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fxus63 kdmx 210517 

Area forecast discussion
National Weather Service Des Moines Iowa
1217 am CDT Thu Jun 21 2018

..updated 06z aviation...

Short term.../tonight through Thursday night/
issued at 334 PM CDT Wed Jun 20 2018

This afternoon through this evening...
20z sfc analysis continued to show a deepening sfc low positioned
over west-central Iowa, with an attendant boundary/warm front to
serve as a focusing mechanism. One could pick up the
vorticity/rotation of winds throughout the atmosphere merely by
looking at vis Sat imagery through this morning. All relevant
parameters (0-1km srh, local heights nearing 500m, etc) in place
and sufficient to support tor threat for this afternoon. Big
question leading into the day was the impact cloud cover would
have on destabilization along and south of Highway 20, and
primarily focus south of Highway 30. By 18z, sfc temps had made it
into the upper 70s to even mid 80s in far southern Iowa,
indicating diabatic heating a go for today. With sfc dwpts in the
low to mid 70s, plenty of moisture present as well.

Ongoing thunderstorms will continue through the evening hours.
Expecting stabilization of convection to occur with waning of
daytime heating. Best bulk shear and other severe parameters to
move northeast of the dmx County Warning Area by around 00z, ending severe threat.
Tor threat may end by around 22z.

rainfall/flash flooding threat will continue across
northern/northwestern Iowa. Hi-res/cams and long-range models show
excellent agreement with keeping upper low over northwest Iowa. Trend
has been to push best moisture, etc. Northeast... and as a result
have significantly trimmed pops south of Highway 30. Given near-
stationary setup of forcing over northwest/north Iowa, 1 to 3 inches in this
area seems prudent. Flash flood potential continues in this area.
Worth noting that ground is decently saturated from rainfall
earlier in the week, and crops are running a few weeks behind
schedule in northern/northwest Iowa.

Tomorrow through tomorrow night...
upper low will propagate southeastward, making it into central
Illinois by 12z Fri. A lingering 30kt low level jet will keep moisture
transport going into central Iowa, however the best forcing will
pull away with the upper low. Have light pops/quantitative precipitation forecast going tomorrow,
but flooding threat should be ended.

Long term.../Friday through Wednesday/
issued at 334 PM CDT Wed Jun 20 2018

Upper low will be drifting off to the southeast on Friday and
precipitation chances will dwindle during the day. Upper flow
pattern remains active this weekend with a shortwave passing through
the plains Saturday night. The 12utc models place the brunt of the
precipitation south of Iowa but rain chances return Saturday night.

The next system to impact the upper Midwest is early next week.
Another upper low is forecast to move through the region on Tuesday.
The 12 UTC GFS/European model (ecmwf) both suggest severe potential with system over
central Iowa on Tuesday and the potential for more heavy rain. For
now, we will continue decent precipitation chances. Temperatures
will remain seasonable for late June.


Aviation.../for the 06z tafs through 06z Thursday night/
issued at 1213 am CDT Thu Jun 21 2018

Main concern overnight will be IFR ceilings at the terminals. The
heaviest rain showers have ended but additional rain shower
activity is possible overnight, especially in northern Iowa. The
overall thunderstorm threat is low. Confidence in ceilings and
visibility is medium-high. Confidence in vcsh versus thunderstorms in the vicinity is


issued at 334 PM CDT Wed Jun 20 2018

A complicated hydrologic situation and forecast continues to play
out today and through the end of the week. Fortunately, up to this
point, no area has been crippled with enough rounds of heavy
rainfall to result in moderate to major flash or river flooding.
Unfortunately, that does mean that a large portion of the western
half to two-thirds of the state has nearly saturated to saturated
soils. With the potential for additional heavy rainfall of 2-4 or
more inches over parts of west central and northwest Iowa continuing
tonight, the potential for flash flooding and increased magnitude
and aerial extent of river flooding increases. A number of river
flood forecasts have already been issued along the Raccoon and Des
Moines River basins based on what is currently being routed and what
is expected to fall through tomorrow morning. It will also be
important to keep in mind that more rainfall is expected to end the
week, though is not of the same magnitude as has been experienced
early this week.


Dmx watches/warnings/advisories...
Flash Flood Watch until 7 am CDT this morning for iaz004>006-015-



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