Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 220813

Area Forecast Discussion
National Weather Service Goodland KS
213 AM MDT Sat Jul 22 2017

.SHORT TERM...(This evening through Saturday)
Issued at 227 PM MDT Fri Jul 21 2017

Latest upper air analysis shows the ridge continuing its slow
progression eastward.  Minor disturbances continue to develop along
its northwest periphery and rotate around the ridge.  At the surface
a pre-frontal trough was bisecting the Tri-State Area from southwest
to northeast.  This feature was also a moisture boundary due to dew
points falling 10-15 degrees north of the trough.  The light
convergence along the feature has allowed cumulus clouds to develop.

As the afternoon progresses lift will gradually increase over the
trough, which should allow a broken line of storms to form.  Further
west am expecting storms to begin forming west of the forecast area
and slowly build east.  By late afternoon storms will be moving into
the forecast area from the west along a weak cold front and upper
level short wave trough.  As the storms approach strong outflow
winds are likely due to the very dry nature of the environment below
the cloud base.  These winds will help speed up the passage of the
cold front.  Models are split as to where the best threat for
damaging winds will be, either over the southwest or northwest.  Due
to the storm coverage expected over the northwest half of the
forecast area, would anticipate this being the more likely area for
damaging wind gusts.  However the resulting outflow winds will
effect the west half of the forecast area. Current wind forecast is
likely underdone, but was unsure how high to go with the winds.
These winds may also spread further east than currently forecast.

This evening the storm activity will increase over the northwest
part of the forecast area as the upper level short wave trough moves
in from the west.  The biggest threat with these storms will
continue to be damaging winds.  The threat will have a short window,
only two or three hours before ending as all the storm activity
cools the environment and reduces the risk for damaging winds. Storm
activity will end an hour or so after midnight if not before.
Meanwhile the cold front will washout.

Saturday another upper level short wave trough will deepen over the
northwest corner of the forecast area in the morning.  As the day
progresses the cold front will become more defined over the northern
part of the forecast area.  During the afternoon the upper level
short wave trough will begin moving to the southeast.  As it does so
the cold front will accompany it.  These two features will cause
storm activity to spread to the southeast in the late afternoon.

.LONG TERM...(Tuesday through Friday)
Issued at 211 AM MDT Sat Jul 22 2017

Tuesday and Wednesday: Upper ridge remains in place across the
Plains with H7 trough forming in the lee of the Rockies on Tuesday.
Instability will be in place during the afternoon; however, with
relatively strong subsidence in place from the ridge, it will be
difficult to develop much if any thunderstorm activity. The H5
ridging will flatten a bit as we head into Wednesday, allowing the
troughing to influence the pattern a little more. Chance PoPs are in
the forecast Wednesday afternoon and with MUCAPE approaching 2000
J/Kg, we could see a few strong to severe storms form. Shear is weak
as indicated by the GFS and Canadian; however, the ECMWF is carrying
enough shear to allow for a rotating updraft or two. Highs on
Tuesday and Wednesday will climb into the middle to upper 90s.

Thursday and Friday: Ridge shifts west on Thursday, remaining
relatively flat as it centers over the Four Corners region. Chance
PoPs remain in the forecast as the H7 trough will be slowly moving
northeastward out of the region. Instability will be quite high
during the afternoon as CAPE values quickly increase through the
afternoon, approaching 3000 J/Kg. Shear remains very low with deep
layer shear only about 20 knots. A few strong to severe storms will
be possible with gusty winds and marginally severe hail being the
main risk per the current guidance. As we head into Friday, the H5
ridge strengthens and begins to shift eastward. Northwest flow aloft
will follow a weak cold front that pushes through on Friday.
Thunderstorms will be possible once more Friday afternoon once more
with good instabilty and low shear.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1056 PM MDT Fri Jul 21 2017

VFR at both TAF sites through the period. Isolated convection near
KMCK will gradually diminish by 09Z...all convection is expected
to remain north and west of KGLD overnight. By 21z Saturday the
potential exists for convection to develop along a stalled cold
front and weak surface low and placed VCTS at both sites due to
uncertainty of coverage and location.




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