Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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629
FXUS63 KFSD 252051
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
351 PM CDT MON JUL 25 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 351 PM CDT Mon Jul 25 2016

Southerly flow will remain across the area through the short term.
As the low level jet increases through the overnight hours,
temperatures will have a hard time cooling off- especially across
central South Dakota.  Further to the east, high pressure will be
more in control keeping winds light allowing for better radiational
cooling.  Could see some elevated storms work into central South
Dakota towards daybreak.  These storms will struggle to work east,
as they will be working into stable air.

Expect a break in the convection through the morning hours, but
could see convection re develop Tuesday afternoon as a short wave
approaches from the west.  Not a great set up for severe weather
with limited amounts of shear and only 500-1000 j/kg of cape.  Have
focused pops across central South Dakota throughout the daytime
hours on Tuesday as limited amounts of moisture further east limit
storm potential.


.LONG TERM...(Tuesday night through Monday)
Issued at 351 PM CDT Mon Jul 25 2016

On Tuesday night, 12Z models now show only a very weak short wave
near our CWA with very subtle height falls. A low level wind
boundary stalls out just to the north and west of our forecast area.
Believe that the convective activity will now be tied close to this
boundary across our northern and western zones, as the remainder of
our forecast area is fairly stable with high pressure exiting to our
east. The latest CAMs involving the ARW and NMM strongly suggest
that it could be tough for convection to develop anywhere in our
forecast area. However did not feel comfortable at this time
eliminating pops in our north and west closer to the boundary in
case some storms drain in from central SD or from the north. Lows
Tuesday night changed very little or none, with a lot of mid 60s
still likely.

On Wednesday, the NAM and ECMWF are little more aggressive in
pushing the aforementioned boundary southward into our northern and
western zones when compared to the slower GFS. Following suit, both
the NAM and ECMWF are stronger with the accompanying short wave
beginning to impact our zones, with this wave deepening as it moves
eastward Wednesday night. Scattered storms will likely begin to
develop along and behind the low level boundary with the timing of
the rainfall extremely difficult to pin point at this time. This is
because it does not look capped, therefore non severe storms could
literally develop at about anytime during the day. The least chance
for rain on Wednesday will be in northwest Iowa, but even there,
cannot totally rule it out at least by afternoon. Likely pops are
warranted in our eastern zones Wednesday night as the remainder of
the short wave moves through along with the low level wind shift.
Still does not look like much of a potential for severe weather
Wednesday evening with wind shear that is not very strong coupled
with lapse rates that are barely more unstable then pseudo-adiabatic
per the ECMWF soundings. CAPES are fairly thin though so there could
be some efficient rain makers. On Thursday, began a trend of being
more aggressive in lowering pops as the short wave and associated
wind shift flushes through. Would not be surprised if future shifts
lower pops more on Thursday.

Concerning temperatures, with the boundary pushing through it
certainly looks cooler Wednesday through Friday, with highs at or
below normal. Even Saturday will only see a modest rebound in
temperatures before becoming more summer like on Sunday and Monday.
The GFS appears to be doing its usual bias however of over mixing
temperatures with its 850mb thermal regime becoming obscenely hot
again by next Monday. The ECMWF is substantially cooler relatively
speaking, so placed highs on Monday a little above normal. Rain
chances from Friday onward will be skittish at best.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1235 PM CDT Mon Jul 25 2016

VFR conditions through the TAF period. Surface high pressure
across the area leading to clear skies and light southerly winds.
Surface ridge will slowly shift east tonight, and some patchy fog
may try to develop in NW Iowa. Confidence and coverage are low
enough that kept mention out of the KSUX TAF for now. Other
concern is elevated thunderstorm potential after 09z in central
South Dakota. This may lower ceilings to 7-8K feet, but no
visibility restriction is expected.


&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...BT
LONG TERM...MJ
AVIATION...BT



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