Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 171149
AFDMPX

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

.UPDATE...
Issued at 632 AM CDT Thu Aug 17 2017

Updated to include 12z aviation discussion below.

&&

.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
impressive.

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 12Z TAFS through 12Z Friday morning)
Issued at 632 AM CDT Thu Aug 17 2017

Surface low over east-central MN will continue to shift ENE into
western WI through late morning. Rain shield will mainly affect
KSTC-KMSP and points eastward, having already moved through KAXN-
KSTC and KMKT. This will keep ceilings mainly in IFR range and,
depending on rainfall intensity, have visibility between MVFR and
LIFR. In addition, sites that are near the circulation will
experience winds in excess of 20-25kt. Conditions will remain
degraded thru mid-afternoon then improvement will come slowly
from west to east. Wind directions will be a bit tricky depending
on the exact path of the low pressure circulation. Those sites on
the backside will become NW; sites to the N will go SE-NE-NW while
sites to the S will go E-S-NW, all in a relatively short amount of
time.

KMSP...Conditions to bounce around 1700ft thru the morning push
then become IFR through mid-afternoon. Some showers will drift
through the area from time to time this morning through around
midday before the rain shield as a whole moves off to the NE. VFR
conditions are not expected to be realized until this evening.

/OUTLOOK FOR KMSP/
Fri...VFR. Chance afternoon/evening TSRA. Wind W 5 kts.
Sat...VFR. Wind W 5 kts.
Sun...VFR. Chance afternoon/evening TSRA. Wind S 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory until 1 PM CDT this afternoon for MNZ065>070-
     073>078-082>085.

     Flood Watch until noon CDT today for MNZ041>044-047>051-054>059-
     064>066-073.

&&

$$

UPDATE...JPC
SHORT TERM...JPC
LONG TERM...DWE
AVIATION...JPC



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