Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 230447
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1147 PM CDT Tue Apr 22 2014

.DISCUSSION...
ISSUED 900 PM CDT Tue Apr 22 2014

Quiet weather is expected the rest of the night as high pressure
has progressed far enough into Illinois to create much lighter
winds and clear skies.

Dewpoints have dipped into the mid 20s from Peoria to Bloomington.
They should rebound upward later tonight as higher upstream
dewpoints advect into the area. The higher moisture levels should
help to keep our lows from dipping too close to freezing. Frost
could develop if air temps dip into the mid 30s. Our coldest lows
look to be in the northeast, where the lower dewpoints and light
winds will linger the longest. Low temps may reach 36-37F, so we will
continue to leave out any mention of patchy frost with the evening
update.

Overall, the forecast grids are on track with expected trends, and
no formal update will be needed this evening.

Shimon

&&

.AVIATION...
ISSUED 1147 PM CDT Tue Apr 22 2014

The surface high will keep skies mostly clear through Wed morning
with some cirrus the only clouds of note. By mid-day, increasing
mid clouds will begin to overspread PIA and SPI as warm advection
clouds progress into NW IL. Guidance is showing potential for a
few rain showers for PIA between 18z/1pm and 00z/7pm. Forecast
soundings show plenty of dry air below the cloud bases to preclude
measurable rain from occurring. A few sprinkles may reach the
ground toward 00z, but we kept vcsh out of the TAFs for now.

Winds will be light north or variable the rest of the night under
the surface ridge axis. Wind direction will become east-southeast
by mid-day on Wed, and remain that direction as low pressure
develops in the Plains through Wed evening.

Shimon
&&

.PREV DISCUSSION...
ISSUED 259 PM CDT Tue Apr 22 2014

Breezy conditions persist across central and southeast Illinois
this afternoon between yesterday`s departing cold front and an
approaching ridge of high pressure. The ridge will continue to
dominate the weather for Wednesday, keeping quiet conditions in
place. The next storm system is still on track for Thursday, with
an associated risk of showers/thunderstorms. The precipitation
threat for the end of the weekend into early next week remains
murky as a slow moving system, part of a developing Rex block,
moves through our vicinity. Main forecast problems today remain
trying to pin point precipitation chances/timing with these two
systems.

SHORT TERM...Tonight through Friday:

The ridge of high pressure to our west will push into the forecast
area overnight. The main concern with the arrival of the ridge is
if temperatures will fall enough to pose a threat of frost. At
this point, forecast lows are only marginal for frost in most
areas. Also, winds appear as though they may stay up enough to
mitigate the frost threat. If winds die off quickly this evening,
the frost threat will need to be looked at more closely.

Return flow on the back side of the ridge increases on Wednesday,
with a warm frontal zone setting up to the east of a developing
storm system in the plains. Many model solutions persist in trying
to produce some precipitation in this warm advection regime,
Wednesday afternoon/evening, mainly across northern portions of
the forecast area. Still feel there is likely to be too much dry
air to overcome initially and that models are a little too
bullish. With this thinking in mind, plan to keep forecast dry
until overnight Wednesday night when some precipitation may begin
to slip in ahead of Thursday`s system.

Showers/storms still expected to spread from west to east on
Thursday as storm system crosses the forecast area. Severe threat
expected to be low overall due to low instability (CAPE values
below 1000 j/kg for the most part), and modest shear profiles
(bulk shear values no better than 35-40 kts). Drier conditions
quickly filter in behind the cold front associated with the system
overnight Thursday into Friday, although the post frontal airmass
is not especially cool.

LONG TERM...Saturday through Tuesday:

Attention turns to the Rex block expected to develop during the
period as we head into the extended range of the forecast. The
ECMWF has been the most aggressive by far with the return of
precipitation chances over the weekend, but it has backed off a
bit in its 12Z run. In any event, once the upper low with the Rex
block is in the vicinity, period of showers and some thunderstorms
are likely for at least a few days. However, due to the model
spread, run-to-run inconsistency, and intra-model ensemble spread,
confidence remains quite low in the details. Unfortunately, this
results in several periods of chance PoPs, starting Saturday
night. Hopefully, a clear consensus with the ultimate forecast
solution will emerge soon. However, considering the trouble models
have entering (and leaving) blocky patterns, we may be waiting a
while.

BAK


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$







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