Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
247 PM CDT Friday may 24 2013
Discussion...
246 PM CDT
Synopsis...high pressure over the region has produced a beautiful
yet cool Friday. The ridge of high pressure over the central Continental U.S.
Will remain in place through the weekend with multiple chances of
showers and thunderstorms throughout the forecast period with a slow
warming trend.
Today and tonight...
high pressure will remain over the region with clear skies and
occasional gusty winds this afternoon. Winds will slowly diminish as the sun
GOES down with light winds expected overnight. The upper level
trough and pool of cool Canadian air has pushed east over the Ohio
River valley...thus temperatures tonight will not be as chilly. Expecting
low temperatures around 40 or higher with temperatures in the middle 40s downtown.
Saturday through Tuesday...
the blocking pattern already in place takes hold over the Continental U.S. This
weekend with toughs on the east and West Coast and a ridge over the
central US. Weak shortwaves will pass over the ridge axis and swing
through the western Great Lakes throughout the weekend and early
next week. Therefore have periodic chances of showers and
thunderstorms forecast through Tuesday.
The surface high shifts east and becomes centered over Michigan tomorrow
allowing the first shortwave to pass through Iowa and northern Illinois.
Given the chilly airmass and middle level inversion...kept thunder out
of the forecast for Saturday through Sunday morning. Thinking
saturdays showers will remain southeast of a Rockford Illinois to
Remington in line. Medium confidence in the location of showers and
limited thunder potential.
The second and slightly stronger shortwave approaches from the west
on Sunday...bringing another round of showers and thunderstorms into
the region. The eastern upper level trough finally slides off to the
northeast Sunday afternoon/night. This allows warm air to move into
the region and showers to spread across the County Warning Area. Expecting only
scattered embedded thunderstorms during the day on Sunday.
Soundings look more favorable for thunderstorms on Monday and
Tuesday as the warm up continues and instability increases. A low
level jet sets up on Tuesday with the nose of the jet in eastern
Iowa/western Illinois Tuesday morning. Model soundings feature a low level
cap and 1500+ j/kg of cape. Wind shear looks favorable...so will
keep an eye on severe potential for Tuesday. Thinking any storms
that due form have the potential to produce heavy rainfall since
precipitable water values will be around 1.5 inches...nearly 2 Standard deviations
above average.
High confidence in more high spread precipitation beginning Sunday...and
thunder/heavy rain potential Monday and Tuesday. Medium confidence
in severe convection on Tuesday.
For temperatures...a warming trend is on tap with near average temperatures
expected by Monday...then above normal temperatures on Tuesday. Persistent
easterly flow will lead to cooler temperatures along the lake. High
confidence on warming trend.
Extended...Wednesday and Thursday...
as the eastern trough moves off to the northeast...the ridge opens
up allowing even warmer air to infiltrate the region. The pattern
remains unstable though with additional shortwaves...showers...and
thunder moving around the ridge. Kept a chance of showers and
thunderstorms in the extended. The best chance of precipitation looks to be
late next week as the western upper level low settles over the
northern plains. Temperatures in the extended continue to rise with well
above average temperatures expected. Currently have middle 80s forecast for
middle week but could see temperatures be even a few degrees higher depending
on cloud cover and precipitation coverage.
Jee
&&
Aviation...
//Ord and mdw concerns...updated 20z...
* NE to east-northeast winds fluctuating in speed but averaging around 9 knots
with periodic gusts of 13-16kt through late afternoon.
* Lake breeze Saturday afternoon increasing wind speeds to near 10
knots.
* A small chance for light rain Saturday afternoon.
//Discussion...updated 18z...
While northeast winds continue across Chicago area taf sites early
this afternoon...high pressure is building over the immediate
region. This will lead to a rapid decrease in wind speed this
evening...but beforehand there will be continued fluctuations in speed
and gusts...all averaging near 10 knots. Saturday morning will see
light southeast winds as the ridge passes. The setup should favor
a lake breeze development at least into northeast Illinois on Sat
afternoon...so expecting winds to become more easterly at Ord and
mdw and approach if not reach 10 knots sustained. Clouds will thicken
tonight and lower to 7k-10k feet Saturday morning. There will be
lift aloft likely to generate virga...but the dry low-levels are
expected to keep it only at that across Chicago sites. Would not
be surprised if rfd sees some temporary VFR light rain late in the
morning into the afternoon.
//Ord and mdw confidence...updated 20z...
* high confidence in wind speeds diminishing to under 10 knots by 00z.
* Medium confidence in east winds nearing 10 knots Saturday
afternoon.
* High confidence that if light rain were to move as far east as
Chicago Sat afternoon it would be VFR.
//Outlook for Ord/mdw for 00z Sunday-12z Friday...updated 12z...
Saturday night...VFR.
Sunday...VFR...slight chance rain showers/thunderstorms and rain Sunday night.
Monday through Thursday...VFR...low chances for shra/tsra. Breezy
south winds Wednesday.
Mtf/mdb
&&
Marine...
228 PM CDT
High pressure will continue to build across the lake this evening
and persist over the central Great Lakes through the weekend keeping
relatively light flow across the lake. Waves which were built up
from previous gales will continue to subside...falling below Small
Craft Advisory criteria in the Indiana nearshore waters later today.
Low pressure develops over the plains and will lift a warm front
across Lake Michigan early next week...with modest southerly winds
of 10 to 20 knots dominating the forecast through most of next week.
Bmd
&&
Lot watches/warnings/advisories...
Illinois...beach hazards statement...ilz006-ilz014 until 7 PM Friday.
In...beach hazards statement...inz001-inz002 until 10 PM Friday.
Lm...Small Craft Advisory...Indiana nearshore waters until 7 PM Friday.
&&
$$
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