Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 172333

Area Forecast Discussion
National Weather Service Des Moines IA
633 PM CDT Wed Oct 17 2018

.DISCUSSION.../Tonight through Wednesday/
Issued at 300 PM CDT Wed Oct 17 2018

A rather benign pattern will hold through most of the current
forecast period. Upper level synoptic flow is highlighted by
a stout rex block over the western conus and broad cyclonic flow
east of the Rockies. This leaves the Upper Midwest under a
northwest flow regime. Weak shortwaves embedded within the flow
will quickly cross through the area, delivering routine frontal
passages through the next several days. The frontal passages scour
out low level moisture availability well to our south and leave
the majority of the forecast dry.

Warmer temps into the 60s expected Thursday as southerly flow
returns behind the passing surface high. Light rain showers are
possible late Thursday night into Friday morning as southerly low
level isentropic ascent increases ahead of the approaching wave,
but dry air throughout much of the troposphere will be a limiting
factor. Westerly winds become quite breezy Friday afternoon as the
local pressure gradient tightens and deep unidirectional winds
promote efficient boundary layer mixing. Bufkit soundings for most
available models show wind speeds approaching 30-35 kts at the
top of the mixed layer ~ 850-800mb. A decent shot of cold air
advection behind a passing cold front may lead to a period of
stronger winds Saturday morning and afternoon, potentially
reaching advisory criteria for parts of the CWA. Winds should
quickly relax Saturday evening as a surface high moves in and the
boundary layer decouples, promoting ideal conditions for a chilly
night possibly in the 20s.

Deep trough entering the Pacific northwest slowly breaks down the
rex block early next week, potentially leading to precipitation
chances by Wednesday as a trough crosses the Plains. High
uncertainty exists with how this pattern will evolve and the
extent of moisture availability in our area, therefore the
extended range forecast remains dry for now.


.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 629 PM CDT Wed Oct 17 2018

Confidence is high in VFR conditions through the period with
clear skies for the most part. Winds will be light and variable
this evening as the surface ridge passes overhead, leading to
winds becoming southerly Thursday.





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