Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
1254 PM CDT Monday may 20 2013
Update...
issued at 1104 am CDT Monday may 20 2013
Quick assessment on this mornings upper air analysis and what is
taking pace currently...seems there may be a delay to later this
afternoon and early evening. Current temperatures in the low to middle 70s
with surface dewpoints mainly in the low 60s will still take time to
improve upon...especially with better surface moisture pooled along
outflow boundary across central MO at this time. The local area under a 850 mb
mb and 700 mb mb lull in moisture as well. Middle and upper jet maximum/S
across the great bsn and shifting into the southwestern plains this
morning will not nose up across the County Warning Area until after 20z-21z this
afternoon. If surface dewpoints only recover into the middle 60s...the 12z NAM
and GFS prognosticated convective available potential energy of 1500-2000 j/kg may be too high. Also high
temperatures may be more in the way of low to middle 80s as opposed to middle
to upper 80s this afternoon. Surface winds currently south and mainly
southwesterly...thus without and low level backing to the southeast the
lower level helicities and shear Don/T appear as impressive as
what may be earlier thought. But there appears to be decent deeper
layer speed shear with uniform vertical profiles. Local levels may
not be as low as what the short range models depict in the
southeast third/1500-2000 feet above ground level/ this afternoon as well limiting
a possible tornadic threat. Thus all in all...less instability
but still strong kinematics/shear suggest a threat for large hail
and damaging downburst winds with still the possibility of
supercell type discrete storms this afternoon...but may be less
widespread then yesterday. The southeast third of the County Warning Area most at
risk of severe storms this afternoon. Still can/T rule out isolated
tornadoes and any watch that does come out will probably still be
a tornados watch for the local area. Second round of storms along the
main front itself...currently across far western Iowa...may sweep across
the area from the west not until middle evening. Will still have to
be very much on guard and watch trends through the afternoon.
12
&&
Synopsis...
issued at 304 am CDT Monday may 20 2013
06z surface analysis has a synoptic low near kmbg with the stationary
front running east through Wisconsin and lower Michigan. Mesoscale
lows were near kfsd...kbvn...and kcsm. Numerous outflow boundaries
ran from Illinois back through Missouri. Dew points were in the 50s
and 60s across the Midwest.
&&
Short term...(today and tonight)
issued at 304 am CDT Monday may 20 2013
Today will be quite interesting. Mesoscale processes will drive the
sensible weather and conceptually...there is a good probability of seeing
severe storms this afternoon and evening.
Mesoscale convective system and lift tools suggest the bulk of the mesoscale convective system moving across Missouri
will remain south of the area. However...vorticity maxes helping to drive
this mesoscale convective system will push decaying rain showers and some thunderstorms and rain into the County warning forecast area through
sunrise with activity dissipating during the morning.
There should be a few hours of quiet weather from middle to late morning
until convective temperature is achieved. Once this occurs...new
convection will develop during the afternoon and build into one or
more severe mesoscale convective complexes by early evening.
The overall placement of the jet structure and instability axis
point to severe storms developing during the afternoon. Large hail
and damaging winds are a given. The shear profiles and buoyancy is
also favorable for tornadoes...possibly significant.
By late evening and overnight...storm activity will be on the
decrease as the atmosphere cools.
08
Long term...(tuesday through sunday)
issued at 304 am CDT Monday may 20 2013
Turning cooler and unsettled with probably cool rains again this next
weekend.
Overview...initialization and verification on larger scales...or
synoptic scale are good but all solutions poor to very poor on
precipitation/moisture/clouds. Again heavy use of conceptual forcing
tools which has aided past several days. This supports more showers
and storms Tuesday turning cooler with clouds and showers Wednesday.
Risk of severe Tuesday is questionable based on convection and next
wave interactions later on Tuesday. Prefer a 60/40 mix of forcing
of hi-res European model (ecmwf) and NAM-WRF into day 4...then a 50/50 of hi-res
European model (ecmwf) and GFS day 4 and beyond.
Tuesday...poor confidence in forecast probability of precipitation as next 24 hours will
impact evolution of upper low and progress of cool front and
associated amount of clearing/clouds. Upper jet supports lighter and
lower probability of precipitation west with risk of lingering wave of showers and storms
that should tend to stay below severe levels. Highs 75 to 80 from
northwest to southeast. Mins middle 50s northwest to the lower 60s southeast sections.
Wednesday...cloudy and cooler with rain or rain showers. Highs in
the north may need lowering with low clouds and possibly even
drizzle with cool north winds arriving from north to south during
the day a bit earlier in the forecast for later shifts. Wednesday
night...low clouds and possibly light rain and probably areas of
drizzle with mins in the 50s.
Thursday and Friday...below normal temperatures mostly in 65 to
72 degree range. Clouds will clear in the afternoon from north to
south as Canadian high pressure moves in. Thursday night...clear
and cool with mins probably many locations 3+ degrees too mild with
lower to middle 40s suggested over north sections. Friday...sunny
and cool with light NE winds.
Saturday and Sunday...westerly winds to upglide over cool airmass
that primes the region for cool highs due to good evaporative
cooling and likely rain and isolated storms possible in south and
west sections. Chance probability of precipitation for now will likely be raised with
timing issues better clarified. Another moderate to locally lower
end heavy rain event with most areas picking up .5 to 1+ inches.
Nichols
&&
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1243 PM CDT Monday may 20 2013
Have pushed back storm development time at Cid and dbq until late
afternoon...brl and mli to 20z to 21z. But some signs most of the
terminals will be VFR through 00z if storm clusters Don/T develop
out of northeast MO or southeastern Iowa this afternoon and then
move toward brl and mli. If afternoon storms Don/T develop or stay
south/east of the terminals...best chance will come later this
evening after 01z as main front approaches from the west. These
storms could be strong to severe too with damaging wind and hail...but
adequate instability questions for both this afternoon and evening
continue with surface dewpoints struggling to get out of the lower 60s.
Otherwise good visibility this afternoon with mainly clear skies or
high cloud blow off from storms in MO. Southwest winds at 10 to 20
kts with some higher gusts...to become south southwest overnight
without the gusts. But still a chance for variable gusts over
35-40 kts with the evening line of storms. Some MVFR fog possible
toward sunrise before southwest winds increase again by middle Tuesday morning.
12
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Update...12
synopsis...08
short term...08
long term...Nichols
aviation...12
