Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 211129
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
529 AM CST Sun Jan 21 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 327 AM CST Sun Jan 21 2018

An upper level low across the four corners region early this
morning will track east-northeast across northeast KS on Monday.
Ahead of this upper level low southwesterly 850mb winds were
advecting residual moisture northeast across eastern KS. At
the surface a stationary front bisected the CWA from northeast
to southwest and extended into southwest KS. At the surface
southerly winds were advecting lower 50 dewpoints northward to
the boundary. Areas of dense fog were developing along and north
of I-70 due to the northward advection of this residual moisture
north into the colder airmass at the surface to the north of the
surface boundary. As the boundary lifts northwest the dense fog
may disperse as the warm sector advances slowly northwest. I think
dense fog will continue through the late morning hours across
northeast and north central KS. Weak isentropic lift at the 925mb
will increase and patchy drizzle will develop. Temperatures this
morning will remain above freezing, and will slowly warm into the
40s through the morning hours.

Through the afternoon a surface low will develop across south central
KS as a 85 KT H5 jet max rounds the base of the upper low across
the TX PNHDL and lifts north-northeast into central KS by this
afternoon. Forecast sounding across the CWA do show an EML
advecting northeast across eastern KS at 800mb, thus I think we
will have have only periods of drizzle through much of the day.
Strong WAA within the warm sector across much of the southern and
eastern half of the CWA will allow highs to warm into the mid 50s
to around 60 degrees.

As the surface low moves northeast across the CWA during the
afternoon and early evening hours, there may be enough sfc
convergence combined with strong ascent in the left exit region of
the H5 jet max for the capping inversion to erode late this
afternoon and through the early evening hours to the east of the
sfc low and a trailing pressure trough, which will extend south-
southwest through east central KS. I cannot rule out some isolated
sfc based thunderstorms developing across east central KS and
possibly north along the warm front across northeast KS between 5
PM and 8 PM. The environment may become favorable for low-top
rotating storms as MLCAPEs increases to 500-900 J/KG and 0-1 KM
SRH increases to 200-300 J/KG as surface winds remain backed
through 2Z. If discrete storms develop they may produce RFDs which
could produce localize 50-60 MPH wind gusts. Thunderstorms may
form into line segments and which could produce some isolated
strong wind gusts. Forecast hodographs show good turning in the
low-levels between 23Z to 02Z, which would suggest stream-wise
generated horizontal vorticity which could be ingested into any
updraft in a stream-wise fashion and could lead to stronger
perturbation pressure gradients which may intensify updrafts,
stretching the vertical vorticity enough for possibly a brief weak
tornado of short duration. Also, there may be baroclincally
produced preexisting vertical vorticity to the east and northeast
of the sfc low and corresponding warm front which may also be
stretched by any updraft. The odds are quite low for a weak
tornado but it will need to be watched. The primary hazard would
be isolated strong wind gusts of 50 to 60 MPH. Once the low-level
winds begin to veer after 2z across east central and northeast KS
the threat for any isolated strong wind gusts will end.

Through evening hours much of the CWA will get dry slotted and
any showers and isolated thunderstorms ahead of the sfc low and
sfc trough will shift east into MO. As the upper low tracks
eastward across north central into northeast KS wrap around
moisture and vertical temperatures profiles will cool below
freezing, causing the light rain to change over to light snow
after midnight across north central KS. The stronger mid level
frontogenetical forcing will remain northwest and north of the
CWA, across central and northeast NE where the heavier snow band
will develop.

.LONG TERM...(Monday through Saturday)
Issued at 327 AM CST Sun Jan 21 2018

The rain will move southeast across the remainder of the CWA behind
the surface cold front through the early morning hours of Monday.
As vertical temperature profiles cool the rain will mix with and
eventually change to snow across the entire CWA by the mid morning
hours of Monday. It looks like the best chance for accumulating
snow of 1 to 2 inches will fall across the western counties of the
CWA. There may be a dusting of snow up to a half inch west of a
Seneca to Emporia line during the mid morning hours of Monday. By
afternoon any light snow may change back to rain as surface
temperatures warm through the mid and upper 30s by 12 Noon on
Monday. Winds will increase to 15 to 25 MPH with gusts of 30 to 35
MPH behind the surface front through the morning and into the
afternoon hours of Monday. There may be a bit of blowing snow
across the far northwest counties but temperatures will be in the
lower 30s by 12Z and there may not be much snow on the ground to
blow around. At this time I do not see blowing snow causing
visibilities to drop too low. I held off on issuing a winter
weather advisory for the western counties of the CWA since my
confidence is low in receiving more than 1 to 2 inches of snowfall
and with temperatures only dropping into the lower 30s before
they warm back into the mid 30s late in the morning hours of
Monday and into the afternoon hours.

The extended forecast Monday night through Friday looks dry as an
upper level ridge amplifies across the plains on Thursday and a
broad upper level trough moves into the western US late in the
work week. Look for a warming trend through the end of the work
week with highs in the 40s Tuesday and Wednesday, with 50s
Thursday and Friday. The Upper level trough will move east into
the plains Friday night and Saturday. There will be a chance of
rain Friday night which may change over to light snow before
ending on Saturday. Highs will drop back into the 40s on Saturday
with highs in the 30s by Sunday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 525 AM CST Sun Jan 21 2018

Visibilities at the terminals will improve through the mid morning
hours to over 6SM after 16Z. The stratus will remain in place
into the mid afternoon hours but increased boundary layer mixing
will allow the stratus deck to rise over 3,000 feet after 19Z.
There may be a chance for showers this afternoon and an isolated
thunderstorm at KTOP and KFOE late this afternoon and into the
early evening hours. The lower stratus and light rain or snow will
move into the terminals towards 12Z MON.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for KSZ008>012-020>024-
026-034-036-038>040.

&&

$$

SHORT TERM...Gargan
LONG TERM...Gargan
AVIATION...Gargan


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