Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 271758
Area Forecast Discussion
National Weather Service Lincoln IL
1258 PM CDT Sun Jul 27 2014
ISSUED 1045 AM CDT Sun Jul 27 2014
Forecast generally looks on track today and main adjustment is
low cloud cover lingering longer than earlier expected se of I-55.
Skies should still become partly to mostly sunny across central
and evenually eastern IL during the afternoon. Will continue
small chances of showers and thunderstorms over eastern IL mainly
east of I-57 this afternoon. SPC has slight risk of severe storms
from the IL/IN border east across IN/KY/OH with moderate risk over
in the foothills of the Appalachians in eastern KY and southern OH.
Cold front was pushing se into far southeast IL near the Wabash
River late this morning with WNW winds increasing behind the front
over central IL and gusting 15-25 mph over IL river valley. Still
muggy dewpoints in the low to mid 70s se of IL river and upper 60s
nw of IL river. Dewpoints drop off into the upper 50s and lower
60s upstream near the IA/IL border and should advect se into
central IL during the afternoon. Southeast IL will still be muggy
today where dewpoints currently in mid 70s but should slip into
the mid to upper 60s during the afternoon. Highs in the low to mid
80s look on track today with return of more sunshine with some
upper 80s near Lawrenceville.
ISSUED 1255 PM CDT Sun Jul 27 2014
One cold front has passed southeast of IL by early afternoon with
scattered strong to severe thunderstorms ahead of it over OH and
eastern KY. Meanwhile another frontal boundary delineated by
enhanced narrow band of cumulus clouds extended from the south side
of Chicago through BMI airport to Jacksonville. Tropical/muggy
dewpoints in lower to middle 70s se of this boundary, while dewpoints
fall through the 60s and even some upper 50s over IL river valley.
Isolated convection recently developed along and just ahead of
this boundary southeast of BMI. Will carry VCSH at southeast airports
of DEC and CMI next few hours until this boundary passes se of
them during mid afternoon. Have scattered cumulus clouds 2.5-5k ft
this afternoon and broken at times from I-55 se next few hours
with high end MVFR ceilings possible. Broken cumulus cloud field
over WI/MN and central/ne IA could skirt northern taf sites of PIA
and BMI later this afternoon and early evening. Breezy WNW winds
12-17 kts with gusts 18-25 kts this afternoon and early evening to
diminish to 7-10 kts after sunset. Drier air advecting into
central IL should limit fog development overnight to patchy
shallow ground fog near rivers/streams especially in southeast IL,
so kept out of TAFS. Expect NNW winds 9-14 kts by 15Z/10 am Monday
with few gusts near 20 kts by midday Monday as scattered cumulus
clouds around 4k ft redevelop.
ISSUED 245 AM CDT Sun Jul 27 2014
Surface map a mess in the wake of yesterday evenings convection.
Broad surface trof/frontal boundary hung up over the region with light
and variable winds. Some patchy fog out there, with only a couple
sites dropping to a mile visibility this morning. Some convection
blowing up over the area turning over some of the air and helping
to block much more of a vis drop in that area...and potentially
limiting the temp drop predawn. Even high res short term models
not handling the current conditions well, much less the next 12
hours. Many mesoscale dynamics out there not being represented.
Front still not yet through the region...and first issue with the
forecast will be hanging on to pops, particularly in the east with
the frontal passage later mid day and this afternoon.
SHORT TERM...Today through Monday night...
Keeping chances in for scattered showers and thunderstorms until
the front can progress through the area. Though today is expected
to get warm in front of the boundary...tomorrow is expected to see
significantly cooler temps with some relatively drier air
filtering in. Precipitation chances drop out of the forecast for
tonight and tomorrow. But it bears mentioning that todays pops
will be complicated by small perturbations that are not being
resolved well in the models. HRRR is closest with some
approximation of the line of showers and thunderstorms across
central ILX...and some reflection of the wave interacting with the
stalled boundary out in KS. NAM also trying to key in on
it...though it dissolves rather quickly in the HRRR, and the NAM
sends it further eastward, diving sw of ILX and interacting with
the boundary later tonight well out of ILX. More eastward
progression with that disturbance may well change the outcome of
the mid day and afternoon thunderstorm chances.
LONG TERM...Tuesday through Saturday...
Cooler air immediately behind the front begins to slowly warm back
up on Tuesday by a few degrees a day. Northwesterly flow dominates
and a deep low digging in a trof over the eastern half of the
CONUS. From mid week on, chances begin to increase with afternoon
instability showers under the deepening cyclonic flow aloft, with
a more stormy afternoon summer pattern. But will be very scattered
and low in coverage. Timing with the next wave diving into the
trof aloft bringing better chances...is lacking continuity in
models. End of the week have better chances for some rainfall...
but certainty and coverage will keep the chances low and diffuse.