Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 221916
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
116 PM MDT Sat Jul 22 2017

.UPDATE...
Issued at 1057 AM MDT Sat Jul 22 2017

Adjusted rainfall chances for this afternoon and tonight.
Temperature lapse rate above 600mb is steep enough and the dew
point depression is low enough for isolated to scattered storms to
form this morning as a weak upper level short wave trough moves
through. These storms are elevated with minimal instability to
work with behind the cold front, so am not anticipating these
storms becoming severe.

This afternoon an upper level short wave trough deepens along and
south of the cold front. Both surface and mixed layer cape will be
open as lift increases overhead. Anticipate scattered storms
developing initially then increasing in coverage as the cold front
approaches. Storm coverage will peak around 7 PM CT then decline
through the evening as the upper level short wave trough and cold
front move south of the forecast area. There is enough deep layer
shear to support hail up to ping-pong ball size in the strongest
storms. DCAPE also supports damaging winds occurring ahead of the
cold front. SPC SHIPS analysis does not support tornadic
development late this afternoon or early evening, however am still
concerned about tornadic development due to storms developing
along the cold front. Have low confidence of a tornado occurring,
but still cannot completely rule one out over Graham and Gove
counties into western Sheridan and Logan counties. Heavy rainfall
will also be likely with any storms that develop this afternoon
and evening due to the nearly stationary storm movement. This may
lead to flash flooding in low lying areas. Currently do not have
enough confidence to issue a flash flood watch due to one hour
flash flood guidance of 2-2.5" and three hour flash flood guidance
of 2.5-3" over Logan, Sheridan, Graham and Gove counties. However
this does bear further consideration.

&&

.SHORT TERM...(Today through Monday night)
Issued at 245 AM MDT Sat Jul 22 2017

Mid-upper level trough will move along the Canadian border with a
weaker shortwave trough passing closer to our CWA. A cold front
stalled near the Nebraska Panhandle should kick south this
afternoon, and thunderstorm coverage should once again increase.
This front is a little slower than previously anticipated, which
allows for a window of heating across our CWA with highs near 100 in
our southeast.

There is uncertainty in regards to coverage as mid-upper level
forcing over our CWA is less organized. Main focus then will be on
cold front where there may be a  narrow corridor of better lift as
this moves through the region. Guidance hasn`t been consistent on
location of best precip signal (though it is generally depicted
along/ahead of cold front). I limited PoPs to chance category during
this update due to uncertainty on how coverage will evolve. Best
instability and shear overlap is shown in our east where there is a
potential for a more organized severe threat. Even on the low end
there is enough instability depicted by models to support at least a
limited severe threat across our entire CWA this afternoon/early
evening. Trend should be towards this activity weakening through the
evening.

Sunday-Monday night: Front stalls south of our CWA, with baroclinic
zone lingering in our south through Sunday night. This could act as
a region for shower/thunderstorm redevelopment and some models are
showing this. Coverage will be a question as best instability axis
will be south and there may be a trend towards a mored subsident air
mass from the north. Surface trough redevelops Monday with drier
more stable layer in place to our west, and models showing a limited
precip signal in our afternoon/evening east of the trough axis (our
eastern CWA). Temperatures Sunday and Monday should be near seasonal
normals (maybe a little lower on Sunday).

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 114 PM MDT Sat Jul 22 2017

Updated timing on both TAFs to account for earlier arrival of
showers and storms...

Previous Discussion: For KGLD and KMCK...VFR conditions expected
through the period. Main concern will be thunderstorms this
afternoon and whether they will directly affect terminals. Line of
storms currently in Dundy and Hitchcock counties are slowly
moving to the east towards KMCK. Some computer models have these
storms dying out before reaching the terminal, but looking at
radar trends, it will be close. Went with VCTS for both terminals
for the afternoon. Tempo for KMCK since one of the approaching
storms could make it to the terminal before dissipating. Winds
overnight become light and slowly turn from NE to W by sunrise.
Went with variable just to account for the direction changes.


&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

UPDATE...JTL
SHORT TERM...DR
LONG TERM...TL
AVIATION...SME



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