Mega-clusters suggest a drier and warmer U.S. Corn Belt forecast Discussion: Forecast trend for the medium-range across the U.S. is a little different this morning. The jet stream to is now forecast to stretch across the U.S./Canada border featuring a showery upper trough in the Great Lakes region days 6-10 and a far-enough north shift into Southeast Canada days 11-15 to support tropical rains in the Gulf/Southeast U.S. days 11-15 (Fig. 1-2). The U.S. Corn Belt trends drier and warmer! Yesterday the forecast discussion mentioned the Mexican Monsoon developing with a spill-over of Interior West wet weather into the western Corn Belt in August indicated by NOAA/CPC climate forecasts. An alternative approach is wet weather shifting north toward the Corn Belt caused by tropical weather in the Gulf of Mexico. The second pattern described may be developing for early August. Fig. 1-2: Most likely precipitation scenario based on mega-cluster forecast for the medium-range across the U.S. Change in the Global Atmospheric Angular Momentum Pattern Fig. 3: Global atmospheric angular momentum index pattern change. Discussion: Global atmospheric angular momentum (GLAAM) is a measure of how fast the atmosphere is spinning relative to the earth’s rotation. The 15-day GLAAM forecast (Fig. 3) indicates a recent pattern change to the negative phase has occurred and will intensify into August. During the negative phase of GLAAM the atmosphere moves more slowly relative to the earth’s rotation causing mid-latitude jet streams to produce higher amplitude ridge and trough patterns (which can cause climate extremes as observed with the heat wave of the past few days in the U.S. and in Europe this week). Negative GLAAM is common when La Nina is present and offers more evidence that the weak El Nino pattern of 2018-19 has ended. The August analog years for Negative GLAAM during neutral ENSO since 2000 are 2005 and 2012 which were active North Atlantic tropical cyclone years. Hot Europe ridge to last 7-10 days Fig. 4-6: Most likely upper air pattern across Europe this week and in the medium-range forecast by mega-cluster model. Discussion: The next heat wave of note is across Europe this week as supported by the amplified upper ridge pattern offered by the mega-cluster most-favored solution (Fig. 4). Temperatures surge to 100-105 in Spain and France. There are questions as to how long the supporting upper ridge lasts. The mega-cluster favors more warmth days 6-10 although less extreme with excessive heat in Spain, France and Germany slowly easing (Fig. 5). In the 11-15 day period the upper ridge is gone and the semi-permanent cool trough in Western Russia returns to prominence (Fig. 6). Black Sea showers this week but drier next week Fig. 7-8: GFS ENS indicates wet weather in Southwest Russia the next 2 weeks although Black Sea region turns drier next week. Discussion: While Europe basks beneath a hot upper ridge pattern this week a downstream trough brings rain to the Black Sea region with showers extending across Southwest Russia (Fig. 7). The focus returns to the persistent Western Russia upper trough days 8-14 increasing wet weather risk while the Black Sea region turns drier (Fig. 8).