Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 170252

Area Forecast Discussion
National Weather Service Lincoln IL
852 PM CST Thu Nov 16 2017

Issued at 852 PM CST Thu Nov 16 2017

Updates this evening are mainly for cloud cover as overcast skies
that were prevalent from Galesburg to Paris northward earlier this
evening have been eroding and are now mainly from Peoria to
Champaign northward. Have updated short term forecast to account
for this, but may need further updates later this evening as well.
Otherwise, temperatures across the area are already in the low to
mid 30s, near forecast lows for tonight, and this looks good as
well as light southeast winds and cloud should keep temperatures
relatively steady.


.SHORT TERM...(This evening through Friday)
ISSUED AT 246 PM CST Thu Nov 16 2017
A narrow ridge of high pressure is located over IL and the
Mississippi River Valley this afternoon/evening. The high pressure
and relatively subsident air effectively trapped a layer of
moisture over the region, resulting in a more cloudy day in the
northern half of the state. Models are struggling with what to do
with the cloud remnants as not enough mixing today to make a
significant impact. HRRR had the best handle on the clouds
earlier, and latest runs keeps the stratus in for the overnight
and expands across the region. Have kept the temps up a bit from
last night...may need some minor adjusting, particularly in the
south if the clouds expand. By morning, winds come around to more
southerly behind the ridge as the next front moves into the
Midwest. Low pops in place for sct showers/mostly drizzle in the
first half of the day. Precip approaching the NW in the
afternoon/evening...and thunder increasing into tomorrow night.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 246 PM CST Thu Nov 16 2017
SPC Day 2 outlook has all of Central IL in a general thunder
threat, mainly for tomorrow evening. Rain chances better for
Friday night and into Saturday. Day 3 Outlook has a general
thunder... and a marginal risk in the far SE...south of I-70.
Concern would be surrounding early morning convection invof the
Ohio River Valley with the rapid development of the storm system
as it moves out to the east. Threat should end early as the
heavier precip moves out. However, on the other side of the
boundary, some models hinting at a weak round of precip through
the afternoon, with the temperatures NW of the IL River allowing
for the potential to see some snowflakes mixed with the rain
threat through the afternoon. Threat is brief and surface
temperatures should remain warm enough to melt most of it. Winds
become very strong behind the front as well, and Saturday
afternoon will see gusts to 30kts at times.

Temps plummet into the 20s again for Sat night and Sun night with
colder air moving into the Midwest. A period of quiet weather sets
up through the remainder of the forecast. Temps warm briefly with
southerly flow and the western ridge shifts eastward slightly for
Monday. Next system moves into the Upper Midwest/Great Lakes for
Tuesday. Pops previously in forecast have come out of the blend
for Tuesday night as the front passes dry in the past few runs of
both the GFS and the ECMWF. A mentionable difference is that the
front is not only dry, but not as cold in the ECMWF...and the GFS
is deeper with the upper trof and colder. Should the trend of the
GFS following suit with the ECMWF shift on a Day 5 forecast...the
temps in the GFS/the blends should start to modify somewhat
Tuesday night and beyond.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 551 PM CST Thu Nov 16 2017

MVFR cigs over KPIA-KDEC northeastward, with trends toward
expanding slowly southwestward. Models generally follow this trend
as well, although perhaps with a bit of a break overnight just
before stratus and drizzle expand northward out of southern IL.
Have not incorporated a break in low cloud cover into TAFs as
this scenario is too uncertain for inclusion at this point.
Overall, ceilings will trend lower and have IFR cigs by 06Z-09Z.
Winds E-SE 5-10 kts overnight, becoming SSE 10-15 kts with gusts
20-25kts after 15Z.




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