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Displaying AFOS PIL: AFDDMX Received: 2017-09-14 04:20 UTC

FXUS63 KDMX 140420

Area Forecast Discussion
National Weather Service Des Moines IA
1120 PM CDT Wed Sep 13 2017

.SHORT TERM.../Tonight through Thursday/
Issued at 349 PM CDT Wed Sep 13 2017

A short wave will ride across the upper ridge across the region
and flatten it somewhat as it pushes a surface low over the 
central Plains towards eastern South Dakota and Nebraska. This 
will increase the warm advection across Iowa bringing even warmer 
temperatures to central Iowa for tonight and Thursday. For 
tonight, the wind across western and central Iowa will remain 
south to southwest and light with the better warm advection 
occurring west. Soundings show a pretty dry airmass in place so 
fog is not a concern tonight with one exception...the wind across 
the eastern part of the forecast area will have a more 
southeasterly component and may advect a little more low level 
moisture in. There is a possibility that areas from Waterloo 
through Ottumwa could see some ground fog towards daybreak but 
confidence is low of this occurring and it would be only for a 
brief period so I am not going to put it in the forecast for now. 

Thursday a south wind will increase bringing in even warmer temps 
and more moisture by late in the afternoon. Eastern portions of
the forecast area will not be as warm as central and west where 
lower 90's are expected but those locations will still see mid to 
upper 80's. There is some hint that a secondary shortwave further 
south across Kansas/Nebraska in the afternoon could spark some 
showers/storms across the southwest and south central portions of 
the forecast area, however we are dealing with some pretty dry air
despite the increasing moisture which will come in late. So even 
though we will destabilize I believe the lack of moisture will 
limit the precip threat. The weather becomes more active after 
Thursday which will be discussed in the long term. 

.LONG TERM.../Thursday night through Wednesday/
Issued at 349 PM CDT Wed Sep 13 2017

Certainly a bit more active weather pattern in store over the 
next several days that Iowa has had in quite some time. A few 
concerns; winds and temperatures on Friday and then periodic 
storm chances Friday into early next week. Leaned toward a blend 
through Saturday then closer to the ECMWF the rest of the period.

Thursday night into Friday...the upper level flow begins to shift 
more zonal to southwest flow during this period.  An increasing 
surface pressure gradient on Friday combined with deep mixing, 
completely mixing dry adiabatically to around 800mb, should yield
a fairly breezy afternoon Friday with some gusts over 30-35 mph 
possible. Confident to raise sustained winds/gusts and even 
maximum temperatures. Utilized a blend of the ECMWF/NAM for 
temperatures on Friday as they have much of central Iowa in the 
lower 90s. The ECMWF seems slightly too warm, but then again with 
the dry air and deep mixing, certainly cannot completely rule out 
a few areas topping the middle 90s. Also on Friday is fire 
weather concerns with the gusty winds and low relative humidity. 
Lowered dew points slightly due to the deep mixing and thus the RH
values get as low as 30-35 percent by Friday afternoon.

Low confidence with any precip chances Thursday night into Friday
with the abundance of dry air in the lower levels and very weak 
upper level support forcing with the shortwave embedded within the
500mb southwest flow. May see a few stray showers and storms 
across the west to northwest late tomorrow night into Friday. 

Saturday through Tuesday...a deepening upper level trough over the 
central to northern Rockies will dig into the central CONUS
Saturday afternoon and evening. There maybe some elevated storms
in the WAA regime Saturday afternoon, but a strong cap remains in
place across the forecast area and have low confidence with any 
storms developing until the cold front/trough advance across 
central Iowa late Saturday night into Sunday. The surface low 
pressure associated with the trough will skirt across central 
Minnesota and drag the cold front through the state b/t 03-09z 
Sunday. This seems to be central Iowa's best potential for any 
measurable precipitation, but not enough to alleviate the drought 
stricken areas. 

GFS has been fairly consistent on bringing the remnants of a 
tropical system, originating off the coast of western Mexico/Baja 
Peninsula, into the state by Tuesday into Wednesday of next week.
If this holds true, certainly some much welcomed rain across the
state. The ECMWF shears apart the system as it comes into Texas 
and keeps any remnants to the south of the state. 


.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1120 PM CDT Wed Sep 13 2017

Few changes to going forecast. Slow return of warmer air across
the region ovn will reduce any chances for fog across the region.
Light/var to south winds will continue through 15z when winds mix
significantly west...closer to KDSM/KFOD/KMCW until 23z. Otherwise
mid level clouds expected through 18z and again aft 00z over the
region as another impulse moves northeast. Airmass dry enough to
keep mention of any thunder out of fcst./rev




LONG TERM...Podrazik