Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
334 am CDT sun may 19 2013
Synopsis...
issued at 249 am CDT sun may 19 2013
06z surface analysis has synoptic lows south of kabr and in southwest
Kansas. Numerous mesoscale lows and highs were across Nebraska/Kansas
behind the now decaying mesoscale convective system in western Iowa and Missouri. The main
front ran from the kabr low into southwest Wisconsin and then into
the Ohio Valley. Dew points over most of the Midwest and plains were
in the 50s and 60s with 40s and 50s over the Great Lakes.
&&
Short term...(today and tonight)
issued at 249 am CDT sun may 19 2013
Nonlinear processes are driving the sensible weather. Thus one must look
more carefully at the models.
Mesoscale convective system and lift tools indicate the current mesoscale convective system over the western parts
of Iowa/MO will continue to slowly decay as it out runs the better
moisture and runs into the upper ridge. Outflow boundaries from the
mesoscale convective system will help fire new convection through sunrise with isolated to
possibly scattered convection entering the western County warning forecast area. This
convection will slowly weaken after sunrise as the low level jet shifts back
into the plains.
Isolated to scattered convection should linger through the morning
across the County warning forecast area as mesoscale induced shortwaves and boundaries move
through the area.
The mesoscale convective system and lift tools indicate new convection should fire in
central Iowa around middle day and enter the western County warning forecast area by middle
afternoon. Mesoscale boundaries will play heavily into the overall
evolution of this convection but it should evolve into an mesoscale convective system by
late afternoon.
Given the moisture/instability severe storms are a threat. The more
significant severe storms should be across eastern Kansas/western MO but
there should be some threat of severe wind/hail during the afternoon
and evening hours.
Tonight...strong to possibly severe storms should be seen across the
area during the evening. Mesoscale convective system/lift tools suggest an mesoscale convective system moving
through during the evening. A more substantial mesoscale convective system should develop by
sunset in the western parts of Iowa/MO and move through the area
overnight. Strong to severe storms may be possible with this mesoscale convective system as
well.
08
Long term...(monday through saturday)
issued at 249 am CDT sun may 19 2013
Showers and thunderstorms into Wednesday then cooler and dry into
next weekend with another rain event by Sunday.
Overview...all solutions again are adequate on kinematic or flow
fields but as is normal with convection are having difficulties.
Verification at 06z supports a 70/30 mix of hi-res ECMWF/GFS. This
suggests periods of showers and thunderstorms with poor confidence
on timing except for likely decent rounds late PM today and once
again late Monday. Run to run variance supports below average to poor
confidence of timing and showers and storms Tuesday/Wednesday with next 36-48
hours Keys to how last upper wave passes. Most locations still on
track to pick up 1 to 3 inches or rain by time event ends Wednesday.
Monday...chance probability of precipitation with lingering showers and storms with enough
heating and forcing for thunderstorms to fire middle to late PM.
Conditions continue to support good chance of severe storms with
shear profiles and moderate instability. Local tools continue to
support good unidirectional shear for mixing down winds aloft for
winds of 60-70 miles per hour and also enough dry air aloft with wbz of 10 to
11k above ground level for large hail up to 1.75 inches. An isolated tornado may
be possible with some backing of surface winds but this does not
suggest any stronger or longer track events unless winds back more
allowing for more scl directional shear. Temperatures and probability of precipitation little
change with highs roughly 80-85 and lows in the middle 60s. Chance probability of precipitation
in the day with likely at night as storms fire well into the evening
hours. Rain amounts could be locally heavy with 1-2 inch amounts in
the strongest storms with precipitable water/S of 1.25 to 1.5 inches and some storm
training potential.
Tuesday...more energy to pass across area with lots of clouds and
showers and storms. Poor confidence on maximum temperatures due to cloud coverage
and how much precipitation moves into area or fires during the day.
Generally highs of 75-80 are suggested based on convective temperatures.
Kept mostly likely probability of precipitation in the day with chance probability of precipitation overnight but
timing is poor when this next organized event occurs. Mins at night
in the lower 60s. Marginal severe potential suggested due to limited
instability.
Wednesday...upper low rotates slowly over area with popcorn showers
and isolated to scattered storms with mostly chance probability of precipitation in the
north and east sections. Highs mostly in the lower 70s with mins
falling into the 50s as winds shift to the north as cold front
passes most areas by Thursday morning.
Thursday and Friday...clearing skies and seasonably cool and
comfortable with highs upper 60s to lower 70s and mins upper 40s
to lower 50s. Mins Saturday morning with surface Canadian high
pressure overhead may need lowering by 3+ degrees with isolated
lower 40s possible in low lying locations.
Saturday...warm and upper disturbance from west to interact with
cool airmass to bring clouds and areas of rain and rainshowers with
strong evaporative cooling by late Saturday into Sunday. Have chance
probability of precipitation that should br raised in the next day or so when timing issues
better clarified. Event looks like another moderate to locally heavy
rain event.
Nichols
&&
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 249 am CDT sun may 19 2013
New convection from the decaying storm complex over the western
halves of Iowa/MO will spread into eastern Iowa through sunrise. The
probability of a rain showers/thunderstorms and rain affecting a taf site is low. VFR conditions
are expected to continue through 18z/19. After 18z/19 diurnal convection
will develop and move through eastern Iowa and Illinois. VFR conditions
should continue but the probability of a thunderstorms and rain affecting a taf site
will increase. After 00z/20 several rounds of convection will affect
Iowa/Illinois with a potential for MVFR conditions.
08
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Synopsis...08
short term...08
long term...Nichols
aviation...08
