Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 202322
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
522 PM CST Mon Feb 20 2017

.SHORT TERM...(tonight through Thursday)
Issued at 307 PM CST Mon Feb 20 2017

One would expect it to struggle to warm up on a cloudy February day,
but temperatures are in the 50s to 60s across the area, with a few
lingering showers. Granted, we had a warm start in the 50s in the
first place. Subjective 12Z upper-air analysis indicates an upper-
level trough from the MT/ND border through eastern CO/eastern
NM/western TX, with downstream ridge from the Great Lakes through
the Southeast.  Modest 500mb height falls of up to 60m were noted in
the central US ahead of the trough. Upper-level jet of 130kt was
coming ashore in northern CA, with ejecting jet segment up to 125kt
ahead of the trough and nearly south to north. Unusually warm 850mb
temperatures in the teens extended as far north as the US-Canada
border in the western Great Lakes and as far west as the High
Plains, with a pool of 8C+ dewpoints from eastern NE into IA/MO
ahead of the 850mb trough. Surface low at 19Z was centered near the
ON/SK border, with surface cold front extending through western MN
and northwest IA toward eastern NE to north central KS.
Temperatures were maybe 10 degrees lower on the cool side of the
boundary, with gusty winds just behind it and significantly lower
dewpoints.

Main forecast concerns are near-record temperatures through
Wednesday, then the storm system on Thursday-Friday.  After
something of a lull in temperatures today, both Tuesday and
Wednesday easily should reach the upper 60s to mid-70s, with
favorable westerly low- to mid-level winds. A weak front may reach
northeast NE/northwest IA on Wednesday and hold back temperatures
just a touch in those areas. Airmass will be on the dry side, making
fire weather a hazard on both days. Will continue the fire weather
watch for parts of eastern NE, and likely will need one on
Wednesday, as well.

Cooler air will continue to descend into the
area on Thursday behind the Wednesday cold front, holding
temperatures in the 40s in northeast NE to around 60 in southeast
NE.  Most solutions begin to bring rain into northeast NE by
Thursday afternoon, and despite sub-0C 850mb temperatures,
precipitation type should remain rain through the daytime with near-
surface temperatures holding warmer.

.LONG TERM...(Thursday night through Monday)
Issued at 307 PM CST Mon Feb 20 2017

Precipitation will continue to spread into eastern NE/western IA and
expand in coverage on Thursday night and Friday as an upper-level
trough closes into a low and ejects across the central US, with the
deepening surface low sliding across the central Plains. Track
differences remain, with ECMWF currently faster and slightly weaker
and further southeast than GFS (which is a bit of a shift from
earlier runs, where the GFS was the faster/weaker model) and GEM the
slowest and farthest northwest of all. Still going with a
consensus/blended solution for now, which would change precipitation
from rain to snow from roughly I-80 northward through Thursday
night. There is enough weak instability that thunder also is
possible in the warm sector, mainly in southeast NE to southwest IA,
and have included an isolated thunder mention. Moisture availability
will not be an issue, nor will forcing for ascent/vertical motion.
One of the main challenges to the snowfall forecast will be the
track of the surface low and where the heaviest band lies;
relatedly, another issue is the rain-snow changeover line that will
limit accumulations on the warm side of the gradient. It is possible
that somewhere in NE to IA, there will be a band of 6+-inch snowfall
amounts. Right now, that risk looks highest along and north of I-80.
The deepening surface low and tight pressure gradient behind it will
help induce gusty northeast to northwest winds, which in turn could
lower visibilities and create some blowing and drifting snow
concerns. The snow might be of a fairly wet character (low snow-to-
liquid ratio), which would dampen some of the blowing snow potential.

Behind the system, temperatures will remain near to slightly below
normal, with highs in the upper 30s to lower 40s and lows in the
20s.  In all likelihood, areas with deeper snow cover will err on
the cold side of that range, while areas that miss the snow may err
warmer, especially in bare ground.  The respite may be brief, with
models hinting at least at the potential for another fast-moving
shortwave/clipper with possibly light snow on Saturday night into
Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 519 PM CST Mon Feb 20 2017

Clouds continue to clear out of the area leaving VFR conditions.
Some hints at patchy fog near the Missouri River early Tuesday
morning but did not add anything at this time.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Fire Weather Watch Tuesday afternoon for NEZ016-030>032-042>044-
     050>053-065>068-078-088>090.

IA...None.
&&

$$

SHORT TERM...Mayes
LONG TERM...Mayes
AVIATION...Kern



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