Area Forecast Discussion
Issued by NWS North Platte, NE

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205
FXUS63 KLBF 220421 AAC
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1121 PM CDT Mon Aug 21 2017

.SYNOPSIS...
Issued at 318 PM CDT Mon Aug 21 2017

Large MCS progressing across southeast SD into IA, northeast NE
and srn MN. Weak development noted across Holt, Boyd and Keya Paha
counties earlier. Elsewhere broad trough across southern Canada
into the northern Plains with PV anomaly just over the Canadian
border. PV axis rotating through Dakotas serving as large scale
support for convergence along associated from now stalled across
the middle of NE.

&&

.UPDATE...
Issued at 730 PM CDT Mon Aug 21 2017

A look at the KLBF 00z UA flight this evening indicates a strong
700mb cap which explains why no thunderstorms have formed. The
focus for storm development is moving south of I-80 at this time
but continues across Custer County. A new forecast is in place
using a 4-way blend of the HRRR models, the RAP and GFS models
for isolated storm coverage.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 318 PM CDT Mon Aug 21 2017

The aforementioned stalled frontal boundary showing increasing
convergence along it with several waves of outflow moving southward
as well. Mesoscale analysis continues to support strong deep moist
convergence  in this vcnty so would expect thunderstorms to develop
along the boundary by 4 PM CDT and would expect some supercell
potential with decent shear (30-40 kts)from LBF northeastward. 0-6km
shear orientation would suggest some storm interactions in the LBF-
BBW area, but more of a linear fashion further north. Despite a
clearing of stratus across southwest NE earlier this morning low
level lapse rates were not overly impressive yet. Think this will
change in the next couple hours though and scattered TSRA
developing, though more isolated the further southwest you go in NE.
Very unstable aloft and hail parameters look good. Heavy rain also a
possibility as PW values around 1.6" on the sounding this morning
which is significant but no where near records. Appears as though
the corridor from LBF to BBW would be favored for TSRA development
with overall progression into Custer Co. which could cause issues
since they`ve had so much rain lately.

TSRA development should exit the area along with the front by
midnight or so and would therefore expect a drier and cooler airmass
in place tmrw.


.LONG TERM...(Tuesday night through Monday)
Issued at 318 PM CDT Mon Aug 21 2017

The main forecast challenge this forecast period will be
precipitation chances towards the end of the week.

High pressure builds across the western CONUS bringing a northwest
flow across the central US through mid week.

The ridge then flattens out towards the end of the week. A short
wave trough then moves across the area Thursday into Friday bringing
chances for showers and thunderstorms. At this time widespread
severe weather is not expected. That being said models show a good
flow of moisture into Nebraska Thursday into Friday which could lead
to the potential for decent rainfall amounts to end the week.

Saturday and beyond...precipitation chances look slim for the rest
of the period. Temperatures will remain seasonal with highs in the
80s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1121 PM CDT Mon Aug 21 2017

SFC high pressure across the northern high plains this evening
will move overhead Tuesday presenting VFR and light and variable
winds.

A check on the short range models for fog development indicated no
fog, anywhere. However KONL is in at 1 mile visibility with calm
winds. Either the models are missing this or it is just a
temporary condition at KONL and it is not expected to spread
elsewhere. The forecast calls this as a temporary condtion and
light north winds should pick east of highway 83 and limit the
spread of the fog.

&&

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

$$

UPDATE...CDC
SYNOPSIS...Stoppkotte
SHORT TERM...Stoppkotte
LONG TERM...Gomez
AVIATION...CDC



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