Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 271725 AAA

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1225 PM CDT Tue Jun 27 2017

.SHORT TERM...(Today and tonight)
Issued at 419 AM CDT Tue Jun 27 2017

The main forecast concerns begin mid afternoon and then carries
through tonight given the potential of strong and severe
thunderstorms. SPC Convective Outlook has the entire local
forecast area in a Slight Risk area with the main hazards large
hail, damaging winds, and brief heavy rainfall. Tornado threat
cannot be ruled out as well.

Latest water vapor imagery shows an upper level closed low in far
western British Columbia with a trough extending south into the
western half of the Intermountain West and a shortwave trough at
the base in western OR. A upper level ridge is downstream to the
east and extends from the Four Corners region into Saskatchewan.
Latest IR and NtMicro RGB satellite imagery shows stratus/fog
developing in south central NEB and southwest NEB.

The lead shortwave trough in western OR will move east across the
Northern Intermountain West early today and then across western
WY and Central Rockies by late afternoon. The upper level ridge
will be breaking down at that time and be displaced east across
the eastern Central and Northern Plains this afternoon. The
aforementioned shortwave trough should be over the NEB Panhandle
by the early evening. Meanwhile, surface trough will deepen in the
Central High Plains with a lee side low forming near northeast
CO/NEB Panhandle in the afternoon. Decent moisture transport will
occur today with surface dew points expected to rise into the
upper 50s and lower 60s as moisture returns to western NEB.
Precipitable water values peak largely near 125% to 150% of normal
outside the NEB Panhandle by late afternoon. Moderate ML and MU
CAPES across western NEB in the afternoon/early evening given
moisture with anticipated diabatic heating and destabilization.
Though convective inhibition will be initially present though
will erode towards late afternoon. A front will be advancing
eastward mid afternoon-evening. Will move east to northeast CO/NEB
Panhandle and then western NEB in the mid afternoon and late
afternoon/early evening, respectively, with initial development
expected to occur in the former. A potential fly in the ointment
is quantity and distribution of moisture given some differences in
guidance across western NEB this afternoon and evening. Current
thinking is the NAM appears overdone with this. However, we will
need to monitor the distribution of low-level moisture and
quantity of with respect to surface dew points over the course of
the day.

Anticipate initially isolated to scattered storms with respect to
coverage then thunderstorms congealing into one or two MCSs in
western NEB in the evening. Multicells/clusters and supercells are
expected for storm mode given parameter space (vertical wind shear
and SRH). Large hail and damaging winds appear as the primary
hazard, however, brief heavy rain is anticipated to be a threat as
well. Tornado threat cannot be ruled out also given SRH and low-
level vertical wind shear. Increased confidence with respect to
convective initiation and coverage given signal in SPC SSEO
spaghetti/paintball plots and neighborhood probabilities. Notable, a
signal is present in updraft helicity for rotating updrafts in their
simulated storms over the southern Panhandle and southwest NEB -
this shows support for supercell storm modes as well. Current
thinking is convection should be moving out of the local forecast
area/ending during the small hours.

.LONG TERM...(Wednesday through Monday)
Issued at 419 AM CDT Tue Jun 27 2017

Near zonal flow aloft and dry conditions are expected most of the
day Wednesday. By late afternoon however, surface winds shift east
to southeast, with some residual low level left in the wake of
Tuesday evening`s expected MCS. A shortwave trough approaching from
the northwest by late afternoon will combine with a weak and
somewhat moist upslope flow, with scattered thunderstorms expected
to develop across the panhandle. These should track east in an
isolated to scattered fashion Wednesday evening. At this time severe
potential looks low. Thursday the shortwave trough progresses east
across the Dakotas and Nebraska, driving a cold front southeast.
Appears that the front should be well southeast of the area by peak
heating, and this would be where the higher potential for stronger
storms would be. Agree with SPC shifting the severe threat mostly
south and east of the forecast area. There will still be some
potential for a strong storm in the post frontal environment due to
some decent elevated instability that lingers.

Flow turns northwest aloft Friday through Saturday, with drier mild
air filtering into the area behind Thursday`s cold front. Appears to
be another pleasant first half of the weekend with highs in the
upper 70s to lower 80s Saturday with light winds. The next shortwave
will dive southeast across the area Saturday night and Sunday. This
will strengthen a leeward trough Saturday night with a south to
southeast wind developing. This will rapidly draw warm moist air
back north into the area Sunday, with possible strong storms and an
MCS late Sunday afternoon and Sunday night.

Models diverge the first of next week, with the ECMWF slowing the
shortwave and attempting to close it off (not indicated in the
previous run) across the northern plains into eastern Nebraska. This
would bring cooler temperatures than currently forecasted along with
possible showers/thunder. The GFS ensemble mean actually has upper
level ridging building into the area during this same time and
supports highs in the 90s all areas. The going forecast forecast
sides toward the ensemble mean with highs in the 80s and mainly


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1225 PM CDT Tue Jun 27 2017

A blend of the GFS1hr, HRRR, HRRR experimental, and RAP models
suggests a 40-60 mile shift west with the QLCS forecast to develop
this evening. This would be from Sutherland to Mullen to Merriman.

There is a chance that very warm air aloft could cap the atmosphere
and limit storm coverage to isolated coverage late this afternoon.
The pacific cold front is forecast to cool 700mb temperatures and
weaken the cap allowing more storm development this evening.

All of the severe weather should exit Ncntl Neb around 06z or so
with some lingering general thunderstorms thereafter. VFR is
expected from 09z onward Wednesday.




LONG TERM...Taylor
AVIATION...CDC is the U.S. government's official web portal to all federal, state and local government web resources and services.