Random weekend downpours, meteorological summer 2014

It's finally here.

The season known as summer finally arrives this weekend.

Meteorological summer, that is.

June 1 marks the start of meteorological summer.

The three warmest months of the year in Minnesota and the northern hemisphere are June, July and August. For record keeping purposes, meteorologists use June to August as "meteorological" summer. Yes, many of us meteorologists march to a slightly offbeat, different drummer.

But I digress.

Here's a good description from the National Oceanic and Atmospheric Administration describing why we break down the seasons meteorologically vs. astronomically.

Meteorologists and climatologists break the seasons down into groupings of three months based on the annual temperature cycle as well as our calendar.

We generally think of winter as the coldest time of the year and summer as the warmest time of the year, with spring and fall being the transition seasons, and that is what the meteorological seasons are based on. Meteorological spring includes March, April, and May; meteorological summer includes June, July, and August; meteorological fall includes September, October, and November; and meteorological winter includes December, January, and February.

These seasons were created for meteorological observing and forecasting purposes, and they are more closely tied to our monthly civil calendar than the astronomical seasons are. The length of the seasons is also more consistent for the meteorological seasons, ranging from 90 days for winter of a non-leap year to 92 days for spring and summer.

By following the civil calendar and having less variation in season length and season start, it becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes.

 Summery forecast?

Forecasting the summer season is about as easy as winning that really big stuffed animal on the midway. You're more likely to walk away with that little plastic thingy and a few less quarters in your pocket.

A developing El Nino has yet to fully manifest in the tropical Pacific. The links to seasonal weather are much stronger in winter (milder) for El Nino events in Minnesota. There's a much lower statistical correlation and forecast skill for our summer weather patterns.

NOAA leans toward a cooler summer at this point for the Upper Midwest. I'm not buying it just yet.

My hunch is we'll see a pretty typical summer. That means a good mix of heavy rainfall early in June, mixed in with our fair share of severe weather this summer.

• 19 days at or above 90 degrees in 2013 at Minneapolis-St. Paul International Airport

• 31 days at or above 90 degrees in 2012 at MSP

• 13 days - average number of 90 degree days annually at MSP

Last summer we sweated through 19 days of 90-plus degree heat after sweltering in 31 days of 90-degree heat in 2012.

This summer?

Who knows. Last year some forecasters confidently predicted we were done with 90 degrees in early August during a cool spell. We went on to log 10 more days at or above 90 in late August and September.

If you've lived in Minnesota long enough you learn not to bet against 90s during State Fair time.

My best guess? We end up somewhere between 13 to 18 days at or above 90 this summer, near or slightly above average. Overall near normal temps and a slightly wetter summer would not surprise me. Recent years have show a strong trend toward wetter early summers, and flash drought later in summer and into fall.

As we say in the weather biz,  stay tuned.

Partly soggy weekend

Our weekend weather is looking wet overall, but latest trends suggest we may not wash out the whole weekend.  Latest timing may favor some dry hours both Saturday and Sunday.

The best chance for metro heavy rains appears to be Saturday night into early Sunday morning. That may leave some dry hours, even some partial sun both Saturday and Sunday.

The European Centre for Medium-Range Weather Forecasts model grabs onto the broad brush trend of occasional downpours this weekend into Monday.

The weekend weather culprit? A slow moving low pressure system that lingers through Monday. Here's the soggy surface map animation over the weekend from NOAA's Weather Prediction Center.

• 2.7 inches GFS rainfall output for MSP through Monday

Flash flood potential?

As moisture begins to stream north this weekend, scattered showers and thunderstorms become more numerous.

Here's a great visual example of how dew points above 60 degrees represent enough low level moisture to produce a "cumulus field" of scattered clouds.

Notice how Friday afternoon's NASA GOES 1 km visible satellite features crystal clear skies over Wisconsin and the Great Lakes where dew points are in the 40s and 50s, with numerous cumulus forming to the west where dew points exceed 60 degrees.

As the moisture pools north along the front this weekend, slow moving storms and downpours will produce some heavy, multi-inch rainfall totals.

There is some potential for the gully washers to exceed flash flood guidance in Minnesota this weekend.

Keep an eye out for potential flash flood watches and warnings this weekend.

Seeley: Wet and warm May finish 

My MPR News colleague and University of Minnesota climate Guru Mark Seeley has a good summary of our wet may finale in this week's Weather Talk.

