Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 172329

Area Forecast Discussion
National Weather Service Topeka KS
629 PM CDT Sat Mar 17 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday)
Issued at 300 PM CDT Sat Mar 17 2018

An upper-level ridge is currently progressing across the Central
Plains with a surface high pressure centered in SD and IA. Residual
moisture in the form of stratus is present over northeast KS.
Diurnal mixing on the southwest periphery of the stratus is slowly
eroding the clouds towards the northeast. These clouds along with
light northerly winds is keeping the temperatures in the upper 40s
to mid 50s. The surface ridge orientated north to south slides
through the area today and tonight keeping winds light and gradually
veering overnight. Areas that receive minimal heating this
afternoon but clear out this evening could have enough radiational
cooling to support fog towards sunrise.

The next midlevel low tracks over CO and NM tomorrow forcing a
northward moisture flux. The surface front is currently over
northern TX so modification of the post frontal air mass in OK
and KS will be difficult given the short amount of time before the
systems arrives. A more modest moisture transport appears to
occur around the 800-700 mb layer beneath a modest EML. This
moisture should be in place once the lift increases Sunday evening
and contribute to marginal elevated instability. A narrow
corridor of surface dew points in the upper 40s advects northward
ahead of the surface cyclone into central and southwest KS by
Sunday afternoon. It appears convection could initiate in the
vicinity of the surface cyclone and then weaken as it progresses
eastward given the narrow zone of positive buoyancy. Therefore
only expected some embedded thunder within the large scale
precipitation shield that is forecasted to move through portions
of eastern KS.

.LONG TERM...(Sunday night through Saturday)
Issued at 300 PM CDT Sat Mar 17 2018

There is still slight discrepancy regarding the track of the
midlevel low pressure Sunday night. The overall consensus is for
the low to pass over the OK/KS state line, which places the upper-
level divergence and PVA along and south of I-70 Sunday night
into Monday morning. The expected rainfall will also be partially
dictated by the northward extent of the moisture advection. The
GEFS shows more spread in the QPF especially for northern KS,
which is likely due to the southward shift and track discrepancy.
This has caused a southward shift in the heaviest axis of rainfall
and an overall reduction in forecasted QPF for the area.

Another weaker shortwave ejects out of the Rockies over SD/NE Monday
night into Tuesday. This may support additional precipitation mainly
along and north of I-70 Monday night. Cooler temperatures advecting
southward and the lack of diurnal heating may support a rain-snow
mix. The QPF expected during this time frame is fairly minor so do
not expect many impacts at this point. The series of shortwave
troughs tracking over the Northern Plains and Upper Midwest
eventually deepen the longwave trough over the eastern US. This
keeps our region in the northwest flow aloft until Thursday. An
approaching shortwave trough embedded within the southwest flow
aloft will drive warm air advection precipitation across the
region starting Thursday night into Friday. The strength, track,
and timing of this shortwave is not certain, but it could support
a surface cyclone in the region. Temperatures will moderate
through out the week with highs in the 60s and 70s and lows in the
40s by Friday.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 629 PM CDT Sat Mar 17 2018

Difficult forecast with MVFR cloud clearing line recently
stalling in TOP/FOE vicinity. HRRR and RAP seem to have the best
handle on this shallow cloud, but still vary notably in its
evolution. At this point have kept it a few more hours but
northeast winds at cloud level could easily keep a BKN deck in
place much of the first half of this forecast. Will also need to
watch BR/FG potential with light winds and crossover temps
expected to be reached, with more concern at MHK, but at this
point expect enough mixing to keep limiting BR in check.




SHORT TERM...Sanders
LONG TERM...Sanders
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