Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 142308
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
608 PM CDT Mon Aug 14 2017

.SHORT TERM...(Tonight through Thursday)
Issued at 314 PM CDT Mon Aug 14 2017

Active pattern persists across the area. Subjective 12Z upper-air
analysis indicates a weakly wavy upper-level pattern, with
troughs over the northern Great Lakes and the northern Rockies, as
well as in the southern Plains, and a ridge from Co through the
northern High Plains. Low-level moisture was increasing in the
central US, with 12-16C+ dewpoints at 850mb nosing into the
central Plains. The mid-level pattern across the central US was
fairly ripply but also fairly weak, with ridging from central SD
into central KS and a small low centered in southwest MN. Surface
low at 19Z was centered in eastern WY, with a mesolow in northern
IA/southern MN and a surface high in northeast ND/northwest MN. A
surface boundary was noted across the KS-NE border toward northern
MO, and a new round of showers/storms were initiating in the KS-
NE-MO mutual border area this hour.

Main forecast concern is convective potential this afternoon/tonight
and again Tuesday evening into Wednesday morning. Have limited POP
mention to areas of southeast NE to southwest IA this evening, with
CAMs suggesting convective development would be limited to areas
near the surface boundary. Scattered showers/storms may expand
across more of eastern NE/western IA tonight as the boundary
retreats northward, and have generally narrowed the axis of
precipitation to follow the boundary as it progresses northward
toward the SD border and northwest IA.

As an upper-level trough digs into the Rockies on Tuesday, a surface
low also will take shape in northeast CO, with aforementioned
boundary sharpening from southwest NE to northeast NE and toward
northwest IA. Thunderstorms should develop along that boundary by
mid to late Tuesday afternoon in central to northeast NE and into
southeast SD. Guidance continues to suggest quick upscale growth
into a line, with abundant rainfall associated with the convection.
The rain would be welcome in many areas, but it still could fall
quickly enough to cause short-lived concerns, and will need to keep
an eye on the heavy rain potential for Tuesday night into Wednesday.
Convective complex should move across NE through the evening and
night, with some weakening toward Wednesday morning. With the CWA
getting more of the complex than the initial development, think that
threat mode will have moved more toward wind and perhaps some hail,
with decreasing severe thunderstorm risk through the night.

Boundary will continue to push southward slowly on Wednesday, but it
may still be laying across the southern CWA by Wednesday afternoon,
when convection is likely to redevelop as a reinforcing shortwave
slides across the central Plains.  Have less confidence in severe
weather potential, as it is likely that the Tuesday night convection
will stabilize the airmass, but certainly some areas could see
additional rainfall. After precipitation shunts southward on
Wednesday afternoon/evening, the remainder of Wednesday night
through Thursday should remain dry as a surface to mid-level high
moves across the region.

.LONG TERM...(Thursday night through Monday)
Issued at 314 PM CDT Mon Aug 14 2017

Active weather will continue through the weekend as a series of
shortwaves brings potential for at least some areas to see at least
isolated to scattered showers/storms. That said, model solutions
differ widely from each other on the details, so confidence in
timing or location of precipitation is low. Slight chances may skirt
the western CWA late Thursday night or Friday morning, depending on
eastward progress of High Plains convection from Thursday
evening/night. Additional chances may arise on Saturday
afternoon/evening and possibly on Sunday night.

ECLIPSE DAY FORECAST (MONDAY)...

For a few runs now, models have indicated some area of
showers/storms in eastern NE and/or western IA on Sunday night into
Monday morning. They have differed slightly in the placement of the
convection, the speed of its exit, and the amount of cloudiness
behind it. For now, it does at least seem to be a reasonable
scenario that there could be chances for showers/storms at least on
some part of Monday.  At the very least, the pattern does not look
like a high and dry ridge. Have shaved a couple of degrees off of
model guidance and included temperatures dipping downward in the
couple of hours on either side of the eclipse peak, consistent with
research on the effect of an eclipse. If the day is sunny, the
amount of dip (and lowering of temperatures away from guidance)
would be several degrees more; for now, this is a conservative
estimate.  Also, based on this research, have dropped a kt or two
from winds near the peak of the eclipse.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 608 PM CDT Mon Aug 14 2017

Possible storm development is problematic for tonight. There are
some signals that some storms could develop over parts of
southeast NE and could affect KLNK prior to midnight. Will monitor
for that but chances seem too low to mention in TAFs at this time.
Chances look better later tonight as better upper level support
moves in from the west. Chances seem highest later tonight for
northeast NE and will include some mention of precipitation in the
KOFK TAF. Generally look for VFR conditions, but some MVFR
ceilings are possible later tonight, especially in any SHRA or
TSRA.

&&

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

$$

SHORT TERM...Mayes
LONG TERM...Mayes
AVIATION...Miller


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