Area Forecast Discussion
Issued by NWS St. Louis, MO

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491
FXUS63 KLSX 300843
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
343 AM CDT Tue May 30 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 341 AM CDT Tue May 30 2017

Mid level trough over the northern Plains will drop southeastward
into the Midwest today.  Surface trough that is currently over the
upper Midwest will move southeastward into Missouri and Illinois by
late this afternoon and this evening.  Scattered showers and
thunderstorms are expected to develop ahead of this boundary this
afternoon and this evening when mid level ascent will increase over
the area ahead of the mid level trough. The atmosphere will become
modestly unstable by this afternoon with MUCAPES in the 500-1500
J/kg range. There could be a few strong to severe storms this
afternoon and early this evening, particularly over central and
southeast Missouri where the instability will be the strongest. Deep
layer shear will be close to 50kts, with the primary threat being
damaging winds given the inverted-V forecast RAP soundings at COU
and FAM.  The showers and thunderstorms will be isolated in coverage
overnight and be confined to southeast Missouri and southwest
Illinois as the boundary moves south.

Highs today will range from the middle 70s to the lower 80s as
temperatures will mix up to 700mb today.

Britt

.LONG TERM...  (Wednesday through Monday)
Issued at 341 AM CDT Tue May 30 2017

Northwest flow aloft will continue over the area on Wednesday due to
the large upper low centered over south central Canada, and a weak
ridge of high pressure at the surface will drift across the Midwest
into the Ohio Valley.  Most of the area should stay dry on
Wednesday, though isolated showers and storms will be possible over
some of our eastern Ozark counties which will be closest to the low
level baroclinic zone.  Low level southwest flow will redevelop on
Wednesday night as the longwave upper level trof shifts east.   This
results in an increasing low level jet over eastern Kansas. Guidance
is showing some decent 850mb moisture convergence over much of the
area by 09-12Z Thursday morning which will likely force convection
along and west of the Mississippi River. The baroclinic zone lifts
northeast through the day Thursday and Thursday night which will
likely continue to produce scattered convection on and off across
the area.

Should have a relatively dry period on Thursday night into Friday
morning as the boundary finally moves northeast of the area.  GFS
and ECMWF print out some pretty widespread QPF over the area during
the day Friday, but I wonder if they`re not too generous with the
areal coverage. No synoptic low level boundaries and weak ridging
aloft points to a dry period despite relatively large values of
CAPE.  Suppose there could be some orographic effects over the
Ozarks to get storms going Friday afternoon, but nothing which would
warrant more than "chance" or "scattered" PoPs.

Medium range models show a succession of shortwaves moving across
the area Saturday through Monday.  While the models are in general
agreement that this will be an active period, the specifics for our
area are quite different.  Both the GFS and ECMWF agree that
Saturday will be wet with a shortwave passing through the area, but
the ECMWF`s solution is stronger, developing a surface low over the
Midwest which drags a cold front through our CWFA by early Sunday
morning.  The GFS on the other hand has a fractured and slower
moving wave which does not move through the Mississippi Valley until
Sunday night.  The GFS therefore continues to produce precip on
Sunday while the EC is dry.  Will hang onto slight chance PoPs for
Sunday since there`s little agreement between the two models. The
GFS pushes a front through our area on Sunday night, and both the
ECMWF and GFS print out some precip on Monday behind the front. Mass
fields in either model don`t really support any precip on Monday so
will stay dry for now.  Temperatures through the period will be
highly dependent upon precip trends, but should be near normal for
late May/early June.

Carney


Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1143 PM CDT Mon May 29 2017

Added in some MVFR fog for early on overnight tonight at KSUS and
KCPS as higher dewpoints have lingered a bit behind the earlier
frontal passage with light/variable winds allowing for radiational
cooling. FEW- SCT midlevel clouds for the rest of tonight with
another boundary moving through late Tuesday afternoon and
evening. Isolated- scattered storms expected during this period
which will have potential to affect terminals. VCTS group added at
KCOU as it has potential of impacting them first. VC groups may
also eventually be needed for the metro terminals.


SPECIFICS FOR KSTL:

FEW-SCT midlevel clouds tonight. Increasing chances for
showers/storms very late Tuesday afternoon and evening. May need a
VCTS mention in future packages.

Gosselin

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     82  58  79  60 /  30  30   5  20
Quincy          77  54  75  56 /  20  10   0  20
Columbia        79  54  79  60 /  30  20   5  40
Jefferson City  81  55  80  60 /  30  20  10  30
Salem           80  56  78  58 /  30  30   5   5
Farmington      81  56  79  58 /  30  20  10  10

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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