Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 240825
Area Forecast Discussion
National Weather Service Paducah KY
325 AM CDT SUN APR 24 2016
.SHORT TERM...(Today through Tuesday)
Issued at 325 AM CDT Sun Apr 24 2016
Widespread dense fog has already developed over the eastern half
of southern Illinois and most of west Kentucky, and it is
beginning to develop over southwest Indiana. With no increase in
winds or clouds expected in these areas, see no reason why it will
not get even thicker through daybreak. We will be issuing a Dense
Fog Advisory for areas along and east of a line from Mt Vernon
Illinois to Hickman Kentucky through 9 AM. This is nearly the
exact area covered by the low clouds yesterday. Westward expansion
of dense fog is not likely due to some light southeasterly winds
that have been persistent over southeast Missouri and adjacent
areas of southern Illinois, but we will keep an eye on it for
possible expansion later this morning.
A storm system will move out of Wyoming and into the northern
Plains today, and then through the Upper Midwest tonight before
being squashed by confluent flow as it moves into the Great Lakes
on Monday. Over our region this will initially push the upper
ridge line east of the area today, and eventually result in
nearly zonal flow by Monday. At the surface, a cold front will end
up parallel to the flow aloft well to our north Monday into
South winds will develop today, and continue through the remainder
of the short term period. The strongest winds should occur on
Monday when some gusts may approach 30 mph. There will be plenty
of sunshine today, after the fog burns off, and Monday. We will
lean toward the warm side of guidance for highs today and Monday,
but will stay close to the consensus of guidance for lows tonight.
Monday night into Tuesday upper-level ridging will develop over
the region as a larger storm system pushes into the Rockies. This
will result in surface cyclogenesis over western Kansas and
will activate the old surface boundary as a warm front somewhere
across central or northern Missouri. Low-level moisture will be
increasing across our area through this period, and if it is
robust enough, there could be some elevated showers or
thunderstorms over much of the region mainly late Monday night
into Tuesday morning. Confidence in the intensity of this moist
advection is low, so will keep PoPs at slight chance levels over
the entire area, except the far southeast which will remain dry.
The 00Z GFS and ECMWF generate quite a bit of QPF near and north
of the surface boundary Tuesday afternoon. The GFS has it south of
the boundary over the northeast third of our area, while the ECMWF
keeps it north of the boundary and to the northeast of our area.
Really prefer the ECMWF, but will have chance PoPs over the
Evansville Tri State on Tuesday just to be safe.
Monday night will see increasing surface dewpoints and cloud
cover, as well as modestly strong south winds, so it will be mild.
Went above guidance for lows. High temperatures on Tuesday will be
dependent on the extent/persistence of cloud cover, and if/how
much convection develops. Hedged toward the drier solutions and
went near the warm side of guidance over most of the area.
.LONG TERM...(Tuesday Night through Saturday)
Issued at 325 AM CDT Sun Apr 24 2016
A progressive southwest flow pattern is expected through the long-
term period. The mean storm track will be oriented from the southern
Rockies to the Midwestern states. This will result in a rather warm
but stormy pattern for our region. The models have come into better
agreement on the timing and placement of synoptic features, both at
the surface and aloft.
As far as the daily details, an east-west frontal boundary will
become quasi-stationary over the Lower Ohio Valley and southern
Missouri Tuesday night into Wednesday. Showers and thunderstorms
will gradually increase in the vicinity of this front as a closed
500 mb low moves east to Nebraska. The influence of the upper low
will combine with moist southerly low-level flow to produce
widespread rainfall. Pops will be in the likely category for most
areas Wednesday. There is some potential for intense convection
Wednesday given moderately strong wind profiles and moderate
instability. The presence of widespread clouds and/or morning rain
could be a limiting factor. Forecast high temps around 80 are based
on the model consensus.
Wednesday night will likely be wet as the weakening surface low and
cold front approach the Mississippi Valley. Limiting factors for
heavy rain and/or intense convection will be the weakening nature of
the storm system, as well as diminishing instability.
From Thursday into Friday, the models are in better agreement than
24 hours ago. Last night`s gfs was slower than the ecmwf, but the
latest 00z gfs has sped up to the quicker ecmwf timing. A weak cold
front will exit our region on Thursday. Dry westerly flow on the
south side of the Midwestern storm system will result in partial
clearing Thursday. Some low pops will be kept in the forecast,
mainly east of the Mississippi River. These pops will account for
any lingering showers or storms with the front. Highs should nudge
80 given increasing sunshine and deep westerly flow.
Friday still appears to be a mainly dry day as a 500 mb ridge
crosses our region ahead of the next system. Weak northerly flow and
some cloudiness should combine to keep high temps a little cooler,
mainly in the 70 to 75 degree range.
Another moist southern stream shortwave will approach the Plains
states Saturday. The chance of showers and storms will increase
Friday night and Saturday. Timing differences are large among the
models, but they all bring the system close enough to warrant chance
pops Friday night and Saturday. The 00z ecmwf is faster than the 00z
gfs/gefs and 12z ecmwf ensemble mean. Despite a return of southerly
flow, highs should be limited to the lower and mid 70s due to warm
Issued at 1203 AM CDT Sun Apr 24 2016
Quite a quandry with weak surface pressure gradient along and east
of the Mississippi River, along the western extension of the high
pressure ridge and a sharper gradient over Missouri as of 04z
Seeing alot of visibility observations dip into the MVFR to
IFR/LIFR category across Southern IL and adjoining parts of KY and
IN. With unrestricted ceilings and an implied ridge axis over the
same area, temperatures/dewpoint depressions have rapidly
diminished, generating dew and some fog. However,
horizontal/slant/vertical visibilities from sites, such as KPAH, are
not exactly matching visual observations of fog development.
With this in mind, am keeping visibilities in the MVFR category
through 12z, but have added a mention of MIFG to account for
transient pockets of lower visibilities. Model suggest some minor
lift for low cloud development around 12z, but not seeing much in
the way of moisture to be lifted near the boundary layer. The LAMP
and short range model consensus guidance appear to have a handle
on the current visibility reductions. The greatest visibility
reductions should remain in Southeast Illinois, and away from the
WFO PAH TAF sites during the first 6 hours. Otherwise, the VFR
forecast remains intact for the remainder of the forecast period.
IL...Dense Fog Advisory until 9 AM CDT this morning for ILZ075>078-
IN...Dense Fog Advisory until 9 AM CDT this morning for INZ081-082-
KY...Dense Fog Advisory until 9 AM CDT this morning for KYZ001>022.