Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 251812
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
112 PM CDT THU AUG 25 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 328 AM CDT THU AUG 25 2016

Showers and embedded thunder ongoing at this hour over the eastern
counties, likely in response to a shortwave trof moving over the
effective surface front which resides generally across the Kansas
turnpike.  Additional showers and thunderstorms approaching the
western and  north central counties as another larger wave lifts
northeast ahead of the main upper trof.  With less available
instability over NC Kansas, not expecting strong storms this
morning. The southern front/boundary moves very little throughout
the first 24 hours, and may provide the focal point for locally
heavy rainfall especially later tonight.

Severe threat for today likely to be limited to the far southern
counties and will be conditional on amount of instability that gets a
chance to develop between rain chances.  Would anticipate a break
later this morning between systems, with NAM calculating around 2500
j/kg of CAPE by 20z for this area. So storms forming in this time
frame may initially have some hail/wind concerns, in addition to
locally heavy rainfall possible.  Difficult in any guidance to find
a time in the next 24 hours where there isn`t a chance for rainfall,
and forecast grids reflect this pattern.  Will want to watch areas
along and just south of I70 this evening as NAM wants to drop 4-6
inches of rainfall along the boundary in response to the next
stronger upper wave moving over the area in that time period.  Other
guidance isn`t so heavy with the rainfall, with 1-2 inches for the
day more common. Have leaned toward the lower amounts but worth
noting here of the risk of some locally higher amounts.  WPC has
placed that area in a slight risk for excessive rainfall as well.
Trimmed highs down in the north central counties where clouds and
rain likely keep temps in the middle 70s, while the far southeastern
counties may rise into the middle 80s as the front lifts just north
of that area.

.LONG TERM...(Friday through Wednesday)
Issued at 328 AM CDT THU AUG 25 2016

Upper flow remains on the quick side Friday with isentropic lift
persisting as the 850mb front pushes into Nebraska. Along with PW
values still around 1.75 inches, precip chances remain well above
normal. Lower levels look rather moist and stratus may dominate
outside convection. Southeast winds should develop through the day,
and if some breaks can occur, instability and shear could support a
few severe storms in/near peak heating, with convection getting aid
from a modest low level jet overnight. Could see a strong high temp
gradient if the clearing occurs and have the range across the CWA
around 10F. Models differ somewhat in mid level reflection of the
upper wave passing to the north Saturday, though they all begin to
dry the troposphere somewhat. Expect more opportunity for insolation
and could see ML CAPES near 2000 J/kg develop in temps in the low-
mid 80s, though weaker shear should keep any severe threat
low/isolated.

Weak southwest flow aloft and limited capping brings at least some
potential for precip going into the mid week periods, though chances
should fall with time. Broad ridging over the central third of the
nation keeps temps rather steady and near normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 105 PM CDT THU AUG 25 2016

For the 18z TAFs, areas of MVFR cigs should gradually improve to
low-end VFR this afternoon. Some short-range models show the
potential for a few isolated showers and storms to develop near
the TAF sites, so added VCTS for a few hours this afternoon.
Short-range models suggest that conditions may be dry initially
tonight with increasing storm potential overnight into Friday
morning, which will be accompanied by MVFR cigs.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...67
LONG TERM...65
AVIATION...Hennecke


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