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Area forecast discussion 
National Weather Service Lincoln Illinois
257 PM CDT Tuesday may 5 2015

Short term...(tonight)
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 18z tafs through 18z Wednesday afternoon)
issued at 1249 PM CDT Tuesday may 5 2015

Latest surface analysis continues to show nearly stationary
frontal boundary draped across north-central Illinois from just
north of kgbg to south of kpnt. Winds in the vicinity of the
boundary are light/variable at kpia...but are southwesterly at 10
to 15kt further south at the remaining terminals. High-res models
suggest the front will sink slightly southward later this
afternoon and evening...resulting in a wind shift to the east/NE at
both kpia and kbmi. Models differ on the exact timing...with the
hrrr showing the shift at about 22z. After that...the front will
remain in place along/just south of I-74 throughout the night.
Have continued with a light east/NE wind at kpia and kbmi
accordingly...with southerly winds at kspi and kdec. The front
will finally get a solid push northward by Wednesday
morning...allowing winds to become southerly at all taf sites.


Ilx watches/warnings/advisories...


Short term...Barnes
long term...Smith

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