Area Forecast Discussion
Issued by NWS St. Louis, MO

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809
FXUS63 KLSX 120259
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
859 PM CST THU FEB 11 2016

.UPDATE:
Issued at 859 PM CST Thu Feb 11 2016

Have made some minor adjustments to snowfall based on this
evening`s radar and satellite trends. Water vapor is showing a mid
level vort max currently dropping southeastward out of eastern
Nebraska into northwestern Missouri with a deformation axis
extending from northeast Missouri into west central Iowa. It is
taking some time for the snow to overtake the dry air in the low
levels, so only reports of snow so far in the CWA have flurries
over northeast Missouri. Do think the accumulating snow currently
over Iowa will move into northeast Missouri and west central
Illinois shortly. It still appears the the intensity of the
snowfall will weaken as it moves southeast per the recent runs of
the the RAP. Do not expect much accumulation of snow as far south
at I-70 before midnight...so have shifted the 1 inch totals
slightly northward into northeast Missouri and west central
Illinois with lesser amounts to the south. It still will be a cold
night, so even light snowfall amounts could impact travel. Also
watching second area of radar returns over western Missouri which
has only one or two reports of light snow with it. Any snow
accumulations with it should be light as it moves across the
southern CWA over the next few hours.

Britt

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 1230 PM CST Thu Feb 11 2016

A northwest flow shortwave now dropping southeastward into western
SD will move quickly through our area tonight.  Light snow will
spread southeastward into northeast MO early this evening, then
through the St Louis metro area around midnight.  Still looking like
a quick shot of dry, powdery snow with most places picking up to 1
inch of accumulation, but there may be a narrow band of 1-2 inches
extending from near IRK southeast through the St Louis metro area.
Latest NAM and HRRR model runs have the band a little further west
than previous model runs.  Most of the accumulating snow should
shift southeast of our forecast area by 12Z Friday.  Low
temperatures will be similar to the previous night, and around 5
degrees below normal.

GKS

.LONG TERM:  (Friday through Next Thursday)
Issued at 316 PM CST Thu Feb 11 2016

A strong cold front will move southeastward through our forecast
area on Friday with strengthening winds as the surface pressure
gradient tightens as a strong 1040-1045 mb surface high builds
southeastward into the area from the northern Plains behind the cold
front.  Temperatures may begin to fall in northeast MO behind the
front already by Friday afternoon.  Much colder temperatures are
expected for Friday night and Saturday with wind chills down to
around 10 below zero late Friday night and early Saturday morning
across northeast MO and west central IL.  Snow should spread
southeastward into at least northeast MO and west central IL late
Saturday night as low-mid level warm air advection increases ahead
of an approaching northern stream shortwave.  It still appears that
the ECMWF model is a little too quick bringing precipitation into
our forecast area already be Saturday afternoon and evening with an
initially very dry boundary layer on the backside of the surface
ridge. The better chance of precipitation should occur on Sunday as
a southwesterly low level jet brings increasing low level moisture
into our area ahead of the shortwave.  It is too early to pin down
exact snow totals, but it initially appears that 2-4 inches is
possible across northeast MO and west central IL with lesser amounts
of 1-2 inches further south for Saturday night and Sunday.  Another
round of precipitation is expected, mainly on Monday, as a southern
stream shortwave and associated surface low pass south of our area.
This precipitation should be confined mainly to southeast MO and
southwest IL.  With temperatures trending up as we head into the
next work week there may also be precipitation type issues with a
mix of snow, sleet and rain possible.  Will keep the rest of the
forecast dry with a warming trend, although the ECMWF model does
depict some weaker weather systems bringing a brief period or two of
light QPF to our area.  The GFS model is dry for the remainder of
the period after Monday with a dry cold frontal passage on Tuesday
afternoon and evening.  Both the GFS and ECMWF models depict a warm
weather pattern by Thursday with upper level ridging over the region
along with strong s-swly low level winds likely leading to well
above normal temperatures.

GKS

&&

.AVIATION:  (For the 00z TAFs through 00z Friday Evening)
Issued at 536 PM CST Thu Feb 11 2016

Snow over Iowa will move southeast this evening into the terminals
bringing MVFR and IFR visibilities during a 4-6 hour window.
Snowfall will be lightest at KCOU where only a dusting is expected
compared to KUIN and the St. Louis area terminals where 1-1.5
inches may occur by the time the snow ends. Then low MVFR or IFR
ceilings will linger into the late morning hours on Friday before
drier air allows for VFR conditions to prevail by afternoon.

Specifics for KSTL: Snow is expected to move into the terminal
later this evening causing visibilities to fall into the IFR range
through early morning before it ends. Accumulations should be
around 1 inch and temperatures in the lower 20s late tonight. Then
low MVFR or IFR ceilings will linger into the late morning hours
on Friday before drier air allows for VFR conditions to prevail by
afternoon.

Britt

&&

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

$$

WFO LSX



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