Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 271951
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
151 PM 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...(Wednesday night through Tuesday)
Issued at 151 PM MDT Tue Jun 27 2017

The long term period is showing to be an active one with storm
chances almost everyday. Starting off on Wednesday night, storm
chances will continue over the region from the afternoon hours. CAPE
and shear values are favorable for severe storm development. Come
Thursday a trough will move over the region and bring with it
continued storm chances. There will also be a cold front that will
move over the area.

That trough will stay over the region through Saturday morning. Then
northwest flow will dominate over the region. Friday looks like a
lull period in precipitation, but there may be some chances along
the northwest part of the region in association with a brief passage
of a shortwave. Saturday brings another round of storms with another
shortwave moving over the region. Sunday is showing a similar
pattern.

Monday and Tuesday brings a ridge over the region, as well as dry
conditions. There could potentially be some brief pop up
precipitation chances each day.

Temperatures during the period will be in the 80s Thursday through
Saturday. Friday will see a slight decrease into the upper 70s to
mid 80s with the passage of the cold front. Sunday through Tuesday
will see a slight increase into the 90s due to the ridge.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1148 AM MDT Tue Jun 27 2017

VFR conditions forecast for the TAFs. Main impact will be if/when
the storms will move through the sites. Am confident storms will
develop, the question is what will the coverage be. Currently
thinking the line of storms that moves east from Colorado will
increase in coverage east of KGLD this afternoon. Due to how close
the storms should increase in coverage relative to KGLD, decided
to place a VC mention in. KMCK may have an isolated storm develop
near the site, but have low confidence this will occur. In the
evening the better storm coverage will be either south or north of
the site so will not place a specific mention in the TAFs. Storms
should be east of KMCK around 6z.


&&

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

$$

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


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