Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 222346

Area Forecast Discussion
National Weather Service Topeka KS
646 PM CDT Thu Mar 22 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 327 PM CDT Thu Mar 22 2018

An upper level ridge across the central Rockies will shift east
across the plains on Friday. A longer wave length trough was located
along the western coast of the US. A shorter wave length upper
trough will lift northeast from southern CA/northwest Mexico into
the central high plains by 00Z SAT. A lee surface low will deepen
across western KS through the day Friday, resulting in a tight
surface pressure gradient across central and eastern KS. The
stronger southerly winds will advect deep gulf moisture northward
across the CWA. An EML will overspread the warm sector across
eastern KS providing for a strong CAP. Most numerical models do
not show surface based convection developing ahead of the dryline
which will move into central KS during the late afternoon hours of
Friday. Expect highs Friday afternoon to reach the upper 70s
across the southwest counties. The weak warm front may become
stationary across brown county where highs may only reach to
around 60 degrees along the NE border.

.LONG TERM...(Friday night through Thursday)
Issued at 327 PM CDT Thu Mar 22 2018

Friday night, the H5 trough will lift east-northeast across NE and
northern KS. Stronger ascent ahead of the H5 trough combined with
weak isentropic lift north of a surface boundary may allow for
some elevated thunderstorms to develop. MUCAPE north of the
boundary will be 1000-1500 J/KG with 0-6KM shear of 40 to 50 KTS.
Therefore, some of the these elevated storms may develop mid-
level mesocyclones which may result in large hail, around half
dollar size. The GFS forecast develops QPF along the dry line
across the southern counties of the CWA by 3Z and forecasts 0-1
KM SRH of 400- 500 J/KG within the warm sector with 1500 J/KG of
MLCAPE. Therefore, if the GFS solution verifies, then the central
and southern counties of the CWA may see surface based supercell
thunderstorms developing during the evening hours, but these may
become more elevated through the evening hours as the boundary
layer cools. The front will push southeast of the CWA late Friday

Saturday through Saturday night, The longer wave length upper
level trough across western coast of the US will remain stationary
as an intense upper trough digs southeast towards the Pacific
Northwest. A weak surface ridge will build southwest into
northeast KS. Expect a slightly cooler and drier airmass. Highs
will range from around 50 degrees across northeast KS along the NE
border to the around 60 across the southern terr of counties.

Sunday through Sunday night, the amplified trough digging onshore to
the Pacific Northwest will phase with the longer wave length trough
along the CA coast and move east into the Great Basin and Desert
Southwest. Strong southwesterly mid level flow across the central
Rockies will cause a lee surface trough to deepen across eastern CO
and extending southwestward across eastern NM. A strong LLJ will
advect deeper gulf moisture northward across eastern KS. The
resulting isentropic lift will cause elevated thunderstorms to
develop. The elevated thunderstorms will continue through the day as
the surface warm front will only slowly lift northward from central
OK to the KS/OK border by 00Z MON. There could be enough elevated
instability for some of the thunderstorms to produce small hail,
though the 0-6KM shear if forecasted to be 40 to 50 KTS, so if
our instability increases to above 1000 J/KG, then some of these
elevated thunderstorms may rotate and possibly produce some severe
size hail.

Monday through Monday night, Both the GFS and ECMWF Forecast the
upper level trough across the Desert Southwest and Great Basin to
slowly shift east. Both extended models show the surface warm
front shifting north of the CWA by 18Z MON. A dryline will move
east into south central KS as a stronger surface cold front
pushes southeast across NE into northwest KS during the afternoon
hours. If we can get some insolation within the warm sector, then
MLCAPE may increase between 1500-2000 J/KG and the vertical
windshear looks impressive with 50 KTS of southwesterly mid level
flow, 40 KTS of southerly 850mb flow and backed surface winds.
Given the environment, severe thunderstorms are possible. The
convective mode may be initially discrete with a line forming on
the front through the evening hours of Monday. All hazards would
be possible with discrete surface based supercells and then
evolving into a wind threat with a line of storms. The front will
push southeast of the CWA during the early morning hours of
Tuesday which should bring an end to the showers and thunderstorms
by 12Z TUE.

Tuesday through Thursday, The trough to the west will shear apart
with the northern branch moving across the northern and central
plains Tuesday night and the southern stream section of the upper
trough digging southeast along the northern Mexico border. The
CWA should remain dry with highs cooling into the 50s to lower


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 646 PM CDT Thu Mar 22 2018

With surface winds expected to become east to east-southeast
overnight at TOP and FOE, went ahead with LLWS inclusion at these
locations where the low level jet should be stronger. Timing of
limiting ceiling development is still not high, but didn`t change
previous forecast much, keeping the MVFR forecast through the end
of the forecast.




LONG TERM...Gargan
AVIATION...65 is the U.S. government's official web portal to all federal, state and local government web resources and services.