Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 300445
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1145 PM CDT FRI JUL 29 2016

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 331 PM CDT FRI JUL 29 2016

20Z water vapor imagery shows northwest flow persisting over the
central plains as a shortwave moves towards IL from the mid MO river
valley and high pressure sits along the AZ/UT state line. There does
not appear to be an obvious shortwave upstream of the forecast areas
the only weak wave seen appears to be over southern Saskatchewan. At
the surface, Weak surface ridging over the northern and central
plains is gradually weakening with a surface trough stretching from
the southern high plains into the mid MS river valley.

The forecast for today and tonight is expected to be largely driven
by mesoscale considerations since there does not appear to be much
in the way of large scale forcing. The isolated showers that have
popped up are likely driven by diurnal heating since it is largely
occurring on the back side of the shortwave. So this should fall
apart by sunset. The main uncertainty in the forecast is what
convection off the higher terrain over WY and CO does. Storms are
already developing and if a MCV forms, it could cause precip to
possibly move across the area overnight. Models prog the low level
jet and return flow to focus across the high plains overnight, so
any isentropic lift is expected to be focused to the west as well.
Nevertheless models continue to show some QPF developing from
northwest KS into southern KS through the morning hours Saturday.
Because of this, have continued with some low end chances POPs
across the southwestern portion of the forecast area. I would expect
the high plains convection holding together with some MCV for this
to verify. Saturday will depend on what happens overnight and
whether there are any boundaries or remnant mid level vorticity in
the area. Forecast soundings show little or no inhibition so it is
just a question of some lift or weak forcing to spark some
convection. At this time have been conservative with the POP
forecast since the models have no forcing impacting the area.

Lows tonight are forecast to fall into the lower and mid 60s due to
reasonable radiational cooling. With the surface ridge axis over the
area, winds should remain light and as along as skies clear out the
forecast should be in reasonable shape. This brings into question
whether there is some ground fog in the area. Storms out west may
cast a cirrus shield over the region limiting the fog potential. So
with low confidence, have opted to not include any mention of fog
and let later shifts monitor the potential. Highs Saturday area
expected to be a degree or two warmer than today as heights rise and
southerly winds start to advect warmer air north. Temps in the mid
to upper 80s are expected for Saturday afternoon.

.LONG TERM...(Saturday Night through Friday)
Issued at 331 PM CDT FRI JUL 29 2016

Late Saturday night into Sunday morning continue to present the most
likely wet periods of this forecast. Details in specifics remain,
and with little if any upper level support confidence is not high in
a widespread rain, but isentropic upglide through much of the mid
troposphere increases through the night with good low level
convergence as PW values increase to support high chance from
southwest to northeast in the overnight into early morning hours.
Again hard to completely rule out a few strong to near severe
updrafts but scenario remains unfavorable for anything widespread.
Could see some training for locally heavy rain as well. Will keep a
small pop in the northeast Sunday night with some chance for the
elevated baroclinic zone to linger, but the warm and dry air aloft
will be moving in from the southwest through the night. Have kept
temps near previous levels with highs well into the 90s by Monday
and apparent temps near Advisory levels.

Tuesday through Friday night time frame will likely be mainly dry
with weak unorganized flow aloft and mainly a high pressure ridge in
place suggesting a fairly strong EML being advected into the area
with generally weak southwest flow aloft.  The main belt of the
Westerlies will remain along the northern CONUS/Canadian border, so
north central and northeastern Kansas will see little in the way of
precipitation producing shortwaves with perhaps Friday being the
best chance for a minor wave to break down the ridge over the
outlook area. Each morning leading up to the Friday time frame will
still keep slight chance POPs in place mainly north of I-70 due to
potential MCS development and movement into portions of south
central and southeast Nebraska with an isentropic response to any
potential cold pools working into the region as a result. Should
some parcels reach the LFC during this time, there could be a few
elevated showers and perhaps a few thunderstorms.  It still appears
that this ridge will be weaker than the last ridge which brought a
heat wave to the region. That being said the heat will still be very
noticeable with heat indices into the low to mid 100s especially
Tuesday and Wednesday.  Overnight lows for the period probably hold
in the middle 70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1140 PM CDT FRI JUL 29 2016

Expect VFR conditions through most of the next 24 hours. There
could be some shallow ground fog developing at KTOP around sunrise
but should mix out by after 13Z. If cirrus cloud cover moves in
then ground fog will not develop. A few model runs show isolated
to scattered showers and thunderstorms developing around the
terminals from the mid morning hours of Saturday into the
afternoon hours.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...Drake/65
AVIATION...Gargan


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