Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 292044

Area Forecast Discussion
National Weather Service Sioux Falls SD
344 PM CDT Mon May 29 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 344 PM CDT Mon May 29 2017

Scattered showers are occurring this afternoon primarily in
southwest MN as expected. The soundings are not displaying as much
of an inverted V currently as they were Sunday afternoon, with
pretty deep moisture from 850-600mb. Therefore convective winds have
been subdued. The synoptic winds are quite brisk however, but will
greatly subside after sunset. More challenging is what to do with
the cloud cover. There is a discernible short wave on water vapor,
currently over north central SD and moving southeastward. Some of
this cumulus will disappear as the daytime heating subsides on the
periphery of the very large upper low northeast of our CWA. However
throughout the northeast quarter of our forecast area, clouds may
have a tougher time totally disappearing where the depth of moisture
is deeper and the short wave expected to have a greater influence.

Lows will be chilly tonight. In our west, preferred the coldest
guidance numbers such as MOS, and even dropped them a bit from MOS
values with very light dry winds and clear skies anticipated toward
central SD. Elsewhere, consensus lows did not look too bad but still
favored the cooler guidance readings. So once again, there will be a
lot of widespread 40s. On Tuesday, one more day of chilly cool
weather, with what will likely be another festival of cumulus
developing across the northeast half of our area, due to cold air
aloft and ample moisture from 800-700mb. Large upper low still in
southeast Canada and the Great Lakes region will provide the
cyclonic flow aloft, and there could be a vort filament extending
into southwest MN during the afternoon. Therefore changed the
sprinkles to some isolated light showers in southwest MN and extreme
northwest IA in case a few showers measure rainfall. Highs on
Tuesday will vary from the lower 60s in southwest MN, to the lower
70s in the MO River valley, similar to today with similar 850mb
temperatures. The northwest winds will once again be very brisk,
averaging 20 to 35 mph with mixed layer winds of 30 knots.

.LONG TERM...(Tuesday night through Monday)
Issued at 344 PM CDT Mon May 29 2017

Cyclonic northwest flow will transition to southerly on Wednesday as
high pressure moves across the area.  This will promote light winds,
but temperatures will remain below normal with 850 hpa temps in the
single digits. As low level jet develops across the plains on
Wednesday night, could see some elevated showers and thunderstorms
develop. Atmospheric lapse rates are nearly moist-adiabatic, so not
much in the way of instability.

Secondary warm front lifts north Thursday possibly becoming the
focusing mechanism for a few more storms across the region. With the
passage of the front, will also see temperatures nudge closer to
seasonal norms. Friday appears to be the warmest day of the week
with temperatures peaking a few degrees above normal. Strong back
door cold front is expected Friday night and with the passage of the
front could see an additional chance for precipitation. Have some
lingering pops in for Saturday based on ECMWF output, but chance of
precipitation may be overstated as upper level ridge builds in from
the north leading to quiet weather. Temperatures appear to be below
normal, but how cool remains uncertain with the ECMWF running about
5 degrees C cooler than the GFS at 850 hpa.  For now, left blend as
is, which is erring towards the warmer side of possible solutions.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1227 PM CDT Mon May 29 2017

Some upper end MVFR ceilings are possible in the Brookings SD and
southwest MN areas through mid afternoon. But otherwise it is
anticipated that the rest of the area will be VFR through midday
Tuesday. Northwest winds will frequently gust around 25 knots or a
little higher this afternoon.




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