Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192110

Area Forecast Discussion
National Weather Service Lincoln IL
310 PM CST Mon Feb 19 2018

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 231 PM CST Mon Feb 19 2018

A strong frontal boundary will lie nearly stationary to the west
of the area into Tuesday morning, extending from Iowa into the
southern Plains. Strong southwesterly flow will continue to
transport unseasonably rich moisture into the area, with
precipitable water values near 1.5 inches. Upper level
disturbances within the deep southwesterly flow will support
rounds of showers and scattered thunderstorms. One of these
disturbances is currently coming through the area, with another
expected to arrive tonight, along with a 60+ kt low level jet.

Opted not to issue a Flood Watch since the rainfall that has
fallen/is expected to fall is spread out over a couple day period.
Also, drought condtions were ongoing over much of the area and
river levels started out quite low. Finally, the ground has
thawed over all but the far northwest portion of the forecast area
(where expected rainfall is lowest), meaning the falling rain
will not all go straight to runoff. Many area rivers are forecast
to exceed Flood Stage later this week, but this is generally
expected after this rain event ends.

The upstream cold front will begin to surge southeast on Tuesday,
However, surface temperatures will remain above freezing through
the day, so any precipitation Tuesday will fall in liquid form.


.LONG TERM...(Tuesday night through Monday)
ISSUED AT 231 PM CST Mon Feb 19 2018

Our initial precipitation event will persist into Tuesday
night/early Wednesday, with a gradual ending from northwest to
southeast. As surface temperatures fall below freezing across most
of the area later Tuesday night into early Wednesday, any
lingering precipitation will change to a wintry mix of freezing
rain, sleet and possibly snow. However, considerable model spread
still exists with how quickly the surface temperatures go below
freezing and/or how quickly the precipitation ends behind the
front. This spread results in freezing rain/ice potential from
none to a couple tenths of an inch or more. Decided to go with a
lower-end ice potential for now toward the stronger model
consensus. Ice totals will also be diminished due to the warm
surface temperatures from today`s & tomorrow`s heating. However,
the ice threat will need to be monitored closely.

After a brief break in the precipitation threat on Thursday, the
next active period in the persistent southwesterly upper-level
flow is on tap for Friday into Saturday. Much like the ongoing
event, there will be numerous waves of showers and possibly
thunderstorms during this period. At this point, the axis of heavy
rainfall during this period appears likely to be a little
southeast of the current event. However, flooding is likely to be
more of a threat with this event since soils will no longer be
dry, and river levels will be significantly higher (if not already
in flood).


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1130 AM CST Mon Feb 19 2018

MVFR and/or IFR condtions will prevail through the 18Z TAF valid
time across the central Illinois terminals. Most local TAF sites
have climbed to MVFR late this morning due to daytime heating and
the bulk of the heaviest rainfall having pushed off to the
northeast. Expect a return to widespread IFR condtions across the
area tonight as diurnal heating is lost and as rainfall coverage
increases again. Only carried VCTS for most of the period.
Thunderstorms will be around, but not too numerous, making
confidence in specific timing/location too low to go with
predominant or TEMPO thunder. Winds off the deck will increase
again tonight, and surface gusts will subside slightly, causing
non-convective LLWS for most of tonight.




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