Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 182106
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
306 PM CST Sat Feb 18 2017

.SHORT TERM...(tonight through Tuesday)
Issued at 306 PM CST Sat Feb 18 2017

The primary feature of interest in the short term is a low-
latitude trough which is evident in early-afternoon water vapor
imagery over Baja. This upper-air system will continue east
through the southern Rockies and northwest Mexico tonight into
Sunday before phasing with a polar-branch disturbance over the
High Plains Sunday night. A full-latitude vorticity ribbon will
subsequently translate across the Great Plains on Monday.

These upper-air developments will support the deepening of a lee
trough over over the High Plains tonight into Sunday, which in
turn, will hasten the poleward flux of an increasingly moist
boundary layer into the mid MO Valley from the southern Plains.
This moisture increase may contribute to areas of fog late tonight
into Sunday morning. High clouds will be on the increase Sunday
which may temper the degree of diabatic warming with highs
commonly in the mid 60s.

Sunday night into Monday, latest model guidance remains consistent
in suggesting that strengthening large-scale forcing for ascent
will coincide with a plume of modestly steep mid-level lapse rates
and increasingly low-level moisture to foster a band of showers
and a few thunderstorms which will develop northeast across the
area. The best chance for measurable precipitation will be late
Sunday night through about midday Monday. High temperatures will
be dependent on how quickly the precipitation and clouds clear
with readings from the mid 60s northwest to lower 70s southeast
being included in this forecast. Record highs for Monday, the 20th
are Omaha - 67/1930, Lincoln - 71/1991, Norfolk - 66/1930. The
record warmest minimum temperature of 37/1996 at Norfolk will also
stand a chance of being broken.

On Tuesday, quasi-zonal flow aloft will enhance the eastward
spread of downslope-induced warming across the central Plains with
highs in the to upper 60s to mid 70s. Record highs for Tuesday,
the 21th are Omaha - 72/1977, Lincoln - 74/1991, Norfolk -
74/1995.

.LONG TERM...(Tuesday night through Saturday)
Issued at 306 PM CST Sat Feb 18 2017

On Wednesday, an amplifying polar-branch disturbance over the
northern Plains into upper MS Valley will encourage the
progression of a cold front into the forecast area with highs
ranging from the lower 60s northwest to lower 70s southeast.

Thursday and Friday, we continue to focus on the potential
impacts of a vigorous storm system which is forecast to track
across the central Plains. The 12z run of the deterministic GFS
remains an outlier and has been discounted from the forecast
process. Instead, we have relied on a blend of the 12z ECMWF,
Canadian, and GEFS mean solutions, which depict a slower and more
southern track of the synoptic cyclone (than the deterministic
GFS). Under this scenario, we expect an increasing chance of rain
showers on Thursday, mainly across the northern half of the area
within a zone of strengthening warm advection and isentropic
upglide.

By Thursday night into Friday, intensifying dynamic forcing for
ascent will associate with a plume of steep lapse rates to yield
an increase in precipitation coverage and intensity with a change
over from rain to snow from northwest to southeast across the
area. The lower-latitude storm track depicted by the current
model runs would suggest a higher probability of accumulating
snowfall, especially over northeast NE within the evolving
deformation band. A few thunderstorms will also be possible,
mainly across southeast NE into southwest IA Thursday evening.

Light snow or a mixture of rain and snow may linger into Friday
evening over far east NE and southwest IA before ending later
Friday night. Temperatures on the backside of the storm system
will be notably cooler with highs on Friday and Saturday ranging
from the mid 30s north to lower 40s south.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1140 AM CST Sat Feb 18 2017

VFR conditions will prevail through early Sunday morning at all
three TAF sites. By 10Z on Sunday increasing low-level moisture
will give way to reduce visibilities and lowered ceilings at OMA
and LNK. The latest model guidance suggests the northward
progression of this moisture may not get to OFK, thus have gone
with a more optimistic forecast for there.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Pearson



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