Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 280325
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1025 PM CDT Sat May 27 2017

.SHORT TERM...(This evening through Sunday)
Issued at 336 PM CDT Sat May 27 2017

Positively tilted 500 mb trough axis continues to sit just west of
the CWA, and is allowing for the continued development of mid-level
clouds, and very light precipitation.  Only a few spots reporting
rainfall this afternoon and anticipating that trend will continue.
Further west, widespread cumulus and strato-cumulus field has
developed over northern and central SD as cooler air begins to pivot
southward behind a weak frontal boundary. Widely scattered showers
could form and impact the MO river valley late this afternoon.

Tonight: Secondary PV anomaly dropping southward across North Dakota
this afternoon will rotate south and then eastward into northern
Minnesota overnight.  An 850mb trough will slide through the Tri-
State area late tonight, and it`s possible to have a few scattered
showers move into the CWA trailing behind yet another surging
surface frontal boundary.

Sunday: Breezy conditions are anticipated on Sunday, with
temperatures mixing into the lower and even middle 70s.  Clouds will
begin to thicken in the afternoon, but any substancial risk for
diurnal based showers should be more closely tied to shortwave
energy not expected to arrive until the evening.

.LONG TERM...(Sunday night through Saturday)
Issued at 336 PM CDT Sat May 27 2017

On Sunday night, a very large upper cyclone is situated over far
northern MN and Lake Superior draining chilly air into this area.
A few showers are possible mainly along and north of I 90 during
the evening as a very weak short wave moves southeastward on the
southwest side of the upper low. The short wave is basically a
weakness between two QG convergent areas to the northwest and
southeast. Otherwise with the winds slackening off, lows will dip
to the upper 40s and around 50. On Monday, moisture in the
850-700mb layer will move southward into our area which with
chilly air aloft could spark some more showers over the northeast
half of this CWA. At this time, soundings suggest it is not
unstable enough for TSRA, and 850mb temperatures point to highs
only in the 60s, perhaps lower 70s in parts of the MO River valley
from Yankton to Sioux City.

With the aforementioned upper low meandering through southeast
Canada through Tuesday night, temperatures will be a fair amount
below normal, before modifying to closer to normal by Wednesday.
Notably, the northwest surface flow will be quite brisk Monday and
Tuesday with mixed layer winds both days around 25 knots, suggesting
a breezy 15 to 30 mph for both days. Temperatures will then warm
further Thursday through Saturday. However, there is quite a bit of
discrepancy between the models late next week in just how much to
warm temperatures. The ECMWF and GEM Global are substantially warmer
at 850mb compared to the GFS, especially by Friday and Saturday. The
GFS keeps a larger influence of the cold upper low in our area as it
moves it slowly eastward across eastern Canada and the northeast
United States. It would be easy to discount the GFS as an outlier.
However overall, many times this spring we have dealt with a large
upper low to our northeast, draining chilly surface high pressure
down into the northern plains. Therefore do not want to totally
discount the cooler GFS solution. Trended temperatures late next
week above normal, but by only a category or two above normal for
now.

There is consensus in the models showing a short wave moving through
the forecast area next Thursday. But discrepancies exist in how much
moisture will exist with this system with the GFS being the most bullish
in terms of QPF. It is certainly worth at least low pops at this point
for showers and perhaps a few thunderstorms.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1023 PM CDT Sat May 27 2017

VFR conditions are expected through the TAF period. Northwesterly
winds will increase on Sunday morning, gusting 20 to 30 kts
through the afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...MJ
AVIATION...JM


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