Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 171045
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
545 AM CDT Thu May 17 2018

.SYNOPSIS...
Issued at 323 AM CDT Thu May 17 2018

H5 Analysis this evening had a fairly disorganized
pattern across the CONUS. A trough of low pressure was present from
the Tennessee Valley south into the Gulf of Mexico. West of this
feature, low amplitude ridging extended from New Mexico north into
sern Wyoming. West of the ridge, a closed low was present over
northern California with a trough extending south into the eastern
Pacific. Numerous weak disturbances were noted across the
intermountain west tonight, most notably over the Idaho Panhandle,
northeastern Nevada and eastern Montana. A second shortwave was
noted over the lower Missouri valley and has led to thunderstorms
overnight across western Missouri, south into the Ozarks. At the
surface, a stationary front extended from western North Dakota into
the UP of Michigan. Further south, a surface trough of low pressure
extended from eastern Montana south into eastern Wyoming. East of
this feature, southeasterly winds were present tonight across
western and north central Nebraska. Skies were mainly clear,
however, some isolated thunderstorms were occurring over portions of
north central Nebraska. Readings as of 3 AM CDT were in the lower to
middle 60s.

&&

.SHORT TERM...(Today and tonight)
Issued at 323 AM CDT Thu May 17 2018

The main forecast challenges are
precipitation chances and the timing of onset of thunderstorms late
this afternoon into tonight, along with the threat for severe
thunderstorms. Looking at the latest HRRR overnight, isolated
convection in the northeastern forecast area, should continue to
drift slowly to the east toward daybreak. Will re-evaluate where the
convection is near forecast issuance, possibly placing a pre first
period in the zone forecast. For today, the surface trough off to
the west of the forecast area, will deepen. This will lead to
increased southeasterly winds, along with low level warm air
advection and moisture advection. With good low level mixing today,
highs were trended higher with readings in the middle 80s expected.
Thunderstorms are expected to initiate over the higher terrain of
eastern Wyoming this afternoon. Further east, Bufkit soundings,
indicate a decent capping inversion from the central panhandle, east
into the western half of the forecast area. Even with SB capes north
of 3000 J/KG in the panhandle, the cap appears to hold through the
late afternoon hours, favoring initiation well west of the forecast
area. Convection is expected to enter the western portion of the
forecast area during the early evening hours, transitioning east
this evening. Favorable deep layer shear and very steep mid level
lapse rates, will facilitate a large hail threat initially across
the far western zones, transitioning to a wind threat later this
evening, as storms take on a more linear mode. The inherited
forecast had high end chance/low likely pops tonight and appears on
track. Timing appears slower however with the 00z model runs
compared to the inherited forecast. With this in mind, decided to
delay the onset of storms roughly 2 to 4 hours tonight.

.LONG TERM...(Friday through Wednesday)
Issued at 323 AM CDT Thu May 17 2018

Active weather will continue for the first part of the extended
period. On Friday, cloudy conditions and rain showers and isolated
thunderstorms are possible throughout the day. The best chance
though for thunderstorms will be late Friday afternoon and into the
evening. Daytime heating and sufficient instability across western
and southern Nebraska will result in some strong to severe storms to
develop. The best chance for severe weather will be south of Highway
2 where SPC has already included in a slight risk. The main threats
with any severe or strong storms on Friday evening will be large
hail and strong winds.

Precipitation will gradually change over to an all rain event for
Saturday and Saturday night. A well-worked over environment will
limit any severe weather for Saturday, however, an isolated
thunderstorm could still be possible. For the most part the main
threat with the precipitation from Saturday through Saturday night
will be the chance for heavy rain. For Saturday alone, rain totals
near an inch could be possible with a grand total of QPF for
Thursday through Saturday near 2.0 to 3.0 inches. This rain combined
with recent snowmelt from the Rockies could lead to localized
flooding and a rise in both the North and South Platte rivers. At
this time, will hold off on issuing any river headlines until a
better handle on total precipitation is known and some we see how
the rivers handle the upcoming rainfall.

By Sunday, surface high pressure will begin to build back into the
region bringing dry weather to much of western and north central
Nebraska. A break in the wet pattern will continue through Monday
before the next chance of precipitation arrives Monday night.
Confidence in precipitation development is low for Monday night and
only a slight chance (about 20 percent) has been put in the forecast
for locations south of I-80. Tuesday night and Wednesday night will
continue the pattern of rain/thunderstorm chances. Again, confidence
is not high and only a mention is put in the forecast at this time.

For temperatures, Friday remains near normal with highs in the mid
70s. Clouds and rain will keep temperatures on the cooler side for
Saturday as temperatures will range from the low 50s across the Pine
Ridge region to the mid 60s across south central Nebraska.
Temperatures will then steadily rise through the remainder of the
extended period with afternoon temperatures back into the upper 70s
and low 80s by the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 541 AM CDT Thu May 17 2018

Showers with embedded thunderstorms this morning will remain east
of both sites. Quiet weather briefly returns for Thursday morning
and early afternoon with ceilings well above 5000 ft. Showers and
thunderstorms return to north central Nebraska this evening.
Confidence is high that thunderstorms will impact both terminals.
These storms will likely have large hail and strong, highly
chaotic winds. Thunderstorms will slowly change over to rain
showers by Friday morning.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Kulik
AVIATION...Kulik



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