...Heavy rainfall from Hurricane Arthur and its extratropical remains will
impact upper New England on Saturday...
...Active monsoonal convection is expected across the Southwestern U.S...
...Severe thunderstorms are possible from the Northern Plains into the
Upper Great Lakes through early Monday...
As of early this morning, Hurricane Arthur has weakened to a post tropical storm while transitioning into an extratropical cyclone later this morning.
Regardless of the classification, this system will continue to have access to moisture originating from deep in the tropics.
This should result in fairly hefty rainfall rates within the stronger precipitation cores.
The current forecast indicates a widespread 2 to 4 inches of rain is likely across northeastern Maine and into Nova Scotia through early
Flash flooding is possible in the heavier rainfall bands with the threat diminishing as the extratropical remains lift into far eastern Canada.
In addition to the heavy downpours, gusty winds will continue as the system maintains a fairly low surface pressure which will keep a
strong gradient in place.
With the exception of the southeastern U.S., surface high pressure building over the East Coast will bring tranquil weather to the region to conclude the holiday weekend.
Further to the south, a stalled frontal zone will keep conditions more unsettled through Monday morning. The combination of lift along the stationary front in addition to the local sea breeze effects will keep thunderstorms in the forecast the next couple of days.
An upper anticyclone anchoring the Four Corners region will facilitate an increase in the monsoonal moisture surging up from the tropical Pacific.
A myriad of smaller-scale disturbances are expected to meander about the upper ridge with each impulse being a trigger for thunderstorm activity. The best coverage of convection should take place during the peak heating of the day with heavy downpours and gusty winds possible across the Desert Southwest and into the Four Corners. The steering flow in this regime will be weak which may allow some convective cells to become quasi-stationary at times. Thus, flash flooding is possible, particularly in areas of more sloped terrain where runoff will occur quickly.
To the northern tier of the country, periods of showers and thunderstorms are expected as a slow moving frontal system works its way through the Central U.S. The mid/upper level winds will be much stronger up across the Northern Plains/Upper Midwest as these locations will be closer to the jet stream. Consequently, storms should be much more organized in nature which will lead to an inherent threat for severe weather.
The Storm Prediction Center has placed portions of the Northern Plains eastward into the Upper Great Lakes/Middle Mississippi Valley in a risk for severe thunderstorms through early Monday.