Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 161830
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
130 PM CDT Tue Sep 16 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 336 AM CDT TUE SEP 16 2014

A broad upper level trough will continue across the eastern US. The
plains will be under northwesterly flow at mid and upper levels of
the atmosphere through the next 24 hours.

At the surface a broad ridge of high pressure extending from the
upper Midwest, southwest across eastern KS and OK will shift east
across MO Today. A lee trough will deepen across the southern high
plains and low-level winds will become southerly across western OK
and western KS. Deeper gulf moisture will be advected northwest
through the day across OK and KS.

South-southeasterly 850mb winds will cause a slow increase in deeper
moisture across the CWA through the afternoon hours. Point forecast
soundings show an EML developing across eastern KS...with a warm
nose of 20 to 24 degrees C at 750 MB. This will cause an unbreakable
CAP for any surface based convection this afternoon. There may be
some increase in boundary layer CU as the surface to 850mb layer
moisten through the afternoon hours. Highs temperatures Today will
warm into the lower to mid 70s across much of the CWA.

Tonight, The 850mb winds will begin to veer to the southwest and
continue to advect deeper gulf moisture northeast across the CWA. As
the southwesterly LLJ increases through the night isentropic lift
will increase across the eastern half the of the CWA after
midnight. There may also be some weak H5 troughs embedded in the
northwesterly flow aloft that could add additional ascent to help
cool the warm nose at 750mb. The NAM, NMM, ARW, ECMWF all show the
potential for elevated thunderstorms to develop, due to isentropic
lift increasing enough at the 310K level for parcels to reach their
LFC. ATTM the WRF (ARW and NMM) show most of the elevated
thunderstorms developing across western MO after 9Z with much of the
CWA remaining dry. The NAM and ECMWF forecast QPF to occur from 9Z
to 12Z across the eastern one third of the CWA. The GFS model breaks
out elevated storms across most of the CWA by 6Z and expands the
coverage of QPF through 12Z. At this time, the isentropic lift
forecasted by the GFS looks too far west. I will forecast chance
pops for the far eastern counties of the CWA after 6Z, with slight
chance pops across the remainder of the CWA.

If elevated thunderstorms develop late Tonight they may produce
quarter to half dollar size hail. MUCAPES are forecasted to range
between 1500 to 2500 J/KG, and 850 to 600 mb effective shear will
be 30 to 40 KTS. This type of environment may lead to some isolated
strong elevated thunderstorm updrafts through the early morning
hours of Wednesdays.

Southerly winds and deeper moisture advection will keep
overnight lows mild with lows only dropping into the upper 50s to
lower 60s.

.LONG TERM...(Wednesday through Monday)
Issued at 336 AM CDT TUE SEP 16 2014

By Wednesday morning elevated convection will continue to linger in
far eastern KS and western MO. The best chances for precip still
appear to be south and east of the turn pike. The isentropic ascent
becomes less widespread and more focused over southwest MO during
the morning hours as the veering low level jet quickly diminishes.
At the surface a low pressure will be centered over western KS, and
a quasi stationary front extends eastward into southeast KS. During
the day it retreats back to the southwest, and could become the
focus for additional isolated development with a weak cap in place.
Any storm forming along the front Wednesday afternoon could
encounter up to 2000 j/kg of cape due to decent mid level lapse
rates, and marginal deep layer shear. This poses a slight risk for a
severe storm mainly south of interstate 35. With the front south of
the area isentropic lift develops again overnight although is not
strongly focused over the area with more of a split flow in the low
levels. The convergence appears sufficient enough for chance pops,
and with not much change in the pattern a strong to severe storm
will again be possible. Kept slight chance pops going during the day
Thursday for any isolated rain showers. Soundings show the
environment should be well capped from any thunderstorm development.

The next main weather system to affect the area appears to be on
Saturday. The models seem to have a better handle on the remnants
of tropical storm Odile tracking the system somewhere over eastern
KS. At this point it is too far out to be specific in large part to
a decent mid level trough progressing across the northern US. The
speed of this trough will likely play a role on where the remnants
are absorbed into the main flow. Moisture content will be very
high Saturday with PWs over 2 inches possible, which could lead to
locally heavy rainfall. The northern trough will bring a cold
front through the region that clears out of the forecast area
Sunday morning. Meanwhile temperatures stay below and near normal
through the extended.

&&

.AVIATION...(For the 18Z TAFs through 18Z Wednesday Afternoon)
Issued at 1227 PM CDT TUE SEP 16 2014

VFR conditions early in the forecast followed by increasing
chances for convection after midnight and possibly some reductions
to visby toward sunrise. For now will carry VCTS as storms may
form near or east of the TAF sites.  67

&&

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

$$

SHORT TERM...Gargan
LONG TERM...Sanders
AVIATION...67





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