Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 060520
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1120 PM CST Thu Mar 5 2015

.UPDATE...
ISSUED AT 841 PM CST THU MAR 5 2015

Surface high pressure has centered over Illinois this evening with
winds becoming light or calm across the area. Clear skies, snow
cover, and an arctic air mass over the region will allow
temperatures to fall rapidly through the evening, likely
approaching record lows for the date at a few sites overnight.
Winds will start to increase in western Illinois shortly after
midnight resulting in an end to cooling there, while eastern IL
continues to cool. Expect lows in the lower single digits west of
I-55, and near zero to a few degrees below to the east. Current
forecast is in good shape with these features, so have only made
minor adjustments to hourly temp/dewpoint trends this evening.

&&

.SHORT TERM...(Tonight)
ISSUED AT 230 PM CST THU MAR 5 2015

A very cold night, with low temperatures possibly reaching record
cold levels in parts of east central Illinois, can be expected. Lows
this time of year are typically in the 25-30 range, so we are
looking at readings about 25 to 35 degrees below seasonal normals.

Surface high pressure ridging from the southern Plains through north
central MO to the Upper MS River valley will move across central IL
by midnight, reaching the IL/IN border by daybreak. This will result
in the coldest temperatures mainly east of a Bloomington-Taylorville
line tonight where readings in the zero to 5 below range will be
common. This same area has the deepest snow cover in the region as
well, so radiational cooling should be at a maximum. Thus, would not
be surprised to see local effects cause a few lows to dip colder
than -5.

Generally west of I-55, a southerly wind will increase as we get
closer to daybreak. This should result in low temperatures bottoming
out between 11 pm and 2 am, and then becoming steady or slowly
rising the rest of the night. Increasing clouds from mid level warm
advection will also help keep early morning temperatures a tad
warmer as well.

With the surface ridge moving across the area, wind chills won`t be
a factor much of the night due to light and variable winds. However,
as we get close to daybreak the pressure gradient will tighten a bit
resulting in wind speeds of 5 to 10 mph. This will produce wind
chills of -5 to -10 in central/west central IL and -10 to -15 in
eastern IL from daybreak until 9 am or so.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 230 PM CST THU MAR 5 2015

Nice warming trend setting up over the weekend as flow becomes more
zonal and heights climb as northern stream flow shifts north.  As
the storm track retreats north, waves rotating through the northern
stream should have less and less of an impact on Central and
Southeast illinois as the period progresses. Models are in good
agreement with the biggest differences related to the strength of
the northern stream waves and whether they can produce enough lift
over the area to produce light precip amounts over the weekend.  NAM
is the moister of the solution from the 00z suite of runs and would
suggest a few periods of sprinkles/flurries or light rain/light snow
will impact the I-74 corridor and north Friday Night and over the
entire area Saturday Night and Sunday Night. Although the CMC and
the 00z ECMWF remain dry through the period, the GFS has moistened
somewhat with these last two waves producing spotty precip as well
in the area.  Will await a better consensus on timing and low-level
moisture before considering adding low pops.

Speaking of low-level moisture, a concern with significant snowmelt
in areas with substantial snow cover may lead to a potential for fog
during the late night and early morning hours early next week.  Will
not put into package at this time due to the potential wind speeds,
but later shifts will have to monitor this possibility closely.

By Monday, cut-off low in the Pacific is expected to produce a break
in energy diving into the Eastern North American trough and
reinforcing a transitional to zonal flow. Models are in good
agreement in keeping region dry from Monday through Thursday with
850 temps climbing well above 0C by midweek.  GEFS spread is quite
low as well adding confidence to the warming trend forecast.  Any remaining
snow may limit warm-up somewhat early in the week, but by mid-week
the bulk of snowcover will likely be gone.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1120 PM CST THU MAR 5 2015

VFR conditions with light and variable winds across central IL
late this evening. Surface high pressure crossing the area is
responsible for the light winds and clear skies. Shortly after
06Z, increasing surface pressure gradients associated with a weak
approaching system will result in increasing southerly winds in
western IL, spreading eastward through the state overnight. Winds
reaching 14-18 kts with gusts 20-25 kts in the late
morning/afternoon. Cloud cover at 10-15 kft is expected in warm
advection aloft with the system crossing the state from around
12Z-22Z. After 00Z Saturday...gusts and mid-cloud cover
decreasing, but SSW winds 8-12 kts continuing.

&&

.HYDROLOGY...
ISSUED AT 230 PM CST THU MAR 5 2015

Deep ground remains below freezing with frost depth readings
between 6 and 18 inches throughout forecast area enhancing
potential for runoff as the snow melts. Some near bankfull river
conditions, particularly across southeast Illinois can be expected
by mid-week.

&&

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

$$

UPDATE...Onton
SHORT TERM...Miller
LONG TERM...Barker
AVIATION...Onton
HYDROLOGY...Barker





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