Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 250457
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1157 PM CDT Mon Apr 24 2017

...06z AVIATION UPDATE...

.SYNOPSIS...
Issued at 342 PM CDT Mon Apr 24 2017

Deep southerly flow continues today, with strong mixing of the dry
air mass resulting in incredibly low afternoon RH levels of 15 to 20
percent. If it were not so far into the spring green up, today would
likely be a serious fire weather day. In the end, it might only be
remembered for a few chapped lips of those outdoors all day.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 342 PM CDT Mon Apr 24 2017

The low pressure moving over northwest MN will keep the south to
southeast winds going overnight, but at a much lower level, around
10 to 20 mph, rather than the 20 to 30 mph levels this afternoon.
The mixed boundary layer will remain mild in the lower to mid 50s
tonight, despite only some high clouds above.

Tuesday will see similar conditions to today, but will notably be
seeing increasing cloud cover through the day from west to east.
Despite the expectation of mostly cloudy skies by early afternoon,
the strong mixing ahead of the cold front will bring highs back the
lower to mid 70s, and even upper 70s from west to east. Dry
conditions are mainly expected as saturation should only occur along
and west of the cold front tomorrow due to the slow moisture
advection into this impressive warm draw. Some very high based
showers are possibly in the far northwest, but pops will be kept
fairly low as this may only be virga ahead of the front.
ERVIN

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 342 PM CDT Mon Apr 24 2017

Tuesday Night through Wednesday:

Longwave trough moving into the Plains will shift a cold front
through the Midwest. Ahead of the front, a broad sfc-850mb area of
low pressure is forecast to follow the low-level baroclinic zone
bringing rounds of showers and thunderstorms. Theta-e advection in
a narrow corridor of southerly lower tropospheric winds
originating over the Gulf of Mexico, will pump anomalously high
moisture into the region with PWATs approaching the 1.25-1.50 inch
range. Forecast soundings show elevated instability with
500-700mb lapse rates near ~7 C/km, and 0-6 bulk shear over 50
kts. Therefore, the strongest storms could produce some hail.
Although MUCAPE profiles are tall and skinny, so mainly small hail
expected.

Wednesday Evening through Thursday:

The next wave embedded in the large-scale upper-level trough, is
likely to cross E Iowa/NW Illinois during this period. Model
consensus with this round is to take the sfc low across our
eastern CWA. The sweet spot for the heaviest rainfall will
probably occur where the zone of 925-850mb frontogenesis sets up.

The previously mentioned cold front is a slow mover. So we`ll be
dealing with the same moisture rich airmass through at least part of
Wednesday night. This is the stronger of the two waves and is the
better chance for moderate to heavy rainfall. As for amounts, a
wide range is likely across the CWA. But focusing in on the
highest values, there is potential for 1-2+ inches in a south-to-
north oriented zone. Difficult to pin down where exactly the
heaviest rain is going to be this far out.

The risk for strong or severe thunderstorms is dependent on the
final track of the sfc low. The current outlook from the Storm
Prediction Center places the eastern CWA in a marginal risk. The
current favored track of the sfc low keeps the better chances for
severe storms to the SE of the forecast. However, this is a
situation we`ll have to continue to monitor.

Friday and Saturday:

Mid-level impulses continue to eject out of the Four Corners area
into the Midwest. Another surge of 850mb moisture and PWATs
warrants periodic chances for showers, possibly some storms too.

Sunday and Monday:

The wet pattern should continue through this weekend into early
next week. The longwave trough that was anchored over the Western
U.S. and the Plains all week, finally moves through the central
section of the country, possibly in the form of a strong low.
Models have shifted a little bit to the ESE with the low track,
keeping E Iowa/NW Illinois on the cool side of this system.
However, confidence on the exact track remains low at this lead
time. Uttech

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1153 PM CDT Mon Apr 24 2017

DVN VWP showing 40-45 kts in second gate from SSE and with surface
winds around 10 kts I have added LLWS mention. Otherwise, vfr
conditions will persist through the TAF cycle with periodic bouts
of mid/high clouds and chance of a high based shower Tue AM. There
is a chance of a shower or storm arriving late in the taf cycle as
well.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Uttech
AVIATION...McClure


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