Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
1150 PM CDT Tuesday may 5 2015
issued at 904 PM CDT Tuesday may 5 2015
Most of current forecast looks OK for now. Only change will be to
make some minor adjustments to the cloud cover in the grids. Could
be some isolated showers still but that should end in next hour or
two. Looks like fog/haze is beginning to develop sooner than
expected, so will adjusting this in the grids. Overall forecast
looks fine, but will be making some minor adjustments. Update to
forecast will be coming shortly.
issued at 250 PM CDT Tuesday may 5 2015
Nearly stationary frontal boundary that has been poised just north
of the kilx County Warning Area for much of the day is now beginning to make a
slight southward shift. 19z/2pm observation show winds switching to the
north at Lacon...right in line with the hrrr/rapid refresh. NAM
also shows the front sinking southward...but is a little too slow
based on current observation. Boundary will settle to near or just south of
I-74 by early this evening...then remain in place throughout the
night. Widely scattered showers and thunderstorms are developing
along the front and will continue into the early evening hours
before gradually dissipating after sunset as daytime instability
wanes. Will carry 20-30 probability of precipitation across the north accordingly. Once
showers fade away...a warm/dry night will be in store with overnight
lows in the upper 50s and lower 60s. Due to the scattered rainfall
this afternoon and evening and dewpoint pooling along the
boundary...think patchy fog will develop after midnight. Hrrr
visibility forecasts suggests the greatest potential for fog will
likely be along and north of a Galesburg to Bloomington line.
Long term...(wednesday through tuesday)
issued at 250 PM CDT Tuesday may 5 2015
Upper level ridging will build across the region Wednesday into
Wednesday night taking the frontal boundary and the associated
rain chances along it to our north. By tomorrow afternoon...most
models indicate 0-6km bulk shear values of around 10 kts in our
area thanks to the building ridge. 850 temperatures around +13c this
morning and forecast soundings not showing much in the way of
change from that tomorrow so we should see temperatures just
as warm as todays with most areas well into the 80s by afternoon.
The shortwave over the southwest U.S. Is expected to track mainly
north-northeast staying well west of US with the better lift and
deeper moisture not arriving in our area with that system until
Thursday west and over most of the area Thursday night. Models
trending further west with the upper forcing so am not real
confident on the eastward push to the precipitation...thinking our
western areas would be most prone to seeing scattered convection
later Thursday into Thursday night.
A much deeper upper level trough is then forecast to slowly migrate
east from the southern rockies into the plains late in the week
sending several shortwaves northeast around the periphery of the
longwave trough. This will bring about periods of showers and
thunderstorms into the weekend with the deep surface low and cold
front forecast to approach our area Monday afternoon or evening.
Still quite a bit of uncertainty with how quickly the actual upper
level trough will push out into the plains and as a
result...uncertainty with respect to the frontal timing. Best
threat for severe weather with this system looks to be Monday as
instability and shear will be Colorado-located in or close to our area
during the afternoon and early evening.
After the front shifts off to our east by Tuesday...we will finally
see an end to the daily threat for showers and storms in our area.
Temperatures averaging above normal into the weekend will trend back
to or slightly below normal once the front shifts to our east by
Tuesday of next week.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1150 PM CDT Tuesday may 5 2015
Frontal boundary sitting just south of I-74 across the area.
Dewpoints are pooling along this front and should continue this
way through the night. Near where rain occurred this evening, fog
has developed, with bmi being the lowest at this point. MVFR
conditions at pia with IFR at bmi. Awss at bmi is reporting a ceiling
at 2oo ft, but remarks says it is scattered sometimes, so will
have tempo broken in the taf at issuance time. Cmi could see some
fog since the front is south of the taf site. Temperature/dewpoint spread
at cmi is 6deg so will just have a tempo for lower visible in the
tafs. Spi and Dec should remain south of the front and pooling
moisture so expecting VFR conditions there overnight. Conditions
will improve tomorrow morning as the front moves north of I-74.
Pia/bmi/cmi winds will be northeasterly north of the front. Spi
and Dec will see southerly winds overnight. With the front lifting
north tomorrow, all sites will have southerly winds tomorrow.