Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 171126

Area Forecast Discussion
National Weather Service Des Moines IA
626 AM CDT Wed Aug 17 2016

.SHORT TERM.../Today/
Issued at 311 AM CDT Wed Aug 17 2016

Currently the overnight scattered showers and thunderstorms will
diminish toward 13z east as the frontal boundary/wind shift moves
into central and southeast Iowa by 00z Saturday. Afternoon instability
will increase though surface convergence and forcing will be nearly
nil so for now will not include any mention of rain this afternoon.
ESRL HRRR shows some isolated showers/thunder possible over eastern
areas but coverage looks spotty at best. Highs today will reach
the upper 80s over the central and south with lower 80s again over
the north. Partly cloudy conditions are expected with the daytime
heating today.

.LONG TERM.../Tonight through Tuesday/
Issued at 311 AM CDT Wed Aug 17 2016

Forecast for the next several days continues on track with
warming into Thursday and Friday along with increasing
thunderstorms from Friday afternoon through Saturday. Cooler
temperatures still on tap for Saturday and Sunday. Subjective
surface analysis shows weak low over southern MN along with
trailing cool frontal boundary into northern Nebraska. This
feature will continue moving south and by 00z tonight the
weakening boundary will be nearer the Iowa Missouri border in the
southeast...then arching back northwest toward northern Nebraska
as a warm front. Though tonight should be mainly dry...weak warm
air advection and moisture return aloft may create a few isolated
showers and thunderstorms over the northwest/west toward 12z. Not
much dynamics...instability...or winds aloft to create anything
more organized. Lows tonight will remain quite warm over the south
in the warm sector while the northeast will see somewhat cooler
readings and potential for some light fog in the river valley
areas of the east and northeast. With the warm air advection
shifting rapidly into Minnesota by 18z...H850 temps aloft will
rise into the 20-26C range by 00z Friday over the area. This will
propel highs into the 80s to lower 90s over much of the region.
With dew points climbing back into the lower 70s...heat indices
will once again rise to 95 to 100 F by late afternoon over much of
the west and south. Consistent with the past 24 hours
now...tonights models have continued to delay the arrival of the
stronger Friday system until Friday afternoon across the
west/north. Until then the region will be partly cloudy...warm and
rather humid Thursday night into Friday morning. The set up for
Friday evening remains the same... lending confidence to the
forecast. Warm cloud depths increase to 3500 to 4000m just ahead
of the boundary aloft with precipitable water values of 1.75 to
2.0 inches ahead of and along the approaching cold front Friday
evening. Forecast storm motions of 15 to 20 kts may allow for a
quick 1 to 2 inch rainfall with some of the heavier storms. Both
the Euro/GFS are developing a weak surface low overnight Friday
night along the front in central Iowa. This should help slow the
boundary and allow for more widespread rainfall over the region.
With this in mind have increased PoP Friday night over the
forecast area. With the passage of the front cooler weather will
quickly follow. The bulk of the precipitation will occur with the
first front and upper level wave Friday night into Saturday. By
late Saturday afternoon/evening some partial clearing will take
place. A second wave will drop into Iowa Sunday with another
chance of light showers Sunday morning. Highs Saturday into Sunday
will fall back into the 70s with the cooler day on Sunday. Lows
will reach the lower 50s north both days and the lower to mid 50s
over the south. The cooler northwest flow aloft will give way to
more zonal flow Monday through Tuesday resulting in warmer
temperatures along with a break from any storms for a few days.


.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 624 AM CDT Wed Aug 17 2016

A few sct low level clouds with bases between 1500 and 2500 ft
possible through around 14z or so this morning. Confidence in
areal and time coverage not enough to warrant MVFR FM group.
Afternoon cu/sc expected to be in VFR range. Winds near to below 5
kts though tomorrow afternoon.




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