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Area forecast discussion...updated 
National Weather Service North Platte NE
843 PM CDT Sat Jul 23 2016

issued at 842 PM CDT Sat Jul 23 2016

The heat and excessive heat advisories are cancelled. Isolated
strong or severe thunderstorms are possible...mainly this evening
along and south of a line from Ainsworth to North Platte to
Ogallala. Strong wind gusts are the concern.

Update issued at 655 PM CDT Sat Jul 23 2016

Some areas of the heat advisory and excessive heat warning be
allowed to expire at 7 PM CDT. Other areas have been extended to 9
PM CDT as high humidity and heat is underway and will not drop
until after sunset.

The hrrr experimental model suggests the ongoing storm activity
across the Cheyenne Divide will become more numerous. It is
uncertain if it would affect North Platte this evening. It is more
likely to affect Imperial and McCook where the effective shear is
favorable given the expected northeast winds at the sfc.


Short term...(this evening through sunday)
issued at 317 PM CDT Sat Jul 23 2016

Mid-level shortwave trough tracking along the Canadian border
has helped break down the strong ridge of high pressure that has
dominated the central conus over the last week. Area of surface low
pressure over the Dakotas will push east into the upper Mississippi
Valley later today, sending a cold front and drier air into the
forecast area. To the east of the front conditions remain hot and
humid, although heat indicies have back off from the widespread 105+
readings seen yesterday. Only sparse cu has been noted on visible
satellite along the frontal axis, so moisture convergence is
rather weak. In addition, the best forcing aloft remains closer to
a robust shortwave trough near the Canadian border. Latest hi-res
model suite has been hit and miss with their thoughts on
thunderstorm development along the front. Only minor changes were
made to the forecast since confidence is rather low and will stick
with isolated pops generally along and east of an Ainsworth to
north plate line starting at 21z. The environment ahead of the
cold front will be quite unstable with SBCAPE above 2500 j/kg,
however deep layer shear of only around 20-25 kts will promote
multi-cellular storm modes and keep the severe potential marginal.
Any storms that do develop should push east of the County Warning Area by mid to
late evening.

Additional isolated storms are possible late this evening and
overnight as activity pushes off the Front Range and may push as far
east as southwest Nebraska. There will be little help from the low level jet
as it is focused off to our east, but forecast soundings show some
elevated instability for the convection to work with.

Sunday will be cooler as the front pushes into northern Kansas and
stalls. Winds become easterly to the north of the front, which will
help keep low level moisture in place albeit much drier than the
oppressive humidity seen over the last several days. The upslope
flow beneath a 60 kt jet aloft may be enough to trigger additional
isolated shower and thunderstorm development during the day, mainly
over the southern half of the County Warning Area. Despite the presence of strong
deep layer shear the threat for severe weather should remain low due
to weak instability.

Long term...(sunday night through saturday)
issued at 317 PM CDT Sat Jul 23 2016

Sunday night through Monday night: period begins with slight
chances for showers/tstms Sunday evening, across mainly the
southern-third of the County Warning Area. Wherein, a 500 hpa shortwave trough
will be moving east across central NE that will provide weak large
scale ascent. Elsewhere, a front will be positioned west to east
across central Kansas at this time. Current thinking is that the best
chances for development will be south of the County Warning Area given the
location of the front though models indicate development north of
the boundary, specifically over portions of northeast Colorado and
south central NE. Much of the inherited slight chances were kept
with thinking that development would be late in the day. However,
moisture and weak instability may be limiting factors. For the
former, GFS proximity soundings and guidance show just modest
moisture across the southern-third of the County Warning Area with precipitable water ~1.0, 850
tds ~7 c, and 700-500 hpa mean relative humidity around 50%. Chances then
diminish early Monday morning as the shortwave pulls away and the
front becomes more diffuse as its associated low moves east. In
the meantime, surface high pressure will be building in over the
upper and middle Mississippi Valley Sun night.

Dry conditions are expected during the day across the County Warning Area Monday
along with a return of warmer temperatures. However, there will be
increased chances for thunderstorms late in the day with strong
storms even possible across western NE. Currently, Storm Prediction Center has the
northwest-third of the County Warning Area in marginal in the day 3 outlook and this
seems appropriate. Where, on Mon, a Lee side surface trough will
develop and deepen during the day while a weak disturbance aloft
moves east. Current thinking, more so for stronger storms, is that
isolated thunderstorm development will occur later in the
afternoon, where they would start and then move eastward off the
higher terrain into western Nebraska. Convective parameter space
is decent with ample instability and 0-6 km bulk shear that's
around 35-40 kts in western NE late afternoon Mon/evening. 850
temperatures in the mid 20s and good insolation will bring
temperatures into the lower 90s. Slight chances/chances then
continue through Monday night for showers and thunderstorms.

Tuesday through saturday: Lee side trough deepens near the Front
Range over the Central Plains Tuesday as the surface high moves
east to near mi/in. Chances for showers and thunderstorms will be
present Tue afternoon/evening and Tue night as a shortwave trough
aloft rounds the 500 hpa ridge positioned over The Four Corners
region. Similar situation occurs on Wednesday with similar
chances for showers/thunderstorms. Cool down in temperatures then
begins Thursday with 850 hpa temperatures largely around 20-25 c
across the County Warning Area Thursday and Friday. Highs Thursday through
Saturday are expected to be in the lower to mid 80s from along and
north of I-80. A weak frontal passage occurs late Wednesday
followed by another cold front early Friday. Slight
chances/chances through the rest of the period, Thursday through


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 635 PM CDT Sat Jul 23 2016

There is a chance the storm activity moving over the Cheyenne
Divide will grow upscale...become more it moves east
and southeast toward southwest Nebraska. It is uncertain if it
would affect klbf this evening. It is more likely to affect kiml
and kmck where the effective shear is favorable given the
northeast winds at the sfc.

Eastern areas of ncntl neb appear to be capped at h700mb
suggesting no storms will develop this evening.

Additional isolated thunderstorm activity may form across swrn neb
Sunday afternoon...from 20z Onward but the NAM is keeping a cold
front south of this area.


Lbf watches/warnings/advisories...


short term...Martin

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