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Area forecast discussion...updated 
National Weather Service Aberdeen South Dakota
1245 PM CDT Thursday may 28 2015

Update...
issued at 1103 am CDT Thursday may 28 2015

Minor adjustments to probability of precipitation as elevated convection continues to
move into western Minnesota and weaken. Added a mention of showers
with some elevated convection moving into northwest counties.

Main focus is afternoon convection as the surface trough slinks
into north central counties. High res guidance continues to peg
20-22z as time of initialization thanks to ample
sunshine...though not just along the trough axis thanks to a weak
cap. Highest cape values are focused along the front...but pre
frontal convection will add a layer of chaos. Plus...shear
appears relatively weak with only 20 to 30kts between the surface
and 500mb...mainly out of the southwest. To top things off...best
dynamic lift is in the late evening/overnight hours. These factors
will likely end up limiting the severe weather potential. As for
adding the mention of heavy rain...storm motion is relatively
slow...and parallel with the surface front...suggesting training
may occur. Once diabatic heating falls off and storms weaken this
evening...upper dynamics begin to improve. This will provide a
second surge of moisture to round out rainfall totals by Friday
am.

&&

Short term...(today through Saturday afternoon)
issued at 408 am CDT Thursday may 28 2015

Areal coverage of showers and storms have decreased dramatically
over the past several hours...but there has been recent
redevelopment in the James Valley and hi res models continue to
suggest increasing coverage through 12z. This remains to be seen but
will maintain chance probability of precipitation over the next few hours.

Focus for today will be on the next approaching shortwave further
back to the west. Hi res models all showing storms developing by middle
to late afternoon and continuing into the evening along and ahead of
the approaching cold front. A few of the cam solutions show a pretty
healthy looking line of storms developing along the front and moving
across the eastern County Warning Area into the early evening. Decent instability
develops along/ahead of the front with MLCAPE values around 2000
j/kg. Although...shear is not real impressive today so mainly
looking at pulse type and multicellular activity. Some storms have
the potential to become strong or even severe.

Cold front will be making its way southeast through the County Warning Area
overnight and into early Friday morning. Much cooler air will be
moving into the County Warning Area as 925/850 mb temperatures fall several degrees through
the day. Highs are still forecast to only be in the low to middle 60s
on Friday with breezy north to northeast winds. Surface high
pressure will then build south across the Dakotas Friday night into
Saturday morning...bringing with it cool temperatures. Lows Saturday
morning are likely to bottom out in the upper 30s for a good portion
of the County Warning Area...especially northern areas.

Long term...(saturday evening through wednesday)
issued at 408 am CDT Thursday may 28 2015

The extended forecast period still looks relatively stable as far as
run to run consistency GOES. High pressure is over the area to
start...but then gives way to return flow and some anomalously warm
air for late may/early June. 925hpa/850hpa thermal forecasts would
support highs in the upper 80s to middle 90s in some
locations...complete with warm middle-level capping inversion temperatures of
+10c to +12c. There should be a frontal boundary around early next
week...the needed focus for surface-based convection...with plenty of
mixed layer instability around Monday through Wednesday. Seems
Tuesday afternoon/evening might hold the highest probability of
seeing strong to severe convection with adequate deep layer shear
forecast to be around. The middle-level cap may end up being eroded
enough to get a few strong to possibly severe thunderstorms to
develop by early Tuesday evening.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1241 PM CDT Thursday may 28 2015

Scattered storms are expected to form over the region by late
afternoon and then persist into the evening. Outside of storms
it will be VFR. Late tonight MVFR/IFR ceilings are expected to advect
into the region.

&&

Abr watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
&&

$$

Update...Connelly
short term...tmt
long term...dorn
aviation...tdk

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