Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 211137 AAA
AFDPAH

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PADUCAH KY
537 AM CST Wed Jan 21 2015

.UPDATE...
Issued at 537 AM CST WED JAN 21 2015

Updated the aviation discussion for the 12Z TAF issuance.

&&

.SHORT TERM...(Today through Friday night)
Issued at 317 AM CST WED JAN 21 2015

Forecast confidence above average through Thursday, then below
average through Friday night.

Zonal flow aloft and high pressure at the surface should keep the
region dry through Thursday evening. Latest model runs have really
changed things around for late Thursday night, Friday, and Friday
evening and the changes seem to be legitimate.

Previous model runs were taking a storm system eastward out of the
southern plains during this period and keeping most of the clouds
and precipitation associated with it skimming by just to the south
and east of our CWA. Latest runs are bringing the system on more of
a northeasterly track thereby developing an overrunning
precipitation scenario over parts of our CWA starting late Thursday
night.

The leading edge of precipitation is expected to barely make it
into the far southeast sections of our CWA by 12Z Friday. Models
bring the deeper moisture and QPF quickly northward across the
southeast half of our CWA through the day Friday. With overnight
lows below freezing Thursday night and thermal profiles pointing
to snow, started precipitation out as snow late Thursday night.

Temperatures are expected to warm some Friday, but with the onset of
precipitation, temperatures should wet bulb down enough to keep
precipitation all snow. There may be a brief time Friday morning
where precipitation begins as rain or a rain/snow mix, but tried not
to get too fancy and wanted to keep the grids as simple as possible.

The GFS is clearly the warmest model for this event, but per model
soundings, 1000-850MB critical thicknesses, etc the predominant
precipitation type should be snow. Expect snow over the same general
areas Friday evening, but with the system quickly pushing eastward,
don`t expect anything after midnight.

Model QPF amounts are not that impressive for the event at this
time, but feel that snow accumulations are possible south and east
of the Ohio River with the best chances for snow accumulation over
the southern Pennyrile region of western Kentucky. With this event
being so far out and the likelihood of future model runs muddying
the waters a bit more, declined from entering snow amounts at this
time.

It wouldn`t surprise me if future model runs bring the precipitation
shield even farther north and west on Friday, and if so would
complicate precipitation type even more. We will need to watch this
system closely.

.LONG TERM...(Saturday through Tuesday)
Issued at 317 AM CST WED JAN 21 2015

By Saturday morning, the Friday/Friday night system will continue to
depart to the east. Northwest flow will commence on Saturday and the
next main system we are watching still looks on track to arrive
Sunday. Models are hinting at a weak wave/sfc front passing through
on Saturday, but right now, it just looks like some clouds. Will
continue to watch that. We could see precipitation creep into
northwest portions of the CWA late Saturday night with the next
system but the bulk of the precip should arrive during the day on
Sunday.

Models continue to be very mismatched when it comes to the track of
the upper low and sfc low system as well as timing, as it develops and
move southeast out of the north central Plains and upper Midwestern
states. The GFS seems to be the most consistent with the sfc low
path, looking back on the past 4 runs. It takes the sfc low
somewhere near St. Louis and then down into either far southern IL or
the EVV tri state region, with the 18Z run being the farthest
northeast with the low. The ECMWF has generally been more northeast
with the sfc low, which is actually closer to the last few runs of
the GFS ensemble mean. In fact, the latest ECMWF indicates that most
of the precipitation will be in our eastern sections only.

Hard to know what type of POP gradient to go with in these
circumstances with the models still not having a great handle on the
low track, but the eastern half of the area does have a better
chance at seeing precipitation given the recent model trends. An
uptick in POPs is definitely needed as it appears as though chances
for precipitation are increasing somewhat. Looking at soundings and
thickness plots, what does fall on Sunday, will be all liquid with
temperatures at the sfc in the 40s, possibly low 50s.

However, as temperatures drop behind the departing low, we will
likely transition to a rain/snow mix or changeover to all snow. Not
sure how much moisture will be left by the time that happens but at
the very least, we could have some flurries or snow showers. Another
lobe of energy drops down across the area for Monday, leading to
another chance for snow showers/flurries for areas mainly east of
the Mississippi River. Conditions for Tuesday/Tuesday night look dry
for now.

&&

.AVIATION...
Issued at 537 AM CST WED JAN 21 2015

MVFR vsbys in fog possible at KCGI/KPAH early. Toward the end of
the period KEVV/KOWB may see MVFR cigs with increasing low level
moisture and the approach of an upper level disturbance, otherwise
VFR conditions will prevail under high pressure. Southwest winds
AOB 5 knots early will veer to the west to northwest and increase
to around 10-12 knots, with gusts up to 18 knots possible at
KEVV/KOWB through 00Z, then out of the northwest AOB 5 knots
through the end of the period.

&&

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

$$

SHORT TERM/AVIATION...JP
LONG TERM/FIRE WX...CW






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