Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 201143
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
643 AM CDT Fri Apr 20 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 311 AM CDT Fri Apr 20 2018

As of 08Z Friday morning the highly anticipated upper low was
centered on the Nevada/Utah border. A narrow fetch of mid-level
Pacific moisture was advecting northeastward across the central
Rockies and high Plains in the form of cloud cover. At a surface, a
ridge axis continues to slowly progress eastward into the
Mississippi River valley, allowing east to southeasterly winds to
return to the CWA. For the remainder of today, increasing mid-level
cloud cover is expected as the upper low encroaches the central US.
Short term solutions suggest BL mixing heights near H85 this
afternoon. With H85 temperatures near 4 to 6C across the CWA, have
bumped high temperatures up slightly to the mid 60s this afternoon.

This evening and overnight: As the upper low overspreads the Plains
this evening, PVA will increase across the CWA after 00Z. While mid-
level moisture and vertical motion will be in-place by 00Z, a stout
dry layer below H7 should hinder precipitation through 03Z.
RAP/NAM/GFS forecast soundings suggest increasing low-level
saturation between 03-06Z across central and north central Kansas.
With the reduction in low-level dry air, expect rainfall to begin
reaching the ground in that timeframe. NAM/GFS soundings nicely
depict the weak WAA pattern and the subsequent slow west to east
progression of low-level saturation. Current indications suggest the
far eastern Kansas counties may remain dry through sunrise Saturday
morning. As far as low temperatures go, the overcast skies will
hinder radiational cooling, yielding temperatures in the 40s.

.LONG TERM...(Saturday through Thursday)
Issued at 311 AM CDT Fri Apr 20 2018

By Saturday morning, a mid-level low will track over the TX/OK
panhandles, progressing ESE near the KS/OK border through Saturday
night.  The center of the main surface low associated with this
system will be well to the south in TX.  The better moisture and
lift look to be focused across OK and into far southern KS, with the
northern edge of precipitation likely extending across much of the
CWA. With a decent amount of dry air in the low-levels initially,
there are some slight model discrepancies with when during the
morning hours conditions will saturate deep enough for precipitation
to reach the ground.  As the surface low progresses into AR on
Sunday, scattered rain showers will diminish from west to east late
Saturday night through Sunday morning, with higher QPF amounts
around 0.5" expected across the far southern edge of the CWA.

With increased cloud cover in place from this passing system, expect
temperatures to remain below the seasonal normals with highs in the
50s/near 60 and overnight lows in the 40s.  A warm-up is expected by
early next week with highs rising near the seasonal normals in the
60s.  This warm-up will be halted though by the next mid-level
trough that will advance from the Pacific Northwest into the
Northern Plains by Tuesday. There is the potential for some light
scattered precipitation to develop and skim across the northern
portions of the CWA as the base of the mid-level trough dives
southeastward toward the Ohio River Valley region.  There are still
some uncertainties with the exact timing/tracking of any associated
precipitation, so have kept just slight to low-end chance PoPs in
the forecast for Tue./Tue. night.  The advancement of this mid-level
trough will help to push surface low pressure southward over the
area and further into the Southern Plains through mid-week, keeping
Wednesday temperatures slightly cooler with highs in the low 60s.
However, as the low tracks further southeast of the CWA, expect
winds to gain a more southerly component by Thursday, which will
support WAA with highs rising into the 70s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 639 AM CDT Fri Apr 20 2018

VFR conditions are expected through the evening hours. Rain
showers are expected to overspread the area from west to east
through the overnight hours. Current indication suggest rainfall
would arrive at MHK near 08Z and the Topeka terminals near the
near the end of period. Cigs are progged to remain low-end VFR
through 12Z Saturday.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Baerg
LONG TERM...Hennecke
AVIATION...Baerg



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