Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1247 am CDT Sat may 25 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 06z...
* east-southeast winds generally 10 kts or less this morning and
early afternoon becoming more east with lake influence middle
afternoon.
* Low probability of showers from VFR middle level cloud deck
overnight and through the day...higher probability rain showers will
remain west/south of chi area terminals.
Mdb
//discussion...updated 06z...
High pressure is centered just east of Lake Michigan with weak low
pressure out across the High Plains. Light and variable low level
winds are in place and will gradually become more focused from the
southeast from west to east through early morning as the high
departs. Bands of showers continue to move southeastward across
northeast Iowa and southwest Wisconsin with some embedded thunder
further west across north central Iowa. Have included tempo for
some light rain at rfd over for a few hour period but the rain
should have an increasingly difficult time making much eastward
progress with very dry low and middle level air across much of the
area. Will leave the remaining terminals dry for now. Expect that
ceilings and visibility will remain VFR though ceilings may lower to 5000-7000
feet at times overnight...with more widespread 6000-8000 feet ceilings
expected during the day. The shower chances will remain highest
west and south of the terminals through the day but rfd may have a
higher chance this afternoon and early this evening as a wave
passes to the southwest. Cannot completely rule out some sprinkles
or light rain at the other terminals today however. Southeast
winds will likely turn more easterly at Ord/mdw and eventually dpa
thanks to a lake breeze that is expected to develop this
afternoon.
Mdb
//Ord and mdw confidence...updated 06z...
* high confidence in wind trends...except medium confidence with
details of shift to East/Lake breeze this afternoon.
* Low confidence in potential for light VFR showers to reach
Ord/mdw...though high confidence in conditions remaining VFR
even if they do.
Mdb
//outlook for Ord/mdw for 12z Sunday-12z Friday...updated 00z...
Sunday...chance of rain showers and a few thunderstorms and rain especially later in the
day/night. Mainly VFR.
Monday through Thursday...VFR. Low probability for periodic
rain showers/thunderstorms and rain especially Monday and again Thursday. Breezy south winds
Wednesday and Thursday.
Ratzer
&&
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...none.
In...none.
Lm...none.
&&
$$
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