Area Forecast Discussion
Issued by NWS Central Illinois

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755
FXUS63 KILX 191552
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1052 AM CDT TUE JUL 19 2016

.UPDATE...
Issued at 1052 AM CDT Tue Jul 19 2016

Synoptic front extended from south central Iowa toward Quincy to
Effingham at 1000 am. Area of convection in central Iowa will
continue to progress eastward along an instability gradient into
NW and west central IL by late this afternoon. Adjusted PoPs west
of the IL River to account for this.

The rest of the forecast area will have the higher clouds from the
convection to the west, but for the most part they should be thin
enough to allow for ample sunshine/heating into the upper 80s.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 338 AM CDT Tue Jul 19 2016

Hot and muggy airmass still in place with a weak boundary draped
across the region this morning will drive the forecast through today
and tonight. Some models, incl NAM12 are dry through the next 24
hours, but HRRR and GFS are hinting at more afternoon showers and
thunderstorms.  Considering the MCS currently out over the Plains
may provide the catalyst, not willing to leave the forecast
completely dry this afternoon.  The boundary location will be the
wild card, as it is caught up in very light flow but will help
provide the focus for showers and thunderstorms. Keeping the chances
low overall, and confined to the west, but will have to monitor for
how far to the east that activity can get through the morning.  As
for the shorter term, light winds and a muggy airmass  is resulting
in some patchy fog across the FA.  Not enough widespread obs to drop
to a dense fog advisory, for now.  But will leave the mention
through the first few hours of the morning.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 338 AM CDT Tue Jul 19 2016

If you`ve been yearning for 110+ degree heat indices, do we have a
deal for you! For the rest of us, late week will be very miserable.

No changes to the Excessive Heat Watch at this time. Main question
would have been to extend it into Saturday. The latest runs of the
GFS and ECMWF have slowed down the arrival of a cold front this
weekend, to Sunday afternoon. Net result will be an additional day
on Saturday with a heat index of 105-110 over most of the CWA. Given
this is a recent development, will hold off on any extensions to see
if this is a persistent trend.

Still looking like Thursday and Friday will see the most brutal
conditions of the upcoming heat wave. Have increased highs by a
degree or so, resulting in 94-98 degrees both days. Plenty of
evapotranspiration, as well as residual moisture from MCS`s earlier
in the week, will allow dew points in the mid-upper 70s. This
translates to widespread heat index values of 110-113 degrees west
of I-55 on Thursday and over the entire forecast area Friday.

In terms of the aforementioned MCS`s, nocturnal "ridge-riders" will
be overtopping the intense 598 dm upper high centered over Oklahoma.
Tuesday night MCS over the upper Mississippi Valley likely to at
least clip the northern half of the CWA on Wednesday, although the
ECMWF is the most pessimistic of solutions and largely keeps it
north of us. After that, the building ridge will shift the storm
track a bit further north for a couple days. As the weekend arrives,
the ridge will start to be squashed into a west-east configuration,
as the upper low currently off the Washington coast breaks off a
piece of energy which tracks along the Canadian border. The
evolution of this energy into a broader wave/upper low will help
drag some cooler air southward early next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 548 AM CDT Tue Jul 19 2016

Patchy fog this morning seems to be more confined to the east,
with CMI and DEC dropping to LIFR vis. VCSH for SPI this morning
as a few showers developed along weak boundary in the area. Expect
morning fog to burn off, and keep very light/predominantly
easterly winds throughout the day with cirrus, and a sct cu deck
after mid-day. Major concern is whether or not the MCS out to the
west holds together long enough to impact ILX terminals in the
west. For now, confidence is low enough to leave out. HRRR and GFS
hinting to potentially other solution with TS chances after 18z.


&&

.ILX Watches/Warnings/Advisories...
Excessive Heat Watch from Thursday afternoon through Friday
evening for ILZ027>031-036>038-040>057-061>063-066>068-071>073.

&&

$$

UPDATE...Miller
SHORT TERM...HJS
LONG TERM...Geelhart
AVIATION...HJS



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