Area Forecast Discussion
Issued by NWS Goodland, KS

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000
FXUS63 KGLD 160813
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
213 AM MDT Wed Aug 16 2017

.UPDATE...
Issued at 1036 PM MDT Tue Aug 15 2017

Based on the elevated instability from the RAP, which has been the
most reasonable given the storm intensity, the threat for large
hail has ended. Elevated instability is less than 1000 j/kg where
the upper level lift is strongest. There will be some pockets of
higher elevated CAPE, but these will be far enough away from the
main upper level short wave trough that severe storms should not
develop. Some storms may have a hail core briefly reach severe
thresholds, but do not expect it to last long enough to produce
large hail. Storms have not lasted long when the hail core was
deep enough for large hail.

UPDATE Issued at 544 PM MDT Tue Aug 15 2017

Updated forecast to refine the timing of storms for tonight based
on latest data and satellite/radar trends. Main mechanism for
storm development will be the upper level short wave trough just
west of the Tri-State Area. This trough will deepen over a dry
line/surface trough just to the west. The upper level feature
will track northeast across the northwest half of the forecast
area tonight. With the strongest lift over this part of the
forecast area, the flash flood watch looks well placed. 600-500mb
frontogenesis will be strongest of Yuma County this evening, so
would expect a good deal of storm activity as a result. The
frontogenesis does weaken through the night and doesn`t move much
further east.

Meanwhile isentropic lift develops over the east third of the
forecast area overnight ahead of the upper level short wave
trough. Models have a second maximum of rainfall over this part of
the forecast area which is outside the watch. Confidence is not
high enough right now to justify extending the watch over that
part of the forecast area. However WPC does have a slight risk for
excessive rainfall over that part of the forecast area. Will
monitor new data coming in to see if the watch needs to be
expanded.

Regarding the risk for severe weather, deep layer shear is very
similar to yesterday as is the CAPE. The lift is even stronger
than yesterday, but the nose of the LLJ is not in as favorable a
position as yesterday. The nose is mainly over the northwest half
of the forecast area this evening, so would anticipate the severe
weather to be confined there for the most part. Flash flooding
should be the main threat with a secondary threat of hail and
damaging wind gusts. Cannot rule out tornadic development due to
0-1km helicity and 0-1km shear being favorable for tornadoes. The
tornadic threat will be confined to the first few hours of the
evening.

Once the cold front begins moving through late this evening,
anticipate the storm activity to decline behind the front.
Soundings show the elevated CAPE diminishing as the front moves
through.

On a side note, near term models not very optimistic with
rainfall over the majority of the forecast area tonight, which is
odd considering the depth of the lift with the upper level short
wave trough moving through. These models keep the storm activity
mostly north of the forecast area or over the far southern
counties. Cannot rule out greater storm activity over the south
than currently forecast, based on the latest radar trends, but
confidence is not as high as over the north half of the forecast
area where the upper level short wave trough will track tonight.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 247 PM MDT Tue Aug 15 2017

Forecast issues will coverage of thunderstorms and associated
hazards. Satellite and upper air analysis show a deep moist air
mass over the region. Main shortwave trough that will help with
the lift is just to our west at this time. Frontal boundary has
retreated some to the north through the day and is now over or
near the western and northern portions of the area.

High resolution/Cams are in disagreement where to put the convective
development which has been a problem they have been having this
season. At this time radar is showing thunderstorms developing near
the surface boundary. The Rap and latest Nam12 is showing this
scenario more than the other output. So at this time will start with
the highest pops in the north and west.

Guidance differs on how long to keep this activity around. Most of
the output is clustering around thunderstorms moving slowly east and
lasting through the night. Dcape looks to be 1000 or above over the
area through this evening and do have decent directional shear at
this time. Front and/or outflow moves across the area during this
time. So do expect a chance of severe with damaging wind and large
hail the main threats. There is an outside chance of a tornado.

Very heavy rainfall causing flash flooding looks to be higher than
normal. Precipitable water values are 1 to 1.5 inches which is near
to just above 1 to 1.5 standard deviations above normal. Locations
from Kit Carson through southeast Yuma and most of Sherman counties
into Cheyenne county Kansas and eastern Rawlins counties received to
2 to 6 inches with Kit Carson having the most widespread heavier
amounts. This combined where the models have the highest qpf and
pws, chose to put a Flash Flood Watch out for the northwest third.

For Wednesday the shortwave and associated precipitation moves
across the area through day and should be east of the area by late
in the afternoon. Models show cooler for tomorrow and used a blend
to cool temperatures off.

.LONG TERM...(Thursday through Tuesday)
Issued at 213 AM MDT Wed Aug 16 2017

The extended period will start out with a west-southwest upper level
flow through Monday night and Tuesday morning. Then the flow will
become northwesterly as a upper level ridge builds over the Rockies
and a longwave trough deepens into the Plains. This pattern will
produce warmer and drier conditions, than what the region saw the
last few weeks, over the weekend. Tuesday a frontal boundary is
expected to move through the local area. This pattern is pulling
moisture into the region from the southwest and with the boundary
looking to impact the region on Tuesday, there is a chance of
precipitation every day through the period.

Afternoon high temperatures are expected to be near to slightly
above normal over the weekend then become slightly below normal on
Tuesday and Wednesday. Overnight lows will remain in the lower
60s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1146 PM MDT Tue Aug 15 2017

VFR to MVFR conditions forecast for the TAFs. The window for
storms to move near KGLD are nearing an end, however KMCK will be
in storms for the next couple of hours. The stronger cells in the
line may drop the visibility down to MVFR briefly. Close to 12z
MVFR conditions will occur at KGLD as low ceilings move in.
Ceilings will raise to VFR by mid morning.  KMCK does not look to
have ceilings this low.


&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Flash Flood Watch until 6 AM MDT /7 AM CDT/ early this morning
     for KSZ001-002-013.

CO...Flash Flood Watch until 6 AM MDT early this morning for COZ090-
     091.

NE...Flash Flood Watch until 6 AM MDT /7 AM CDT/ early this morning
     for NEZ079>081.

&&

$$

UPDATE...JTL
SHORT TERM...BULLER
LONG TERM...BW
AVIATION...JTL


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