FXUS63 KDMX 181739
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1239 PM CDT Thu Apr 18 2024

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

.KEY MESSAGES...

- Widespread precipitation this morning before ending from
  northwest to southeast through the afternoon. 

- A few chances for below freezing low temperatures over mainly
  northern and west central Iowa tonight and Friday night and
  area wide Saturday night.

- Next chance for precipitation is early next week.

&&

.DISCUSSION...
Issued at 335 AM CDT Thu Apr 18 2024

Two well defined areas of precipitation have developed this morning. 
The first area of precipitation extends from southern Minnesota, 
though northwest Iowa and all the way back to northeast Colorado. 
That band is associated with mid-level frontogenesis and the arrival 
of colder air. This precipitation is mostly stratiform though there 
are a few areas with lightning associated with it in Nebraska. The 
second area of precipitation is associated with low pressure moving 
into southeast Kansas with a warm front extending north towards 
Topeka and Kansas City. A few strong storms have been occurring 
along that boundary. The low level jet extends further north and is 
pointing into southern Iowa and this is a region where strong theta-
e advection is ongoing along with a broad area of rain while 
thunderstorms have been developing into southeast Nebraska. A few 
storms are expected into southern Iowa but any strong storms should 
remain to the south of the area.

These two areas of precipitation will continue to move 
east/northeast across the area this morning before gradually 
weakening/diminishing by late morning. Renewed shower and 
thunderstorm development is possible this afternoon over the 
southeast. One of the challenges for today is how much the In-
Between (in this case central Iowa) will fill in with precipitation 
or will there remain a null void. Central Iowa should fill in with 
precipitation as overrunning and isentropic lift continues to lift 
northward this morning. There likely will be lower precipitation 
values in that region. Overall, precipitation amounts of one to one 
and one half inch are possible far south, one half to one inch north 
and one quarter to three quarters inch central. By this afternoon, 
much drier dew points will move in to northwest Iowa and move 
southeast quickly, dropping values into the 20s and 30s. The wind 
will become gust as the boundary moves through the state and the 
switch to northwest wind occurs. Peak wind gusts will be in the 25 
to 30 mph range and will drop off this evening as decoupling occurs. 
High temperatures today are currently in the low to mid 50s. This 
may be overly optimistic, especially if cloud cover hangs around 
much of the day.

Another push of cooler air arrives Thursday night and the wind will 
become light from the west. With the growing season ahead of 
schedule, the Frost/Freeze headlines are now turned on and available 
if needed. Temperatures will fall into the 30s and likely below 
freezing in some areas north and west. Frost potential is not 
certain pending how low the wind is and the dew point depression 
could remain large enough to inhibit frost. Therefore, no headlines 
at this time.

A ridge of high pressure will settle and be just south of Iowa on 
Friday. Gusty west winds are expected across northern Iowa where 
better mixed layer winds exist and the pressure gradient will be a 
bit stronger than southern Iowa which will be near the ridge. Wind 
criteria could be approached over far northern Iowa on mixing layer 
wind potential. The lack of any strong cold advection will prevent 
the realization of peak mixed layer winds from reaching the surface 
though. High temperatures Friday will be in the 50s. Another cold 
front will reach northern Iowa by late Friday and will move through 
the remainder of the area Friday night and Saturday morning. The 850 
mb temperatures Saturday morning will be in the -5C to -10C range 
over the northern half of the state, which is quite cold for mid 
April. The boundary layer may remain slightly mixed Friday night and 
along with the breezy winds, temperatures may again hold into the 
30s over northern Iowa. Saturday will be the coolest day of the 
period with highs in the upper 40s to low 50s. Ridge of high 
pressure will move across the state Saturday night and this will be 
the period with greatest potential of widespread freezing or below 
temperatures with overnight lows in the upper 20s to low 30s. Highs 
next week will be in the upper 50s and 60s. The next chance for 
precipitation arrives Monday and Monday night with a few showers and 
thunderstorms possible then another system possible late next
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1231 PM CDT Thu Apr 18 2024

MVFR and IFR ceilings across the area this morning will begin 
to see improvement as clouds depart from northwest to southeast  
this afternoon and evening. Rain is also diminishing in coverage,
but a few showers and isolated thunderstorms will continue near
KOTM through the next few hours, resulting in periods of 
lower visibility, gusty winds and potentially some lightning.

After clouds depart, VFR conditions prevail through the
overnight hours and into tomorrow morning, barring a few 
scattered low cumulus developing towards mid-day tomorrow. Gusty
west northwest winds are also expected after sunrise tomorrow. 

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Donavon
AVIATION...Dodson