Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 051030
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
430 AM CST Thu Mar 5 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 344 AM CST Thu Mar 5 2015

An upper level TROF axis extends from MN to central KS early this
morning with a W-SW flow resulting over our region.  Canadian high
pressure was centered over the Mid-MO river valley.  The primary
cold front is well to our south, near the Gulf of Mexico coastline,
and there appears to be a weak secondary cold front pushing thru
northern MO and central IL now as evidenced by some pressure rises,
a lull in the winds, and a reinforcing shot of CAA.  Some weak lift,
either from this or from something immediately following the front,
also seems responsible for additional clouds and patchy light snow
in IA.  Temps were in the teens and lower 20s across our region with
no precipitation (for the moment).

The upper level TROF axis is expected to swing thru by early this
afternoon leaving behind NW flow aloft in its wake.  The weak lift,
which seems to be shown best on the GFS model, tracks southeastward
towards the Quincy area this morning before its various component
parts split apart by midday off to our east and southeast.  The
atmospheric column is very dry already and so we do not expect much
more than scattered flurries for some areas in northeast MO and into
west-central IL, with an isolated heavier snow shower possible but
the coverage of which is not significant enough to account for in
the forecast at this time as there are some doubts as to how well
even the scattered flurries will hold up as they try to move
southeast.  Either way, it looks to all be gone by early afternoon.
This area of lift will also bring some extra clouds into the area as
well and delay our full clearing until later in the day.

Otherwise, it will be a very cold day today, with max temps not
expected to exceed the mid 20s, with readings remaining in the teens
for many areas north and northeast of STL metro.  A MOS blend was
used for most sites.  This will result in temps being about 30
degrees below the norm for this time of year.

TES

.LONG TERM: (Tonight through Wednesday)
Issued at 344 AM CST Thu Mar 5 2015

Tonight will be unseasonably cold again, particularly across
southeast MO and southwest IL near the surface ridge axis with good
radiational cooling expected.  Will go below MOS temperature
guidance, especially in areas with snow cover.  Temperatures across
northeast and central MO will fall this evening, but should become
nearly steady or rise slightly late tonight as surface winds become
southerly on the west or northwest side of the surface ridge, and as
low level warm air advection increases over this area.  A northwest
flow shortwave will move southeastward through northeast MO and west
central IL late tonight.  There may be a little cloud cover ahead of
this feature, but it will be too dry for any precipitation.  Friday
will be the start of a warming trend as surface south-southwesterly
flow becomes established across the area.  The models shift the zero
degree C 850 mb isotherm eastward to the Mississippi River by 00Z
Saturday.  Temperatures by Friday night should be near normal for
early March, and eventually above normal by Saturday.  The NAM model
generates some very light qpf Saturday night across IL ahead of a
northwest flow shortwave, but this is likely more of a reflection of
boundary layer moisture and possible low level cloudiness and not
likely any light precipitation.  A weak and dissipating cold front
will drop southeastward into our area Saturday night.  Little if
any cooling is expected behind the front, maybe a few degrees cooler
across northeast MO and west central IL, but most areas will
continue to have above normal temperatures for the remainder of the
weekend.  The dry and tranquil weather pattern will continue for the
next work week with surface ridging across our area on Monday.  Even
warmer temperatures are expected for Tuesday and Wednesday with any
precipitation remaining south and southeast of our forecast area
ahead of a southern stream upper level trough and assoociated
surface low.

GKS

&&

.AVIATION:  (For the 12z TAFs through 12z Friday Morning)
Issued at 430 AM CST Thu Mar 5 2015

VFR conditions will prevail at the TAF sites thru much of the
valid period. Only concern is a small stubborn area of low CIGs
that continues to snake its way down into northeast MO. There are
also some flurries in this area. Low level flow would encourage
this area of clouds/flurries to move SSE but the weak lift that
seems to have generated it in the first place looks set to weaken
with time and so there is some measure of doubt how far south this
will go. Will add some scattered clouds in and watch closely the
next few hours. Otherwise, look for northerly surface winds to
become light and variable by sundown and then from the SE later
tonight.

Specifics for KSTL: VFR thru the period. Only questionable item is
how well will small area of low CIGs and some flurries hold
together as they are expected to drop SSE thru eastern-central MO.
Will maintain scattered cloud coverage for now and continue to
monitor considering what generated them in the first place is
expected to weaken. Otherwise, winds will be the main driver of
new TAF line groups as they go from N to light to SE.

TES

&&

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

$$

WFO LSX



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