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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
350 am CDT Friday Jul 25 2014

issued at 345 am CDT Friday Jul 25 2014

Elevated convection has fired in the past few hours across portions
of northern/central Iowa and into western/southern Minnesota. This is occurring
on the nose of a 50+ knot low level jet on the eastern edge of a capped
elevated mixed layer. Storm Prediction Center mesoscale analysis shows the better moisture
transport is still west of the dvn County Warning Area with the highest bulk shear
values in southern Minnesota. Precipitable waters range from 2.10 inches
in western Iowa to less than an inch in northern Illinois. Infrared satellite
loops indicate tops continue to rapidly cool as the thunderstorm
activity moves southeast. A short wave trough was also lifting
eastward across the northern/Central Plains around a closed upper
low in southern Alberta.

A cool/stable surface layer was noted across the dvn County Warning Area with 3 am
temperatures in the middle 50s to middle 60s...while readings were well
into the 70s to lower 80s in the central/Southern Plains.


Short term...(today and tonight)
issued at 345 am CDT Friday Jul 25 2014

Forecast focus on thunderstorms mainly this morning and temperatures.

Today...forcing and rapidly increasing moisture will allow thunderstorms
to continue to develop/spread across much of the County Warning Area this morning on
the nose of the strong low level it veers into the area. Due
to the elevated nature of the storms and the cool/stable surface environment
severe weather is not expected. Freezing levels are quite high at nearly
15k feet. However...some of the stronger storms may produce frequent lightning...
sub-severe hail and locally heavy rainfall. Later this morning the low
level jet will weaken considerably along with the passage of the short
wave trough. A strengthening cap will also spread eastward into the
County Warning Area. This will diminish or end the thunderstorm activity by afternoon
so will have likely to categorical probability of precipitation this morning and only small
probability of precipitation this afternoon. Expecting extensive cloud cover to linger into
the afternoon especially in our east while more sunshine develops in
our west. Models really surge the warm 850 mb temperatures into our
western County Warning Area with +20c noted later in the afternoon. I will forecast
maximum temperatures ranging from the middle 80s SW to the middle 70s NE.
However...depending on amount of lingering clouds (or lack of) this
afternoon these readings may need to be re-visited.

Tonight...strong capping environment overspreads the County Warning Area except
possibly our far eastern County Warning Area. Models insist on developing convection
in our eastern County Warning Area as the low level jet strengthens again...but there
is the potential the storms may end up firing east of the dvn County Warning Area.
Will have chance probability of precipitation to cover this scenario but confidence is rather
low at this point. This will be a warmer night with minimum temperatures
in the middle 60s to lower 70s.

Long term...(saturday through thursday)
issued at 345 am CDT Friday Jul 25 2014

Chances for showers and storms through the weekend then mainly dry and
cooler much of next week.

Sat-Sat night...coverage of storms and severe potential are the main
challenges. Model soundings generally show decent elevated mixed
layer or cap developing over much of the area suppressing convection
for much of the day. This will also spell very warm and humid
conditions with highs middle 80s to near 90f and dewpoints upper 60s to
lower 70s for PM heat indices from near 90 north to around 100 south.
Several forecast soundings though show the cap weakening after 20-21z
with passage of surface-850 mb cool fronts and therefore would anticipate
increasing storm coverage by late afternoon/evening mainly south of I-80
vicinity of front and elevated convergence and moisture advection on
nose of increasing southwesterly low level jet. A few severe storms possible
given moderate to strong instability (sbcape 2500-3500 j/kg) and
shear (0-6km 35-50 kts). Main threat being damaging winds with large
hail risk secondary and confined to supercells or decent mesocyclones
given abundance of moisture in atmospheric column characterized by
precipitable waters of 1.6-1.9 inches and warm cloud depths up around 13kft above ground level...
which poses risk of locally heavy rain of 2+ inches with potential
for backbuilding and isolated higher amounts with veered southwesterly low level

Sun-Sun night...digging pv anomaly from upper Midwest into Great Lakes
to usher in secondary and stronger cool front Sunday PM. Will see
chances for additional showers and storms mainly during the PM into
early evening with this front with best chances over northeast 1/3-1/2 of the
County Warning Area. NAM and GFS showing 40-50 kts of 0-6km bulk shear and with
inverted v soundings and drier air aloft will need to watch for potential
of more organized and stronger storms containing gusty winds and hail.
Sunday looks to be the last warm day for a while... which of late means
last day around normal.

Mon-Thu...medium range models and ensembles in good agreement with the
overall pattern depicting a deep upper trough over the eastern half of the
Continental U.S.. this will result in another period of generally below normal
temperatures...which may feature a morning or two of near record lows Tue-Wed.
Challenge aside from temperatures will be whether any PM shower chances exist
with the cooler air aloft and any impulses in northwest flow... but too
far out and probs appear too low for much mention of precipitation until possibly
late week ahead of potentially another shot of cooler air beyond the
scope of the current extended.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 345 am CDT Friday Jul 25 2014

VFR conditions will be seen through 25/09z as high pressure moves east
into the Great Lakes with increasing middle/hi clouds. After 25/09z...a late
nocturnal complex of storms and showers should move southeast into eastern
Iowa and Illinois. Clouds will become partly to mostly cloudy to cloudy
with areas of showers and non-severe storms...VFR conditions may briefly
lower to MVFR with any stronger thunderstorms and rain. Coverage is too uncertain to
include in anything more than a vicinity wording in the terminals.
Some clearing is possible...mainly at mli and brl terminals after 18z/25.


Dvn watches/warnings/advisories...


short term...haase
long term...05

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