896 
FXUS63 KDMX 181715
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1215 PM CDT Mon Jun 18 2018

...Updated for 18z Aviation Discussion...

.SHORT TERM.../Today through Tonight/
Issued at 346 AM CDT Mon Jun 18 2018

Boundary has entered northern Iowa this morning with non severe 
convection across the far north. This will continue to gradually 
decrease in coverage and intensity through daybreak as low level 
jet continues to veer with convergence decreasing. With the 
boundary remaining in northern Iowa today, the southern half of 
the state will once again be quite warm with highs into the low 
90s with low 70 dewpoints. Heat advisory will remain in place and 
in fact added Tama and Marshall counties back in as they will also
see index values over 100 once again. This will be the last day 
of the more intense heat and the heat headlines as temperatures 
will be cooler the rest of the week. 

CAMs output suggest thunderstorms development increasing around 2-
3pm this afternoon along the highway 20 corridor near the boundary. 
Deep layer shear is rather weak despite some decent CAPE across
the state and this will limit overall severe weather 
organization. While a few severe storms with large hail seem 
likely with initial development, the threat for a widespread 
severe day seems minimal. Bigger concern will be shifting to a 
heavy rainfall/flash flood threat. There will be ample moisture 
with PWATs of around 2" or even slightly higher along with deep 
warm cloudy layers in excess of 12kft by late afternoon into 
tonight. Training of cells along the nearly stationary boundary 
seems likely with efficient rainfall producing high rates. WPC has
highlighted the area with a slight outlook for later today into 
tonight and with some of the basins from Pocahontas county down 
toward Story and Jasper having been hammered last Thursday night, 
there will be real concern for flash flooding. A flash flood watch
will likely be needed for some locations for late today/tonight 
for this potential. The convection will shift slightly southward 
overnight as the outflow eventually moves southward and have 
trended POPs in that direction overnight. 

.LONG TERM.../Tuesday through Sunday/
Issued at 346 AM CDT Mon Jun 18 2018

The active weather pattern persists through much of the week work 
and then confidence is increasing with finally a dry period by 
Friday night into Saturday. Models continue to be in decent 
agreement with the wet, cool, and cloudy pattern throughout the 
week and utilized a blend of the ECMWF/GFS.

Tuesday into Friday...thunderstorm activity looks to be ongoing or 
redeveloping over central to northern Iowa during the morning 
Tuesday as a shortwave cuts across the state. The GFS is certainly
a bit stronger with the forcing, but the NAM/ECMWF do suggest a 
shortwave to move through at the same time frame b/t 12-18z 
Tuesday. The shortwave looks to quickly move east during the 
afternoon with some lingering showers/storms possible past 18z. 
The main concern remained focused on the isolated heavy rain 
threat in the morning as the severe weather threat looks minimal 
with weak instability and shear available. Likely to see the 
northeast sections of the CWA see a break in the precipitation 
Tuesday night into Wednesday morning as the focus shifts south 
with the frontal boundary stalling across southern Iowa.

By early Wednesday, a surface low pressure develops and slowly 
tracks east along the Kansas and Nebraska border with the GFS 
slightly deeper with the low by 12z Wednesday. This low remains 
stalled and even looks to retrograde back northwest as a strong 
surface high pressure (over the Great Lakes) blocks its eastward 
movement until Friday when the high finally shifts east. This low 
provides a long duration period of rain across Iowa beginning 
Wednesday afternoon through early Friday. The highest pops and QPF
look to be across the west to south past 18z Wednesday into 
Wednesday night before shifting northeast across the state 
Thursday. Precipitable water values remain around 2 inches for 
Wednesday into Thursday and warm layer cloud depths continue to be
around 13-14kft. Certainly likely to see some efficient rain 
producers past 18z Wednesday to 00z Friday and the potential for
some high rainfall totals during this time frame is highly likely. 

Friday night through Sunday...finally some low pops and even dry 
weather is in store Friday night into Saturday as the stubborn low 
shifts east into the Ohio Valley.  However, the GFS brings another 
surface low and boundary to set up across the CWA from west to
east by Sunday morning suggesting additional heavy rain. The 
ECMWF depicts more of an open wave is further south, so low 
confidence with pops late in the extended period. 

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1215 PM CDT Mon Jun 18 2018

Surface front stretches from La Crosse, WI to near Mason City to 
Sioux City at midday with primarily VFR cumulus south of this 
boundary. North of the boundary, conditions are also VFR at 
present, but there are FEW to SCT clouds at around FL025. 
Thunderstorms are expected to develop along the boundary as it 
meanders southward. Under these storms, MVFR or IFR conditions are
likely. With this front moving slowly, there could be prolonged 
periods of restrictions at any given terminal. Low clouds in MVFR 
or perhaps IFR category will spread in north of the front later 
tonight. Additional storms are likely Tuesday with so addition of 
prevailing/vicinity wording will be added in time.

&&

.HYDROLOGY...
Issued at 530 AM CDT Mon Jun 18 2018

This week continue to appear hydrologically very active with
several rounds of rainfall expected across the forecast area.
Given the areas of heavy rain over the last week and expected
rainfall, both flash flooding and river flooding may become
problematic during the upcoming week. WPC already has much of
the state highlighted for slight risk of flash flooding today 
through Wednesday (Day 3). In addition, the 5-day and 7-day QPF
has widespread 3 to 6 inches of rainfall across the state by next
weekend. This would likely put some rivers into minor flood if not
possibly moderate by weeks end. Confidence continues to increase
as deterministic models remain consistent from run to run. As
mentioned in the short term discussion above, the initial concern
later today into tonight will be from flash flooding with the
inclusion of river flooding increasing as a concern as the week 
continues with repeated rounds of rain. 

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for IAZ049-050-057>062-
070>075-081>086-092>097.

&&

$$

SHORT TERM...Cogil
LONG TERM...Podrazik
AVIATION...Ansorge
HYDROLOGY...Cogil