Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 160831
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
331 AM CDT Tue Sep 16 2014
.SHORT TERM /Today through Thursday/...
Issued at 330 AM CDT Tue Sep 16 2014
Main concern today is the widespread post-frontal stratus and its
effect on temps. At 08z...the back edge of the stratus extended
from northern Missouri across the KSPI area of Illinois to far
northwest Indiana. The back edge of the stratus is making slow
southward progress around 10 to 15 knots...which brings the
clearing line to KMVN around 19z. This timing is considerably
slower than previously expected. As a result...temps will be
lowered slightly. The clearing trend will likely accelerate by
this afternoon as daytime heating increases mixing heights.
Even so...southeast zones may not clear out until late in the
Any lingering stratus/stratocu should dissipate or move south of
the area early this evening. The overnight hours should be mainly
clear...except for increasing mid clouds over southeast Missouri.
It looks like a pretty good setup for patchy ground fog late
tonight...especially near bodies of water. This is the start of
the climatological fall fog season. Will introduce mention of fog
in the forecast for late tonight. Lows will be very near the dew
points...around 50 degrees.
Main concern Wednesday into Wednesday night is the potential for
clouds/light rain in association with a northwest to southeast
oriented baroclinic zone. This feature is evident in the 00z gfs
900-800 mb frontogenesis fields. Most of the model guidance
indicates the bulk of the moisture and rain will stay west of the
Mississippi River. This includes the 00z ecmwf. The 00z nam and
gfs bring some qpf into western KY and southern IL on Wednesday.
At the very least...expect periods of broken to overcast clouds to
spread into west KY and southern IL during the day. Whatever rain
occurs will be very light...with qpf less than a tenth of an inch.
Pops will be no higher than slight chance east of the Mississippi
River...rising to chance in southeast Missouri. Southwest Indiana
and the Pennyrile region of Kentucky will remain dry. Once
again...clouds may keep temps a little lower than most
guidance...especially over se Missouri.
Thursday should be a mainly sunny day as 500 mb ridging builds in
the wake of the departing 500 mb trough. Strong surface high
pressure over the northeastern states will produce a seasonably
cool and dry easterly flow.
.LONG TERM /Thursday night through Monday/...
Issued at 330 AM CDT Tue Sep 16 2014
The 00Z GFS, ECMWF, and GEM are in good agreement synoptically
through the extended portion of the forecast, which leads to a
fairly high confidence forecast. Surface high pressure will be
loosening its grip on the region as ridging aloft builds over the
region Thursday night through Saturday. Meanwhile, a rather compact
storm system will form over the central Plains, and ultimately move
southeast through our region, along with a cold front, Saturday
night into Sunday. Surface high pressure and cyclonic northwest flow
aloft can be expected next Monday.
The remnants of Tropical Storm Odile get caught up in this
developing storm system in all 3 models, so there is likely to be
some enhanced mid and upper-level moisture available with it. The
problem is a lack of low-level moisture return and steep mid-level
lapse rates. Showalter Indices do become negative, so there will be
some meager elevated instability, but would be surprised to see
anything approach severe limits.
The low-level jet in the GFS cranks up to 50kts Saturday night,
which results in some very high 0-3km storm-relative helicity
values, but there is little chance of surface-based convection,
especially with the 06Z-18Z passage of the front and storm system.
The primary concern is likely to be locally heavy rainfall, with
precipitable water values around 1.9". The ECMWF is not quite as
strong with the upper-level storm system and hangs the front up over
west Kentucky and southwest Indiana into Sunday evening. This could
lead to some training which could lead to a greater heavy rainfall
potential. The GFS and GEM are more progressive and would pose
little heavy rainfall potential.
Will confine 40ish PoPs to the Saturday night to Sunday night
periods, with primarily a Sunday cold frontal passage. Temperatures
will trend warmer early on, maxing out a few degrees above normal on
Saturday, and then fall back below normal Sunday and Monday.
Issued at 1149 PM CDT Mon Sep 15 2014
The drier and faster solution proposed by the GFS numerical
guidance appears to be occuring at this time. With that in mind,
began the forecast period with IFR conditions along and immediately
behind the cold front. Rapidly improve conditions after 12z with
VFR conditions dominating the rest of the forecast.