Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 132342

Area Forecast Discussion
National Weather Service Des Moines IA
642 PM CDT Fri Oct 13 2017

...Updated for 00z Aviation Discussion...

.SHORT TERM.../Tonight through Saturday/
Issued at 320 PM CDT Fri Oct 13 2017

Frontal boundary in place across the forecast area has been
wavering around southern/eastern half of the CWA all day, and will
continue to linger through the night before pushing north as a
warm front during the day Saturday. Sfc low centered around east
central KS with a lobe stretching back toward the TX/OK panhandle.
These area of low pressure will gradually lift north and east
through Saturday as deepening upper trough continues to drop
through the Rockies tonight and then ejects eastward through the
central US through the day Saturday. As the front slowly sinks
further south and east could continue to see additional
development of showers/storms across mainly the south/east
portions of the forecast area with clouds spreading across the
area late tonight. WAA/moisture advection to then increase ahead
of the approaching wave for late tonight into Saturday with more
widespread showers/storms expected across the south by early
Saturday. Showers and storm chances to spread across the entire
forecast area Saturday morning into early afternoon as widespread
lift is over the area. Elevated thunderstorm activity possible
across the majority of the area, with some sfc-based storms
possible near the warm front expected to lift northward through
the far southeastern portions of the CWA. This will be the main
area of concern regarding a severe threat with sufficient shear
and instability expected. As the cold front approaches the area
expect a line of storms to start pushing through
southern/southeastern CWA by late afternoon/early evening. Dry
slot to start nosing into the west central forecast area by early
evening, so have lowered pops in that area at that time.

As for temperatures should cool off across the north where some
clear skies possible this evening, then temps to steady
off/slightly warm tonight with clouds increasing and waa
beginning. Temperatures Saturday to remain cool across the north
with a large spread between the cooler area expected to top out in
the mid 50s northwest to areas near/south of the warm front into
the low 70s southeast.

.LONG TERM.../Saturday night through Friday/
Issued at 320 PM CDT Fri Oct 13 2017

The main forecast concern was focused on the strong winds
Saturday night into Sunday and warming trend throughout next week.

Saturday into Sunday...strong PV anomaly punches across northern
Iowa into southern Minnesota between 03-09z Sunday behind of the
cold front that will sweep across the state. Significant pressure
rises with this PVA, roughly 4-5 mb change in 3-hours Saturday
night.  Surface pressure gradient tightens to around 15 mb
difference from east-to-west across the state by 06-09z Sunday with
fairly steep lapse rates and wind atop the mixed layer increasing
to 40-45 knots (or greater in the north).  Confident to increase
winds Saturday night into Sunday and certainly looks borderline wind
advisory during this time and something to continue to monitor.
Precip looks to quickly come to an end from west to east Saturday
night and likely out of the forecast area by around 09z. However,
some falling rain may cause some visibility concerns across the
north and east when the winds increase.  Clouds move out by midday
Sunday providing a breezy and sunny afternoon.

Monday through Thursday...large ridge of high pressure remains in
control of the weather pattern throughout the week and providing dry
conditions and warmer temperatures by Tuesday into Friday.  Nudged
up maximum temperatures on Wednesday to Friday with decent WAA and
clear skies in place.  ECMWF and GFS continue to trend warmer and
leaned toward the slightly warmer ECMWF.


.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 638 PM CDT Fri Oct 13 2017

Low-medium confidence TAF forecast. Confidence high in widespread
IFR conditions. Confidence not quite high enough to include LIFR
in this update, as LIFR occurrence would likely occur beyond 12
hours out. Confidence high in widespread, frequent precip through
Saturday. Heavier rain possible from around 15z to 18z, and then
another round of heavier rain possible from 20z-23z. Severe
weather cannot be ruled out at KOTM. IFR cigs to gradually rise to
MVFR by around 03z Sun...this will be covered some in next




SHORT TERM...Beerends
LONG TERM...Podrazik
AVIATION...Kotenberg is the U.S. government's official web portal to all federal, state and local government web resources and services.