430
FXUS63 KSGF 251947
AFDSGF

Area Forecast Discussion
National Weather Service Springfield MO
247 PM CDT Wed Sep 25 2024

.KEY MESSAGES...

- Pleasant weather expected today and tomorrow with near normal
  temperatures in the mid 70s and mostly sunny skies. Low
  chance (15%) of an isolated shower across the eastern Ozarks
  this afternoon.

- Rain chances increase Thursday night into Friday due to the
  remnants of Hurricane Helene. The highest rain chances are
  Friday afternoon across south-central Missouri and the eastern
  Ozarks.

- There remains a high degree of uncertainty regarding forecast
  rainfall totals this weekend.

- Breezy conditions are likely Friday with gusts up to 30 mph.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 247 PM CDT Wed Sep 25 2024

An upper-level trough axis was situated over the Mississippi
Valley this afternoon with a cutoff low sitting over eastern
Missouri and southern Illinois. To the west, high amplitude
ridging was set up over the Plains, with broad high pressure at
the surface.

Dry air and subsidence aloft will keep our area mostly dry
today. Scattered cumulus have developed across the region this
afternoon in response to modest surface heating and a shallow
layer of mid-level moisture. Hi- res guidance suggests there
may be just enough moisture and forcing from the upper-level low to
spark a shower or two later this afternoon and evening across
the eastern Ozarks, though most areas remain dry, and PoPs have
been limited to 15-20%.

Cool conditions return overnight with lows in the low to mid
50s. With light winds and strong enough radiational cooling,
there could be some light ground/valley fog in the early morning
hours, but widespread dense fog is not expected at this time.

For Thursday, the upper-level low will slink down into
northeastern Arkansas; otherwise, little will change with the
synoptic pattern until Thursday night. Therefore, tomorrow`s
sensible weather will be similar to today`s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 247 PM CDT Wed Sep 25 2024

Rain Chances from Hurricane Helene:

Helene has officially reached hurricane strength as of this
morning. Model forecast tracks have remained fairly consistent
and tightly clustered over the last 48 hours, making landfall
somewhere along the Florida Big Bend/Panhandle Thursday evening
and tracking to the NNW from there. Greater uncertainty is
naturally introduced into the forecast with time, but the
uncertainty is further increased by Helene`s apparent
interaction with the aforementioned cutoff low over northeast
Arkansas. Most guidance depicts some degree of Fujiwhara effect
occurring, which would act to swing Helene`s remnants to the
northwest as it passes through the Tennessee Valley.

What exactly this means for precipitation in the Missouri
Ozarks remains highly uncertain. The latest NBM PoPs increase
Thursday night across southeast Missouri and spread to the
northwest on Friday. The highest PoPs (50-60%) for our CWA
remain across the eastern Ozarks and south-central Missouri
during the day Friday, with lower chances (20-40%) lingering
into Saturday and Sunday. Instability appears fairly minimal
with this activity, so the lightning potential will be limited.

Analysis of ensemble clusters reveals two distinct solutions.
The majority of GEFS and ENS members more closely follow the
NHC`s official forecast and bring Helene`s remnants farther
west into the Mississippi Valley and potentially into eastern
Missouri. This solution would bring more precipitation to our
area. GEPS members, on the other hand, tend to favor a more
easterly solution, which results in low precipitation totals
for our area. Another variable to consider will be available
moisture as dry antecedent air will have to be overcome by the
tropical moisture return from Helene. A glance at forecast PWATs
suggests a decent gradient in moisture from west to east across
the forecast area, which will influence rainfall rates and
totals. For what it`s worth, the extended reaches of the hi-res
guidance tends to fall more in line with the GEFS and ENS, but
they will become more reliable in the next 24 hours.

These discrepancies-- among others-- produce high uncertainty
in the rainfall forecast. This uncertainty is depicted well in
the fairly large spread (2-4 inches) of 25th-75th percentile
QPF differences in the NBM. It is entirely possible there will
ultimately be a large rainfall gradient that sets up somewhere
across our forecast area. Notably, the QPF signal from the
Extreme forecast Index and Shift of Tails has decreased and
shifted east slightly since yesterday. This decrease is
consistent with the overall decrease in model QPF.

Given the high uncertainty in the rainfall forecast, we will
stick with probabilistic messaging for now. The latest NBM
probabilities of rainfall totals from Thursday night through
Sunday night are as follows:
>1 inch: 0% (west) to 50% (east)
>2 inches: 0% (west) to 40% (east)
>3 inches: 0% (west) to 30% (east)

Moderately Gusty Winds Friday & Saturday:

Wind gusts will also have to be monitored with Helene`s
remnants as they will also be affected by this system`s
eventual track. We have nudged gusts closer to the NBM 75th
percentile on Friday and Saturday (with gusts up to 30 mph) as
the NBM tends to have a low bias in gustier setups.

Seasonable to Slightly Cool Temperatures:

Temperatures will stay seasonable or a bit below normal through
the long term. NBM interquartile spreads remain moderately large
(6-7 degrees) through the weekend owing in large part due to
uncertainty with precipitation coverage. Beyond that, Helene`s
remnants and the cutoff low are progged to eventually drift east
early next week. Global models suggest the passage of a cold
front will occur during this time period, which may keep
seasonable temperatures over the region, at least for the time
being.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1151 AM CDT Wed Sep 25 2024

VFR conditions are expected through the TAF period. Light winds
will prevail out of the NNW until after 00Z where they will
shift to the NE. High pressure and dry air will keep skies
mostly clear over the TAF sites into Thursday.

&&

.SGF WATCHES/WARNINGS/ADVISORIES...
KS...None.
MO...None.

&&

$$

SHORT TERM...Didio
LONG TERM...Didio
AVIATION...Didio