Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 151133

Area Forecast Discussion
National Weather Service Topeka KS
533 AM CST Thu Feb 15 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 335 AM CST Thu Feb 15 2018

Early this morning a sheared positive tilt upper trough extended
from south central Canada, southwest into AZ. The northern stream
section of the upper trough will dig east-southeast across Great
Lakes State late Tonight. The southern stream section of the upper
trough will continue to shear apart with a section of the H5
through moving into NM by 12Z WED.

Increasing low-level CAA across the northern and central plains
will push a surface front, located across central NE early this
morning, southeast across the CWA through the morning and early
afternoon hours. The front should push southeast across the
northern counties of the CWA by 15Z, then across the southeast
counties of the CWA by 21Z. Ahead of the front during the early to
mid afternoon hours, southwest to westerly surface winds. along
with deeper mixing, will help to warm temperatures into the mid
60s to mid 70s. North of the front across north central and
northeast KS, temperatures will probably slowly drop through the
50s into the 40s during the afternoon hours. As the front pushes
southeast across east central KS temperatures will drop back into
the 60s and 50s by late afternoon. Most of the stronger ascent
ahead of the H5 trough digging southeast across the northern
plains will be well northeast of the CWA and front will go through
dry. During the evening hours scattered showers may develop along
the front across far southeast KS, as the front pushes southeast
into deeper residual moisture.

Tonight, a 1038 MB surface ridge will shift southeast across
western NE into north central KS by 12 WED. Overnight lows will be
colder, with mid teens along the NE border to lower 20s across
the southeast counties.

.LONG TERM...(Friday through Wednesday)
Issued at 335 AM CST Thu Feb 15 2018

The weekend features a warm up with a strong cold front sweeping
southward on Monday and bringing with it the chance for showers
and even some thunderstorms to east central Kansas.

Canadian high pressure builds southward into the Central Plains
at the start of the period on Friday morning, but under a
progressive WNW flow regime, quickly scoots east of the CWA by
the afternoon. Highs on Friday still look to be confined in the
30s with H850 temps in the -4 to -6 C range but WAA commences
quickly on the backside of the high. Downslope modified air works
into the region Saturday morning behind an H850 trough and will
aid in boosting highs into the low 50s.

An amplifying west coast trough late in the weekend will promote
lee cyclogenesis and increasing WAA across the Central Plains on
Sunday and into Monday. Increased winds in the warm sector given
the strong pressure gradient, and likewise trended temps and
dewpoints closer to the raw guidance blend given the strong return
flow signal ahead of the deepening cyclone. Highs on Sunday look
to reach the low 60s as a +12 C H850 downslope air mass works into
the region on WSW flow. The aforementioned cyclone pulls off the
Front Range Sunday night and reaches north central Kansas by 12Z
Monday. Models are in modest agreement in the evolution and
timing of the low/trailing cold front as it moves through Monday
afternoon and evening, though the EC has started trending slower
with the passage of the front with a more amplified H300 trough in
the west. Highs on Monday could reach the low 70s ahead of the
front in east central Kansas while locations in north central
Kansas fail to each 40 degrees.

With temps in the upper 60s to low 70s and dewpoints in the mid
to upper 50s, showers and thunderstorms are growing increasingly
likely from Topeka/Emporia eastward on Monday afternoon. GFS bufr
profiles depict MLCAPE values of 500-800 J/kg with weak inhibition
and ample deep shear to support organized convection--though the
deep flow orientation and forcing type would suggest a linear
storm mode. It is interesting that the recent 00Z EC run depicts
more of anafront structure to the cold front while the GFS/GEM
have a katafrontal structure. This results in the EC producing a
large quantity of QPF behind the surface cold front and, given
the warm nose aloft, produce freezing rain well into Tuesday. At
this point, have continued to lean towards the GFS at the present
time but will continue to assess future runs of the EC to see if
this trend continues. Have maintained low POPs into Tuesday as
well to account for this EC solution, but kept the forecast dry
for midweek as high pressure spreads over the Northern Plains.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 525 AM CST Thu Feb 15 2018

Expect moderate vertical windshear between the surface and 1,000
feet this morning through 14Z. Southwesterly low-level jet was
moving east of the terminals but the west edge of the low-level
jet had 30 to 40 KTS winds. However, since surface winds are 10 to
15 KTS with higher gusts the low-level wind shear will only be in
the 25 to 30 KTS range. Southwesterly surface winds will be gusty
this morning but should decrease as they veer more to the west. A
cold front will move through the terminals between 18Z and 20Z,
and will shift winds more to the north. The north winds will
pickup this evening to 15 to 20 KTS with some gusts to 25 to 30
KTS. A period of stratus with 2000 to 3000 feet ceilings will move
south across the terminals after 6Z FRI.


Issued at 335 AM CST Thu Feb 15 2018

Deeper mixing ahead of a surface cold front across southern
portions of east central KS will allow minimum RHs to drop around
24 percent. Southerly surface winds will veer to the southwest by
Noon and then to the west during the mid afternoon hours with wind
speeds of 10 to 20 MPH and some gusts to 30 MPH. Late this
afternoon a surface cold front will push southeast across the
southeast counties of the CWA, switching the winds to the north-
northwest. Expect a very high fire danger along and south of I-35
from the late morning hours through the afternoon hours. Any
planned outdoor burning should be postponed.




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