Tuesday, September 10th – Morning Forecast

Tuesday: Mostly Sunny. High: 86°F

Tuesday Night: Mostly Clear. Low: 59°F

Wednesday: Partly Sunny. High: 87°F

Wednesday Night: Partly Cloudy. Low: 64°F

Thursday: Partly Sunny. High: 85°F

=============================================================================

General Discussion:

Expecting mostly sunny and clear conditions until Thursday when we are starting to have influence from Francine, bringing in increased cloud cover. Expect Fall like weather in the mornings and summer temps in the afternoon.

– John

=============================================================================

Forecasters: Chirpich, John, Beach, Alcorn

Date Issued: 09/10/2024 9:00 AM CDT

Technical Discussion:

Key Messages 

• Low moisture and clear conditions allow afternoon temperatures to rise throughout the week (mid-to-upper 80s). 

• Tropical Storm Francine moves into the region late in the forecast period bringing Gulf moisture and possible clouds on Thursday. 

The majority of this forecast was created using a combination of the GFS and NAM, leaning more towards the GFS at the lower-levels. While the NAM started with a well-defined structure, as it moved towards the surface it became more disorderly. At 250 mb there is little-to-no activity for the start of the week with winds and height lines staying zonal. However, late in the day on Wednesday, winds shift more southerly as Tropical Storm Francine starts to move into the Arkansas Basin area. Along with the wind shift, there is a small amount of divergence predicted which could bring in some upper-level clouds.  

At 500 mb, there is a minimal temperature change (cooler) along the same time scale as the winds start to shift. This change, along with the upper-level divergence, supports the possibility of clouds developing late Wednesday into Thursday morning. While clouds may develop, there is little-to-no chance for rain during those times (09z Tuesday to 18z Wednesday). Moving to 700 mb, this theory is supported by the lack of lift in the atmosphere dampening any chances for precipitation to develop. Late in the forecast period, as TS Francine (expected to be TD) pushes in, relative humidity starts to increase.  

Lower in the atmosphere at 850 mb, humidity is still presenting within the models, while continuing to be low impact. This moisture primarily is being transported from the Atlantic Ocean during Wednesday evening. As TS Francine pushes into the Arkansas basin and further towards the Bootheel, the moisture starts to change from Atlantic to Gulf transport. During that time instability is predicted to rise, mirroring the lift at 700 mb. To further bolster the forecast, soundings were utilized looking primarily for any cloud cover signatures and any possibility of precipitation.  

Soundings showed low-level moisture at the surface from mid-Wednesday into the afternoon. This is supported by surface maps, as during 15z Wednesday moisture advection into Missouri is predicted to start from the south. Aside from the moisture advection, upper-level clouds are shown in the soundings early Thursday alongside TS Francine’s advance. Future forecasters should be watching the chances for rain Thursday night moving into the late work week as TS Francine moves into southeast Missouri. 

-Chirpich, John, Beach, Alcorn