Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 100010
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
710 PM CDT Wed Jul 9 2014

.MESOSCALE DISCUSSION...
Issued at 640 PM CDT WED JUL 9 2014

Thunderstorm complex over Nebraska has finally shown a bit more of
a push toward Kansas over the past 2 hours, as well as general
intensification along the western flank of the system in central
Nebraska. The primary forcing with this complex appears to be a
broad short wave trough now moving into north central Nebraska
from the northwest. There is a sharp instability gradient across
the region with little to no MUCAPE in far eastern KS and 2000+
j/kg in western KS with a modest instability as far east as north
central KS. For any storms able to become nearly surface based,
such as the cells in central Nebraska, deep layer wind shear is
more than sufficient for well-developed supercell structures. A
zone of low level convergence in advance of the trough as well as
an axis of slightly better low level moisture (surface Td in the
upper 50s to low 60s) from much of Nebraska into north central
Kansas, and isentropic upslope flow along the eastern side of the
axis of greatest MUCAPE will continue to support these
thunderstorms as they progress to the southeast this evening. The
likelihood of widespread severe weather seems rather low locally,
but could have a few storms produce large hail or damaging winds
mainly west of a Washington to Council Grove line this evening.

Furthermore, as the evening and early morning progresses, expect
the MUCAPE axis to shift a bit east and expect the isentropic
ascent to increase into the area as well. This should continue to
support thunderstorm activity into the local forecast area after
midnight and even through 12Z or so...especially in south and west
portions of the forecast area. Beyond 12Z, the short wave axis
should begin to cross the area with decreasing large scale ascent
and probably decreasing storm coverage despite the continued
presence of modest elevated CAPE.

&&

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Thursday)
Issued at 328 PM CDT WED JUL 9 2014

12Z upper air data and recent water vapor imagery show moderate
northwest flow over the Central and Northern Plains. Rather strong
mid level baroclinic zone was along the Front Range with 700MB
temps of 15C at Riverton and Boulder, with 7C and 8C at Rapid City
and North Platte, respectively. Mid levels are rather moist
upstream as well with 0-4C dewpoints at 700MB. Low level ridging
remains across much of the Central Plains at 19Z per nearby radar
winds. Thunderstorms have repeatedly formed and dissipated in
north central Nebraska during the daytime hours.

Convection to the northwest may slowly intensify in the next few
hours as moisture slowly recovers on low level southerly winds and
the boundary destabilizes, but still believe convection will
struggle with its southeast track as it approaches Kansas. Greater
precipitation chances still on track for the late evening into
post-sunrise hours as warm air advection and deeper moisture combine
over central portions of Kansas and a weak upper wave passes through.
Instability remains rather marginal with high cloud bases and winds,
despite turning nicely with height, remain limited to keep severe
weather threats somewhat low but still present in steepening
mid-level lapse rates and area possibly downstream of possible MCS
from northeastern Colorado. NAM in particular has been rather
consistent with convection remaining nearly anchored over central
portions of the state through late night and early morning and given
what has been going on in north central Nebraska today, this cannot
be discarded. A minor concern for heavy rains would exist in this
scenario, but low level jet remains focused to the west and north
and precipitable water values will be recovering to near July
normals. Moderate mid level warm air advection continues Thursday
and may keep precip going for at least a few hours, but passing of
the upper wave should produce a drying trend through the day.
Dropped highs a bit with good cloud potential through at least the
late morning.

.LONG TERM...(Thursday Night through Wednesday)
Issued at 328 PM CDT WED JUL 9 2014

For Thursday night and Friday, mid level ridging is expected to
remain over the central Plains with the thermal ridge gradually
 laying over across the state. Models seem to be in good agreement
with the overall pattern and there remains a signal for elevated
storms along the nose of the low level jet Thursday night.
Isentropic surfaces show the better saturation and lift setting up
mainly over northwest MO. Because of this have kept only a chance
for thunderstorms across far northeastern KS. The bigger concern
may be the increasing heat for Friday as low level winds veer to
the south southwest and 850 temps warm to around 24C. The NAM
appears to be a warm outlier, but given the pattern and good
insolation through the day I didn`t want to completely rule it
out. Therefore have maintained highs in the mid and approaching
100 in central KS. With the winds veering, surface dewpoint temps
could mix out and have trended them down some. Because of this,
heat indices remain below heat advisory levels but will need to
watch this in the coming days.

The main focus of the extended forecast is the timing of a couple
cold fronts expected to move through this weekend and early next
week. Precip chances will likely be tied to when the fronts are in
the area. The models are in reasonable agreement in amplifying
the synoptic pattern with ridging along the west coast and into
the Canadian Rockies with a closed low digging south over the
Great Lakes. However the NAM seems to be a fast outlier in
bringing an initial front into the area on Saturday. The
GFS/ECMWF/GEM solutions want to keep the boundary mainly along the
NEB/KS state line through the day Saturday. Have opted to go with
the consensus solution and keep some small precip chances mainly
across the northern counties Friday night and Saturday with
warmer temps over east central KS than the NAM would show. A
stronger cold front is expected to have pushed through much of the
forecast area by Tuesday morning. Because of this, I`ve trended
POPs down for Tuesday night. Think the best chances for precip
should be Saturday night and again Monday night into Tuesday as
these fronts move across the area.

Other changes to the forecast were to trend temps cooler for
Tuesday and Wednesday as the ECMWF brings a stronger high pressure
system into the plains sooner than earlier runs. Have been a
little conservative on the cooler trend given the ECMWF prog of
850 temps around 8C suggesting highs in the 70s. Its hard to go
quite that cool for mid July just yet and the forecast has lows
around 60 with highs around 80.

&&

.AVIATION...(For the 00Z TAFs through 00Z Thursday Evening)
Issued at 640 PM CDT WED JUL 9 2014

VFR conditions are expected for the vast majority of the TAF
period, with the only potential for reduce conditions accompanying
any potential thunderstorm activity...primarily via reduced vis in
periods of heavy rain. Have highlighted the most likely TS timing
at each site generally between 05Z and 13Z with some smaller
potential for TS lingering past sunrise through mid morning. Have
still maintained VFR even during the most likely period for TS
activity as even with TS any reduced conditions should be short
lived and VFR predominant. Expect south winds to gust to 20 kts or
stronger for much of Thursday.

&&

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

$$

MESOSCALE...Barjenbruch
SHORT TERM...65
LONG TERM...Wolters
AVIATION...Barjenbruch






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