Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291753

Area Forecast Discussion
National Weather Service Lincoln IL
1253 PM CDT MON AUG 29 2016

Issued at 952 AM CDT Mon Aug 29 2016

14z/9am surface analysis shows 1018mb low over eastern South
Dakota, with stationary frontal boundary extending E/SE from the
low into northern Illinois. Based on observed dewpoint gradient,
it appears that particular boundary is roughly along the I-80
corridor. Meanwhile further south, an outflow boundary from
thunderstorms last evening is present...although its difficult to
locate. Most likely location for this boundary is from roughly
KUIN to near KRSV. Latest radar imagery shows mostly dry
conditions across the KILX CWA this morning, although a few
showers have developed over Vermilion County. As was the case
yesterday, am expecting scattered thunderstorms to develop along
the synoptic front and perhaps also along the old outflow
boundary later today. 13z HRRR focuses much of the afternoon
convection near the stationary front...mainly along/north of
I-74..but it also shows numerous storms firing over Missouri into
west-central Illinois. Given current satellite imagery showing
clear skies across Missouri, am not sold on the western CWA
storms. Will continue to feature chance PoPs across the northern
two-thirds of the CWA, with just slights along/south of I-70. Any
storm that develops will be slow-moving and capable of torrential
rainfall. High temperatures will mainly be in the middle to upper
80s, with lower 90s across the SE.


.SHORT TERM...(Today and tonight)
ISSUED AT 334 AM CDT Mon Aug 29 2016

Today will be another day with a warm and humid air over the area,
along with a weak boundary somewhere in or near the CWA. This means
that scattered showers and thunderstorms will still be possible
today through early this evening. With mid level ridge over the
area, steering flow will be quite weak and this means storms and
associated outflow boundaries will move in odd directions. Due to
the lack of a strong surface features for storms to develop on, will
just have chance pops for the whole area. Like last night, storms
should diminish after sunset again this evening. Light fog could be
an issue tonight, but could be some issues with cloud cover, that
could keep fog in check, so will not be including in forecast at
this time.

Afternoon highs will be slightly cooler than yesterday, being in the
middle 80s in the north to around 90 in the southeast. Overnight
lows will be in the upper 60s to around 70.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 334 AM CDT Mon Aug 29 2016

A strong 594 dm 500 mb subtropical high pressure ridge from the mid
Atlantic states and ridging westward across the Ohio and mid MS
river valleys today and Tuesday will give way to a fairly strong
upper level trof digging southward over the Great Lakes and Ohio
river valley Wed/Thu. Forecast models have been consistent with this
and forecast confidence is good for this pattern change during 2nd
half of week. At the surface, 1026 mb high pressure over lower MI
and into Ontario will be replaced by a stronger/larger Canadian high
pressure moving slowly southeast into the Great Lakes region late
this week. A moist air mass with 1.5-2 inches of precipitable water
will be in place over central/southeast IL until a cold front pushes
SSE through the area on Wednesday and brings drier air Wed night and
Thu. Expect more chances of showers and thunderstorms through Wed,
with locally heavy rains possible from slow moving thunderstorms
within the tropical airmass. SPC has a marginal risk of severe
storms nw of the IL river late Tue afternoon into Tue evening for
gusty winds and possible hail as well. Highs Tue will range from the
mid to upper 80s, with Southeast IL near 90F. Heat indices Tue
afternoon will be back in the 90s with dewpoints in the lower to
middle 70s. Muggy lows Tuesday night in the upper 60s to around
70F with patchy fog overnight, though more cloud cover expected
especially nw of I-70 to limit coverage of fog. Highs Wed range
from around 80F from I-74 north to mid 80s south of I-70. Still
humid Wed with dewpoints in the upper 60s and lower 70s, highest
in southern CWA.

Drier, cool and more pleasant conditions expected Thu-Sat due to
Canadian high pressure over the Great Lakes pushing drier dewpoints
in the mid 50s to lower 60s into central IL. Also having upper level
ridge pushing back east over IL by Sat morning ensuring dry weather.
Highs Thu and Fri in the upper 70s, except around 80F in southeast
IL on Thu. Highs Sat around 80F. Lows Thu night and Fri night in the
mid to upper 50s, and lower 60s for lows Sat night. Most of our area
remains dry on Sunday with just slight chance of showers and
thunderstorms by Galesburg as disturbances ejecting northeast from
the central plains into the western Great Lakes. Have 20-40% chance
of showers and thunderstorms over the IL river valley from I-55 nw
on Sunday night and Monday as these disturbances get closer to
central IL, while strong upper level ridge keeps southeast IL dry.
Temps and humidity levels will gradually rise Sun/Mon as surface
high pressure pushes east and get into an increasing southerly flow.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1253 PM CDT Mon Aug 29 2016

Robust Cu field with high MVFR/low VFR bases has developed
along/west of I-55 early this afternoon. Based on persistence
forecast from the past couple of days, will include a period of
MVFR ceilings at KBMI through 20z before ceilings rise to between
3500 and 4000ft. Elsewhere around central Illinois, will introduce
VFR ceilings and VCTS over the next couple of hours. HRRR seems to
have a good handle on the current situation, suggesting scattered
convection will mainly be confined to the western half of the CWA
this afternoon/early evening. Will hold off on any TEMPO thunder
groups until convective trends at specific terminals become better
defined. Once diurnal storms dissipate by 01/02z, mostly clear
conditions will be noted tonight, with patchy fog forming toward
dawn Tuesday. Have lowered visbys to between 4 and 5 miles after
09z accordingly.


.ILX Watches/Warnings/Advisories...


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