871 
FXUS63 KDMX 030906
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
406 AM CDT Sat Apr 3 2021

.DISCUSSION.../Today through Friday/
Issued at 406 AM CDT Sat Apr 3 2021

Today Through Sunday Afternoon: 

Short-wave trough is moving across the northern Great Lakes early 
this morning but did not bring much activity to Iowa other than a 
few high clouds. The western two-thirds of the CONUS remains in the 
flow of the broad scale H5 ridge. The axis of main ridge will slowly 
push eastward out of the Front Range this afternoon and into the 
High Plains. Surface high pressure will sit over the eastern Ohio 
River Valley expanding eastward to the Atlantic Coast. This will 
steer the near surface flow across the Midwest in a south-southwest 
direction through most of Saturday and promote a WAA regime. For 
today, this should send temperatures into the low to mid 70s across 
most of the forecast area. With flow being somewhat weaker, mixing 
does not look to be overly robust, thus will be looking primarily at 
insolation being the source for warmer temperatures this afternoon. 
Moisture transport will not be overly meaningful, leading to rather 
low RH values this afternoon. While it will be quite dry, 
southwesterly winds will only be 5 to 10 MPH. Thus, the calm winds 
will mitigate what would otherwise be an elevated fire danger. For 
Sunday, a couple of H5 short-waves develop. These waves do not quite 
make it to Iowa, but there appears to be a few downstream 
perturbations that will act to enhance the southwesterly flow during 
the afternoon. This will provide a small boost to WAA, and lead to 
slightly increased mixing. This will lead to the warmest 
temperatures during this warming trend of the past few days. 
Expecting most locations to reach the upper 70s, with a few stations 
likely to hit the 80 degree mark. Guidance continues to hint that 
moisture transport should pick up a bit in this flow, but dewpoints 
could actually drop some with mixing in the afternoon. This concern 
for lower dewpoints is further augmented by mixing potential noted 
in model sounding analysis. With that being said, this is not 
shaping up to the most robust mixing scenario. RH values Sunday may 
drop as low as 30-35 percent. Wind gusts around 20 kts could present 
some elevated fire concerns, but still far from any headline 
criteria (and that is assuming mixing if fully realized, which there 
is some potential this may not happen). Attention will then turn to 
a more active weather pattern for the next work week across the 
region. 

Sunday Night and Beyond: 

During the evening Sunday and into Monday morning, 00z GFS and GEFS 
members are pointing to increased convergence with the weak short-
wave perturbation that will be capable of producing shower activity. 
Some of the 00z guidance does depict a decent amount instability 
that develops across the region, but am concerned about what 
developing cloud cover may end up doing to this, as well as how much 
moisture is actually transported into the region. Should better 
instability be realized on Monday, could see some thunder mixed in 
with rain showers. As the week progresses, will be monitoring a 
couple of closed lows at H5 that will be moving across the Plains 
and southern Canadian Prairie Provinces. Tuesday, most of the 00z 
deterministic guidance and many ensemble members continue to 
increase convergence across Iowa, leading to continued chances for 
precipitation. On the higher end, some solutions are depicting 
surface based CAPE values reaching between 1500 and 1750 J/kg, which 
would certainly support thunderstorm development if this is 
realized. As previously mentioned, lingering cloud cover may have a 
detrimental affect on achieving boundary layer destabilization. In 
this environment, flow could be stronger that may increase the 0-6 
km bulk shear, but at the current moment the signal for favorable 
deep layer shear is not consistent between all solutions for 
Tuesday. At this time, the threat for severe weather appears low. 
But, if the instability is realized and the shear environment comes 
in on the stronger end, severe potential may increase. By Wednesday, 
stronger surface cyclone develops and forcing increases across the 
region. This will keep rain showers and thunderstorms in the 
forecast through much of Wednesday and Thursday. Eventually narrow 
surface ridge moves across Friday morning into the afternoon, which 
will push the aforementioned systems eastward into the Great Lakes 
Region. Rain showers this week should help bring some relief to the 
rather dry ambient conditions that have been ongoing over the past 
week.  

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1136 PM CDT Fri Apr 2 2021

Wind remains the main concern through dawn. LLWS overnight 
through 14z then light winds with weak trough pushing through 
region. Southwest to west winds will remain south sites KDSM and
KOTM while north sites see mainly northwest to northeast winds aft
15z. VFR conditions to continue. 


&&

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

$$

DISCUSSION...Krull
AVIATION...REV