Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 241954
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
254 PM CDT Sun Sep 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 252 PM CDT Sun Sep 24 2017

The upper trough has continued to move slowly east per the 19Z water
vapor imagery, and now the upper low is over Salt Lake City. At the
surface, the cold front has moved into northwest KS through
northeast NEB with the pre-frontal trough just northwest of the
forecast area. A few thunderstorms have developed in the heat of the
day over northern KS.

There is not a great deal of change to the forecast for tonight and
Monday. The few changes are some subtle adjustments to the timing of
precip and the expected affects on temps. Think this afternoon`s
isolated to scattered showers and storms over northern KS are likely
to fall apart with the loss of daytime heating. But POPs will be on
the increase from west to east overnight as the upper trough
continues to move east and the front slowly enters the forecast
area. Synoptic scale dynamics do not look all that impressive, and
instability/sheer parameters remain on the marginal side for strong
thunderstorms. So the expectation is for the observed precipitation
from today to shift east a little further. Isolated to scattered
storms should develop by the afternoon hours Monday over eastern KS
while occasional rain showers move into north central KS.
Thunderstorms will be more probable in the warm sector across
eastern KS where highs should be aided by a little more insolation
and warm into the mid 80s. Cooler temps across north central KS near
the frontal boundary should favor more of the general shower
activity seen across northwest KS today. The rain and cloud cover is
expected to create a tight gradient in the temps tomorrow afternoon
and have highs for the far northwestern parts of the forecast area
holding in the lower 60s. There remains some concern for locally
heavy rainfall since the upper flow will continue to parallel the
surface boundary. Models show decent moisture along the front so if
there are more convective elements near the front that train to the
north, there could be rainfall amounts over 1.5 inches.

.LONG TERM...(Monday night through Sunday)
Issued at 252 PM CDT Sun Sep 24 2017

By Monday night, a deep mid-level trough will be centered over the
Rockies, with this trough lifting into the Northern Plains through
Tuesday night.  This advancing trough will continue to push surface
low pressure southeast of the area with the cold front exiting east
central KS by Monday evening.  Models show post-frontal
precipitation overspreading the CWA Monday night as a weak low-level
jet and isentropic lift remain in place over the area. With the low-
and mid-level flow looking to be nearly parallel to the post-frontal
precipitation Monday night into Tuesday, cannot rule out the
potential for some locally heavy rainfall due to training storms.
However, the light to moderate rainfall rates should be spread out
enough time-wise to limit flash-flooding concerns. Weak mid-level
lapse rates will limit MUCAPE values to generally less than 500
J/kg. Due to the combination of limited CAPE and 0-6km bulk shear
values of 25-30kts, the potential for any strong or severe storms is
low. CAPE values will continue to diminish through Tuesday and
Tuesday night, so expect mostly showers with a few isolated
thunderstorms possible. This widely scattered precipitation on
Tuesday will gradually diminish from northwest to southeast over the
CWA through Tuesday night as surface high pressure advances into the
central U.S.  A few isolated showers may still be lingering across
east central KS on Wednesday, but otherwise expect dry conditions
across the area. Models show the forecast area remaining under the
influence of surface high pressure through the end of the week and
into next weekend, so have a dry forecast in place.  There are some
slight model discrepancies in the mid-level pattern during the
Friday through Sunday time period, with the GFS being an outlier in
showing a weak embedded wave clipping north central KS Friday
morning. Otherwise, there is the potential for a shortwave trough to
shift into the central U.S. by late weekend, which may bring another
chance for scattered precipitation.

As for temperatures, cold-air advection behind the frontal passage
Monday night will drop temperatures closer to the seasonal normals
with high temperatures ranging from the upper 60s to mid 70s Tuesday
through Sunday.  Low temperatures will gradually drop through the
week with lows generally in the 50s through late week before
plunging into the 40s by next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1218 PM CDT Sun Sep 24 2017

The upper trough and associated precip continues to gradually
move east. With models forecasting the main upper low lifting
northeast into the northern plains, the slower timing for precip
may be the way to go. Because of this only have a VCSH in at TOP
and FOE after 12Z and mention prevailing -SHRA at MHK after 12Z.
It appears the terminals will remain on the warm side of the front
at least through 18Z Monday, so VFR conditions are likely to
prevail. Lower CIGS and VSBY should not come into play until after
the FROPA sometime Monday night or early Tuesday morning.


&&

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

$$

SHORT TERM...Wolters
LONG TERM...Hennecke
AVIATION...Wolters



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