FXUS63 KDMX 302350

Area Forecast Discussion
National Weather Service Des Moines IA
650 PM CDT Thu Mar 30 2023

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

.SHORT TERM.../Tonight through Friday Night/
Issued at 339 PM CDT Thu Mar 30 2023

Forecast Impacts for the week:

...Major storm arrives with significant severe potential/synoptic
wind threat over the region tomorrow
...Warm spring conditions Sunday to Tuesday
...Next major storm next Tues/Wed will be similar to tomorrow

Confidence Short Term: Medium

Questions remain about the initiation timing and location as some of
the higher resolution models are suggesting the location may be
east of I35 or possibly as far east as the I380 corridor to the
Mississippi River. Confidence is unfortunately lower today
regarding the evolution of the timing and placement of the higher
end severe weather this period. Transition day today as warm air
advection now in full force. High pressure already exiting to the
northeast today with large scale system beginning to shed some
energy into the lee of the Rockies. Initial surge includes some
mid level lift which is brought some elevated returns and a few
showers on radar at mid to later morning. A large shield of
stratus is also being advected north into Missouri and has caught
up to Iowa late this afternoon, though we did have some sunshine
in the afternoon hours. Subjective surface analysis at 900 am
shows sfc low pressure near Denver with a warm front extending
east across KS, southern NE and over north central MO. A rapid
increase in dewpoints is occurring in a corridor from Texas north
to northern Oklahoma where dewpoints have already reached the 50s;
around 60 in central Texas. A pronounced dryline has developed
from eastern Colorado to New Mexico and will eventually work
northeast during the night into Friday. H850 subjective analysis
shows a 135 dm low near Cheyenne, WY with a strengthening low
level jet this morning of 45 to 55 kts already from Dodge City to
Topeka. Judging by the height fields, there are about 3 separate
waves embedded in the flow with the strongest low over Wyoming.
Moisture is expanding north out of the Gulf with a 10C area of
dewpoints riding a 40 to 45kt low level jet over southeast Texas.
By 06z tonight, synoptic models are fairly consistent with a
992-995mb surface low over southwest NE with a warm front
extending northeast to the Iowa MN border. Convection will fire
along and just north of the boundary with some thunderstorms
focused into northern Iowa from 06-12z. Though the CAPE/Shear
parameter space varies among the NAM/GFS/Euro/HRRR solutions, the
NAM and HRRR show a few stronger elevated storms near the border.
So, a small hail potential there overnight while most of the
remainder of the forecast area will see lesser chances of some
scattered convection overnight. Both the HRRR and most of the
synoptic models are now suggesting that the dryline will outrun
the onset of convection due to limited mass convergence at the
surface along the trailing dryline. The more ominous models
continue to be the NAM/NAMNest with lesser emphasis in our area
for convection in the GFS/HRRR mainly occurs nearer the
Mississippi River. The Euro/NAM still show initiation closer to
the I35 corridor or just east of here. For now we will still
consider the potential for storms initiating near the I35 corridor
with the higher end potential ramping up as it tracks toward the
Mississippi River. There is the potential that few if any storms
may initiate soon enough to affect our forecast area in central
Iowa and we will need to look at more mesoscale details;
especially the amount of surface convergence, through late evening
tonight into early Friday morning. Given the spread of solutions,
if the earlier initiation takes place, very strong wind gusts and
some tornadoes would still be favored as the primary concerns
with large hail possible as well.

Despite the major uncertainty in initiation, there remains a signal
in the model data over southern Iowa especially into Missouri and
portions of Illinois, where the upper level jet will have a better
chance of descending toward the surface due to increasing subsidence
behind the system. By 18z the surface low is forecast to be near
Spencer with the warm front over northern Iowa. As the system
translates and deepens into far northern Iowa/southeast MN the
dryline/front will race into western Illinois with the trailing
stronger cold front near Ottumwa. Winds at H850 increase to 45 to
55kt over the south with 40kt common south of I80 through 06z while
another burst of higher momentum air will accompany the deformation
axis and band of snow tracking southeast from 06z to 12z. By the
early afternoon, we also will see some increase in fire weather
threat over the south behind the line of storms as drier air mixes
into the region. Have addressed that with a Fire Weather Watch for
18z through 00z in the south third of the area. We will likely need
wind advisories over much of the area during the later day to
overnight periods, but with everything else now occurring will opt
for the mid shift to work that into the forecast. There remains a
conditional chance that jetstream level winds may follow the storms
tomorrow afternoon, but this remains conditional as well. Lows
tonight will drop to the mid 50s; highs tomorrow in the 50s to lower
70s and mins tomorrow night in the lower 20s northwest to the lower
30s southeast.


.LONG TERM.../Saturday through Thursday/
Issued at 339 PM CDT Thu Mar 30 2023

Confidence: Medium

Saturday will remain cooler, but with few changes expected. By
Sunday, increasing warm air advection will move into the region with
a chance for some light precipitation over the area. Temperatures
continue to warm into Sunday and Monday ahead of the next stronger
system to reach the Central Plains. A similar storm in strength and
evolution is anticipated, caveat, looking at the guidance today. The
bulk of the forcing will come through Tuesday into Wednesday with
cooler air heading in for Thursday. Plenty of time to dig into the
details in subsequent shifts as the bulk of todays discussion has
been focused on the impending significant storm and myriad of other


.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 638 PM CDT Thu Mar 30 2023

VFR cigs will become MVFR within the next six hours with
thunderstorms expected near northern terminals. Low confidence
showers for southern terminals so left out of TAF. Gusty winds
will continue overnight and into most of tomorrow. Thunderstorms
become increasingly likely after 18z and will be focused east.
Winds increase upon thunderstorm passage, gusting to 40kts at
times through the end of the TAF period.


Fire Weather Watch from Friday afternoon through Friday evening
for IAZ070>075-081>086-092>097.




NWS DMX Office Area Forecast Discussion