Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 202348

Area Forecast Discussion
National Weather Service Topeka KS
648 PM CDT Fri Apr 20 2018

Issued at 300 PM CDT Fri Apr 20 2018

19Z water vapor imagery shows a closed upper low over the four
corners region. This system has caused precip to develop over the
central high plains and western KS with high clouds spreading
east over the forecast area. At the surface, high pressure was
centered over the Great Lakes with a trough of low pressure along
the lee of the central and southern Rockies. This has allowed
southeasterly winds to persist. However these low level
trajectories have not been favorable for moisture advection and
latest obs show the better moisture advection moving up the Rio
Grand valley and into the southern high plains.


...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday)
Issued at 300 PM CDT Fri Apr 20 2018

For tonight, think the precip should spread west to east across
the forecast area as the upper closed low moves east. This
movement east could be slow paced though, as forecast soundings
show low level dry air still in place across the forecast area.
For the majority of the forecast area, the onset of rain may hold
off until after midnight and probably closer to dawn for far
eastern counties. Models show the better forcing for precip
occurring through the night and into Saturday morning.
Interestingly much of the guidance shows the upper low wobble or
propagate to the southeast into southern KS or northern OK on
Saturday. Think this may be the reason for the higher QPF amounts
remaining south of the forecast area. So think there will likely
be precip are throughout the day Saturday, it may be more
scattered in nature as the better synoptic scale dynamics impact
areas to the south. Think areas south of Interstate 70 could see
around a quarter of an inch of precip, but for the most part the
rain looks to be light. Forecast soundings also show little in the
way of instability. So Saturday looks to be a cool with scattered
showers. Have trended cooler with highs Saturday expecting the
cloud cover and weak low level cold air advection to keep temps in
the lower 50s.

.LONG TERM...(Saturday night through Friday)
Issued at 300 PM CDT Fri Apr 20 2018

There are some timing differences with taking the upper energy to
the east of the forecast area. The ECMWF is slower and hangs onto
some wrap around moisture over eastern KS into Sunday. As a
result it shows some light precip persisting into Sunday. Have
held onto some small POPs for this. Have also trended highs for
Sunday cooler with readings in the mid 50s to around 60 expected.
If indeed the ECMWF is correct, temps may be even a little cooler
due to the cloud cover and northerly winds.

For Monday through Friday, the general consensus is for
northwesterly flow aloft to persist with occasional waves moving
over the region. The next chance for precip looks to be Tuesday
and Tuesday night. Again there is some timing discrepancy among
the models with the shortwave but think there is at least a small
chance for light precip. Again there does not appear to be much
instability develop ahead of the shortwave so thunderstorms do not
appear to be a big concern. Temps are expected to trend warmer for
Monday. And currently have highs from the upper 50s north central
to the mid 60s east central on Tuesday. But if the frontal
boundary moves in sooner, this forecast could be to warm.

Wednesday looks to be cooler with highs in the 60s as the
shortwave departs east and weak surface ridging passes through
the central plains. The bigger change to the forecast may be
needed for Thursday and Friday as the GFS and ECMWF are trending
towards another shortwave moving through the area on Thursday.
Both solutions show a frontal boundary moving through on Thursday
with some QPF. However consistency with these solutions has left
something to be desired. For now have opted to remain with the
prev forecast that is dry and warmer with highs in the 60s and near
70. Will need to watch later model solutions to see if they
continue to show this wave and cold front. There may be some
potential for precip on Thursday with cooler temps on Friday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 621 PM CDT Fri Apr 20 2018

Dry low levels continue for the first part of the 00Z forecast
period. Gradually, as the mid levels saturate, mid level clouds
will build over the terminals. Thinking rain will hold off until
near the 12Z time frame for TOP/FOE and near the 10Z time frame at
KMHK. Light rain will carry through the rest of the period off and
on before tapering off into the late afternoon but may linger
into the next period. CIGS are expected to lower but most
indications are that if IFR conditions do occur they may not be
long lasting as short term models do only dip into MVFR
categories over the terminals with lower CIGS south with better




SHORT TERM...Wolters
LONG TERM...Wolters
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