National Weather Service Raw Text Product

442 
FXUS63 KDMX 231114
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
614 AM CDT Thu May 23 2019

.DISCUSSION.../Today through Wednesday/
Issued at 413 AM CDT Thu May 23 2019

There is little change in the primary weather messaging this 
morning with our pattern remaining active for an extended period. 
Outside of what looks to be break today and then again Sunday, 
there will be off and on showers and thunderstorms through the 
holiday weekend and into the middle of next week. Although there 
are differences with frontal positions and pinning down details 
with each potential MCS, the GFS, ECMWF and their associated 
ensembles are in good agreement with the progression of our long 
wave pattern at least starting with upper level ridging building 
into the MS Valley today, and then a return to SW flow aloft into 
the weekend before this cycle repeats itself Sunday and into the 
middle of next week before the long wave trough axis finally 
reaches IA in some form by Wednesday. This will include multiple 
instances of severe weather potential to some degree, and a 
incremental increase in flooding potential with each event as rain
accumulate. The good news however is that the latest RFC
contingency forecasts from yesterday, and precip through 12z
Monday, suggest only isolated potential for more extensive minor  
river flooding through that period.

At onset today fair weather and seasonal temperatures are 
anticipated, but this will quickly change into tonight. The 
current frontal boundary across OK, MO and IL will move northward 
again as the ridge builds, washing out to some degree, but still 
allowing at least weak instability to return. The associated 
warm/theta-e advection will produce nocturnal showers and storms 
to some degree, although confidence is not the best with varied 
solutions among the parameterized and non-parameterized model 
depictions in terms of areal coverage. Regardless the severe 
potential seems to be on the low end with limited instability and 
better effective shear pushing north. Some moderate to locally 
heavy rains are possible however with 30kt 925-850MB flow and 
associated moisture convergence focused into IA in seasonal 
absolute moisture content and warm cloud depths.

The weak surface low associated with this progression will move 
north through the central Plains and dissipate somewhat as it 
leaves the warm front just to our northeast by late Friday. This 
will leave a much more favorable thermodynamic environment into IA
with MLCAPEs to around 2K j/kg and easily favorable deep shear 
for organized severe weather. The question will be how the trigger
materializes as the aforementioned low progression will leave a 
thermal boundary in place into northwest IA, but little surface 
convergence in broad southwest surface flow. This may be initially
be inefficient for surface based development, but the maturing 
low level jet and subtle lift in the southwest flow is expected 
to blossom a line of convection across central or southeast IA. 
The shear may not be favorable into the night, but with 
increasing precipitation efficiency parameters, weak Corfidi 
vectors and the mean wind parallel to the boundary the training, 
heavy rain potential will increase leading to WPC noting a 
Moderate Risk of excessive rains.

The front should retreat north again by Saturday, and although the
heavy rain potential seems somewhat less favorable, the severe
potential may increase with MLCAPEs to 3K j/kg and strong deep 
shear. Both the GFS and ECMWF depict the boundary over northern IA
during peak heating so the Day 3 SPC outlook probabilities may 
eventually increase to the north. This convection will likely 
linger into the night before exiting to the south and east for a 
welcome break by Sunday. Details for the remainder of the period 
will be more sketchy, but the nocturnal warm advection, frontal 
surface peak heating cycle looks to repeat into early next week 
with the Monday/Monday Night looking like a peak in intensity due 
to more favorable instability and shear parameter space. The 
potential for active convection persists into Tuesday and 
Wednesday as well, but confidence is low. As mentioned above the 
model larger mass fields are in good agreement, but short wave 
details and associated surface reflections are not resulting in 
anything from a more active ECMWF into the middle of next week 
down to the more tranquil GFS pushing the boundary off to the 
south and east.

&&

.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 612 AM CDT Thu May 23 2019

VFR conditions are anticipated through much of the period, but
precipitation and lowering and thickening cloudiness is
anticipated tonight. Conditions should remain VFR during the
evening, but will likely transition to MVFR in spots overnight. 
Confidence is not great enough for inclusion of thunder at this
lead time.

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

DISCUSSION...Small
AVIATION...Small