10/03/2023, 8:40 am EDT

U.S. Week 2-4 Outlook: East is cooler for mid-to-late October.

Chart of the day: U.S. drought worsening during early autumn. Discussion: The U.S. drought worsened entering October including rainfall deficits reaching the 12-15 in. range in parts of Southeast Nebraska and Southeast Iowa. Drought restrengthened in Kansas, parts of the Southeast States, and the Carolinas. Only the southern half of Florida, southern New England, and the coastal Northwest turned wetter. Week-2 Ahead Forecast valid October 10-16, 2023: Cooler East. Discussion: The upper trough in the East is triggered by a sharp -NAO pattern early in the period. Unseasonably cool air into the East into the middle of next week moderating late week. Forecast trend is wetter in the northern Great Plains and Louisiana but that rain is unlikely to raise low water on the Mississippi River. Substantial rain is forecast for the Northwest States. Week-3 Ahead Forecast valid October 17-23, 2023 (previous below): Wetter East. Discussion: Upper trough keeps the Central/East-central U.S. temperate (and possibly cooler than shown) while on the East Coast, the trough causes a wet regime. Hot and dry in the Southwest U.S. to the north of late season tropical cyclones impacting Western Mexico. Week-4 Ahead Forecast valid October 24-30, 2023: Cooler look for October continues. Discussion: The cooler look to the October outlook is maintained for the last week of the month as much of the U.S. is near normal except very warm in the Southwest U.S. A showery pattern near the U.S./Canada border with a tropically wet regime indicated in the Caribbean Sea.
10/03/2023, 8:31 am EDT

South America Week 2-4 Outlook: Southeast Brazil rains are substantial. However, elsewhere in Brazil, dry and hot weather is widespread.

Charts of the day: South America September 2023 climate. Discussion: September 2023 was hot across most of Brazil especially North-central Brazil to the Paraguay border. The hottest anomalies across North-central Brazil were inspired by an attendant dry climate. The southern 30% of South America was exceptionally cool. Heavy rains affected far Southeast Brazil. Week-2 Valid October 10-16, 2023: Southeast Brazil rains, remainder of Brazil is dry. Discussion: Strong subtropical ridge is centered on the East Brazil Coast and is responsible for widespread hot and dry weather. An upper trough off Northeast Argentina creates a vigorous frontal zone bringing heavy rain to Southeast Brazil. Week-3 Valid October 17-23, 2023: Southeast Brazil stays wet; elsewhere is dry. Discussion: The East Coast of Brazil upper ridge strengthens and sustains hot and dry weather across much of Brazil except the southeast corner where heavy rains continue. Week-4 Valid October 24-30, 2023: Southeast Brazil rains shift farther south to Uruguay, remainder of Brazil stays dry/hot. Discussion: Upper trough across Southern Chile and an upper ridge off Southeast Brazil continues. The wet weather in Southeast Brazil shifts farther south and into Uruguay while elsewhere stays dry.
10/03/2023, 8:22 am EDT

AG Market Early Notes: U.S. short-term rainfall.

    Fig. 1-4: Severe thunderstorms across the western Great Plains today, a rainstorm in the Mid-south tomorrow, heavy rain for the Northeast FRI/SAT, and a big cooldown in the East next Sunday. Discussion: A late season severe thunderstorm outbreak is forecast for today across most of the western Great Plains to western Texas (Fig. 1). The severe weather loses strength tomorrow (except Texas) while dynamics to cause a heavy rainstorm convenes over Northeast Texas to Western Arkansas where 2-5 in. could occur featuring some flash flooding (Fig. 2). By FRI/SAT the rainstorm shifts into the Northeast U.S. and Quebec bringing 1-3 in. of rain (Fig. 3). After the rainstorm in the Northeast departs Sunday, a sprawling much cooler autumnal air mass spreads across the eastern half of the U.S. for Sunday (Fig. 4).    
10/03/2023, 8:17 am EDT

U.S. Medium-range Forecast: Cool blast East days 6-10; most of U.S. near normal after mid-October.

Chart of the day: Possible tropical cyclone in Gulf around October 13th. Discussion: GFS is on-and-off with a tropical storm risk in the Gulf of Mexico for later next week. Formation in the Bay of Campeche is becoming more certain. Where a system may track is not certain. Medium-range 6-10 Day Forecast Valid October 8-12, 2023 Discussion: The slightly cooler GFS (75% input) is favored over the ECM (25% input) in the East where an early autumn chill develops next week. Risk of <32F is apparent in Wisconsin and the eastern Ohio Valley early next week. Medium-range 11-15 Day Forecast Valid October 13-17, 2023 Discussion: The warm-up remains in the forecast biased toward the West (warmer change) while the East stays near normal. U.S. Medium-range Precipitation Forecast Discussion: Maintaining the 75% GFS/25% ECM combination, the medium-range percent of normal precipitation forecast yields a dry national climate in the 6-10-day period while the Mid-Atlantic States are wet in the 11-15-day period. Note the wet pattern across the Gulf of Mexico and Florida where late season tropical activity is possible. Days 16-20 Extended range Temperature Forecast valid October 18-22, 2023 Discussion: The U.S. is temperate in the extended range. Other previously warm models are also showing a cooler trend. California could see some late season hot weather. Wet weather is focused on the East and extends into the Southern U.S.