April 27, 2015: Real Spring Begins / Late Frost Potential

There was a noticeable difference in maximum temperatures across the NDAWN (North Dakota Agricultural Weather Network) yesterday (Sunday) with temperatures ranging from near 70° in eastern North Dakota to a strip of 40s from southwestern to north central North Dakota.  The difference was cloud cover and eventually some light rain fall that reduced the maximum temperature potential in some portions of the state.

Sunday, April 26, 2015 Maximum temperatures
Sunday, April 26, 2015 Maximum temperatures

The rain that did fall was generally in the 0.10 inch to 0.30 inch range.  The rain was moving generally from southwest to the northeast meaning that the eastern part of North Dakota will probably record minimal amounts of moisture from this event.

rain
Overnight Rain Fall

Although the main band of rain is moving from the southwest to the northeast, the overall system is slowly working to the east, so although amounts look very light there should be at least some moisture moving into eastern North Dakota later today or tonight.

radar
Morning Radar

Because the rain will be moving into much drier, more stable air, the rain totals in far eastern North Dakota will on average likely stay below 0.10 inches.

Projected Radar for April 27, 2015
Projected Radar for April 27, 2015

Because of the rain and cloud cover that will be prevalent in central and western North Dakota there will be, like yesterday and even to a large degree Saturday, a big difference in air temperatures across the state this afternoon.

9:00 AM Satellite imagery
9:00 AM Satellite imagery

The 4 KM NAM (WRF) estimated high temperatures can be observed below.  Maximum temperatures should range from around 70° to the middle 50s this afternoon.

Monday, April 27, 2015 Projected Maximums
Monday, April 27, 2015 Projected Maximums

The cloud cover that has hindered maximum temperatures in central and western North Dakota should move out of the state after today,  The warmth that the Red River Valley has recorded the past couple of days will in turn be the general “norm” for temperature in the next week and beyond.  Whereas the average temperature last week was in the 5 to 10 degree below average range, temperatures this week into the first full week of May is projected to be in the 5 to 10 degree above average range.  With average temperatures now in the 60s, that should mean temperatures any where from 65° to 75° most of the week, with some localized 80° temperatures possible, especially as we approach the upcoming weekend.

The 500 mb height / anomaly projections from the ECWMF (European Model WMO Essential) indicates above normal heights, therefore, temperatures for much of the northern tier of the United States for the next 10 days.

ECMWF WMO-Essential Projected 5 Day Mean Heights and Anomalies for next 10 days
ECMWF WMO-Essential Projected 5 Day Mean Heights and Anomalies for next 10 days

 

With this pattern, minimal precipitation is foreseen for much of North Dakota.  Besides the threat for the next 18 hours, there will be another light system late Thursday into Thursday Night and perhaps again on Sunday, but amounts look under 0.25 inches in the locations that do record precipitation.  With the next 10 + days appearing so warm, any cool weather will be tempered by the time of year, meaning this stretch will likely be the true start of the warm season for the region.

Because “Plant 15” will likely be completed in the first 10 days of May, the attention then turns to the prospect of a late freeze.  One strong element in favor of a freeze near or after May 15 is the dry conditions.  Strong radiative cooling associated with the dry conditions will enhance the prospect for a late freeze.  As an example after reaching near 70° yesterday, low temperature this morning were near freezing in the Red River Valley with Oakes, Brampton and Leonard all recording a low in the 20s.

 

April 27 2015 minimums
April 27 2015 minimums

 

In my private conversations and recent public talks I have been hinting at frost potential in the May 15 to May 20 range, which would not of course be unusual for our climate and near the long-term average for northern North Dakota, but with early planting this year and emergence of some crops, depending on the strength of the cold, certainly could be a major factor.  Time will tell.

Daryl Ritchison