Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151202

702 AM CDT Wed Apr 15 2015

.SHORT TERM: (Today and Tonight)
Issued at 349 AM CDT Wed Apr 15 2015

Cutoff low over the Kansas/Nebraska border will get absorbed into
the mean flow today and the resulting shortwave should pass
northeast over the region today into tonight.  Weak warm advection
will continue above the surface at 850mb and guidance continues to
show weak and transient areas of moisture convergence through the
day and into tonight across the lower Mississippi Valley up toward
the STL Metro.  NSSL and SPC 4km WRF models show some fairly
widespread showers over Arkansas in this region of warm advection,
but the showers tend to break up into scattered and isolated pockets
by the time they reach the eastern Ozarks.  Think this is due to the
drier air continuing to be pumped into the Mid Mississippi Valley by
the high over the Great Lakes and southeast Canada.  As a result,
have kept scattered showers in the forecast across much of the area,
except isolated in north/northeast areas today.  Guidance refocuses
the axis of precipitation further east tonight into the Ohio Valley
but I can`t rule out continuing isolated to widely scattered showers
primarily along and east of the Mississippi.  As mentioned
yesterday, temperatures will be highly dependent on cloud
cover/precip so have stuck pretty close to MOS numbers for highs
today and lows tonight.


.LONG TERM:  (Tonight through Tuesday)
Issued at 420 AM CDT Wed Apr 15 2015

Guidance seems to be pointing to a break in the precipitation
chances for Thursday and Thursday night as shortwave ridging builds
across the area in response to the deepening low over the Four
Corners Region.  That break looks like it may come to an end Friday
as the low moves east a bit into Colorado or New Mexico.  The NAM is
likely too aggressive with the return of precipitation into
Missouri...but the ECMWF may not be fast enough.  Went with a
compromise between the GFS and NAM in this case with slight chance
to low chance pops overspreading the area by Friday afternoon and
continuing through Saturday.  More widespread mid and high chance
pops Sunday into Sunday night as the low finally opens up and gets
swallowed up in the developing longwave trof that medium range
guidance continues to advertise for next week.  GFS and ECMWF look
to agree pretty well on the development of the aforementioned trof
Sunday into Monday with the energy cutting off over the Upper
Midwest or south central Canada Monday or Tuesday.  Medium range
guidance shows some precipitation chances again Tuesday night as a
shortwaves moves through the area on the southern periphery of the
cutoff low, but cannot justify anything more than slight chance at
this time that far out in the forecast given the uncertainties
dealing with cutoff lows.  Temperatures should be near or a bit
above seasonal normals at least through Saturday ahead of the first
wave.  Should see temperatures dip down below normal by early next
week as the deep cutoff low strengthens over the Upper Midwest
allowing for cool Canadian air to penetrate into the Mid Mississippi



.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 700 AM CDT Wed Apr 15 2015

Ceilings across the FA today and into this evening should remain
aoa 5kft as lowest levels of the AMS are progged to remain quite
dry. Band of showers centered from sw MO into e TN should continue
to lift north and these could impact KCOU and STL Metro sites
later this morning and/or early this afternoon, but given very
light intensity these should have no operational impact. By
tonight, surface ridge pushing into the northeast U.S. will allow
frontal boundary and associated low level moisture currently
stalled to our south to begin drifting north. MOS and dynamically
driven guidance both suggest a fairly rapid transition into MVFR
and IFR conditions later this evening and overnight for at least
the KCOU and STL metro sites, with these deteriorating condtions
coming about due to a combination of advection and development of
ST and fog.

Specifics for KSTL: Ceilings aoa 5kft are expected today and into
the evening. There will also be a few sprinkles in the area early
this afternoon, but these should not cause any operational impact.
As mentioned in the primary aviation discussion, there is good
agreement in all of the guidance that conditions will likely
deteriorate into MVFR this evening as stratus advects into the
area, with further deteriorating conditions into IFR in both ST
and fog after midnight. Daytime heating should cause a rapid
improvement in these IFR conditions in the 14-17z time frame on
Thursday morning.



Saint Louis     69  55  73  57 /  30  30  10  10
Quincy          67  51  71  55 /  20  20  10  10
Columbia        66  52  74  56 /  40  20  10  10
Jefferson City  67  52  74  55 /  40  30  10  10
Salem           68  55  71  55 /  30  40  20  10
Farmington      66  55  72  56 /  40  40  10  10




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