Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 201732 AAB
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1232 PM CDT Thu Jul 20 2017

.UPDATE...
Issued at 854 AM CDT Thu Jul 20 2017

Cool air has invaded parts of North Central Nebraska and this
should prevent hazardous heat and humidity from developing this
afternoon. A new forecast is in place using a 3-model blend of
HRRR,HRRR exp and RAP. The models have been performed the best
with the warm weather Wednesday.

The heat advisory has been cancelled in many areas. Just Hayes and
Frontier counties remain in the advisory.

&&

.SHORT TERM...(Today and tonight)
Issued at 418 AM CDT Thu Jul 20 2017

Local radar display shows disorganized low-end convection over the
Sandhills and northern NEB. Appears to be all showers at this
point with little in the way of lightning activity based on NLDN
and ENI total lightning. The activity has waned in intensity over
the one to two hours. Current thinking is this activity will
continue to remain weak with respect to intensity while gradually
moving northward through early morning. Any showers and
thunderstorms are anticipated to by isolated by mid morning and
confined more so to northwest NEB.

Forecast concerns revolve around storm chances and heat impacts.
Latest water vapor imagery shows broad mid-level high roughly
centered over the Southern Plains to the Middle-Lower Mississippi
Valleys. Apparent weak mid-level disturbance over the Central
High Plains per water vapor imagery will be rounding and moving
eastward across the Central Plains today. Near neutral to minor
height rises expected overhead with the upper level high
anticipated to move little today. Stationary front presently lies
roughly from extreme northeast CO across west central NEB to
central NEB and will lift gradually northward today. Skies will
gradually decrease in cover from south central NEB north and west
today while skies staying partly sunny in the Sandhills and over
northwest-northern NEB. Another round of possible showers and
thunderstorms this afternoon-tonight. Though some uncertainty
surrounding the location of boundaries and mesoscale details.
Current thinking is the best chances will be across northern NEB
and the eastern Panhandle/far western NEB late this afternoon into
the early small hours. Primarily expect convection in the form of
multicells/MCS given the anticipated environment with vertical
deep layer shear largely 25-35 kts. Otherwise, heat impacts are
expected in the far south and far east with heat index readings
between 100-105 expected with heat advisories in effect. Conditions
should improve in the early evening due to decreasing temperatures
thus the heat advisories expires at 7 PM MDT/8 PM CDT.

.LONG TERM...(Friday through Wednesday)
Issued at 418 AM CDT Thu Jul 20 2017

The upper ridge across the southern 2/3 of the U.S. remains
flat Friday, leaving Nebraska on the northern periphery and in quasi
zonal flow. The ridge builds again across the West over the weekend,
transitioning Nebraska to northwest flow, then progresses east onto
the Plains by midweek. In the low levels, a series of fropas and low
pressures will keep temperatures near normal with periodic precip
chances.

Friday... This will likely be the warmest day over the next several
as an H85 thermal ridge builds ahead of an approaching front. The
NAM, GFS, and ECM are in general agreement with H85 temps around 30C
for the whole forecast area with southerly flow to begin the day.
Forecast soundings indicate a very deep mixed layer, suggesting
ample sunshine through the mid afternoon. Kept max temps in the
upper 90s to around 100F per model trends and latest guidance. Due
to high humidity, heat headlines will likely be needed from IML to
ANW and points east. Highest indices will be around 105 in Frontier
and Custer counties. The cold front will work through the area
during the late afternoon, which will provide the forcing for
evening thunderstorms. Decent low level moisture remains, especially
across central Nebraska where dew points are in the mid to upper
60s. Thinking the best chance of TSRA will generally be east of IML
to TIF to ONL, where forecast soundings suggest elevated CAPE up to
1000 j/kg, near dry adiabatic lapse rates to around 500mb, and
sufficient deep layer shear for strong to briefly severe storms,
around 25 to 30 kts. Another concern is heavy rain, as storm motion
will be rather slow and NAEFS ensembles indicate PWAT values around
the 90th percentile.

Saturday and Sunday... A surface low tracks across Kansas and a mid
level shortwave dives southeast across Nebraska. The combination of
the features will allow sufficient moisture and lift for at least
isolated storms across SW Neb during the afternoon and evenings.
Severe indices appear marginal at best with soundings at KIML
showing less than 500 j/kg CAPE and 0-6 km shear under 25 kts. H85
flow is variable for much of this time, which isn`t conducive for
WAA. Made little change to highs in the upper 80s to lower 90s,
which may be a little warm for SW Neb depending on cloud and precip
coverage.

Monday through Wednesday... A surface low develops off the Rockies
and slowly moves into SoDak by Wed night. H85 flow turns southerly
across western Neb, but temps remain somewhat limited in the mid
20s C. Perhaps a gradual warmup into the mid 90s by Wednesday.
Precip chances are rather scant attm, just schc across the far
north Tuesday night which may be on the edge of convection in the
Dakotas and Wednesday night with the fropa.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1232 PM CDT Thu Jul 20 2017

VFR is generally expected this afternoon, tonight and Friday
morning.

Despite east winds tonight, the SREF and other models show no
indicate of fog.

The HRRR models, RAP, GFS and NAM were the basis for isolated to
perhaps scattered coverage tonight. The HRRR model suggests a weak
disturbance across the Tetons will spark MCS activity this
afternoon. This storm activity should translate through the Black
Hills this evening and perhaps affect nrn Neb overnight. Storm
activity, if it develops across nrn Neb, should diminish 12-15z
Friday morning.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for NEZ070-071.

&&

$$

UPDATE...CDC
SHORT TERM...ET
LONG TERM...Snively
AVIATION...CDC



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