9/2/15: Summer to Autumn

There is no Crop and Pest Report this week.  Here is a quick analysis of the expected weather the next several days.

Yesterday maximum temperatures were mostly in the upper 80s to the lower 90s across the North Dakota Agricultural Weather Network (NDAWN) mesonet.

September 1, 2015 Maximums
September 1, 2015 Maximums

The lack of smoke in the atmosphere allowed temperatures for the first time in over a week to reach the actual potential of the day.  Today should be similar to yesterday but perhaps 1-2° warmer.  Also, it does not appear smoke will be an issue today either, although that may change a bit tomorrow and Friday.  Keyword:  may.

Surface map has a weak low in South Dakota that should gradually fade away, but the main feature is an area of low pressure in the Canadian Rockies.  That system will move very slowly to the east over the next several days.

6:00 AM Surface Map
6:00 AM Surface Map

 

Ahead of that low pressure center will be a stiff southerly breeze, not only bringing in warmer temperatures but also higher dew points.  So both warm and humid (by our standards) the next few days.  That low will begin to impact far western North Dakota on Thursday Night, but likely not impact the Red River Valley until very late on Friday, if not Friday night.  The impact of that low will eventually be rain in the form of thunderstorms.  Because of the slow movement of this mid-latitude cyclone, in the short term will be three days (4 if you count yesterday) of well above average temperatures for early September.  But also, once the low approaches, it will mean two or three days of thunderstorm threats.  Because the air ahead of this low is not only warm near the surface, but aloft, meaning a “cap” will be present, making thunderstorms difficult to form during the peak heating of the day, but rather having a higher probability to form at night, meaning nocturnal rain will be more likely in many locations once the low moves across North Dakota.

Friday AM
Projected Friday, September 4, 2015 Surface Map at 10 AM

The storm will begin to cool western North Dakota off on Thursday, but the Red River Valley may record temperatures well above average through Saturday, with the warmest days today and tomorrow.  Western North Dakota the warmest days were yesterday and today.

Because of the slow motion of  this low and several disturbances in the upper atmosphere that will move along the cold front associated with the storm, plus the abundance of low level moisture, the thunderstorms that do form will have the ability to produce localized one to two inch rainfall totals.  As has been the case frequently this summer, northern North Dakota into northwestern Minnesota would have the highest probability of this occurring, but of course, any given spot elsewhere could also produce such amounts, it is just the odds favor the north more than the south as the system passing through.

Beyond this storm system, most of next week, including to some degree Sunday, but especially Labor Day and beyond temperatures will be either near or slightly below average as autumn weather moves into the region.  It does not appear at this time that there would be any frost threat from the air mass behind the front.  I am still looking more in the September 20-25 range with a stronger cold frontal passage for that opportunity.

Daryl Ritchison