Area Forecast Discussion
Issued by NWS Topeka, KS

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774
FXUS63 KTOP 160455
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1155 PM CDT Fri May 15 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 246 PM CDT FRI MAY 15 2015

This afternoon a mid-level ridge was in place  across the eastern
U.S. with a deep mid-level closed low spinning across the western
U.S. Water vapor imagery showed the embedded shortwave that helped
to support the morning showers and thunderstorms across the
outlook area quickly lifting northeastward into NE/IA/MO, with a
narrow zone of some drier air quickly surging in behind the
shortwave. With the broken line of storms having progressed north
of the forecast area, expect only some isolated showers and
thunderstorms this afternoon through early this evening. Visible
satellite showed cloud cover trying to scatter out some across
central Kansas, which will help afternoon temperatures rise a few
more degrees with highs ultimately reaching into the mid/upper 70s
across much of the outlook area. The only exception is across far
northeast Kansas where continued cloud cover may hinder
temperatures a bit.

Much of the region should remain dry tonight with southerly winds
and increasing low-level cloud cover overnight keeping low
temperatures mild in the low/mid 60s. A weak embedded wave may
skim over the area Saturday morning, however, short-range models
have trended much drier through the morning hours so have
decreased PoPs to slight or low-end chance categories. If, in
fact, there is little in the way of morning precipitation, then
there becomes heightened concern for the severe potential later in
the day and into the evening hours. While model soundings show
periods of cloud cover through much of the day, inhibition is
looking to be very weak across the area with decent low-level
lapse rates developing by the afternoon. Better forcing and lift
also look to move into the area during the afternoon hours as the
mid-level trough lifts northeastward and becomes more negatively
tilted. The dryline looks to strengthen across western Kansas
during the afternoon hours with some discrete storms developing
along and ahead of the boundary by mid-afternoon, tracking
eastward and transitioning to a more broken line by late
afternoon/early evening. Short-range models suggest that a quick-
passing vort max may support some scattered storms across portions
of north central and central Kansas during the afternoon hours
ahead of the dryline convection. With upwards of 1000-2000 J/kg of
CAPE, 35-45kts of 0-6km bulk shear, and increasing 0-1km helicity,
any storms that are able to develop during the afternoon hours
will have the potential to become strong to severe with large
hail, damaging winds, and a few tornadoes possible.

.LONG TERM...(Saturday Night through Friday)
Issued at 246 PM CDT FRI MAY 15 2015

As discussed in short term, convective evolution of severe weather
still forecast to be impacted by amount of convection and cloud
cover produced over the course of Saturday afternoon. However with
large scale upper wave and associated winds and dynamics moving
across the area, clouds and precip wont have much of an impact on
increasing wind shear and lifting mechanisms moving over the area.
NAM12 continues to have around 25kts of 0-1km bulk shear and
approx 40-45 kts of 0-6km bulk shear through the evening. GFS
increases toward these values also around 0z, and inhibition
remains low across the board. MU CAPES calculated in the
1500-2000J/kg range but would impacted by cloud cover and daytime
precipitation. Storms still forecast to develop out west along the
dryline and move to the northeast, with stronger storms impacting
areas along and west of Manhattan in the early evening then
progressing eastward across the area in the late evening hours.
Still some uncertainty as to coverage and strength, but given
dynamics of the upper system moving through, and the wealth of
evening outdoor activities across the area, would anticipate
severe weather, watch for updates, and plan accordingly.

Better news on Sunday as convection exits to the east in the
middle of the night, leaving breezy warm conditions in place for
the daytime hours Sunday. Highs forecast in the upper 70s to lower
80s, with winds diminishing into the late afternoon. Lows fall
into the 50s, then cooler high pressure moves in on Monday
bringing northerly winds and highs only into the upper 60s.

Heading into Tuesday and the last half of the week, high pressure
begins to have less of an impact over northeast KS.  Meanwhile, a
positively tilted trough begins to move into the Central California
which will be a potentially important feature for the last half of
Memorial Day weekend.  This feature will create a response in the upper
flow pattern which will cause some shortwave energy to move out of
the Central Rockies by Wednesday and possibly still affecting the
region early Thursday.  This does appear to be strong enough to help
develop a surface low over or near the TX panhandle into
southwestern KS.  However, there is some slight disagreement in the
GFS, GEM and EC solutions on exact positioning of any surface low.
However, it does appear to stay largely South of the outlook area.
With mostly weak ridging in place, this does make sense that not
much deep moisture makes progression back into our area with theta-e
values still lower during this time.  Therefore, not expecting too
much in the way of instability to cause much in the way of severe
weather.  Most of the precipitation looks to be in response to
isentropic lift and vertical motion caused by the shortwave energy
associated with the troughing feature itself.  Friday and Saturday
should remain mostly dry for a nice first part of Memorial Day
weekend.  Sunday could be a different story with the upper level
pattern suggesting possibly some hint of a severe set up.  However,
this is still outside of this particular forecast time frame.
Temperatures look to remain in the 60s and lower 70s with no
significant WAA having taken place while lows should remain mostly
in the 50s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Saturday Night)
Issued at 1148 PM CDT FRI MAY 15 2015

VFR prevails initially with increased low level moisture bringing
in a MVFR stratus deck with haze closer to 10Z according to short
term guidance. Line of TSRA in central KS is forecast to weaken
west of terminals and will need to monitor trends. Scattered TSRA
are possible after 15Z at KTOP/KFOE where VCTS mention is placed.
Believe the better forcing arrives late afternoon/early evening
where storms develop in central KS and track east through the
evening. Confidence in timing or duration is too uncertain to
mention at this time. Gusty south winds prevail throughout period.

&&

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

$$

SHORT TERM...Hennecke
LONG TERM...67/Drake
AVIATION...Bowen






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