Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 162346 CCA
AFDPAH

Area Forecast Discussion...CORRECTED
National Weather Service Paducah KY
546 PM CST Fri Feb 16 2018

.UPDATE...
Issued at 457 PM CST Fri Feb 16 2018

Updated Aviation discussion for 00Z TAF Issuance.

&&

.SHORT TERM...(Tonight through Saturday)
Issued at 336 PM CST Fri Feb 16 2018

Rain has pushed east of the region this afternoon, with low clouds
hanging around. As high pressure slides by to our north, clearing
will spread in from the northwest, although it may not make it into
all of our southern counties. Northerly winds have been gusty
today with some observations up to 25 mph. Winds will subside this
evening and become light overnight.

Main concern this period is with a disturbance that is currently
over New Mexico, which will spread quickly east/northeastward
towards are region late tonight into tomorrow morning. Precipitation
looks to enter our southern counties of southeast Missouri late
tonight after 3am, and progress northeastward through the morning
hours. Thermal profiles appear cold enough for some snow to mix in,
especially at the onset of the precipitation. However, most areas
are expected to change over to rain fairly quickly in the morning.
The short duration of the snow, combined with warm ground temps,
should lead to little if any accumulation in most locations.
However, there is some potential at a little accumulation in a
narrow zone in southeast Missouri, generally from Van Buren to
Greenville and Marble Hill. Amounts here are expected to range from
a light dusting up to several tenths of an inch.

The majority of the rain should quickly exit from west to east from
late morning into mid afternoon, with only some lingering shower
activity left behind. QPF amounts look to range from around a
tenth of an inch in far northern counties to over a half inch in
southern counties of western Kentucky into the bootheel of
Missouri.

.LONG TERM...(Saturday Night through Friday)
Issued at 336 PM CST Fri Feb 16 2018

NOTE: An erroneous discussion was sent for the long term section
earlier this afternoon. The following is the correct discussion.

The vast majority of the extended forecast period will be devoted
to a prolonged period of wet weather and possibly flood producing
weather for the Quad State region.

A hydrologic statement (ESF) will be sent to discuss the major
points of the potential excessive rainfall and impacts.

The overall synoptic pattern next week will be dominated by a
broad cyclonic flow, with periodic shortwaves diving down from
western Canada toward the four corners region of the desert
southwest U.S. As these waves move into the southern plains, they
will shear out over the WFO PAH forecast area, channeling energy
and lift across the Quad State region.

There has been a good forecast signal centered on next Tuesday and
Tuesday night for significant rainfall production over the WFO
PAH forecast area. Although the initial rainfall for this event
may develop as early as Sunday night and last through early
Wednesday, the best lift and forcing will occur on Tuesday.

A secondary, but not yet consistent signal, suggests another heavy
rainfall event next Friday and going into next weekend.

The 12z Friday model runs for the European (ECMWF), Canadian
(CMCnh), and GFS guidance have shifted the focus for the heavy
rain further north than just 24 hours ago. The Canadian places
storm total rainfall from southwest MO to east Central MO and west
central IL, while the GFS and ECMWF move the heavy rain axis over
southeast MO, southern IL, and part of southwest IN. The ECMWF
does have an extension into the Purchase area of west Kentucky
between Monday and next Friday. All of the guidance suggest a
relative minimum of precipitation over the West Kentucky Pennyrile
region.

With this package, forecast rainfall amounts for Monday through
next Friday are expected to range in excess of 3.5 inches over
southeast MO and southeast Illinois to near one and a half inches
in the west Kentucky Pennyrile. The axis and amounts of heavy rain
will likely change until the guidance settles into a specific
geographic area, which will likely not occur until late Sunday or
later.

With this package, modified the regionally blended model
initialization to weight QPF (rainfall amounts) and temperatures
closer to the GFS guidance, although the Canadian initialized and
the high resolution guidance did very well with temperatures, as
well. This adjustment produced a drop of 1-2 degrees over
southeast Missouri, southern Illinois, and southwest Indiana,
where the mean rainfall axis is expected to set up based on this
forecast package. With the potential for a rain-cooled boundary
setting up in southwest flow aloft within a compressed baroclinic
zone gradient from northwest to southeast, we could see sharp
temperature deviations. North of the boundary, temperatures could
range from five below to twenty degrees above normal. South of the
boundary, temperatures could span from five to twenty-five degrees
above normal. More record or near record highs or lows could be
set next week again.

Given sharpness of the baroclinic zone, there may also be some
capping south of the impressed rainfall boundary (stretching from
southwest to northeast across the WFO PAH forecast area). This
could limit any strong to severe thunderstorm development.

The forecast signal for the secondary potential heavy rain system
remains within the 7-10 day time frame at this time. However,
given the potential for antecedent rainfall from the first system
on Tuesday, runoff for the second system will be increased. This
time of year is always tricky for flood potential, as temperatures
and antecedent (past) perception have a significant impact on the
ability of water to percolate into the soil and sub-soil layers
versus running overland and/or into bodies of water immediately.

&&

.AVIATION...
Issued at 457 PM CST Fri Feb 16 2018

MVFR bases look like they will linger a few hours into the night,
and we`ll have to watch and make sure they don`t get stuck there,
but all indications are that they`ll scatter to VFR overnight.
Then, MVFR cigs develop again tmrw with rain chances dropping
vsbys thru the MVFR range. Conditions continue to deteriorate with
numerical guidance suggesting at least some periods of IFR cigs
until system passage, which will be toward the close, or after,
the effective 24 hour valid time range (tmrw evening).

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

Long term...Smith



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