Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
1153 PM CST Sat Nov 22 2014
issued at 900 PM CST Sat Nov 22 2014
A band of steady rains southeast of I-55 will advance to the
northeast over the next few hours. The latest model runs indicate
that after midnight, coverage of rain should diminish for much of
the time up until late morning tomorrow. We will try to adjust
pops to account for the lull in measurable precip later tonight
and Sunday morning. Drizzle could develop after midnight as the
low level clouds drop below 1k ft, especially for areas northwest of
I-55. Areas of fog could affect northwest areas later tonight as well,
although dense fog is not expected.
The push of heaviest precip looks to be Sunday afternoon, when the
bulk of our rainfall amounts could occur, with 0.5" to 1" possible
in that time. Any change over to snow would hold off until late
Sunday night, but no accumulation is expected by Monday morning.
Winds tonight will remain steady in the 10-15 mph range, with a
few locations seeing gusts still over 20 mph at times.
Lows tonight should remain relatively steady the remainder of the
night, with additional temp falls of only 3-5 degrees in most
areas under a blanket of clouds and periodic showers/drizzle.
The update the evening was mainly for weather grids, with a minor
bump up with lows in a few spots.
issued at 252 PM CST Sat Nov 22 2014
Weakening 1031 mb high pressure drifting off eastern NC shore while
strong and deepening 985 mb low moving east into SW Saskatchewan.
This was giving a tight pressure gradient over central and southeast Illinois
this afternoon with very breezy SSW winds 12 to 22 mph and gusts of
25 to 30 mph. South-southwest winds advecting in much milder and more moist air
from western Gulf of Mexico with temperatures in the mid 50s to lower 60s
(warmest SW areas with Mount Carmel Airport at 64f) and dewpoints in
the middle to upper 40s. Cloudy skies across much of central Illinois with
some breaks in clouds se of I-70 in southeast Illinois. Isolated light
rain showers over eastern Illinois this afternoon while showers more
numerous over SW Illinois from I-64 south into southern MO along and se of
I-44 where a few thunderstorm were a few hours ago. Mid level
moisture spreads northward tonight across areas se of the Illinois River
and this to increase chances of light rain showers though rainfall
amounts will be light due to weak lift/forcing. Also have patchy
drizzle with lower clouds over Illinois River valley tonight and areas of
fog overnight (currently getting fog over parts of NW Illinois and se ia).
Went a few degrees above similar met/mav guidance for lows tonight
in the mid to upper 40s due to cloud cover and southerly winds of
10-15 mph and gusts to 20 mph especially this evening.
Long term...(sunday through saturday)
issued at 252 PM CST Sat Nov 22 2014
The vigorous short wave, lifting out of the Southern Plains will
phase with a northern stream system tomorrow; the related surface
system will strengthen over the County Warning Area and lift northeast east tomorrow
night through Monday. The associated cold front with this system
will move through the area Monday night and bring the return to
colder air in the region for the beginning of the coming week. This
system is the main challenge with this forecast package this
afternoon. The resulting weather with this system will be for mostly
rain across the whole area tomorrow with the possibility of isolated
thunderstorms in southeastern IL, along and south of I-70, for
tomorrow afternoon through tomorrow evening. The dynamics of this
system do not look very strong, so severe storms are not expected in
southeast Illinois tomorrow afternoon or evening. Areas across the
north will see the areas of fog continuing through tomorrow and
tomorrow night. The fog will dissipate in the north once the low
pressure area moves northeast and the cold front moves through the
area, tomorrow night. The colder air that moves in Sunday night and
Monday, as the system deepens and moves northeast, will bring a
change to the p-type, resulting in rain mixing with snow in the west
Sunday night, and then becoming all snow by Monday. Snowfall
accumulations will be a half inch or less; since the pcpn will be
ending as the system moves northeast.
Temps will remain warm tomorrow but then fall from tomorrow night
through Monday night. Temps on Monday will be steady or slowly
falling in the afternoon, with the 24hr highs likely being around
midnight tomorrow night, and lows late Monday evening.
The remainder of the forecast period, through Saturday, will be
relatively dry. However, the models are bringing in a weak clipper
system Wed through thur, that will bring a chance of snow to the
northern third of the County Warning Area. Models are fairly consistent with the
location of the track of the low pressure area, but differ on
timing. So will still with a blend of the two models and keep the
chance of snow Wed and Wed night, as with previous forecast; and
then have a chance in the northeast parts for thur to accommodate
the slower timing of the European model (ecmwf).
Temps will warm some on Wed, ahead of the clipper system, but then
turn cold again after the system moves through and colder air
advects into the region again.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1153 PM CST Sat Nov 22 2014
A short period of IFR ceilings will affect pia and bmi at the
start of this taf period, but a return to MVFR ceilings is
expected for a couple hours after that. Some area could climb to
VFR based on upstream cloud reports. Spotty showers or sprinkles
will be the main precip the rest of tonight and into Sunday
morning. A strong SW low level jet will continue tonight, providing low level wind shear
conditions for much of the night and into Sunday morning.
As the main wave of rain overspreads the area later Sunday
morning with moderate rains Sunday afternoon, visibility will dip
to MVFR at all taf sites, and possibly as low as IFR for Dec and
cmi Sunday afternoon during any moderate rains. Kept the more
pessimistic IFR ceilings at all terminals Sunday afternoon, when
categorical rain chances are forecast for all taf sites. Winds
will remain somewhat gusty the rest of tonight. South-southwest winds 12-16
kts with gusts 18-24 kts may continue for a few hours for spi and
bmi. The other terminals seem to have diminished enough to keep
gusts at Bay. Gusts will return to all taf sites on Sunday as the
low pressure approaches, then moves across northwest Illinois. Wind directions
will become complicated near the low Sunday evening. For now we
show a backing from S to se, but directions could become NE for a
time ahead of the low Sunday late afternoon/early eve.