Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 171754

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1254 PM CDT Thu Aug 17 2017

.SHORT TERM...(Today and tonight)
Issued at 345 AM CDT Thu Aug 17 2017

Surface analysis and KMPX radar imagery early this morning show
the center of low pressure over south-central MN, roughly
between KHCD- KMKT. Its warm front extends SE into the southern
tip of Lake Michigan continuing into central Ohio while its cold
front curls into eastern Iowa then SW over northern Missouri.
Aloft, a bellowing trough with a cutoff low within it over
southwestern MN is helping the surface feature along. Both
features at the surface and aloft will shift into WI by midday,
being replaced by weak surface high pressure and a minute ridge
axis within the progressive flow aloft. A fairly impressive rain
shield persist over central into western MN this morning, at times
with rainfall rates exceeding 2"/hr. As the tilted low shifts
east, the rain shield will also steadily shift east with rain
persisting within an airmass that continues to feature PWATs over
1.5". While the heaviest rain will still be featured over western
MN today, periods of moderate-heavy rain certainly cannot be ruled
out as the overall area of rain moves east. Another concern is
strong winds directly under and trailing the surface low. Have
already seen sustained winds around 30-35 kt with gusts 40-50 kt
(including a 51kt gust earlier at KRWF). This punch of wind
generally coincides with the track of the low so have opted to
issue a Wind Advisory for near and downstream of the surface low.
The duration of the winds is not expected to be more than a
couple/few hours but the speeds and coverage do warrant the
advisory. As the low spins off, conditions will gradually improve,
such that clearing skies may well be experienced this afternoon
in western MN, translating east into eastern MN and western WI
this evening. After skies clear out this evening into the early
morning hours, clouds will return from the west overnight through
daybreak tomorrow in advance of a weaker surface low and its
associated north- south oriented surface trough. A few showers are
possible in far western MN by daybreak tomorrow but nothing

As for temperatures, cooler again looks to be the way to go as the
today`s system will be slow to exit and likely block much
insolation for today. After early morning lows in the low-mid 60s
this morning, highs will range from the upper 60s in eastern MN
and western WI to the mid 60s in far western MN (owing to faster
clearing out west).

.LONG TERM...(Friday through Wednesday)
Issued at 345 AM CDT Thu Aug 17 2017

Main concerns in the long term remain timing and strength of
short wave moving through Friday and timing of next frontal
passage Sunday into Monday night.

Deterministic models are in decent agreement in bringing a short
wave through the region Friday/Friday evening. Instability is
there and shear will depend on how strong the wave be as it moves
through. Marginal risk over the southwest looks good for day 2
outlook at this time.

Drying is expected as high pressure builds over the area into the
first part of the weekend. Temperatures are expected to warm out
ahead of the front into the lower and middle 80s as winds become
more southerly and warmer air tries to make a return. Timing of
the next front still looks to be later Sunday afternoon/night and
Monday. This system will have to be monitored for severe weather
potential as well as heavy rain. Hydro concerns will likely become
more evident if widespread rains develop as antecedent conditions
are now moist across much of the region.

Cooler and drier conditions follow this weather feature through
the rest of the period. Temperatures are expected to range
slightly below normal through midweek.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1254 PM CDT Thu Aug 17 2017

Main change to TAFs was to delay improvements to VFR an hour or
two at all terminals. Precip is pretty much done for today, save
for some occasional dz/-ra out in WI. Main question for tonight is
do we see fog form. Skies will be clearing early this evening,
with surface winds dropping to under 5kts. Those are the pluses in
the fogs court. However, cloud cover from the next system will be
rapidly moving in from the west tonight. How far east it gets
will determine where the fog potential resides, but WI terminals
look to have the greatest risk for fog, with mid/upper cloudiness
keeping the fog at bay in MN. Expect an area of showers at the
nose of the LLJ to be sliding across southwest/south central MN
Friday morning, which may graze RWF/MKT, so have VCSHs there
Friday morning.

KMSP...Confidence is pretty high in the TAF. Given the holes
showing up in the cloud field across MN, expect it to dissipate
quickly this afternoon, with 2z even looking a bit late to go VFR.
There is a threat for shra tomorrow, but best chances look to
slide south of MSP in the morning, with afternoon activity
confined to western MN.

Sat...VFR. Wind SW 5 kts.
Sun...VFR. Chance TSRA overnight. Wind SW 5 kts.
Mon...Chc MVFR/-TSRA. Wind S 5 kts.




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