Dense Fog in Missouri, November 3, 2015

AREA FORECAST DISCUSSION
National Weather Service Paducah KY
502 PM CST TUE NOV 3 2015

.UPDATE...
Issued at 447 PM CST TUE NOV 3 2015

Updated Aviation discussion for 00Z TAF Issuance.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 313 PM CST TUE NOV 3 2015

Main concerns for the short term portion of this forecast package
are cloud/fog development tonight, and then storm chances Thursday
night.

The low clouds have been gradually eroding this afternoon, but am
not sure if they will completely clear Perry county Missouri and
Illinois. The remainder of the area should clear out shortly. For
tonight, most guidance indicates that MVFR ceilings will spread
northwest over the region through the night. This should prevent
fog from developing over the southern third to half of the area.
Farther north, fog may develop before the clouds arrive, so there
may be a period of fog before daybreak. Also will have to watch
for fog development expanding from the cloud deck left behind from
this afternoon. Will not issue a dense fog advisory at this time
given the complicating issues.

A storm system will be weakening as ejects northeast from the
southwest states Thursday into Thursday night. The flow aloft will
be strengthening, as will the flow over the entire column. We
already have decent surface moisture, and consensus guidance takes
surface dewpoints into the low to mid 60s ahead of the system and
its cold front Thursday. Precipitable water values will be an inch
and a half or more ahead of the front. The NAM hints at more
discrete convection, but with the forcing, cold front and
nocturnal timing, figure that it will be linear. The low and deep
layer shear will be significant, and could support severe storms
with damaging winds and even tornadoes, regardless of the
convective mode. Typically, this time of year we are struggling
for moisture and instability, but moisture should not be a
problem, so it is just a matter of lapse rates. This definitely
bears watching closely.

Some guidance is indicating the potential for drizzle late tonight
and Wednesday morning. With the fog/low cloud debate above will
not mention drizzle at this time. It does not look like we will be
clearing much of the area Wednesday. Much of the area may not see
much sunshine until the front has passed. Decided to stay on the
mild side of guidance for lows, and the cool side for highs
through the period.

.LONG TERM...(Friday through Tuesday)
Issued at 313 PM CST TUE NOV 3 2015

Medium to high confidence in the extended through the weekend...
medium confidence into next week.

Models are in fair agreement on system exiting the area Friday
morning. There is some timing differences among the models and with
successive runs of the individual deterministic models. However the
timing difference is mostly less than six hours for the latest
runs...which leads to higher than average confidence in the
solutions. Friday morning convective parameters for thunder will be
limited to the far eastern counties at the most. The slowest
solutions still have the rain out of here after 15z Friday.
Depending on the extended init and collaboration will try and follow
that scenario. Any severe threat should be out of the area after 12z
Friday but will monitor closely for any lingering threat after that
time frame. For the weekend expect cooler and dry conditions under
the influence of high pressure. By late Monday the models are
hinting at a weak short wave generating some precipitation over the
area. Convective parameters indicate no surface based convection. In
contrast there will be some elevated instability with K index values
in the mid 30s. Finally the next big system will move into the area
Wednesday or Thursday depending on which solution you choose between
the GFS and the slower ECMWF.

&&

.AVIATION...
Issued at 447 PM CST TUE NOV 3 2015

Models are attempting to develop some very minor precipitation
late tonight-early tmrw, most likely in the form of drizzle.
Could see MVFR conditions developing around 06Z with a gradual
lowering to IFR levels late. The best window for drizzle appears
to be near 12Z and well into/thru the morning, so conditions will
be slow to improve through the course of the day, esp east.

&&

.PAH Watches/Warnings/Advisories...
IL...NONE.
MO...NONE.
IN...NONE.
KY...NONE.

&&

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