Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
1252 PM CDT Wednesday may 22 2013
Synopsis...
issued at 252 am CDT Wednesday may 22 2013
Large and quite seasonably cool upper low pressure system over
western portions of Midwest to pin wheel over forecast area next
24 hours. Deep occluded system ideal for large areas of clouds
and light showers and potentially areas of drizzle tonight in cool
conveyor belt north side of system. Verification at 06z and 08z
suggests cool air near surface moving into area a bit faster than
most solutions from the northwest. Upstream energy supports below
normal temperatures then return to zonal flow and unsettled and still cool
for days 4-7.
&&
Short term...(today and tonight)
issued at 252 am CDT Wednesday may 22 2013
Today...lots of clouds with a few brief periods of sun mostly along
Mississippi River into early afternoon. Nowcast tools support vorticity
maximum over SW Missouri to rotate over area and with heating and
forcing producing scattered to areas of showers today. Highs will
be a challenge based on cloud cover with deep clouds west of I-380
corridor and Highway 218. Hence...lower 60s west to around 70
along and east of the Mississippi River. Same concern as yesterday
with cool air as if moves in faster...as what happened yesterday
with clouds...high may need trimming by at least a couple degrees
for later shifts. Any precipitation that falls should be less than
a tenth of an inch.
Tonight...upper occlusion to move southeast with north winds arriving
over at least north 1/2 by morning. Low level profiles and forcing
are supportive of widespread light rain and drizzle for later shifts
north of upper occlusion. Mins in the upper 40s suggested north due
to evaporative cooling with north winds of 10-20 miles per hour. Quite cool for
late may. South section less chance of light rain and drizzle with
lower probability of precipitation. Additional rain totals again likely below to well below
a tenth of an inch.
Long term...(thursday through tuesday)
issued at 252 am CDT Wednesday may 22 2013
Showers will linger across most of the area Thursday morning as the
upper low slowly moves east into Indiana. Dry conditions with a
clearing trend is expected during the afternoon. Temperatures will
be below normal.
Thursday night/Friday a very cool Canadian high pressure will build
into the Midwest. Light winds and generally clear skies will drop
temperatures into the 40s with upper 30s likely in the favored cold
areas of the northern County warning forecast area. Temperatures on Friday will average
below normal.
Friday night return flow aloft develops across the area. Initially the
dry air will win out and keep precipitation west of the area. The
models may be a bit too quick with warm air advection precipitation entering the
County warning forecast area during the evening. Thus the introduction of showers will be
delayed until late evening over roughly the western half of the
County warning forecast area. After midnight all models show a respectable Theta-E gradient
moving across the area along with continued flow off Lake Michigan
in the low levels.
These features combined with the return flow aloft will create an
effective boundary to allow precipitation to develop/move into the
County warning forecast area. Although the amount of instability is in question...thunder
was kept after midnight due to the Theta-E gradient.
Saturday on...
the effective boundary created by flow off Lake Michigan will remain
over or near the County warning forecast area Saturday through Tuesday. The increased
convergence and stronger thermal gradient from this boundary will
help enhance precipitation with each disturbance coming out of the
plains.
The model consensus has mainly chance probability of precipitation from Saturday through
Tuesday across the area. There will likely be periods of dry weather from
Saturday through Tuesday. However...smoothing of model features and
disagreement on timing/placement of significant features precludes
including dry periods in the forecast right now. Temperatures will
average below normal over the weekend with moderating temperatures
early next week.
08
&&
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1236 PM CDT Wednesday may 22 2013
Wrap around low VFR to MVFR cloud deck to continue across all taf
sites this afternoon...with sctrd showers still yet possibly to pop
up. Other showers already developed in central Iowa will try to
rotate this way around middle/upper low pressure circulation over the
north central Iowa/Minnesota border region. The cloud deck may become more
widespread lower MVFR tonight...with areas of showers or rain
becoming more widespread as well in the vicinity of Cid and dbq
around midnight as they pivot southeast around middle level circulation.
This activity then moving toward mli and brl through Thursday morning. Some
IFR decks possible after 02z tonight in vicinity of all terminals...
with 3-5sm fog and mist where the rain lets up. Generally a west
wind though this evening before it veers to the north as the
overnight progresses. Northeast winds increasing to 10-20 kts by
late Thursday morning and passage of upper low across the Great Lakes should
help conditions improve late morning into the afternoon. ..12..
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Synopsis...Nichols
short term...Nichols
long term...08
aviation...12
