Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kpah 210934 
afdpah

Area forecast discussion
National Weather Service Paducah Kentucky
334 am CST Thu Nov 21 2019

Short term...(today through Saturday night)
issued at 334 am CST Thu Nov 21 2019

The cold front is just moving into northwest Missouri and should
reach our region around sunset. In the meantime, an upper-level
disturbance will move eastward through Iowa and to Lake Michigan
by the end of the day. A larger-scale upper trough will then push
southeast tonight which will push the cold front through our
entire region by 12z Friday.

Immediately behind the cold front tonight, significant low-level
frontogenetical forcing will develop. This forcing will sag south
of the area by midday Friday, and then we will await the arrival
of a closed upper low Friday night and Saturday. The 00z models
have trended slower with the low, and thus the associated forcing
and precipitation may linger through Saturday in our far eastern
and northeastern counties.

Scattered light showers are already streaming along our northwest
border early this morning. The showers will become more widespread
over southeast Missouri and southern Illinois through daybreak and
then will attempt to push through southwest Indiana and into west
Kentucky by midday. The showers will tend to dissipate as they get
past the Ohio River early this afternoon, resulting in a dry
afternoon for most of the region. The 00z NAM does develop some
slightly negative showalter indices indicative of some elevated
instability, so have added a slight chance of thunder to southeast
Missouri and southern Illinois this morning. Quantitative precipitation forecast should still only
be a tenth or two.

The 00z models have trended a bit wetter with the Post-frontal
frontogenetical rains tonight into Friday morning. This round of
moderate to heavy rainfall may total an inch and a half across the
southern third to half of the area. However, the northern edge of
the persistent rains should be somewhere near I-64, so there will
likely be a pretty sharp gradient somewhere near our northern
border.

Most of the area should dry out by midday Friday, leaving the
afternoon and much of the evening dry across the region. The
isentropic lift associated with the approaching upper low will
eventually spread rain back northward across the region overnight
into Saturday morning. As stated above the models have slowed the
progress of the low a bit, so there is some potential for the
rains to linger well into the afternoon in the northeast and east
portions of the area. With low temperatures Saturday morning
expected to be 35 or greater throughout the area, we have no
mention of wintry precipitation at this time. Quantitative precipitation forecast with this event
should average around a tenth of an inch.

As for temperatures we will have one more day of highs near 60,
and then fall back into the 40s for Friday and Saturday. Lows will
trend lower through the period and will finally end up a few
degrees below freezing Saturday night.

Long term...(sunday through wednesday)
issued at 334 am CST Thu Nov 21 2019

The primary forecast concern in the long term is the chance of rain
from late Monday night Onward, with a focus on Tuesday. Forecast
confidence starts off higher than average Sunday and Monday with
decent model agreement, but decreases to below average thereafter as
substantial model differences persist.

An active weather pattern is forecast to continue into next week as
a series of shortwave disturbances traverse the fast quasi-zonal
flow pattern aloft, which starts off as west-northwesterly early in
the week and transitions to more southwesterly by mid week. This
will result in periodic chances of showers. The primary time frame
in focus runs from late Monday night into Tuesday night as energy
over the Pacific northwest early Monday develops into a shortwave
trough and pivots east into the upper Midwest by late Tuesday. This
will force the passage of a cold front on Tuesday, marking a peak in
rain potential.

Temperatures should be warm enough to support liquid precipitation
with this event. In addition, the potential for thunder appears to
be very low at this point. The 00z GFS does suggest a narrow sliver
of elevated instability immediately along and ahead of the front
Tuesday afternoon and evening, so slight thunder chances may need to
be added at some point if this signal persists in later model runs.

The next question is what to do with Wednesday and Thanksgiving day.
Both the deterministic 00z GFS and European model (ecmwf) build high pressure back
into the region on Wednesday, resulting in dry conditions for the
busiest travel day of the year. However, the 12z ECMWF, 00z CMC,
and about half the gefs ensemble members are not in agreement due to
pattern variations and timing. This keeps enough uncertainty in the
forecast to warrant the nbm slight chances Wednesday into Wednesday
night. Both the GFS and European model (ecmwf) suggest a renewed chance of rain on
Thanksgiving day with the approach of more shortwave energy in an
increasingly amplified southwest flow pattern. As a result, the
forecast contains some chance of rain from late Monday night on.
This will obviously be a target of opportunity to fine tune as model
agreement hopefully improves in the coming days.

As far as temperatures are concerned, a warming trend is expected
early in the week as highs moderate from near 50 on Sunday into the
upper 50s and near 60 degrees by Tuesday. Highs should be about 5
degrees lower on Wednesday behind the cold front. Lows are generally
forecast in the 30s, except for remaining in the 40s ahead of the
front Monday night.

&&

Aviation...
issued at 1148 PM CST Wed Nov 20 2019

Isolated rain showers will be possible before sunrise, but main area of
showers will move west to east during the morning/early afternoon
hours. Cigs will lower quickly, becoming MVFR in the west during
the morning and progressing east to encompass the entire area by
later afternoon. Low level wind shear is a concern this morning, mainly between
09-16z. On the back side of the shower activity, a period of
gusty southwesterly winds of 25-30 kts is expected. A lull in
precipitation is expected during the afternoon, before increasing
again from the southwest during the evening. Lower MVFR cigs,
with possibly some IFR conditions are expected with this second
batch, along with reduced vsbys into MVFR territory. Winds will
become northwest late in the period and just beyond as a cold
front moves through.



&&

Pah watches/warnings/advisories...
Illinois...none.
MO...none.
In...none.
Kentucky...none.
&&

$$

National Weather Service Glossary of Abbreviations