Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 280913
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
413 AM CDT Fri Apr 28 2017

...HYDROLOGY UPDATE...

.SYNOPSIS...
Issued at 330 AM CDT Fri Apr 28 2017

Upstream upper trof noted on water vapor imagery acrs the west
central plains, will roll out east-northeast over a llvl
boundary/baroclinicity oriented west-southwest to east-northeast
acrs the southern CWA for a rain event today into tonight along with
sub-normal temps. Then a much larger system with a substantial
moister conveyor off the western gulf will make for several rounds
of rain over the weekend.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Fri Apr 28 2017

Today...Will let the frost advisory ride for now but may cancel
early if temps improve around sunrise. Convergent south to southwest
20-25 KT LLJ with increasing moisture/THTA-E feed will fuel
scattered to clusters of mainly elevated showers today into this
evening as the above mentioned upstream trof ejects out acrs the
area. The process will battle some mid level ridging this morning
which will act as an erosion agent with precip trying to push toward
the area from the southwest, but saturation and lift will eventually
overcome this by mid morning. Before then may just have high based
sprinkles trying to advance northward. General ensemble placement of
the sfc/LLVL boundary has it falling short of I80 by evening or even
further south...maybe from Princeton IL to Keosauqua IA by 00z Sat.
Expect a large temp gradient from the southeast upper 50s to around
60, to mid to upper 40s in the northwest with cold start to the day
and advancing clouds/evapo-cooling processes. Expect more organized
showers and coverage along and north of the H85 MB front which would
target generally the northwest half of the CWA by this afternoon.
Showers in the southeast may taper off to sprinkles or intermittent
light showers by mid to late afternoon. Generally moderate to high
POPs for a light precip event of 0.10 to 0.30 acrs most of the CWA
by mid evening. But with extent of precipital waters advecting up by
elevated flow, some concern model QPF underdone and would not be
surprised to see a strip of locally higher rain amounts along and
just north of i80...the elevated convergent zone.

As far as thunder, the NAM and GFS fcst elevated MUCAPEs supportive
of some embedded thunder especially in the southern third later this
afternoon and into the evening. But confidence is low with extent of
low to mid level saturation taking place. May be a better chance as
more robust activity first arrives from the southwest late morning
and midday if it doesnt "fall out" as it tries to arrive out of KS.

Tonight...Lift shifts off to the east-northeast with passing wave,
and just see lingering cloud decks, possibly low based, and light
spotty sprinkles or drizzle after mid evening. The next trof
organizes acrs OK and KS and llvl northeast flow shunts the boundary
to the south into early Sat morning. Will keep late night POPS in
the south for the next arriving overrunning shower event before
dawn, but a few solutions delay better overrunning surge until after
12z Sat. Lows generally in the 40s, except the far north and
northwest in brunt of north to northeast cool advection may get back
into the upper 30s.     ..12..

.LONG TERM...(Saturday through next Thursday)
ISSUED AT 330 AM CDT Fri Apr 28 2017

A prolonged warm frontal precipitation event will continue to unfold
Saturday through Saturday night, followed by a strong upper low and
surface low passage overhead Sunday into Monday. This low duration
of rain chances will add up to potentially heavy amounts of rain,
though over all confidence on placement of short term heavy rain
amounts are very much uncertain.

Looking at Saturday and Saturday night, the primary surface boundary
will remain south of the CWA, keeping any convection rooted near the
surface boundary well south of our area. The east to northeast winds
will be rather strong at 15 to 25 mph, and with temperatures
struggling through the upper 40s to lower 50s,  we will have wind
chills in the lower 40s all day Saturday. Light rain and rain
showers will be an ever present threat through the day and night,
with the south seeing the greatest coverage and amounts as the
moderate rain shields of 1 or more MCS impact the southern 1/3.
Thus, hourly rainfall will range from a few hundredths to 0.20 per
hour Saturday and Saturday night.  This is not likely to bring rapid
run off, but again, over time, heavy totals are expected.

Saturday night, this same process is expected to shift north a bit,
but otherwise remain the same, with widespread light rains north,
and light to moderate rains, with some embedded thunder south 1/2.

Sunday and Sunday night, the strong upper low and surface low will
make a significant shift northward, and this process will both
greatly increase the deep lift over the region, and begin forcing
much more of the high PWAT moisture back over the cold side of the
occluding storm. This means rainfall over the central and northern
CWA should become more efficient, and shorter duration heavy amounts
will become more possible.  Thunderstorms will become more numerous
as MU CAPE increases with strong lift especially Sunday afternoon
and evening. While a very low threat, if strong storms occur, that
is when they are going move through the CWA.  With dewpoint rising
Sunday afternoon as the low moves up over the area, temperatures
will inevitably rise as well, likely to the upper 50s to mid 60s
over the south 1/2 of the CWA, while locations northwest of the Quad
Cities to Sterling remain cold, in the upper 40s to lower 50s.

A potential dry slot will sweep over the area late Sunday night,
with rain become spotty, at least until Monday morning, when the
occluded low wraps moisture back around over the area. Monday
appears cool, windy, and very damp under the mature low, possibly
drizzly day if not plagued by near continuous light rain.

Tuesday, cool high pressure is forecast by models to move into the
Dakotas, while the upper trof begins to elongate and shear out. This
will likely keep the active front well to the south, and should keep
our temperatures seasonally cool, but not rain cooled. Thus, the
rest of the week`s highs forecast in the mid 50s to lower 60s,
should be substantially more pleasant than this extended wet and
cold pattern we are currently in.

ERVIN

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1143 PM CDT Thu Apr 27 2017

Vfr conditions anticipated through 12z Friday as increasing
mid/high clouds and developing northeast winds should mitigate
fog potential overnight. An upper level disturbance coupled
with an elevated warm front and moisture advection will lead
to increasing coverage of showers during the day on Friday
with conditions lowering to mvfr. Anticipate the coverage
of showers tapering off by evening as the forcing pulls away,
and kept general mvfr cigs Friday evening on cool, moist northeast
flow.


&&

.HYDROLOGY...
Issued at 406 AM CDT Fri Apr 28 2017

There is high confidence on widespread rains over 1 inch this
weekend. There is substantially lower confidence for the
placement of rains exceeding 2 inches, and lower yet for 3 inch
amounts. The heaviest totals in the 2 to 3 inch range are likely
to bring significant rises and possible new flooding to area
rivers near and downstream of these amounts. As of now, there is
considerable differences in model guidance position of the track
of this weekends storm system, and that track will have a large
impact on locations of heaviest rainfall.

As of now, minor flooding will continue along the Mississippi
River from around New Boston down through Burlington Iowa.
ERVIN

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Frost Advisory until 8 AM CDT this morning for Buchanan-Delaware-
     Dubuque-Jackson-Jones.

IL...Frost Advisory until 8 AM CDT this morning for Carroll-Jo
     Daviess-Stephenson.

MO...NONE.
&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Ervin
AVIATION...McClure
HYDROLOGY...Ervin



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