 Topic: Heat and dewpoints

The Memorial Weekend began a string of warmer than normal days (8 days in a row) in Minnesota not seen since the end of last September.  The long wait for the return of 80 F weather ended as many observers reported consecutive days with afternoon highs of 80 degrees F or above.  Some individual climate observers reported new record daily high temperatures this week, including the following:

May 24: 91 degrees F at Crookston (tied 1967), 87 degrees F at Thorhult, and 84 degrees F at Duluth

May 25: 85 degrees F at Duluth

May 26: 88 degrees F at Minnesota City

May 27: 87 degrees F at Aitkin, and 88 degrees F at Wolf Ridge

In addition, dewpoints rose to near record levels at many southern Minnesota locations, making the outside temperatures fee tropical and more like mid-summer.  Over May 26-27 dewpoints ranged between 65 and 70 degrees F in many counties.

Topic:  Preliminary climate summary for May 2014

Despite the warmer than normal temperatures over the last week of the month, most observers around the state are reporting average May temperatures that are 1 to 3 degrees F cooler than normal.  A few observers are reporting near normal May mean temperature values.  Extremes for the month ranged from 91 degrees F at Crookston on the 24th to 23 degrees F at Park Rapids and Crane Lake on the 17th.

Moisture wise, many central and northern Minnesota communities reported above normal rainfall for May, while some areas of western and southern Minnesota reported less than normal. A number of communities had a very wet May indeed, including Hibbing and Mora with 5.06 inches, Milaca with 5.14 inches, Cambridge with 5.18 inches, and Lester Prairie with 5.23 inches.  There were numerous reports of hail and two tornadoes were reported on May 8th, near St James and Madelia.  Straight line wind damage occurred near Waseca, Montgomery, and Red Wing.

This cool, wet spring produced a late planting season for farmers, but nearly all of the state corn acreage was planted by May 30, and over half of the soybean acreage was planted as well.  Southern Minnesota farmers began harvesting alfalfa the last week of the month.  Moderate drought remained in the extreme southwestern counties of the state.

Hurricane season 2014: What to expect?

Forecasts seem to favor a sub-par hurricane season. The problem with seasonal hurricane forecasts? Even in a quiet season, one bad hurricane making landfall in the wrong place can ruin your decade.

Weather Underground's Jeff Masters asks some great questions about the upcoming hurricane season. Here's a peek.

The 2014 Atlantic hurricane season is officially underway on Sunday, June 1. What will this year's hurricane season bring? My top six questions for the coming season:

1) When will the first "Invest", tropical depression, and named storm of the 2014 Atlantic hurricane season form? We have a chance of all three of these events occurring in the Gulf of Mexico during the first week of hurricane season, though the models are currently hazy about this.

An area of disturbed weather in the Eastern Pacific located a few hundred miles south of Southeast Mexico is forecast to move slowly northwards towards the Gulf of Mexico Sunday through Tuesday. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave this system a 50% chance of developing into a tropical depression or tropical storm by Wednesday. The 06Z Friday run of the GFS model predicts that this disturbance will make landfall in Southeast Mexico on Tuesday, then spread moisture northwards over the Gulf of Mexico late in the week.

The model predicts that wind shear will be light to moderate over the Gulf late in the week, potentially allowing the disturbance to spin up into a tropical depression. The 00Z Friday run of the European model has a different solution, predicting that the Eastern Pacific tropical disturbance will remain south of Mexico through Friday.

However, the model suggests that moisture streaming into the Gulf of Mexico late in the week will be capable of spawning an area of low pressure with the potential to develop in the Southern Gulf of Mexico's Bay of Campeche. In any case, residents of Southeast Mexico and Western Guatemala appear at risk to undergo a multi-day period of very heavy rainfall capable of causing flash flooding and dangerous mudslides beginning as early as Monday.

This disturbance may cross over Mexico and into the Gulf of Mexico and create the Atlantic's first "Invest" with the potential to develop late in the week, sometime June 5 - 7.

2) All of the major seasonal hurricane forecasts are calling for a below-average to near-average season, with 9 - 12 named storms, 3 - 6 hurricanes, and 1 - 2 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2013 averaged 15 named storms, 8 hurricanes, and 4 major hurricanes. Will an El Niño event indeed arrive, bringing reduced Atlantic hurricane activity, allowing the pre-season predictions to redeem themselves after a huge forecast bust in 2013?

3) How will the steering current pattern evolve? El Niño years tend to feature more storms that recurve out to sea and miss land; will this be the case in 2014?

4) Will the U.S. break its 2006 - 2013 eight-year run without a major hurricane landfall, the longest such streak since 1861 - 1868?

5) Will the 170,000 people still homeless and living in makeshift shelters in Haiti in the wake of the January 2010 earthquake dodge a major tropical cyclone flooding disaster for the fifth consecutive hurricane season?

6) Will the new experimental National Hurricane Center products be useful and popular? I am most looking forward to the Potential Storm Surge Flooding Maps, interactive zoomable maps that will show where the storm surge has a 10% chance of inundating the coast at 3, 6, and 9 feet above ground level. The newNHC blog (first post: May 29, 2014) and 5-day graphical weather outlook (begins July 1) should also be of interest.