July 31, 2015: The weekend and August

High pressure is building across the high plains in western North and South Dakota as well as in Saskatchewan and Alberta.  That will shift to the east gradually.  There is still a touch of a pressure gradient today in the Red River Valley where the wind is expected to blow from the northwest in the 10-20 mph range, lighter in western North Dakota.

Surface Analysis

Surface Analysis

A weak upper-air disturbance sliding through southern Canada may trigger an isolated storm or two later today into tonight, especially in northeastern North Dakota and northwestern Minnesota, but precipitation should continue to be sparse in the region until perhaps the middle of next week.

Friday 4:00 PM CDT Projected Radar

Friday 4:00 PM CDT Projected Radar

The upper level mean wind flow will continue from the northwest in the next week, with the flow sharpening a bit early next week to drawn in slightly cooler air.  Maximums are expected in the 80s through Sunday, then mainly 75° to 80° days with minimums in the 50s for early next week as the flow becomes a bit more northerly.

ECMWF WMO-Essential

Projected 500 mb Heights and Anomalies From August 3 through 8

The best threat of rainfall at this time besides the isolated threats will probably arrive toward the middle of next week (Wednesday).  Near average and dry the next few days, then a bit cooler than average and mostly dry through the middle of next week looks to be the trend for the next 7 days.

Beyond the short term, the last two stronger El Nino summers produced drier than average August.

August 1982 and August 1997 Averaged Precipitation Anomalies

August 1982 and August 1997 Averaged Precipitation Anomalies

 

With slightly below average temperatures.

August 1982 and August 1997 Averaged Precipitation Anomalies

August 1982 and August 1997 Averaged Temperatures Anomalies

Western ridge and eastern trough (sound familiar?) seemed to dominate those two years.  Yet, two years do not necessarily make a good sample, plus, oceanic patterns in the Pacific Ocean outside of the El Nino signature are not all that similar to this year, plus the Atlantic Ocean was also not similar those years to what is currently occurring.  The western ridging so far this summer had tended to be farther east than in the two examples above which has brought slightly above (not below) average temperatures this summer.  I think that trend will continue through August.

Temperature departure from average from June 1 through July 30

Temperature departure from average from June 1 through July 30

Precipitation since the very wet May has in typical summer fashion been very hit and miss, although the general trend since June 1 has been for drier than average conditions with the big exception of northeastern North Dakota with more spotty above average conditions in other parts of the state.

Precipitation Departure from Average from June 1 through July 30

Precipitation Departure from Average from June 1 through July 30

With a northwest flow expected to dominate through much of August, the odds currently favor the month overall finishing with near or below average rainfall.  This will mean my current project is for slightly above average temperatures and slightly below average rainfall for most of the state.  Especially with rain, there are generally exceptions when you are dealing with thunderstorms bringing much of the precipitation.

I am on vacation next week.  My next forecasting blog post will come on August 10.

Daryl Ritchison

 

 

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