Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 271706
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
1106 AM MDT Tue Jun 27 2017

.UPDATE...
Issued at 1046 AM MDT Tue Jun 27 2017

A challenging forecast for today/this evening regarding storm
development/timing due to the very warm environment behind the
warm front leading to high dew point depressions and large CINh
values.

Latest thinking is there could be as many as two to three rounds
of storms, depending on the location. The first two will develop
at roughly the same time but at opposite ends of the forecast
area, over the west and east.

The western storms I have much more confidence in occurring due
to the presence of the upper level short wave trough, surface low
and lessening CINh values. This line of storms will start out as
fairly isolated around 1 or 2 PM MT due to the low CAPE and
somewhat high CINh in East Central Colorado near the surface low.
Storm coverage will increase as the storms move east into higher
CAPE and the warming temperatures lower the CINh. Due to the
proximity to the surface low tornadoes may occur with these storms
in Colorado. The threat for tornadoes will end the further east
the storms move due to the high cloud bases.

The next round of storms I have much less confidence in due to a
very subtle upper level short wave trough moving over the dry line
on the northeast end of forecast area near McCook to Norton.
There will be a fairly narrow corridor of lower CINh near the dry
line that may allow isolated storms to form. However stability
quickly increases east of the dry line until the late afternoon.
If storms do develop along the dry line they will quickly become
severe with 2 inch diameter hail or larger, 70+ MPH wind gusts and
tornadoes.

The final round of storms will develop during the evening ahead of
the cold front. There may be some isolated severe storms with this
activity due to elevated CAPE. This group of storms will be east
of Norton/Graham/Gove counties by 11 PM CT. Confidence is not as
high with this group since another round of storms behind the
first line coming from Colorado is not very likely due to the
stabilizing effect of the first line of storms. However there are
lower dew point depressions ahead of the cold front with stronger
lift so a final round of storms is certainly possible.

Regarding the threat assessment, large hail looks more likely in
the early afternoon, with the threat lessening gradually as the
afternoon progresses due to the CAPE shifting east. The threat for
larger hail and tornadoes will be more north and east of the
forecast area, east of the dry line.


&&

.SHORT TERM...(Today through Thursday night)
Issued at 327 AM MDT Tue Jun 27 2017

Upper level ridge remains in place across the western US with NW
flow across the plains this morning. A shortwave trough is currently
moving along KS/OK border, with subsidence (apparent on WV
imagery) is in place over most of our CWA. Stalled front on western
and southern extent of surface high pressure remains just south of
our CWA over SW Kansas and SE Colorado.

This morning: Continuing to monitor fog potential with east southeast
flow feeding good moisture in the boundary layer north of stalled
front. Models currently have best overlap across our east, but I
can`t rule out fog most places, particularly near frontal zone where
moisture pooling along edge of developing stratus could lead to
denser fog to develop. Added patchy fog mention most of CWA, with
improvement quickly after sunrise due to increased mixing and change
in air mass as front lifts north. I can`t rule out a few showers or
even an isolated thunderstorm early this morning, with good elevated
instability in place and elevated frontal zone extending north.
Subsidence overspread on west will play a role in limiting the window
for this, and currently short range guidance shows this threat only
lasting a few hours before sunrise.

Today-Tonight: Better chance should be this afternoon/evening as
another shortwave trough flattens the ridge and transitions across the
plains through tonight. By this afternoon we should see surface
trough developing towards the CO border, while a cold front
approaches from the north. Temperatures will increase well into the
90s ahead of this front, and we may see some locations reach the
upper 90s. Developing westerly flow could result in deeper dry air
advecting over our CWA, but this will also aide in increasing strong
wind potential due to dry air entrainment/precip loading potential.
Severe indices look good for hail and wind, and adequate deep layer
shear could support supercell and at least a elevated tornado
threat particularly near pre-frontal trough/frontal zone in the
north.

Wednesday-Thursday night: Progressive pattern remains in place with
series of shortwave ridges/shortwave troughs. There will be a severe
weather threat almost every afternoon/evening with atmosphere
reloading between shortwave trough passages. A stronger cold front
approaches the region Thursday and should be through our CWA by late
Thursday night. Severe indices are good both days, and while
coverage/location could be question marks confidence is high in
severe threat. Seasonably warm temperatures are expected through
these periods with highs averaging near normal values (upper 80s),
lower 90s on the warm end.

.LONG TERM...(Friday through Monday)
Issued at 327 AM MDT Tue Jun 27 2017

Friday: Cooler daytime temps and drier conditions behind the cold
front for this period. Highs predominately in the low 80s. Only a
slight chance of storms in extreme NE portions of the CWA overnight.
Lows near normal.

Saturday: NW flow aloft with an embedded series of shortwaves will
bring the area a chance of thunderstorms during the afternoon and
through the overnight. Temps will continue to run a little below
normal for this period.

Sunday: This looks to be the most active day of the extended time
frame. Cold front lifts back into the area as a warm front and will
provide lift at the surface for storm formation. Combined with a
shortwave trough moving into the area, will have the potential for
strong to severe storms. 0Z GFS soundings showed MUCAPE around 3700-
4000 J/kg, 0-6km bulk shear of 60-65 kt, DCAPE above 1500 J/kg, and
SHIP near 2.5 areawide. There will be some CIN, but any storms that
are able to form would have a good chance of being severe in this
type of environment, with all severe modes possible. Being Day 6 in
the forecast, there`s plenty of time to see what evolves and the
forecast will most likely be modified as we go forward in time. Just
something to keep an eye on at this time.

Monday: This period looks to be dry, except for a slight chance of a
shower or thunderstorm overnight. Temperatures should be near normal.

Looking beyond the period...Right now, long range models show a
slight chance of showers during the morning for Independence Day,
with the rest of the day being dry and highs around 90.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 537 AM MDT Tue Jun 27 2017

LIFR stratus has developed over NW KS including KGLD and IFR cigs
have spread north toward KMCK. Better low level moisture will tend
to be near front as it lifts north in NW KS, but both terminals
are likely to see at least temporary vis restrictions. A period of
dense fog (1/4sm) is possible at KGLD, but confidence is not high
enough to introduce conditions that low due to uncertainty in
coverage. VFR conditions should spread north behind the front
after sunrise from the south to the north, and then prevail by
late this morning.

Gusty south winds will develop at both terminals through the
afternoon, and a strong low level jet may lead to a period of low
level wind shear at KMCK. Thunderstorms look to develop this
afternoon in eastern CO and spread east towards both terminals.
Currently highest confidence/better coverage looks to be at KMCK
in the evening.


&&

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

$$

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



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