Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 171145

Area Forecast Discussion
National Weather Service Quad Cities IA IL
545 AM CST Fri Nov 17 2017


Issued at 310 AM CST Fri Nov 17 2017

Aloft quasi-zonal flow dominates the central US, with an upper
trough impinging on the West Coast. At the surface, high pressure
spans from the Great Lakes to the Gulf of Mexico, while low pressure
deepens in the plains.  The result is a relatively tight pressure
gradient over the Mississippi Valley.


.SHORT TERM...(Today and Tonight)
ISSUED AT 310 AM CST Fri Nov 17 2017

South winds and continued moisture advection will hold clouds in
place over the area today. Forecast soundings still supportive of
drizzle developing this morning. By this afternoon, upper flow backs
to slightly more southwesterly as upper trough moves into the
Rockies. Broad scale lift ahead of this trough will aid saturation
of the column and rain chances will increase late this afternoon and
into the evening. The surface front will cross our area this
evening. Instability is limited, so have kept mention of thunder to
southern parts of our area.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 310 AM CST Fri Nov 17 2017

The main forecast issues in the short term period are
precipitation type and amounts Saturday.

Strong cold air advection will be underway Saturday morning in the
wake of a potent surface cyclone. Forcing from the main upper wave
will be sufficient for an area of precipitation spreading from
west to east into the early afternoon. Forecast soundings indicate
rapid cooling aloft, with near surface temperatures determining
precipitation type. There are still differences in the strength
and timing of the cold air among the warmer ECMWF and colder
GFS/NAM, so confidence is rather low regarding the potential for
accumulating snow. Frontogenesis/dendritic lift diagnostics
suggest some potential for a decent Fgen band resulting in faster
dynamic cooling and more snow, similar to the recent event.
However, relatively warm ground and road temps and the daytime
occurrence should keep any accumulations to just a light dusting
on elevated and grassy surfaces. Areas along/north of Highway 30
are favored for light snow, with a rain/snow mix or all snow to
the south. Precipitation will end east of the Mississippi River by
late afternoon.

Looking ahead, dry weather is expected through the rest of the
long term period. Monday will likely be the warmest day of the
week with highs in the upper 40s to mid 50s. Northwest flow will
cool daytime highs into the 30s by Wednesday, followed by another
modest warming trend late in the week.


.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
ISSUED AT 539 AM CST Fri Nov 17 2017

IFR/LIFR conditions will prevail through the majority of the TAF
period. Low clouds will overspread the region this morning,
followed by drizzle and rain increasing this afternoon and
evening. There is a low chance of thunder at KBRL this evening as
a front approaches. When the front moves through tonight, surface
winds will shift to northerly.




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