Highlight: 12Z GFS is stormy East-central U.S. in medium-range.
Fig. 1-2: Heavy precipitation, both rain and snow are indicated in the 6-10-day forecast by the 12Z GFS.
Discussion: This week, a warm and mostly dry pattern for the central and southern Great Plains but changes are on the way in the 6-10=-day forecast. Based on the 12Z GFS forecast two large areas of heavy precipitation are likely next weekend into early the following week in the Midwest and Upper Midwest U.S. In the Midwest, several inches of rain are likely heaviest from central Missouri to northern Ohio (Fig. 1). Heavy snow is forecast by 12Z GFS with 4-8 in. across Iowa to one foot or more from Wisconsin to Southeast Ontario (Fig. 2).
The 12Z GFS also maintains the stormy risk in the 11-15-day period. A western U.S. trough is amplifying, attendant cold weather expanding and the clash with warmth in the East maintains an active stormy pattern. The 12Z GFS indicates potential for 5-7 in. of rain centered on the western Tennessee Valley and also >1 foot of snow in Kansas (Fig. 4).
Fig. 3-4: Additional heavy precipitation, both rain and snow are indicated in the 11-15-day forecast by the 12Z GFS.
In South America, the 12Z GFS indicates a narrow band of heavy rain associated with a cold front across Northeast Argentina in the 1-7-day period while to the north, the recent dry pattern change across Brazil continues (Fig. 5). However, in the 8-14-day period a forecast change is indicated. The outlook stays wet across Northeast Australia and into Uruguay extending northward across southwest and central Brazil (Fig. 6). Coastal Southeast Brazil stays dry.
Fig. 5-6: The 12Z GFS 1-7-day and 8-14-day rainfall anomaly forecast across South America.
Tropical cyclone risk is evident in Australia. A tropical cyclone brings heavy rain to northwest Australia this week (Fig. 7). Tropical moisture is entrained into an upper trough in Eastern Australia causing heavy rains. A major tropical cyclone shifts toward New Zealand. Additional heavy rain risk is evident on the East Coast in the 8-14-day period (Fig. 8).
Fig. 7-8: The 12Z GFS 1-7-day and 8-14-day rainfall amount forecast across Australia.