Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
1133 PM CDT Wednesday Jun 19 2013
Synopsis...
issued at 345 PM CDT Wednesday Jun 19 2013
Latest surface analysis was indicating Great Lakes high maintaining far
enough west to provide another fair weather day/comfortable dewpoints across the
County Warning Area...while low level return flow was organizing up the plains.
Pressure falls increasing in vicinity of initial warm front across
southern South Dakota. Aloft...water vapor imagery and this morning/S 12z
upper air analysis was indicating a large trough/wave complex slow
rolling across the western inter-mountain region and northern
rockies. Combined with lingering East Coast l/west troffiness...this
process putting The Squeeze on upper ridge axis across the plains
and upper MS River Valley.
&&
Short term...(this evening through thursday)
issued at 345 PM CDT Wednesday Jun 19 2013
Tonight...expect a mainly dry night as lingering ridging and dry
air mass in place have their effect. Mesoscale convective system-forcing tool suggests
convective inducing parameters take place more across the central and
northern plains into Minnesota. Maybe just some debris clouds streaming
across the area from the west off upstream convective processes
later tonight into early Thursday morning. With low surface dewpoints from northeast-
to-southwest thanks to lingering western Great Lakes anticyclone...will
play lows in the same gradient with middle 50s in the far northeast...to
the low to middle 60s in the southwest. Another pleasant late June night.
Thursday...some waning support/elevated thta-east advection under-
cutting continued upper ridge amplification process along and west
of the middle to upper MS River Valley region to possibly allow some
higher based showers and a few storms to drift across the County Warning Area from
the west at times. Current forecasts suggest the far west and
northwestern third of the dvn forecast area more at risk of
experiencing some precipitation. South to southeasterly low level return flow
to advect warmer air mass supportive of highs well in the upper
80s...but worried convective debris/clouds may temper the warm up
potential some and will go more with middle 80s across much of the
area. Highs may be held in the lower 80s in the north. ..12..
Long term...(thursday night through wednesday)
issued at 345 PM CDT Wednesday Jun 19 2013
Right on Quebec with Summer solstice /1205 am CDT Friday/ the pattern
throughout much of the period will be that of a fairly typical
summertime regime featuring very warm/hot and humid conditions
along with nearly daily chances of storms as pattern aloft is
fairly stagnant for most of the period featuring mean western
troughing with broad ridging from the Great Lakes to the Gulf Coast.
For most of the period the area will reside in or near the active mesoscale convective system
zone or ring of fire... with County Warning Area conceptually in or near favored
18c to 24c 850 mb thermal gradient for genesis and track of convective
complexes. While precipitation chances cant be ruled out at about
any time there will be plenty of dry hours... but in this regime
the best chances of convection favor the nighttime and early am hours.
Unfortunately cannot get away from broad-brush 20-40 probability of precipitation through good
portion of forecast for now as confidence low with timing of features
and due to challenges of where convection fires at night will affect
where it develops the following day and this not evident often until
6-12 hours prior. Temperatures generally above normal with mainly range of 86-93f
on highs and 67-74f on lows. Heat indices likely approaching 100 degrees in
some locations for several days by Sat through Tuesday.
Models generally depict the stagnant pattern breaking down around the
middle of next week... with the retrogression of the upper ridge
/heat dome/ out west allowing for broad troughing over the eastern Continental U.S..
this should eventually result in return of more pleasant conditions...
with the exact timing still in question. The 12z hi-res European model (ecmwf) has
sped up the next cold front to Wednesday. If this trend persists then will
need to really lower temperatures for next Wednesday.
&&
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1132 PM CDT Wednesday Jun 19 2013
Surface high pressure will gradually move east allowing southeast
winds to be strengthen to around 10-12 kts by 15z/20. Skies should
be primarily clear overnight...with scattered high based
altocumulus at times. Thus...a scattered cloud group around 12000
feet is included throughout the entire period. There may be a few
scattered showers or thunderstorms from 18z/20 to 00z/21...but
coverage is expected to be very scattered...if not isolated.
Thus...I have left any mention of showers and storms out of the
terminal forecasts at this time. Should a shower occur...a brief
reduction in visibility due to rain is the primary threat.
Ervin
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Synopsis...12
short term...12
long term...05
aviation...Ervin
