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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
700 am CDT Thursday Aug 21 2014

Synopsis...
issued at 315 am CDT Thursday Aug 21 2014

Analysis at 3 am shows developing mesoscale convective system system in SW Minnesota and northwest Iowa
moving east southeast with supporting pressure fall center axis and
backing winds for a decent rain event near or increasingly in
north sections of forecast area with some decent rains suggested
next 4 to 8 hours. Upstream energy to keep area near thermal
boundary for episodes of convection near or over forecast area
lasting into this weekend.

&&

Short term...(today and tonight)
issued at 315 am CDT Thursday Aug 21 2014

Short term forecast confidence...fair to poor to very poor (average
to below to well below average). As in yesterday...clouds and precipitation
risks appear to be rising next 8+ hours that may require lowering highs
north and increasing probability of precipitation with higher to much higher quantitative precipitation forecast amounts. The
mesoscale convective system will take another 3 to 5 hours to better assess. Along and south
of Highway 34...looks fairly reasonable today. Tonight rain possibilities
will be impacted by the convective event this morning into early afternoon.

Today...large thermal gradient for high temperatures suggested with
highs along and especially north of Highway 30 possibly 5 plus degrees
again too high. The magnitude of the mesoscale convective system outflow boundary later this
morning will be key. Locations near Highway 20 and possibly near Highway
30 may pick up a half inch or 1+ inch or more of rain if trends continue.
Along and south of Highway 34...highs should reach around or into the
lower 90s with partly to mostly sunny skies with heat index values into
the upper 90s to possibly around 100f. Probability of precipitation 20-50 percent north may
need raising depending on track of mesoscale convective system. Strongest storms today may
be strong with marginal severe risks of gusty winds maybe up to near
60 miles per hour the main threat and .50 to 1 inch hail secondary threat.

Tonight...area in favored corridor of another mesoscale convective system event near or over
the region middle/late evening into overnight. Later shifts depending on
today/S event may need to raise probability of precipitation and quantitative precipitation forecast amounts over again north
and central sections based on favored mesoscale convective system track metrics. Lows of 70
to 75 may be too high north 1/2 if another decent convective event
occurs. Assessment is central and north sections most at risk. Nichols

Long term...(friday through next wednesday)
issued at 315 am CDT Thursday Aug 21 2014

Friday through Sunday...another round of model runs generally
suggesting the upper ridge will look to amplify across the middle to
upper MS River Valley regions Friday into Sat with substantial thermal
ridge/heat dome sustaining along and south of the County Warning Area. Big concern
for Friday another day where convective debris or elevated warm air advection clouds
squelch the heat up potential over portions of the dvn County Warning Area...probably
north of i80. If clouds or even showers/storms fester late into the
afternoon...temperatures could be held well down in the 80s or even in the
upper 70s in those areas...while areas with mostly sunny or even
partial sunshine with a southwesterly breeze warm into the 90s with
near heat advisory or heat advisory criteria indices. Ongoing
uncertainty into Friday evening and overnight if mesoscale convective system or storm clusters
can fire over portions of...or propagate into the area from the west
or northwest. Upper ridge axis arc/S right up the upper MS River
Valley and obvious best forced and low level jet convergent zone to produce
mesoscale convective system/S or even an mesoscale convective complex look to occur across the west Central Plains up
through the Dakotas and western Minnesota. But a secondary swath of mesoscale convective system
forcing parameters by the NAM and even the new 00z European model (ecmwf) suggest a
secondary mesoscale convective system or storm cluster generation area possible from central
Iowa eastward to northeastern Illinois into west central Indiana late Friday
night. Will keep low to moderate chance probability of precipitation across most of the County Warning Area.
Shear and thermodynamic profiles suggest heavy rain and isolated severe
storms possible with any convective systems that can make it across
the local area Friday night into Sat morning. Ongoing ridge
amplification continues into Sat...and this should finally shunt
most of the ring of fire potential west/north/northeast of the area.
But many of the models now suggest lake front or portion of warm
frontal boundary stalling across the northeastern third of the County Warning Area
with low level easterly flow into these areas. Besides being a big temperature
bust area with much cooler values occurring than what will be forecast...
this area could be a focal for new shower/storm development. Will
leave low to moderate chance probability of precipitation going north of i80 for Sat...while
areas to the south of the Interstate possibly warm back up into the
low to middle 90s with heat indices of 100-105+. Convective spawning
grounds continue across the north half of the plains into the
northwestern Great Lakes Sat night with bulk of the latest 00z run
medium range models suggesting the local area dry under the thermal
ridge. But with ongoing model mistrust will keep at least slight chance
probability of precipitation going north of i80. Upper trough and jet energy really dig across
the northern rockies and into the plains the second half of the
weekend with the potential for some of the convection induced by
this process bleeding in from the northwest and clipping portions of
the local area late Sunday or Sunday night. Otherwise if convective
debris can be held at Bay...Sunday could be the day with widespread
low to middle 90s in enhanced southwesterly mixing flow ahead of
incoming low level boundary from the northwest. Another heat advisory
potential day for at least portions of the area if this unfolds the
way the solutions currently advertise it to do.

Monday through next Wednesday...long range indication suggest models
are having trouble resolving incoming trough energy and battling with
upper ridging and ridge placement/break down. Early to middle next
week could potentially be an unsettled period depending on low level
frontal strength and placement. Sweeps through or stalls across the
region...along with orientation. More confidence on synoptic feature
evolution this period probably not going to happen until the weekend
as eastern Pacific and Gulf of Alaska jet/wave energy gets better
sampled. Until then...low chance probability of precipitation almost every day and general temperature
tend at or above normal until the ridge breaks. ..12..

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 658 am CDT Thursday Aug 21 2014

Generally VFR conditions...north of I-80 and areas of showers and
thunderstorms until late morning for dbq/Cid terminals. After
17z...fair skies with VFR conditions expected all terminals until
after 22/02z when risk of another convective system may result in
periods of MVFR and IFR conditions due to thunderstorms. Winds
east to southeast 5 to 15 kts becoming southwest at terminals by
21/21z.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.

&&

$$

Synopsis...Nichols
short term...Nichols
long term...12
aviation...Nichols

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