Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 201236
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
736 AM CDT Thu Apr 20 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 327 AM CDT Thu Apr 20 2017

An upper level trough across the eastern plains this morning will
lift east northeast into the upper Midwest Today. At 2AM the surface
cold front extended from Atchison, southwest to west of Topeka, then
southwest to near Council Grove. The front will move southeast of
the CWA by 14Z. A weak line of scattered showers and isolated
thunderstorms were located along the front from I-70 northeast into
northwest MO. A heavier area of rain was located along the western
edge of deeper moisture southeast of I-35. Both lines of showers and
thunderstorms will shift southeast of the CWA by 15Z. Very light
rain or sprinkles were developing across north central KS and
southern NE. These light showers were in response to the larger
scale ascent ahead of the H5 trough axis. I suppose the northern
counties could see scattered light rainshowers or sprinkles through
the mid morning hours but they should end as the H5 trough axis
shifts northeast into IA later this morning.

Otherwise, Today will be dry with decreasing clouds from west to
east across the CWA during the late morning and early afternoon
hours. Low-level CAA will keep highs in the mid to upper 60s despite
insolation this afternoon.

Tonight, Another upper trough will move east across the central
Rockies into the central high plains by 12Z. A lee surface low will
deepen across eastern CO through the night and 850mb winds will
begin to veer to the south and southwest across OK and western KS,
allowing deeper moisture to advect northward across OK and and
southwestern KS. The better isentropic lift will occur across
northern OK into southern KS, therefore I kept the CWA dry late
Tonight. But the cloud cover will increase through the early morning
hours. Overnight lows will be in the mid to upper 40s.

.LONG TERM...(Friday through Wednesday)
Issued at 327 AM CDT Thu Apr 20 2017

By Friday morning, a negatively-tilted mid-level trough will be
stretching from the Pacific Northwest into the Rockies, with a
surface low over Texas advancing to the northeast.  Models show the
forcing of these two systems nearly converging over central/eastern
KS by Friday evening. A nearly stationary boundary will extend into
northeast Oklahoma and Arkansas from the surface low in Texas.
Models show showers and isolated thunderstorms along and north of
this boundary extending northward into the CWA during the day on
Friday before additional forcing and moisture move into the region
from the approaching mid-level low. As a result, have increasing
PoPs Friday afternoon through Friday night as the mid-level low
looks to pivot along the southern part of the CWA.  Models have
continued to trend with the faster eastward progression of this mid-
level low. Precipitation likely will end across north central KS
Saturday morning, with precipitation chances continuing to diminish
from northwest to southeast across the CWA through the morning and
early afternoon hours.  With the stationary frontal boundary
remaining well south of the area, models continue to show limited
instability Friday-Saturday, with MUCAPE values only reaching
upwards of 100-200 J/kg.  As a result, only isolated thunderstorms
are expected with this precipitation. The main concern during the
Friday through Saturday period will be the potential for locally
heavy rainfall, which could cause some minor flooding concerns.
While the higher QPF amounts are looking to be focused predominantly
across southeast KS, there is still model uncertainty with how far
north into the CWA these higher QPF amounts may extend due to the
tracking of the mid-level low over the area.  Future shifts may need
to consider whether or not a Flood Watch will be needed across
portions of east central KS.

Conditions will dry out through the day on Saturday as surface high
pressure advances across KS. As this high pressure progresses just
east of the CWA through the day on Sunday, expect the shift in winds
to the south to support WAA Sunday into Monday with highs reaching
into the upper 60s on Sunday and into the 70s on Monday. There is a
slight chance for some scattered showers and thunderstorms across
far north central and far northeast KS Monday night as a weak
shortwave skims across southern NE.  Otherwise, the next potential
for more widespread precipitation may be Tuesday night into
Wednesday, however there is still a great amount of model
uncertainty in the timing and tracking of any precipitation due to
model discrepancies in the surface and mid-level flow patterns.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 722 AM CDT Thu Apr 20 2017

Expect VFR conditions for the next 24 hours.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Gargan
LONG TERM...Hennecke
AVIATION...Gargan



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