timing of the exit of the upper
trough Thursday. Then timing of the next short wave through the
eastern CONUS trough will occur Friday with the next frontal
passage for late in the weekend/early next week.

The trough exits to the east of the area through Thursday
afternoon. Will taper PoPs and overall thunder chances from west
to east. Temperatures should remain on the cool side with ample
cloud cover remaining over much of the area through late
afternoon.

The deterministic models trend another short wave moving through
the area Friday/Friday night with attendant weak instability. We
should see some drier conditions through Saturday and into Sunday
across the region as flow aloft becomes more zonal with slowly
rising heights. This should allow warmer temperatures ahead of
the next frontal system which is progged to move across the area
Sunday night through Monday night. Temperatures are expected to
warm through the lower and mid 80s through the weekend with
increasing dewpoints ahead of the front. Passage of the front
could produce locally heavy rain, especially if it moves slower
than progged. Severe weather threat is possible be as the front
moves through Monday/Monday night as well.

Drier and somewhat cooler conditions will develop in the wake of
the front through midweek.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1134 PM CDT Tue Aug 15 2017

Late night onset of precip appears to be on track. A small area of
thunderstorms in south central MN has continued to develop in warm
advection zone, and a number of the convection allowing models
picked up on this. Quite a few of the models are developing storms
in southern and west central MN overnight, tracking northeast by
12Z. Once showers start, a drop to IFR looks quite likely, and we
are already seeing that in southwest MN. After showers depart,
ceilings will take a while to improve to MVFR, and areas north and
west of an surface low may even remain MVFR through the
afternoon. Areas southeast of the low, such as KMKT/KMSP/KEAU may
all see some VFR tomorrow afternoon as warm sector arrives. Then
more storms tomorrow late afternoon and evening.

KMSP...
Area of storms in south central MN may clip KMSP in the 08z-10z
time frame. Otherwise a drop to IFR is anticipated after 12Z in
wake of showers. The IFR ceilings should rise during afternoon,
maybe even going VFR for a few hours before another round of
storms Wed eve. Those have the potential for rather heavy rain.

/OUTLOOK FOR KMSP/
Thu...VFR. Wind N-NW 5-10 kts.
Fri...VFR. Chance afternoon/evening TSRA. Wind SW 5 kts.
Sat...VFR. Wind W 5 kts.


&&

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

$$

SHORT TERM...JPC
LONG TERM...DWE
AVIATION...TDK


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