Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 190452
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1152 PM CDT Tue Jul 18 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 256 PM CDT Tue Jul 18 2017

Main focus for the short term period will be the heat with another
hot day seen this afternoon.  Temperatures have risen into the low
90s this afternoon with dewpoints generally in the lower 70s and
upper 60s.  Heat indicies from the upper 90s to near 105 degrees
mark the first day of the prolonged heat warning through Saturday.
Tonight, southerly winds continue and temperatures are only expected
to drop into the mid-70s.  The GFS has been the most aggressive
generating precipitation this evening mainly north of I-70, with the
NAM/ECMWF coming in relatively dry.  Hi-res guidance have hinted at
some generation of storms in north central Kansas and southern
Nebraska in response to the increasing low level jet.  These may
skirt into northeastern Kansas by the early morning hours and have
continued PoPs north of I-70 for this potential.  Any morning
convection should clear quickly and another hot day is in store with
temperatures rising into the upper 90s and low 100s as the mid level
ridge continues to dominate over the central plains. With dewpoints
similar to today, heat indicies will be hotter Wednesday afternoon
ranging from 103-107 degrees.  Precautions for the heat should be
taken if spending a long time outside.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 256 PM CDT Tue Jul 18 2017

Wednesday through Friday should be hot and dry as the upper ridge
remains over the southern and central Plains. Models are in
agreement that the ridge will be at its strongest Thursday
afternoon with it beginning to weaken Friday. By Saturday, the
upper ridge brakes down with the mean westerlies moving south and
weak perturbations getting closer to the region. This should allow
a frontal system to move through the area Saturday. There are
differences in the timing and strength of the frontal system,
with the GEM being the strongest with high pressure moving south.
Think the GFS/ECMWF are a little more reasonable in hanging the
boundary up near the KS/OK state line and should still bring
cooler temps for Sunday through Tuesday. There are small precip
chances scattered through the forecast for Saturday through
Tuesday. Although none of the models show an especially obvious
signal for precip chances outside of the frontal system Saturday
afternoon and overnight. So POPs are kept in the 20 to 40 percent
range.

Temps really are the main concern through the end of the work week
and beginning of the weekend. Will maintain the excessive heat
warning without any changes. There remains good confidence that
the area will experience heat indices around 105 through the end
of the week. The one question mark may be temps Saturday if the
front moves through sooner. Although at this point it looks more
probable to remain hot Saturday than a big cool surge moving
through early in the day. Thursday and Friday look to be the
hottest days of the week with the upper ridge and thermal ridge
across the central plains. Have once again adjusted the dewpoint
forecast to use a little more bias corrected MOS data. This keeps
dewpoints from mixing out quite as much as the raw models. It
also produces heat indicates in the 105 to 110 range those two
days. However there does appear to be some dry air aloft advecting
in from the southwest as 850MB dewpoint depressions increase to
between 10 and 20 degrees C. So there is some chance for the
higher dewpoints to mix out. Later shifts may want to reevaluate
this potential.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1146 PM CDT Tue Jul 18 2017

For the 06Z TAFs, LLWS concerns should continue to diminish
overnight into the morning. There is a weak LLJ aloft now, but due
to the surface winds forecast to not completely decouple have not
added LLWS. Also, radar wind profiles suggest winds up to around
30kts just above the surface, so speed shear is currently not as
strong as would be expected if winds were calm at the surface.
Too low confidence in precip chances to develop near the 12Z time
frame so have held off any mention at this time.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT Saturday for KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Heller
LONG TERM...Wolters
AVIATION...Drake


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