Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 232040
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
340 PM CDT SAT JUL 23 2016

.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 CWA 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 LLJ
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 CWA. 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 CWA. 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 KS at this time. Current thinking is that the best
chances for development will be south of the CWA given the
location of the front though models indicate development north of
the boundary, specifically over portions of northeast CO 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 CWA with PW ~1.0, 850
Tds ~7 C, and 700-500 hPa mean RH 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 CWA 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, SPC has the
northwest-third of the CWA in MRGL 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 CWA 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
Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1221 PM CDT Sat Jul 23 2016

VFR conditions will prevail across western and north central
Nebraska through the next 24 hours. Isolated thunderstorms are
possible between 21z-03z, generally along and east of a KLBF to
KONL line. However, forecast confidence is not high enough to
mention in the TAF at this time. Winds gradually switch around to
out of the northwest this afternoon and evening. A few gusts in
excess of 20 kts are likely this afternoon in northwest Nebraska.

&&

.LBF Watches/Warnings/Advisories...
Heat Advisory until 7 PM CDT /6 PM MDT/ this evening for NEZ058-
069-070.

Excessive Heat Warning until 7 PM CDT this evening for
NEZ006>010-026>029-037-038-059-071.

&&

$$

SHORT TERM...Martin
LONG TERM...ET
AVIATION...Martin


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