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afdilx

Area forecast discussion
National Weather Service Lincoln Illinois
1147 PM CST Thu Feb 23 2017

Update...
issued at 851 PM CST Thu Feb 23 2017

Strong low pressure, currently centered over southeast Kansas,
will lift northeast into far west-central Illinois by sunrise
Friday. A warm front extending east-northeast from the low cuts
across southeast Illinois. The front should lift rapidly north
across the forecast area during the next few hours. Still looking
like precipitation along the advancing warm front will be pretty
minimal despite strong elevated warm air advection/isentropic ascent in its
vicinity. Precipitation chances may begin to climb in advance of
the cold front trailing from the surface low late tonight, but
expect most of the cold frontal forced precipitation to hold off
until midday Friday as diurnal heating increases. Already updated
forecast into midday Friday for latest trends, especially pops.
Otherwise, forecast is in pretty good shape.

&&

Short term...(this evening through friday)
issued at 247 PM CST Thu Feb 23 2017

This afternoon, looking at the observations across the region...the
front seems to be just north of I-70, with northeasterly winds
behind it...and warm air still to the south of the boundary. The
short wave riding up the front in this system is spreading
precip...mainly to the north and west of the Illinois River valley.
The surface low at the next storms center is invof the Oklahoma
Panhandle. This system will continue to move to the northeast,
deepening and sending todays front back to the north as a warm
front as the warmer airmass in the southeast pushes back with more
significant warm advection...keeping much of central Illinois in the
warm sector overnight. This warmer and minimally higher relative humidity air
will be the instability that will potentially fuel the storms that
may develop tomorrow afternoon after the low passes to the north,
dragging the cold front across eastern Illinois. The slight risk
for eastern Illinois for tomorrow has lost a little bit of area
with the latest model runs. Seems the surface convergence has
become weaker and the boundary less distinct...but the divergent
exit region of the jet will assist with the vertical lift of the
airmass. 1000 j/kg of MUCAPE available by mid morning and
intensifying as the front shifts eastward out ahead of the system.
Storms look to be initiating over central Illinois tomorrow...and
becoming more organized as they slip to the east. Damaging winds
are the biggest threat with these storms, with 0-3km and 0-6km
bulk shear 35 to 40kts or 60-70 kts respectively.

Long term...(friday night through thursday)
issued at 247 PM CST Thu Feb 23 2017

The low pressure area of the ongoing weather system should be in the
Great Lakes region Friday evening. There remains a possibility that
convection could still be ongoing in the eastern part of the County Warning Area
during the first few hours of the evening. So, will keep likely pops
in the southeast and the chance for thunder east of I-57 til about 9
PM. Beyond that, showers will continue in the east the later part of
the evening in the east. In the northwest, colder air will begin to
wrap around the system and into the northern part of the state. This
will bring rain chances during the evening, but then changing to
snow as colder air advects into the region. This change over to snow
in northern part of the County Warning Area will continue into the overnight hours
and then in extreme northeastern parts of the County Warning Area...northeast of pia
and bmi...Saturday morning. This system should push well east and
northeast of the County Warning Area Sat morning so that Sat afternoon will be dry.
All models are in good agreement with the movement, location and
timing of this system and expected weather through the weekend.
Cooler high pressure will then bring dry weather to the region Sat
afternoon through Sunday morning.

Beyond Sunday morning, the models have major differences. The GFS
has precip for Sunday afternoon through Monday while the Canadian
and European model (ecmwf) are dry. Then the European model (ecmwf) and Canadian have precip for
Monday night through Tuesday while the GFS is dry. Even beyond
Tuesday, the models do not agree with timing and location of the
next chances of precip. Though do not like pops in some many
continuous periods of the forecast, will go with a model blend
forecast for most of the extended and have some form of pops for
Sunday afternoon through Wednesday. Hopefully in the next couple of
days the models will come to some agreement.

Cooler temps are in store for the first part of the weekend and with
overnight lows falling to below freezing Fri night, Sat night and
Sun night, any trees or plants that have begun to Bud may get bit by
the freezing temps, especially Sat night. Remainder of the extended
forecast, temps will warm back up to above normal levels.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1144 PM CST Thu Feb 23 2017

VFR conditions, with spotty thunderstorm, are expected for much of
the remainder of the night across the central Illinois terminals.
Ceilings should lower into the MVFR category late tonight or early
Friday as a strong cold front pushes into the area. This front
will be accompanied by scattered showers and storms, but these
will be the most numerous over the eastern portion of the state.
Winds will be gusty for much of the period once a warm front
pushes north of the area over the next few hours.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

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