Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 061120

Area Forecast Discussion
National Weather Service Omaha/Valley NE
520 AM CST Wed Dec 6 2017

.SHORT TERM...(Today through Friday)
Issued at 313 AM CST Wed Dec 6 2017

Northwesterly flow continues, with an attempt at precipitation
today. Subjective 00Z upper-air analysis indicates a stacked low
centered in northern ON, with the trough extending from the northern
Rockies to the mid-Atlantic, and with a southwestern US weak upper
low that was largely cut off from the main flow. An embedded
shortwave in the northwesterly flow had moved from MT into western
NE through the last few hours. An upper-level ridge was centered off
the coast of OR/northern CA. A 130-150kt upper-level jet streak
extended from the OH River valley through the eastern Great Lakes,
with split jet flow in the western US. 850mb sub-0C temperatures
extended across much of the central to northern Plains and eastward
through the Great Lakes, as well as south to the OH-MS River
confluence. Surface low at 08Z was well northeast in northern ON,
with surface ridging in western MT/western WY, and still a rather
distinct pressure gradient between across the central US. Pockets of
sprinkles/flurries were sliding southeastward through the Dakotas
into NE/IA/MN this morning associated with the embedded shortwave.

Main forecast concern is the evolution of aforementioned
sprinkles/flurries today and whether they will amount to measurable
precipitation. A reinforcing shot of cold air will slide southward
through the Dakotas/MN into NE/IA through the day, and the
associated mid-level frontogenesis will provide some lift. Mid-level
moisture is fairly meager, though, and there is considerable
uncertainty whether any precipitation will measure. If it does, it
is not likely to be very widespread, and have stuck with low-end
POPs for that reason, with coverage mention for sprinkles/flurries.

In wake of the cold air push today and tonight, 850mb temperatures
will fall into the lower teens below zero into Thursday. Updated
forecast continues to hold high temperatures below freezing for the
first time this cold season. Climatologically, the average first day
with a high below freezing is around November 15-20, and a December
7 occurrence would be around the 5th to 15th latest on record across
the area. As mid-level temperatures rebound on Friday, so will
surface temperatures, despite persistent (and dry) northwesterly
flow. A surface to mid-level trough passage on Thursday night may
bring increased clouds, but forcing and moisture both look too
meager to wring out (measurable) precipitation.

.LONG TERM...(Friday night through Tuesday)
Issued at 313 AM CST Wed Dec 6 2017

Northwesterly flow will continue through the period, with a trough-
east/ridge-west pattern locked in for some time. The central US will
remain in the transition/gradient area, and thus temperatures are
likely to fluctuate on either side of normal during this pattern. A
consistent signal for warming on Sunday continues, with 850mb
temperatures popping into the single digits above 0C, before colder
air returns on Monday. With normal highs in the mid to upper 30s at
this time of year, forecast temperatures are more above than below
normal from Sunday through Tuesday. As long as the baroclinic zone
remains near the area, weak and transient shortwaves could possibly
generate enough lift for light precipitation (more in the
sprinkles/flurries than rain/snow variety). There are low POPs in
the grids on Monday and on Tuesday, but ultimately, confidence is
very low in receiving measurable precipitation during the period


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 520 AM CST Wed Dec 6 2017

It is a fairly low confidence in the exact ceiling heights through
the period. For the most part, expect cloud bases to be above 4000
feet, but some periods of MVFR ceilings are possible. That would
be mainly in any light pcpn, which will be difficult to time due
to fast flow aloft and scattered coverage of pcpn. Winds will
increase and become gusty mid to late morning, then remain fairly
gusty into the evening.




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