Area forecast discussion
National Weather Service Lincoln Illinois
656 am CDT Sat may 25 2013
Discussion...
issued 242 am CDT Sat may 25 2013
Unsettled weather through the Memorial Day weekend...followed by
much warmer/drier conditions for the middle and end of next week.
Short term...today through Monday
Convection currently developing along the nose of a 45-50kt low level jet
over Nebraska is expected to track east/southeast into the area today. Main
question will be how far east the precipitation can penetrate into
sprawling surface ridge axis extending from the Great Lakes to the
Gulf Coast. 00z kilx upper air sounding showed a very dry profile
from the surface up to about 500mb. Any precipitation moving into this
hostile environment will initially evaporate until the airmass is
sufficiently moistened. Due to the continued dry east/NE low-level
flow...have removed probability of precipitation across east-central and southeast
Illinois for the morning hours. Further west...high-res hrrr
suggests Nebraska convection will eventually spread into
west-central Illinois toward midday. Will therefore carry chance
probability of precipitation during the morning...then likely this afternoon for locations
along/west of I-55.
Initial area of convection will dissipate as it moves into
east-central Illinois later this afternoon and evening.
Meanwhile...low-level jet will once again strengthen and focus a
renewed round of showers/thunder upstream across Iowa tonight.
This activity is then expected to track east/southeast into central Illinois
late tonight into Sunday. With airmass moistened from initial
precipitation today...think rain chances will be higher across the board
tonight/Sunday. Will therefore carry likely probability of precipitation everywhere except
the far southeast County Warning Area.
Additional showers/storms will fire on Monday...as persistent
frontal boundary finally begins to shift slowly northward across
the area. Will continue to hit probability of precipitation hard...especially across the
central and northern zones. Total rainfall from this multi-day
event will be lightest along the Illinois/Indiana border where
amounts of one half to one inch will be common. Higher rain totals
will be focused further west...especially west of I-55 where one
and a half to two inches will be likely.
Long term...Tuesday through Friday
As upper trough digs over the western Continental U.S....downstream ridge
will build across the Midwest/Ohio River valley. This will finally
give the surface front a good push northward by Tuesday...resulting
in lower probability of precipitation and higher temperatures. Will only carry low chance probability of precipitation
across the far northern County Warning Area...while high temperatures climb into the
lower to middle 80s. After that...model solutions vary somewhat
concerning how quickly the upper ridge eventually breaks down.
Given amplified pattern...think this will be later rather than
sooner...so have gone with a very warm and dry forecast through
Thursday. Weakening frontal boundary may push into the region by
the end of the week...so have included chance for showers/thunder
on Friday with continued warm temperatures well into the 80s.
Barnes
&&
Aviation...
issued 657 am CDT Sat may 25 2013...for the 12z tafs
Showers are advancing into the dry airmass across central Illinois from
the W-NW. Radar images are a little misleading with most of the
returns below 40 dbz associated with virga at this point. The
airmass will eventually succumb to the isentropic lift...moisture
convergence and strengthening low level jet...as heavier rains and
a few thunderstorms become more prominent this afternoon and
tonight. Most areas should remain VFR with cloud heights above 3k
feet. Visible may dip to MVFR 3-5sm during heavier showers and
storms...but any periods of IFR conditions during storms will be
brief.
Frequent rains and isolated thunderstorms will continue tonight
despite losing low level instability. A saturated airmass and weak
instability above an elevated mixed layer with provide enough
support for some storms and persistent rain.
Winds will start out easterly...then veer to the southeast and
increase into the 10-14kt range as the next mesoscale-vortex arrives
from the west later this morning and afternoon. Winds may back to
the east again this evening as warm frontogenesis increases
across central Illinois from west to east.
Shimon
&&
Ilx watches/warnings/advisories...
none.
&&
$$
