Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 220421 AAB
AFDLBF

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

.SHORT TERM...(This evening through Monday)
Issued at 318 PM CDT Sun May 21 2017

Latest water vapor imagery shows a closed upper low over the MN
Arrowhead region with cyclonic flow prevailing across much of the
central CONUS. Latest satellite imagery shows cu development
across much of the local forecast area, except for portions of
north central NEB. Isolated- scattered showers have developed
upstream in the NEB Panhandle on west with a few widely isolated
thunderstorms also, albeit short- lived. Mid- level lapse rates
have steepened, albeit still modest, and there is marginal
instability over the NEB Panhandle thus there will be slight
chances for thunder in western NEB as well. Activity will diminish
will the loss of daytime heating this evening with skies clearing
tonight. However, lows will not be as cold as this morning,
ranging from upper 30s in far northwest NEB to lower/mid 40s
towards central NEB.

As this aforementioned low evolves and moves eastward slowly over
the upper Great Lakes tomorrow, a short wave trough on the
western periphery will track into the Central High Plains. There
will be sufficient instability for thunderstorms, however, no
strong or severe t-storms are expected. Deterministic guidance
continues to show decent consistency among each other and run-to-
run continuity thus increased chances for showers tomorrow
afternoon.

.LONG TERM...(Monday night through Sunday)
Issued at 318 PM CDT Sun May 21 2017

Amplified large scale pattern in place with a broad long wave
trough present over much of the central and eastern CONUS at the
start of the period with a ridge upstream extending from the West
Coast into western Alberta. The period will start off with a
short wave trough in progress of crossing western NEB associated
with the aforementioned broad trough. There will be predominantly
slight chances Monday evening across much of the local forecast
area where showers and thunderstorms will begin to diminish/move
out. Thereafter, the ridge over the West Coast will become
displaced east and south with the axis moving to Northern High
Plains to Saskatchewan and then Southwest US to the Red River
Valley Tuesday and Wednesday, respectively. This could be
attributable to the next incoming upper level trough that will be
moving into British Columbia Tuesday then into the Northern
Intermountain West and Northern High Plains Wednesday. By
Wednesday, a closed low will have evolved and will be over
southern Saskatchewan. This pattern will be supportive for
generally dry conditions through Wednesday, albeit slight chances
for showers on Tuesday. Largely cooler conditions will prevail on
Tuesday compared to Monday as cooler air filters into western
and north central NEB. Tuesday highs will span about 10 to 16
degrees below normal. Conditions will then warm up some as the
ridge moves overhead Wednesday. Southerly flow develops Wednesday
while a surface low pressure system develops in the central
Canadian Prairies with a trough extending southward along the
MT/ND border to the Central High Plains. Highs will be warmer but
will remain below seasonal normal values Wednesday, mid 60s to
lower 70s with warmest temperatures in far western NEB.

Although temperatures will be warming beginning on Wednesday,
highs Thursday and beyond are expected to stay below seasonal
normal values. The upper level ridge will be of low amplitude by
Thursday and east of the Central High Plains as the broad trough
upstream amplifies. Beyond Thursday, the upper low shows little
movement while filling in and is forecast to stay over the
Canadian Prairies through much of Saturday. Meanwhile, quasi-
zonal flow looks to persist across the Central High Plains through
the weekend. Multiple short wave toughs rotating around the
periphery of the broad upper low will contribute to precipitation
chances Thursday, Friday, and Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1121 PM CDT Sun May 21 2017

VFR is generally expected all areas overnight and Monday and
Monday evening.

An upper level disturbance...currently entering northeastern MT...
drops south through the High Plains Monday. This disturbance is
expected to produce scattered to numerous shower coverage and
isolated to scattered thunderstorm coverage from 15z onward
through 04z Monday evening. Scattered thunderstorms develop during
the afternoon/early evening...generally 19z-03z. All of this
convection will present opportunities for local MVFR/IFR cigs and
vsbys.

&&

.HYDROLOGY...
Issued at 318 PM CDT Sun May 21 2017

Rivers of concern include: North Platte, South Platte, and
Elkhorn. A flood warning continues on the North Platte near
Lewellen affecting Garden and Keith counties due to reservoir
releases upstream and recent precipitation. The North Platte
river is expected to stay high there through the rest of the new
week. Elsewhere, the South Platte river is expected to go up
from northeast CO to Roscoe, NE to North Platte, NE attributable
to heavy precip and snow melt across eastern CO. However, there is
uncertainty in how much river levels will rise beyond Julesburg,
CO (at Roscoe and North Platte) thus confidence is lower. Those
with interests near or on the South Platte river should stay tuned
for updates. Lastly, Elkhorn River near Atkinson has rose to
action stage this morning where low lying areas along the Elkhorn
river could see minor impacts.

&&

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

$$

SHORT TERM...ET
LONG TERM...ET
AVIATION...CDC
HYDROLOGY...ET



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