Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151650
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1150 AM CDT Wed Apr 15 2015

.UPDATE:
Issued at 1150 AM CDT Wed Apr 15 2015

Upper level disturbance providing modest support for SHRA in a
broken band across western, and to a lesser extent, southern MO.
Based on where this is expected to go and orient for later this
afternoon, should see primarily focus for SHRA to be in central MO
with a secondary focus for more isolated SHRA or spotty sprinkles
to gradually expand into the remainder of the forecast area.

Enough sunshine expected between the clouds for most areas to
allow a rise in temps to around 70 degrees, with the coolest
values in central MO where persistent clouds and best rain chances
will keep temps in the 60s.

TES

&&

.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.

Carney

.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
Valley.

Carney

&&

.AVIATION:  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1150 AM CDT Wed Apr 15 2015

VFR conditions will prevail for the TAF sites thru the evening
hours with light showers or sprinkles gradually expanding thru
central MO thru the afternoon and to a much lesser extent develop
into STL metro late and into this evening. Dry air at the low
levels is locked into place for areas near and north of I-70 and
will only yield ground very slowly, especially with low level flow
persisting from the east for so long. The main northward push of
the low clouds currently over AR and far southwest MO will come
with translation of weak low pressure later tonight, but there are
increasing indications that there may not be much northward push
on these lower CIGs except in STL metro but even then that looks
to be on the edge more than it did 6-12 hours ago. Have maintained
IFR CIGs for STL metro for now but toned it down too for areas
west of the MS river, but did pull IFR for COU where confidence
was higher. CIGs should at least keep VSBYs no worse than the MVFR
range. Improvement back to VFR is then expected by midday
Thursday. Otherwise, east flow will become light and variable late
tonight.

Specifics for KSTL: VFR conditions into late tonight before IFR
CIGs move in with weak low pressure area. Confidence on the IFR
CIGs a bit less than 6-12 hours ago, but with no clear signal to
remove, have kept with this issuance. Otherwise, east flow will
continue until late tonight when it becomes light and variable.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX



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