Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
223 PM CDT Tuesday Sep 1 2015
issued at 223 PM CDT Tuesday Sep 1 2015
Last of the morning thunderstorms east of I-57 has finally faded
away. Latest water vapor imagery shows the upper low near
Indianapolis has moved only slightly northeast...so some deeper
moisture remains in place across the eastern County Warning Area. Nice area of
subsidence shown on visible imagery expanding across northeast
Illinois and Northwest Indiana...associated with the outflow from
the morning convection...with some diurnal cumulus developing to the
west. Radar showed a couple cells trying to fire along the
boundary... but these faded off quickly.
Currently think that any residual showers that do form will fade
with sunset...so will maintain the dry forecast for tonight. Have
also kept mention of patchy fog along and east of I-57...as there is
now quite a bit of moisture from the earlier heavy rains and a weak
wind flow at the surface. Winds just off the deck prognosticated to 15-20
knot range...so any fog should be rather shallow. Temperatures
expected to be fairly uniform overnight...mainly 67-70 degrees over
the forecast area.
Long term...(wednesday through tuesday)
issued at 223 PM CDT Tuesday Sep 1 2015
High pressure ridge will build into the plains tomorrow and continue
the hot and humid conditions through the week and into the weekend.
With all models forecast 850 temperatures around +18 to +20c...am expecting
highs to be around 90s into the lower 90s through the rest of the
week and through the weekend...and likely into Monday...Labor Day.
Conditions through the period should be dry until late in the
weekend and early next week. However...there is one period where a
short wave trough is forecast to come over the top of the ridge Wednesday
and Wednesday night through the Great Lakes region into Indiana. This
could bring some quantitative precipitation forecast to the northeastern parts of the state...which
could effect northeastern and eastern parts of the County Warning Area. NAM
continues to have precipitation in the area but varies with the
amounts...while GFS brings some in but also seems to overdo the
amount of quantitative precipitation forecast. 12z European model (ecmwf) seems most consistent with keeping precipitation to
the north. For now will keep precipitation out of the County Warning Area Wednesday night and Thursday
and let overnight shift take a look after another model run.
The next chance of precipitation will then be late in the weekend and the
beginning of next week and a stronger middle level low pressure system
flattens the ridge out and trys to drag a cold front into the area.
Models differ on the surface solution through the period but GFS and
European model (ecmwf) does appear to be in better agreement with some quantitative precipitation forecast moving
into the area Monday. However...they do not agree with amounts as
the GFS weakens the system as it moves into the area. Given that the
precipitation will be moving into a strong ridge...am inclined to limit quantitative precipitation forecast
and have gone with slight chance for Monday through Monday night. This
boundary does look to sag south enough that Monday night and Tuesday it
looks to develop more precipitation that moves into the area for Tuesday.
Temperatures will finally cool as well with most of the County Warning Area being north of
the boundary and effected by clouds and precipitation. Highs Tuesday look to
have cooled down into the lower to middle 80s...with upper 80s close
to the front.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1223 PM CDT Tuesday Sep 1 2015
Little change needed from previous taf set. Convection that
affected kcmi earlier has largely faded...but will maintain some
thunderstorms in the vicinity mention for a few more hours there as there is still some
activity nearby. Well defined outflow boundary from the earlier
storms is extending northwest and recently passed through
kbmi. Hrrr model has recently been hinting at this as a focus for
additional convection over the next couple hours...so will monitor
this closely although confidence is low enough to preclude any
mention at this time.