Area Forecast Discussion
Issued by NWS North Platte, NE

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270
FXUS63 KLBF 241715 AAA
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1215 PM CDT Mon Jul 24 2017

.SYNOPSIS...
Issued at 343 AM CDT Mon Jul 24 2017

H5 analysis from earlier tonight had an upper level high over
Colorado with a ridge extending north to the US/Canadian border. A
strong shortwave was located over west central Alberta with a
trough extending south into Washington state. East of the high, a
trough of low pressure extended from eastern Ontario south into
the mid Ohio valley. Across the central and northern plains, a
weak disturbance was located over northwestern Wyoming. This
disturbance has since moved into northeastern Wyoming, and has led
to thunderstorms across western South Dakota overnight. Further
south, skies were mostly clear overnight across western and north
central Nebraska. Temperatures as of 3 AM CDT ranged from 64 at
O`Neill to 70 at Gordon.

&&

.SHORT TERM...(Today and tonight)
Issued at 343 AM CDT Mon Jul 24 2017

Over the next 24 hours, the main forecast challenges are
thunderstorm chances late this afternoon and this evening, along
with temperatures today. For today: A warm front will lift into
western, then central Nebraska today. H85 temps with passage of
the front, will approach 30+C west of a line from Ainsworth to
Ogallala. H85 temps will top out near 33C in the west by mid
afternoon. This will result in highs in the upper 90s to around
100 this afternoon with the hottest temps noted in the northwest
and north central Nebraska. With the warm front east of the area
and an approaching cool front over South Dakota, temps could
really torch out over northern Nebraska. Decided to increase highs
in the north over guidance. This yielded highs around 100 in the
north, with upper 90s elsewhere. Later this afternoon, a weak
upper level disturbance will approach eastern Wyoming and far
western Nebraska, leading to thunderstorm development. At this
time, the most favorable area for thunderstorms is across the far
northwestern cwa, where a decent amount of cape is located and is
co-located with an area of weak capping. Deep layer shear is on
the order to 25 to 30 KTS this afternoon into the evening hours in
the northwest, so there is some limited support for strong
thunderstorms. Storms should linger as they pass east into north
central Nebraska this evening before dissipating late evening into
the night time hours. Under clearing skies tonight, lows will
range from the mid 60s in the west, to the lower 70s in north
central Nebraska.

.LONG TERM...(Tuesday through Sunday)
Issued at 343 AM CDT Mon Jul 24 2017

A large upper ridge centered over the Great Plains on Tuesday
flattens midweek and retrogrades to the Desert Southwest,
transitioning Nebraska into northwest flow. At the surface, one low
pressure over SoDak drags a cold front through the forecast area
while a secondary low develops in Kansas. A strengthening high then
settles into the Upper Midwest late week. Convection and temps
associated with the fropa are the primary forecast challenges.

Tuesday temps... The NAM, GFS, and ECM are in general agreement with
placing the front across the western Sandhills/panhandle region by
Tuesday evening. Strong southerly flow coincides with the thermal
ridge at H85 ahead of the front, about 25 kts across the Sandhills
and temps approaching 30C. Soundings indicate a deep mixed layer
through the afternoon at LBF and VTN, and kept max temps about a
degree or two above guidance. However, if thick cirrus moves in
during the early afternoon, highs may be too warm. Regardless, temps
should reach at least the mid to upper 90s. Combined with mid to
upper 60s dew points, some locations may require heat headlines. The
best chance of 100+ heat index is currently over Boyd and Keya Paha
counties.

Tuesday precip... Convective initiation should occur in the
panhandle mid/late afternoon and spread east through the evening/
night. NAM and GFS soundings suggest sufficient CAPE (>1000 j/kg)
and deep layer shear (30 kts) after dark to support organized
convection and perhaps severe. With low/mid level wind profiles
being more unidirectional and deep shear being borderline
conducive for supercells, a linear or cluster event appears more
likely. Will have to monitor the heavy rain threat as the storm
motion vectors are nearly parallel to the frontal boundary. NAEFS
ensembles also show PWAT values around the 97th percentile
overnight Tue-Wed across north central Neb.

Wednesday... The cold front is slated to be just south and east of
the forecast area by 18z, while the secondary sfc low will be near
the central KS/NE border. Continued moisture advection combined with
strong forcing with the sfc low and H7 shortwave will keep some TSRA
around through the afternoon and evening, especially east of Hwy 83.
Mid level dry air begins to entrain into the area Wed evening.
Tapered all PoPs to schc after 06z Thu. Dropped highs areawide into
the low/mid 80s to account for expansive cloud cover and CAA at H85.

Thursday and beyond... The sfc high settling into the northern
Plains/Upper Midwest sets up return flow for western Neb. Maintained
periodic precip chances, primarily in the west. Persistent upslope
and a developing sfc trough may lead to convection off the
mountains, some of which may work into Neb. Temperatures will
gradually warm through the weekend as a weak WAA pushes H85 temps
toward 25C, translating to lower 90s by Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1215 PM CDT Mon Jul 24 2017

The HRRR, HRRR exp, RAP and NAM models suggest isolated
thunderstorms will develop KMER-KAIA around 21z today. The area
impacted is generally along and north of a line from KOGA-KTIF-KONL
and storm motion will be 27-30020kt. Storm activity should
dissipate around 03z this evening.

Otherwise VFR is expected today, tonight and Tuesday morning.

&&

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

$$

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Snively
AVIATION...CDC



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