Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 221707
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1207 PM CDT FRI APR 22 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 300 AM CDT FRI APR 22 2016

07Z water vapor imagery showed an upper trough over IL moving to the
east and an upper low off the OR coast. In between these two lows
was an upper ridge along the Rockies. Surface obs showed a weak
ridge of high pressure gradually building south through the central
plains.

The forecast continues to call for dry weather today and tonight due
to no real forcing for precip within the upper ridge. Additionally
there should be some modest dry air advection with the surface ridge
through the day preventing any real chance for precip. There is an
area of low clouds moving south through the MO river valley. RAP and
NAM progs show these clouds should hold together long enough to move
into northeast KS this morning. Otherwise there should be good
insolation by the afternoon. Because of this and with forecast
soundings mixing the boundary layer to near 800 MB, have adjusted
highs for today up a little from the prev forecast expecting
readings between 70 and 75. The surface ridge is progged to move off
to the east tonight with winds freshening from the southeast.
Although the gradient does not appear to be all that strong.
Therefore think low lying areas may decouple with winds remaining
fairly light through the night allowing lows to fall into the mid
40s. Elevated locations may see enough wind through the night for
lows to be around 50.

.LONG TERM...(Saturday through Thursday)
Issued at 300 AM CDT FRI APR 22 2016

Only minor edits to the extended forecast with model guidance
remaining fairly similar to the previous forecast package. Upper
ridging in control with a developing sfc trough to the west Saturday
afternoon will bring gusty south winds to the CWA. Speeds between 15
and 25 mph are likely with gusts peaking at 30 to 35 mph. Gulf
moisture increases dewpoints to the 50s while highs warm back into
the upper 70s and lower 80s. Chances for thunderstorms commence
Saturday evening as a lee trough lifts eastward over the western
plains. GFS and NAM runs at 00Z continue to advertise a slightly
faster progression of the sfc low and weak upper impulse, developing
scattered showers and thunderstorms over north central Kansas
overnight. The ECMWF is slightly slower with these features with the
optimal chances arriving Mon at 12Z. Have adjusted pops accordingly,
increasing the probabilities Sunday afternoon and evening as the
upper trough axis crosses southern NE, while the sfc low and dryline
are depicted similarly over central Kansas 00Z Monday. Steepening
lapse rates and warm moist conditions ahead of the system translate
up to 2000 J/KG of sfc based CAPE with little CIN to prevent
thunderstorm development. Main uncertainty will be mesoscale in
nature such as cloud cover and morning precip which could hinder
severity of convection overnight. However, with this setup any
updraft that does form in the late afternoon will likely be severe
with speed shear up to 6 km near 40 kts. 0-1 km shear enhances with
the LLJ by 00Z as well increasing the threat for tornadoes with any
isolated convection. Otherwise large hail and damaging winds are the
most likely hazards as convection is likely to congeal into a line
as tracks over the CWA Sunday evening.

The passing frontal boundary is still hanging up over southeast
Kansas on Monday with the GFS and ECMWF generating additional
convection Monday evening near the boundary over far east central
and southeast Kansas. Enough MUCAPE and effective shear in this area
will support a few strong to severe storms.

Long term models are still advertising a possible severe weather
event for a portion of the central plains region Tuesday afternoon
and evening as a strong negatively tilted trough lifts out of the
Inter-mountain West. Main discrepancies lie with the exact position
of the frontal boundary and timing of the approaching system as the
boundary lifts northward as a warm front through the day. ECMWF is
faster with the sfc low, lifting the warm front further north
with convection, placing the boundary over northern KS and most of
the CWA within the warm sector. The GFS however is still showing the
warm front bisecting the CWA west to east by 00Z with severe
convection focusing along and north of the boundary. er north with
the dryline centered over central KS. Meanwhile the slower GFS has
been persistent with the warm front bisecting the CWA from west to
east by 00Z Monday. GFS has also been the stronger solution with
over 2000 J/KG of sfc CAPE, minimal CIN and 0-6 KM bulk shear up to
50 kts. Lower lvl shear is stronger as well, enhancing the tornado
threat. Will need to keep monitoring changes, but it does appear
likely for a few severe storms in the area and have increased precip
chances during this period.

The remainder of the extended is more uncertain as the upper low
slowly exits eastward and dry conditions return on Thursday. Next
upper trough appears slower with this package so have backed off on
pops for Thursday at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1156 AM CDT FRI APR 22 2016

For the 18z TAFs, VFR conditions should hold for the afternoon
into the evening as current stratus deck continues to erode with
the heating of the day. Not confident enough at this point to add
fog for the 11-13Z time frame in the morning. However, there is a
possibility for some reduced VIS and patchy FG around 12Z mainly
at KTOP/KFOE. Have left mention out of the TAFs for now, but this
will be something to monitor TAFs for if decoupling allows for the
set up to occur. Winds will increase by late morning from the
SSE.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...Bowen
AVIATION...Drake



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