...An upper low barreling through the Deep South will be the focus for
heavy rainfall the next couple of days...
...Another closed low across California should bring a return to the
onshore flow regime...
The 500-millbar pattern over the country will remain very blocked in
nature with a pair of closed lows dominating the nation's weather.
The forecast models are in agreement that these lows will position themselves across the Deep South and California, respectively.
Meanwhile, much of the northern tier of the U.S. should be under the influence of a west-to-east oriented ridge which will keep the prevailing westerlies up in Canada.
Beginning with the upper cyclone currently moving from the Ozarks toward the South-Central U.S., this system should continue its slow movement toward the south and east. It appears this closed low will maintain its general intensity and feed off an active plume of moisture from the Gulf of Mexico. An additional factor to account for now is upslope flow against the Southern Appalachians which will easily aid in additional heavier rainfall amounts.
This combination of moisture, terrain, strong mid-level dynamics, along with slow overall motion will support a threat for flash flooding. At this time, the Weather Prediction Center has indicated such a risk in their excessive rainfall forecast across the Tennessee Valley and Southern Appalachians through Sunday evening.
The other major feature affecting the lower 48 is yet another upper low
center expected to retrograde from the Central Great Basin toward Northern California tonight. Instability aloft may trigger scattered thunderstorms over sections of interior Northern California although they likely will not produce any measurable rainfall given the very dry air mass currently in place.
Per a recent Storm Prediction Center fire weather outlook, dry thunderstorms may lead to an increased wildfire danger as the region
remains under drought conditions.
As this upper system continues shifting back toward the west and south, a return to onshore flow is expected which will quickly increase relative humidity values. This will definitely be welcomed by any fire relief efforts across areas of Southern California as they recently battled very hot and dry conditions.