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Area forecast discussion 
National Weather Service Paducah Kentucky
545 am CST Monday Mar 2 2015

issued at 545 am CST Monday Mar 2 2015

Revised aviation discussion for 12z tafs.


Short term...(today through wednesday)
issued at 327 am CST Monday Mar 2 2015

Main concerns in the short term are many...and include the
potential for heavy rain and thunderstorms Tuesday and Tuesday
night. The focus then shifts to the potential for another snow
event on Wednesday.

Fortunately for today...the region will enjoy a brief reprieve
from the active weather pattern as high pressure slides by to the
north of the region. Even though middle and high clouds will be on
the increase throughout the day...a good deal of sunshine will be
mixed in. Highs from 35 to 40 will allow for a continued slow melt
of existing snow cover.

The chance of light precipitation will be on the increase tonight
as warm advection develops on the back side of the departing high.
Temperatures over southwest Indiana and north of Route 13 in
southern Illinois will be cold enough that the rain may start as
a brief period of freezing rain after midnight. This may create
some minor issues for 2 or 3 hours...but temperatures across the
entire region should be above the freezing mark my daybreak

Copious subtropical moisture will stream into the region on
Tuesday as a strong cold front approaches from the northern and
Central Plains. This will result in the development of more
widespread and steadier rains as the day progresses. With highs
Tuesday in the 50s across most of the area...the development of
elevated instability will result in the chance for thunderstorms
Tuesday into Tuesday night. Severe weather does not appear to be a
concern at this point.

With precipitable water values approaching 1.5 inches and on the
high end of what is expected in early March...heavy rain is also
likely Tuesday afternoon and especially Tuesday night. Substantial
low level moisture convergence along and ahead of the approaching
cold front in combination with ideal jet dynamics will likely
focus the heaviest rain in a southwest to northeast oriented band
across western Kentucky and far southeast Missouri Tuesday night.
Rainfall totals of 1 to 2 inches will be possible by daybreak
Wednesday in Kentucky...with a sharp gradient to much lighter
amounts northwest of the Ohio River.

Our next blast of Arctic air will follow the passage of a strong
cold front Tuesday night. As temperatures fall late Tuesday night
and Wednesday...lingering precipitation will transition to snow...
which may be mixed with a period of sleet. Exactly how much snow
falls is the big question...with some forecast models hinting at
another potentially significant winter weather event. Though it is
on the increase...forecast confidence still has some room to
improve. Given this...we based our quantitative precipitation forecast and snow amounts on a blend
of model guidance and wpc. Most of the snow is forecast to fall in
the 5th and 6th period of the most of our neighbors
agreed to hold off on any watch issuance for another period.
Nonetheless...Wednesday is definitely one to watch.

Long term...(wednesday night through sunday)
issued at 327 am CST Monday Mar 2 2015

Strong cold advection will be well underway by 00z
Arctic surface high pressure descends southward through the plains.
With strong southwest flow aloft...there will be considerable
moisture lifted over top of the low-level Arctic airmass at least
through Wednesday evening. The precipitation will come to an end as
a major short-wave trough aloft sweeps through the region late
Wednesday night into Thursday morning.

The main question is how much precipitation will be left after 00z.
The 00z GFS is actually quite dry...relative to the 00z European model (ecmwf) and
Canadian...and only generates around an inch of snow in the far
southern portion of the forecast area. However...the 00z GFS
ensemble mean has considerably more precipitation through Wednesday
night and closely resembles the operational European model (ecmwf) and Canadian.

Confidence is increasing in a half inch or more of liquid equivalent
precipitation falling over southern portions of southeast Missouri
and most of west Kentucky after 00z Thursday. Temperature profiles
indicate that it would most likely be cold enough through the column
to support a pure snow event. This would be in addition to whatever
falls on Wednesday.

The Canadian...European model (ecmwf) and GFS ensemble mean keep some very light quantitative precipitation forecast
in the far southeast Thursday morning...but decided to keep Thursday
dry for now. Quantitative precipitation forecast would be accumulations into Thursday
would in the noise compared to Wednesday and Wednesday nights
potential accumulations.

The Arctic surface high will settle over the region Thursday
night...and light south winds will try to develop Friday or Friday the flow aloft becomes zonal. The weekend will start off
dry...but the models diverge for Sunday and Sunday night.

The Canadian and GFS keep more of an emphasis on the northern stream
and end up with a rather amplified ridge west/trough east pattern by
Sunday morning. This would suggest cooler and continued dry for
Sunday into next Monday. The European model (ecmwf) is not as amplified and draws
moisture northward into the region with a disturbance in the
southern branch of the upper flow.

For now decided with lmk to add in a slight chance of what would
most likely be rain over west Kentucky Sunday night into Monday. If
the European model (ecmwf) is right we will be plenty warm enough for all rain...but
the consensus approach we typically take on the details of the
extended forecast will keep things cold enough at night to force a
mention of freezing rain or snow to make the forecast internally

Thursday will be quite cold with the entire area well below freezing
for highs. Temperatures moderate quickly Friday and Saturday...but
this may be too optimistic given the potential for several inches of
fresh snow across the region.


issued at 545 am CST Monday Mar 2 2015

VFR conditions and northeast winds 5 to 10 knots will prevail today
as high pressure slides by north of the area. High clouds will be on
the increase through the day...but MVFR ceilings will wait until
tonight to overspread the area ahead of an approaching warm front.
There is some potential for light rain and IFR conditions late
tonight...but that is late in the forecast period and is better
addressed in the next forecast update.


Pah watches/warnings/advisories...


Short term...rjp
long term...drs

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