Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 232316

Area Forecast Discussion
National Weather Service Topeka KS
616 PM CDT Wed May 23 2018

...Update to aviation forecast discussion...

.DISCUSSION...(This evening through Wednesday)
Issued at 613 PM CDT Wed May 23 2018

The overall synoptic pattern will change little over the course
of the next week with well above normal temperatures and periodic
chances for showers and storms.

The early afternoon synoptic setup featured an amplified upper
tropospheric ridge axis centered along the Mississippi River
valley. A Rex Block was in the process of breaking down over the
western CONUS with the weak and complex low over Montana/Wyoming
lifting northward into southern Canada. Broad, weak south to
southwesterly flow could be found over NE Kansas with H850 temps
of +17 to +19 C and surface highs approaching 90 degrees in many
locations. Dewpoints more typical of June and July were in place
owing to an open Gulf, with values in the 60s to low 70s at times.

Isolated showers and storms developed near Emporia midday along a
very weak ribbon of 305-310K isentropic upglide coincident with
1500- 2500 J/kg of MLCAPE and minimal CINH, but given the
negligible deep shear profiles, these pulse storms quickly
collapsed. However, the residual convective perturbations/outflow
boundaries may serve for additional thunderstorm development
throughout the course of the afternoon--waning this evening after
peak heating. However, as with earlier convection, the fact that
winds are 20 kts or less through the entire troposphere will
hinder organization and longevity. A stray downburst would be the
main threat with any storm.

Convection has started redeveloping with a remnant MCV over
Norton and Graham counties in north central KS early this
afternoon. The HRRR has been pegging this development with its
last five runs and tracks it eastward along the KS/NE border
before it decaying at sunset. Have leveraged the time-lagged HRRR
for POPs in the NW this evening to account for this possibility.

As the cutoff low over the western CONUS ejects into SW Canada
tonight, a trailing shortwave drags eastward over the High Plains
on Thursday. A few CAMs maintain some reflection of overnight High
Plains convection into northeast KS Thu morning, but confidence
in this solution is not very high. Additional peak heating showers
and storms are possible Thursday afternoon with a better chance
for storms on Thursday night/Friday morning as a thunderstorm
complex over southern Nebraska advances southeastward with the
upper level trough. As with convection the previous two days, the
lack of deep shear through the column will limit organizational
potential and result in new convection being forced on the
advancing cold pool. There remains a modest amount of MUCAPE in
place and a strengthening LLJ to support convection through the
overnight hours and into Friday morning as the line moves through
NE Kansas. Large hail and potentially gusty winds would be the
main impacts.

As we roll into the holiday weekend, the main theme will be the
continued summertime heat and humidity. H850 temps increase to +20
to +24 C by Friday morning and persist well into next week as a
new cutoff low becomes established over the western CONUS. This
will translate into surface highs in the low 90s throughout the
entire forecast period. Weak southerly flow will sustain the Gulf
moisture plume already anchored over eastern Kansas. Continued
ill-timed chances for pulse showers and storms will also persist
through the weekend, with the next decent chance of a more
organized storm threat not coming until Tuesday night as the
cutoff low devolves into a wave and ejects ENE.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 613 PM CDT Wed May 23 2018

VFR conditions are expected throughout the period. There is still
a chance for some isolated storms to form near terminals tomorrow
afternoon but predictability is too low at this time to include
in this TAF issuance.




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