Area Forecast Discussion
Issued by NWS Goodland, KS

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250
FXUS63 KGLD 280847
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
247 AM MDT Wed Jun 28 2017

.SHORT TERM...(Today and tonight)
Issued at 247 AM MDT Wed Jun 28 2017

Westerly flow is in place across the Central Rockies with sever
shortwave troughs propagating through the mean flow. The strongest
is currently east of our CWA with a general trend towards
subsidence in wake of shortwave trough and associated thunderstorm
activity. At the surface a Cold front has moved into our western
CWA, with surface low pressure over southeast Colorado.

Early this morning: Showers and isolated thunderstorms continue to
rebuild along/ahead of frontal zone in our north where axis of 1500
J/KG elevated CAPE is lingering. This should continue a eastward
transition and weakening trend before sunrise, supported by
RAP/HRRR.

Today-Tonight: Mid-upper level jet stream approaches region this
afternoon and moves into a position to put our CWA in line of a
couple jet structure over our CWA by this evening/overnight. Another
mid level shortwave trough rotates across the region from the west,
and showers/thunderstorms will begin to initiate in the west where
CAP weakens near surface trough. Coverage should increase this
evening with increased forcing, then transition eastward overnight.
NAM and to a lesser degree RAP were favored for severe parameters
with GFS possibly overly mixed. Tds in the lower levels in NAM may
be running high, but even conservatively we should see moderate
instability with increasing shear after 00Z with approaching mid
level jet and intensifying LLJ. Parameters continue to favor large
hail/damaging wind potential with thunderstorm activity. I increased
PoPs particularly in the evening and added severe mention to wx grids
during this mornings update.

Thursday-Thursday night: Larger upper level trough finally starts to
dig south out of Canada, with stronger forcing and a much stronger
cold front moving into our CWA. Current models depict main
instability axis across our south and east where NAM depicts MU CAPE
around 4000 J/KG. Shear is also much stronger during peak timing of
event. As would be expected this overlap of good deep shear, steep
mid level lapse rates, and higher CAPE values would support a much
better chance for super cell development and eventual MCS
development. The question will be if this favorable overlap is in
our area or shifted too far south or east based on frontal
timing/position of surface low. I went ahead and added severe
mention to wx grids.

Friday-Friday night: Post frontal air mass, increasingly stable air
mass, large scale subsidence should all support dry conditions. I
could see a window for lingering showers or weak thunderstorms
Friday morning as some models are still showing a lobe of mid level
vorticity transitioning east, but there isn`t a strong enough precip
signal to deviate for dry trend favored by model mean.

Regarding temperatures: Seasonally warm temps around 90F (maybe a
few warm spots in the middle 90s) are expected today as WAA rebounds
east of surface low. There is less confidence on highs Thursday due
to falling heights and approaching cold front. Current bend shows
spread of lower 80s post frontal (in our northwest) to near seasonal
in the lower 90s ahead of the pre frontal trough. Overnight lows
will tend to be seasonal tonight (50s west to upper 60s east). Post
frontal air mass Friday-Friday night will support below normal
temperatures in the upper 70s/80s and overnight lows in the 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 247 AM MDT Wed Jun 28 2017

Saturday: Surface troughing combined with an upper level shortwave
approaching the area will bring another chance of showers and
thunderstorms during the afternoon and evening. Temperatures will be
near normal for this period.

Sunday: This day still looks to be the most active in the extended
forecast, although models are now showing the better dynamics for
thunderstorm development over northeastern portions of the CWA.
Surface low and associated warm front will begin to approach from
the south during the day. Shortwaves in the NW flow aloft moving
across the area will help to enhance storm development. Model
soundings for McCook, NE show MUCAPE near 3500 J/kg, 0-6km bulk
shear of 40 kt, DCAPE over 1400 J/kg, and Significant Hail Parameter
values near 1.7. All modes of severe weather will be possible.
Thunderstorms should initiate during the afternoon and be out of the
area by midnight. Temperatures will be near or slightly above
normal.

Monday-Tuesday: Both days look to have upper level troughs
transverse the area and bring afternoon and evening chances of
thunderstorms. Models are not in good agreement on daytime temps
right now. GFS has flipped to a warmer solution, whereas the ECMWF
is now cooler than previous runs. Temperature forecast is
essentially a blend of the two.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1125 PM MDT Tue Jun 27 2017

VFR conditions should prevail through the TAF period at both KGLD
and KMCK. Radar/obs support thunderstorm activity continuing to
move within the vicinity of KMCK early in the TAF period before
clearing out. Another disturbance will bring thunderstorm chances
back to NW Kansas and SW Nebraska Wednesday afternoon and evening.
Coverage is still enough of a question to hold off on prevailing
thunder towards the later half of the TAF period, but this will
need to be considered as we are able to fine tune timing/location.

Other than the gusty winds related to departing thunderstorm
activity early in the TAF period, the rest of the TAF period
should see winds below 12kt prevailing. Thunderstorm activity late
in the TAF period could have the same impact on winds, but this
will be dependent on location/coverage.


&&

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

$$

SHORT TERM...DR
LONG TERM...SME
AVIATION...DR



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