Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 221957

Area Forecast Discussion
National Weather Service Omaha/Valley NE
257 PM CDT Wed Mar 22 2017

.SHORT TERM...(tonight through Saturday)
Issued at 256 PM CDT Wed Mar 22 2017

Milder and more active pattern is at our doorstep. Subjective 12Z
upper-air analysis indicates broad upper-level ridge across the
central US, with 500mb height falls up to 60m over the Rockies to
southern CA. Southwesterly upper-level jet streak up to 95kt was
noted from southern/central CA to ID. An 850mb ridge was noted
through the Mississippi River valley, with southerly winds over the
High Plains. Moisture was returning northward through TX into OK,
along with warmer 850mb temperatures from the southern Plains to the
northern Rockies.  Surface lee trough at 18Z was noted in eastern
WY/eastern CO, with high pressure over MI and southeasterly surface
winds across the mid-Missouri River valley. Surface dewpoints were
still in the teens to lower 20s, with higher dewpoints well south in
TX/OK, but temperatures were moderating into the mid-40s to lower
50s even with thinning clouds.

Main forecast concern through Saturday is potential for
precipitation as an upper-level trough moves into the Rockies
through Thursday, then closes into a low as it ejects across KS/MO
Friday. Agreement in trajectory and timing is good for this first of
several lows, leaving some devil in the details of rain onset and
placement. Strong warm/moist air advection tonight should bring
stratus and perhaps some drizzle and fog through Thursday morning.
Think anything more showery would hold off until afternoon, if it
falls at all (GFS is something of an outlier here in precipitation
extent). Also have held off any mention of isolated thunder until
after midnight Thursday night, as forecast soundings struggle to
support elevated instability until maybe very late. Have very little
temperature fall-off tonight, and have bumped max temperatures down
in the northern half of the CWA, which is more likely to remain
cloudy longer, but bumped up a touch on the southern border, where
clearing and dry slotting may allow some warm air to surge

Coverage of showers/rain will increase on Friday as upper-level low
ejects, with surface low also sliding across KS/MO. Though the CWA
will mainly be on the cold side of the low, the temperature
difference is not stark, and precipitation should remain all rain.
That said, it may take on a banded character somewhere in northeast
NE/northwest IA, with higher rainfall amounts. Kept spotty isolated
thunder mentions on Friday, but not terribly confident in thunder
potnetial so far north of the low in a cooler and saturated airmass.
Rain may linger through Saturday morning, especially in the eastern
CWA. Am suspicious that the diurnal swing of temperatures Thursday
night through Saturday may be too broad, especially in the northern
CWA, with lingering clouds and rain - the lows may be too low and
the highs too high.

.LONG TERM...(Saturday night through Wednesday)
Issued at 256 PM CDT Wed Mar 22 2017

Active pattern continues through next week, with more upper-level
lows progged to cross the southern to central Plains and toward the
mid-MS River valley. The coherency (model agreement) of each wave
decreases with time, of course. The next wave looks likely to eject
across KS-MO on Sunday/Monday. Indications are that it will be a
closed low that opens into a wave as it moves across the Plains.
Have trended downward on precipitation chances on Sunday night
through Monday midday as the trough and associated precipitation
linger more in KS-MO.  After a respite on Tuesday, a deeper low is
progged to cross the Plains on Wednesday-Thursday, with the initial
effects at the end of this forecast package.  With considerable
uncertainty regarding the placement and speed of the low, the best
we can say now is that there may be some potential chances for rain
on Wednesday in advance of the low.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 103 PM CDT Wed Mar 22 2017

Weak short wave exiting the area early this afternoon, and as such
mid-level subsidence overspreading the area. Isentropic upglide
persisting 305K and below, allowing VFR ceilings 8-12K to persist
at all three TAF sites. Expect VFR conditions to continue through
the first 8 hours of the TAF cycle, with deteriorating conditions
thereafter. Access of H5 ridge will shift eastward, and will allow
deep, moist ascent to invade northern plains. Developing LLJ will
result the advection of MVFR then IFR ceilings into all three
TAF sites between 08 and 12 UTC. Forecast soundings will take
some time to saturate, so any precipitation will be in the form of
light drizzle.




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