Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 011809
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
1209 PM CST Sun Dec 1 2013
ISSUED AT 1207 PM CST SUN DEC 1 2013
This update combines the near term forecast update (i.e., today
through tonight) and 18z Sunday TAF discussion (see separate
As suggested by the Saturday morning Canadian (GEM) numerical
model guidance, the cloud layer was thin enough to mix out along
and behind the shallow and weak cold frontal zone. Based on winds
alone, the boundary was near a Perryville to Olney Illinois line
Diurnal mixing due to insolation along the top of the thin cloud
layer and weak warm air advection below the cloud layer should
move the clearing line along or just south of a line from Poplar
Bluff Missouri, Paducah, and Owensboro Kentucky this afternoon.
As daytime heating occurs this afternoon, a few locations over
Southern Illinois, Southeast Missouri, and Southwest Indiana may
see some scattered cumulus cloud redevelopment.
Clouds will return tonight across the most, if not all of the WFO
PAH County Warning Area. Given the mixing today, the residual
boundary layer moisture and effective pooling of this moisture
will occur about 25 to 30 miles further southeast than forecast
on Saturday for tonight. Will not rule out the need for a dense
fog advisory, but the maximum areal coverage over the Quad State
region will likely be limited to a 3 am to 8 am CST time period.
In addition, any subtle rain or drizzle probabilities should
remain south of the Ohio River ahead of the stalled frontal
boundary tonight and completely dissipate before noon on Monday.
Given the sunshine, made a slight upward adjustment in
temperatures, roughly 1 to 2 degrees for this afternoon.
.SHORT TERM...(Today through Tuesday)
ISSUED AT 312 AM CST Sun DEC 1 2013
Current surface analysis shows a weak frontal boundary to our
northwest. Low level moisture has been on the increase ahead of this
feature and low level clouds have developed. This front will sag
southeast into the area today...and end up stalling out over the
region. Low pressure develops on the front in southeastern OK by 06Z
Monday...which moves east and tends to dissipate as it does so.
Meanwhile, the front over our region tends to lose its identity by
Monday afternoon and starts to move north as a warm front.
With the amount of low level moisture and the weak front in the
vicinity today through Monday afternoon, expect mainly mostly cloudy
skies. Still toying around with the idea of some drizzle tonight
into Monday morning and the possibility of fog. SREF ceiling
height/vsby ensemble probabilities support this idea mainly late
tonight. Some of the higher resolution models are also indicating
the possibility of very light precipitation later tonight into
Monday morning...in association with a weak short wave aloft.
Temperatures will be tricky today as was expected a few days
ago...given the lack of confidence on the extent of cloud cover. The
06Z RAP/NAM indicate pretty heavy cloud cover. We will generally
stay in the lower to mid 50s...unless we are able to obtain more
sunshine. Mondays high should be in the same ballpark as today`s -
in the 50s, although the models are showing winds becoming south
across the entire area and warmer air advecting in, as the front
begins moving north. In fact, the 00Z MET guidance is showing low
60s across the southern zones. Will stay in the 50s for now...but
will definitely be higher than today`s highs.
Things should stay dry for Monday night and Tuesday as we await the
arrival of our next system, which models have definitely sped up
with recent runs. The GFS wants to produce precipitation over the
area as early as Tuesday another front is knocking our western
doorstep. The NAM and Euro has also sped up but not as fast as the
GFS so will maintain a dry forecast for Mon night - Tuesday.
However, we will raise temps for Tuesday into the 60s given this
.LONG TERM...(Tuesday night through Saturday)
ISSUED AT 357 AM CST SUN DEC 1 2013
Trying to blend and account for model differences will continue to
make this a challenging long term forecast. The GFS has gone out on
its own and sped up FROPA in response to a fast ejecting H5 low
from the nrn Plains into the Great Lakes region Tue night into
early Wed. Some of the other models account for this feature, but
keep it farther west and not as strong. Therefore, while faster
with FROPA vs. prior runs, they are still not as fast as the GFS.
Will speed up frontal passage to Wednesday evening (which is a
blend of the 00z ECMWF/UKMET/GEM/DGEX), but discount the much
faster ops GFS. Much different timing overall given yesterday`s
models, even the GFS, had the front into the middle part of our
CWFA 15-18z Thursday.
Will keep with small chances of light showers Tuesday night
through Wednesday. Slightly higher chance PoPs in for Wednesday
night (per the GEM/ECMWF), and elevated thunder chance as that
signal remains in the model data. Ahead of the front, we believe
guidance and blend data continues to lag behind what will be
reality, which is a surge in sfc dew points, and mild air upon
gusty SSE/S winds. We have adjusted the numbers up accordingly.
Thursday through Friday evening will have to be monitored closely
over the next couple of days. This broad, longwave trof that
evolves over the nation`s mid section, placing us in southwest mid
level flow, overtop of a strong southward sinking arctic high
could set the stage for a wintry precip mess, especially Thursday
night into Friday, as the ECMWF/GEM and GFS all show more than one
round of precip through the duration moving from SW to NE across
our area. The raw model temperature output is essentially colder
than MOS guidance, and that is concerning, given MOS limitations.
At the time of this writing, we have multiple precip types in place
for Thursday night through Friday evening, especially over the NW
2/3 of the CWFA including SW Indiana, SRN Illinois, SE Missouri and
a part of WRN Kentucky. There will be plenty of time monitor the
models trends, and fine tune the forecast accordingly. Winter
weather impacts are possible Thursday night into Friday/Friday
ISSUED AT 1207 pm CST SUN DEC 1 2013
Given the effective mixing of the shallow moisture layer in the
vicinity of the cold front, moved all WFO PAH TAF`s back into VFR
ceiling category. Between 04z-06z Monday, MVFR to local IFR
visibilities and MVFR to VFR ceilings were returned to each of the
WFO PAH TAF sites, depending on their proximity to the decaying
cold frontal boundary. By 16z Monday, all of the TAF sites should
be back in VFR category.