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fxus63 kdvn 271722 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
1222 PM CDT Sat may 27 2017

Update...
issued at 1208 PM CDT Sat may 27 2017

A dissipating mesoscale convective vortex from last night continues to move northeast
through central Iowa. It is largely dissipating, but retains
convection in the north flank, with new cells forming on the east
edge, then rotating up north. It is unclear how long this activity
will persist, but it is certain we will see cloud cover from this
mesoscale convective vortex. The combination of persistent low clouds this morning and new
clouds this afternoon, has already warranted an update to lower
highs to the lower to mid 70s.
Ervin

&&

Synopsis...
issued at 330 am CDT Sat may 27 2017

Areas of fog under pass surface ridge this morning, then warming today
ahead of the next incoming wave/mesoscale convective vortex seen on water vapor imagery
currently acrs central neb. This feature as well as digging northern
plains upper trof will produce rounds of showers and thunderstorms
acrs the area this weekend.

&&

Short term...(today and tonight)
issued at 330 am CDT Sat may 27 2017

Today...several fcst challenges to deal with for the short term
period. Have already issued a dense fog advisory for much of the dvn
County Warning Area that isn't currently being cloaked by incoming high clouds from
the west, or lingering lower stratus in the east, for early this
morning. Will watch visibility trends through sunrise so as to add or
subtract from the current headline area. Then the challenge of how
warm to go for highs today. Air mass in place or being advected into
the area supports highs in the upper 70s to lower 80s, but again
cloud cover and fog to erode, sfc moisture, and east to
southeasterly sfc winds which arn't the warmest of winds, suggest
going cooler as a hedge. Will advertise temps more in the way of mid
to upper 70s which may still be too mild in some locations.

Then attention turns to the upstream mesoscale convective vortex and associated storm
clusters acrs neb into northern Kansas. Don't see why they won't just
keep moving along and enter the western County Warning Area by early to mid
afternoon, and progress acrs the rest of the County Warning Area through early
evening. But several models including some hires/cam's, decrease and
decay the activity as it moves acrs the local area mid to late
afternoon and early evening. This while strong thermodynamic, shear
and convergent forcing support strong storm systems acrs the
southern/Central Plains and acrs MO into southern Illinois. Thus energy
imbalances and focus to the south may rob to the north acrs the
local area reducing local storm feed, as well as lingering ridge
axis to the east that processes will encounter. Some of the models
may be picking up on these factors and thus the decrease in
intensity and coverage as they arrive and move acrs this afternoon.
But at the same time, the afternoon peak heating and cape build up
along with locally increasing shear profiles, suggest you can't rule
out a locally strong to severe storm as they move into the area as
well. Large hail and gusty winds the main concern with any strong
storm that manages to move into the area and maintain, or develop in
the area with the mesoscale convective vortex arrival during afternoon heating. Locally
heavy rainfall swaths over an inch possible too with any maintaining
storm cluster.

Tonight...again the general idea may be that while a large mesoscale convective system steam
rolls east and southeastward acrs MO, we may have a continued decreasing
of storm coverage during the evening to the north of the complex to
the south. But then as the upper trof axis digs southeastward acrs
central into eastern Iowa overnight, several models suggest that this
feature will utilize secondary thta-east feed and unused convective available potential energy to
generate nocturnal shower/thunderstorm clusters mainly after
midnight and into early Sunday morning and mainly acrs the northern
half of the dvn cwa, with isolated cells possible to the south of I-
80. Will lean toward this scenario, but it will only unfold if there
is minimal or decreasing convection during the evening. Other models
which are more bullish with stronger storms hanging on during the
late afternoon and evening leave the atmosphere/air mass worked over
and thus the late night trof will have a hard time generating any
new convection of consequence. Any stronger late night storm may be
capable of producing hail. Overnight lows down in the 50s to around
60. ..12..

Long term...(sunday through next friday)
issued at 330 am CDT Sat may 27 2017

Nice, pleasant late may weather with mostly slightly below normal
temperatures and essentially dry.

Long term forecast confidence assessment...good or above average.
Little sensible weather issues and consistent northwest flow and
subsidence supporting minor day to day changes in temperatures. Some
potential in light winds at night for cooler lows but mostly Max/min
forecast should be within 3 degrees of forecast otherwise.

Sunday through Friday...only minor changes made. Northwest upper
flow should result in fair to mostly fair skies with low or no
chance of precipitation due to surface and upper high pressure.
Highs still on track for upper 60s to middle 70s with coolest in
northeast to generally warmer in southwest sections. Area mins
mostly low to middle 50s with upper 40s possible with clear skies
and light winds supporting good radiative cooling conditions for
favored low lying areas along and north of I-80. This period overall
should be roughly 5 degrees below average.

&&

Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1208 PM CDT Sat may 27 2017

Extensive low clouds and fog are lifting quickly as of 17z. This
is true in all sites. A dissipating area of showers and storms
will possibly move through eastern Iowa, but this is now looking
more like scattered showers now. I have a vicinity shower possible
later this afternoon, followed again by this potential after 06z
tonight when a cold front moves through. Conditions should be
mainly VFR until that cold front arrives late tonight, followed
then by gradual improvement back to VFR by mid to late morning
Sunday.



&&

Hydrology...
issued at 330 am CDT Sat may 27 2017

No changes made. Trends and forecast indicate rises continue on the
Mississippi River from earlier rains well north of the region with
crests in the north sections Monday and by Friday in far south
sections. Crests at most locations still suggested to be at minor to
moderate stages with very little change in forecast crest levels the
past 24 hours.

&&

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

$$

Update...Ervin

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