Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 201742

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1242 PM CDT Tue Jun 20 2017


Issued at 340 AM CDT Tue Jun 20 2017

An upper level disturbance moved into northern Minnesota overnight
and was helping sustain an area of showers and isolated
thunderstorms in central Minnesota. Across eastern Iowa and
northwest Illinois, the sky was mostly clear. The wind was light
and variable and early morning temperatures were in the 50s to low


.SHORT TERM...(Today and Tonight)
ISSUED AT 340 AM CDT Tue Jun 20 2017

The main forecast issue in the short term period is the potential
for isolated strong to severe thunderstorms this afternoon.

In the near term, a shortwave trough diving southeast into
Minnesota is producing scattered showers and isolated
thunderstorms. This batch is expected to brush the far northeast
counties this morning but remain sub-severe. The bigger concern is
this afternoon, especially over the southern and eastern portions
of the forecast area, from far NE Missouri, through Burlington to
the Princeton area, as the shortwave moves through the area along
with a weak cool front. Favorable ingredients for strong to
isolated severe storms include deep layer shear above 40 kts,
0-3km MU Cape around 1500 J/kg, steep mid and low level lapse
rates and WBZ heights below 10k feet AGL. Hail and isolated
damaging winds will be the main threats, similar to Monday.
Convection will head south of the area this evening.

Favorable southwest flow will boost afternoon highs into the 80s
over most of the area, very close to normal for the first day of

.LONG TERM...(Wednesday through Monday)
ISSUED AT 340 AM CDT Tue Jun 20 2017

Forecast focus on increasing thunderstorm chances later this week
then below normal temperatures this weekend.

Wednesday:  ECMWF develops thunderstorms along an advancing warm
front in the morning, while the GFS is dry. This will need to be
monitored by later shifts as the grids currently favor the GFS.
During the afternoon, dewpoints will be creeping upward into the mid
60s in our sw cwa. Highs should push into the 80s, with close to 90
in our far south.

Wednesday night through Thursday night: A stormy period with zonal
flow aloft and frontal boundary meandering in the region. Warm,
moist and unstable air will be in place to support thunderstorms,
some possibly severe. Forecast soundings indicate a cap in place
Thursday afternoon, which should suppress convection. However, by
evening a cold front will be arriving into a moderately unstable
airmass, with strengthening deep layer shear. While there is a
marginal risk for severe storms Wednesday night, the better
opportunity is Thursday night, when SPC has a slight risk over the
cwa. At this time, the main threats appear to be damaging winds and
large hail. Torrential rain is also in the offing as PWAT`s increase
to over 2 inches.  Highs will be well into the 80s to near 90, with
lows well into the 60s to lower 70s.

This weekend into early next week: Models depict a deepening upper
level trough diving into the area with a strong cold front sweeping
across the cwa this weekend. The ECMWF is much more aggressive
showing widespread rain and embedded thunderstorms, especially
Saturday night. Temperatures will be below normal with highs in the
70s and lows in the 50s. The cooler than normal readings should
continue into Monday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1242 PM CDT Tue Jun 20 2017

VFR conditions are expected through the period. Main concern for
aviation will be thunderstorms in the next 6 hours. With low
confidence of when they will occur opted to go with 4 hour tempo
blocks at MLI and BRL. It is likely that these sites wont see
thunder for longer than an hour this afternoon.




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