Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/25/24

Area Forecast Discussion

National Weather Service Des Moines IA

 1054 PM CDT Thu Oct 24 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Showers and thunderstorms expected late this afternoon and
  this evening. Some may be strong with hail or gusty winds and
  at least moderate rainfall

- Dry again starting Fri. Windy and warm with elevated fire
  weather conditions early next week

- Another rainfall window around the middle of next week with
  best potential for appreciable precipitation southeast

&&

.DISCUSSION...
Issued at 206 PM CDT Thu Oct 24 2024

Our weather pattern will be more active than the recent past
with two precip windows of note and atypically warm and windy
conditions in between early next week. The first is on the
doorstep with a short wave advancing through SD/NE with noted
thermodynamic and kinematic forcing out ahead into the MO
Valley. The associated strong theta-e advection across MO and IA
is along the leading edge of higher 1-3km moisture aloft, and
is already started to generate a few cells over southern IA and
northeast MO. This should expand rapidly as forcing attendant
to the short wave moves east, and is further aided by increased
thermal support with the maturing low level jet. This lift
should blossom elevated convection over much of central and
eastern IA from the late afternoon into the evening hours,
especially during the evening.

Recent RAP soundings across southern/southeast Iowa support
elevated storms with hail and wind potential, especially the
former. Effective CAPEs reach >1000 J/kg at times and are
coincident with effective shear of 30-40kts suggesting at least
a blend of discrete/multicells are likely. While the elevated
nature of the convection will preclude some of this being
realized, hodographs become quite enhanced and loopy as the
low level jet increases with ESRH still inflating to >300 m2/s2
at times. Thermodynamically, LFCs are just below the freezing
level, enhancing the percentage of positive area below freezing
and in the hail growth zone, so there is the potential for
numerous cells producing at least small hail, with larger severe
hail certainly possible. Dry low levels below the elevated
bases would also support some wind potential, with 12Z HREF
output suggesting that potential southeast.

Rainfall could very well be more significant than we have seen
recently. 40-50kts of flow along the 305K isentropic surface
into the base of the elevated convection is expected this
evening, with several hours of persistent moisture convergence.
00z EPS/GEFS both suggest non-trivial precip amounts by Friday
morning with 24hr accumulations >=0.50" likely (60+% chances)
south central and southeast. Regarding a more localized
potential, 12Z HREF probabilities of >=1" are 30-50% across
east central sections, recent HRRR runs depict 1+" amounts, with
the HREF 24hr localized probability matched mean as high as 2",
so as the previous discussion mentioned these certainly
wouldn`t be widespread to any degree but localized amounts
greater than an inch may occur considering the healthy
convection and degree of moisture transport.

Fair weather and seasonal temperatures can then be anticipated
Friday through the weekend with upper level ridging reaching the
MO Valley by late Sunday. Above normal temperatures are forecast
next week, mainly around Tuesday, with record or near record warm
low temperatures possible Monday night. Wind gusts of at least
30-40 mph are anticipated Tuesday when highs may again reach the
lower 80s. This combination of warm temps and strong winds will
re-introduce elevated fire weather conditions with any lingering
precip from tonight no longer affecting fuels after several dry
days.

Attention will then turn to an amplifying pattern and an
approaching long wave trough by the middle of next week. Although
possibly unrealized with little focus initially, anomalously high
moisture parameter space develops Monday night through Tuesday
night versus climatology in both the 00z NAEFS and EPS, and may
set the stage for another round of semi-appreciable showers and
storms by the middle of next week, most likely southeast half
around Wednesday or Wednesday night.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1053 PM CDT Thu Oct 24 2024

Convection moves east out of central Iowa during the overnight
with VFR conditions becoming common across the area as skies
clear. KOTM (Ottumwa) terminal is likely to be impacted by
showers and possible thunderstorms early in the TAF period with
improving conditions by sunrise. Widespread VFR conditions are
expected on Friday with unrestricted ceilings and visibilities.
Surface winds increase from the northwest in the morning with
gusty winds into the afternoon.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Cogil