Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 180417 AAA
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1117 PM CDT Tue Jul 17 2018

.SYNOPSIS...
Issued at 310 PM CDT Tue Jul 17 2018

H5 analysis from this morning Had a broad trough of low
pressure extending form northwestern Quebec-south into West
Virginia. Ht. falls of 50 to 60 Meters extended from northern
Michigan into srn Quebec this mroning. Further west, northwesterly
flow extended into the northern Rockies of the CONUS and Canadian
Rockies. West of this flow, a strong shortwave trough of low
pressure was centered over central Idahao/far swrn Montana this
morning. South of this feature, high pressure was anchored over
southern Nevada, central Texas and the western Caribbean. WV imagery
as of midday had the Idaho shortwave slightly farther east into
Western Montana with a secondary shortwave noted in northwestern
Wyoming. At the surface, a stationary front extended from
southeastern Montana into northern Iowa. Low pressure was noted over
sern Montana with a sutrace trough extending south into central
Wyoming. Across western and north central Nebraska this afternoon,
skiws were partly cloudy and readings as of 3 PM CDT ranged from 81
at Imperial to 85 at North Platte.

&&

.UPDATE...
Issued at 838 PM CDT Tue Jul 17 2018

A new forecast is in place using the RAP and HRRR plus time
lagging. The models are backing off on the thunderstorm coverage;
probably because of increasing nocturnal stability. The new
forecast focuses the best rain changes across ncntl Nebraska which
would appear to be consistent with lack of thunderstorm coverage
across the Panhandle.

UPDATE Issued at 616 PM CDT Tue Jul 17 2018

A forecast update is in place which carries the thunderstorms
across Northeast WY southeast through wrn and ncntl Nebraska
overnight. The forecast uses a blend of the HRRR, HREF and RAP
plus time lagging. This might be too aggressive as the RAP dives a
MCS mostly west of highway 83 and while the HRRR carries it right
over North Platte. HREF splits the system and weakens its as it
approaches highway 83 toward sunrise.

The westward moving plume of low level moisture located near
highway 83 on radar adds some uncertainty to the forecast as the
models don`t seem to capture this. The RAP does show a 20-30kt low
level jet developing tonight and this should fuel the forecast
for likely thunderstorm development. If the storms across WY move
south of the Black Hills in a few hours then the forecast sould
verify.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 310 PM CDT Tue Jul 17 2018

Precipitation chances continue to be the main forecast challenge
in the near periods. A strong shortwave, currently over
southwestern Montana/northwestern Wyoming will initiate convection
across the Bighorn Mountains mid afternoon. As this activity
moves east into the northern panhandle, the models congeal it
into a MCS this evening. As to where the MCS tracks overnight is
somewhere up in the air with this mornings model runs. The GFS is
the outlier at this time, lifting convection due east overnight.
Other model solutions including, the Canadian, WARW, and NAM 12
solutions lift this convetion southeast into the northwestern
forecast area, then central and southern forecast area late
tonight. The prescence of a decent low level jet and enhanced
moisture axis, extending from swrn into northwestern portions of
the forecast area tonight. That being said, am favoring the latter
model solution which forces convection se across the forecast
area overnight. PWATS once again will be above 1.5 inches in my
west, which will facilitate a heavy rain threat tonight. In
addition, wouldn`t be surprised if we see some strong wind gusts
as the complex pushes southeast. With this in mind, and given
portions of Sheridan county which are prone to flooding saw some
heavy rain last night, am going to hoist a flash flood watch for
Sheridan county tonight. South southeast of Sheridan county, a
swath of decent rainfall fell across the western sandhills and far
swrn Nebraska overnight. In these areas, the main concern for
flash flooding would be in swrn Nebraska. Given the latest model
forecasts track the heaviest rainfall east of this axis of heavy
rain from last night, am not as concerned about a flash flood
watch attm. The convective complex will push into south central
Nebraska overnight with a lingering threat for thunderstorms in
the east and sern forecast area Wednesday morning. The shortwave
trough will track across South Dakota and northern Nebraska on
Wednesday. There will be a lingering threat for thunderstorms,
mainly east of highway 83.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 310 PM CDT Tue Jul 17 2018

Wednesday night through Friday...The upper level trough
will slowly track into eastern South Dakota Wednesday night with the
trough axis aligned with the Missouri River Thursday morning. There
will be a lingering threat for thunderstorms Wednesday evneing,
before convection pushes east of the area. The upper level low will
lift slowly east Thursday into central Minnesota then Wisconsin on
Friday. Subsidence behind the exiting trough and drier air will push
into the region with dry conditions expected. Temperatures will
remain seasonal with readings in the 90s for Thursday, followed by
upper 80s for Friday.

Friday night through Tuesday...Ridging will amplify across the
central and northern Plains Friday night into Saturday with dry
conditions continuing. On Saturday night, the ridging will break
down thanks to a strong shortwave approaching the northern Rockies.
Mid level warm air advection will increase as the ridging breaks
down. This will lead to a chance for thunderstorms Saturday night
into Sunday. Another round of thunderstorms are possible Sunday
night into Monday as a cold front is forced through the forecast
area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1117 PM CDT Tue Jul 17 2018

Scattered thunderstorms are expected to develop on and off
overnight through early Wednesday evening, mainly affecting areas
along and east of highway 83 and along highway 20.

MVFR cigs, currently across eastern Nebraska, are expected to
develop westward to near highway 61 overnight with VFR developing
by 17z Wednesday.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 6 AM MDT Wednesday for NEZ004.

&&

$$

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


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