Strong thunderstorms today?

There appears to be a marginal set up today for strong to severe thunderstorms along a narrow corridor across central Minnesota.  Any storms that do pop, are working in a favorable environment of 30 to 40 knot winds to intensify.  Large hail and strong winds are the primary threats. I really don’t see much tornado potential out of this.  Storm coverage is expected to be isolated.

The high resolution WRF-NMM forecast model, which was pretty darn good at handling the storm activity yesterday, although I failed to buy into what it was displaying, is showing some stronger activity near the Twin Cities metro by the evening hours.

Anyone with outdoor plans might want to keep an eye to the sky today for changing weather conditions!

RS

Recap of Saturday storms

Saturday was an interesting day for thunderstorm activity.  Morning storms over northern Minnesota, triggered by a slow-moving cold front, really wreaked havoc on the forecast for the remainder of the day due to the complexities of the situation with cloud clover and boundaries established from previous storms.  If I can be honest, it was one of those days where I really had no idea where storms would fire, and if they would become severe.  I like being straight-forward with people, and I’ll be the first to admit I was wrong about something.  I knew the possibility of storms across the northland in the morning, which would eliminate the greatest threat for severe weather over that area where upper-level winds were the strongest for organized storms.

Here a satellite image from around the noon hour Saturday.  With the cloud cover, the best chance for any severe storms appeared to be over the southern half of Minnesota.

The National Weather Service in Chanhassen put together this illustration showing the position of fronts and boundaries later in the day at approximately 4:45 PM:

The Storm Prediction Center wasn’t really sure about this day either.  It had issued a severe thunderstorm watch during the early afternoon hours until 9 PM for southern Minnesota, then cancelled it soon after, and re-issued another watch in the evening until 1 AM Sunday.

Initial severe thunderstorm watch:

The “do-over” of the watch:

With all the complications to the forecast, and with the storms working in a weaker wind environment, I decided against storm chasing in the afternoon, and instead worked on some projects around home.  Although it’s an interesting puzzle to attempt to solve, I didn’t want to sit around idle and wait to see what would happen, if anything did.  With the price of gas these days, it just didn’t make a lot of sense for this level of uncertainty either.

First storms arrive into the Brainerd lakes area before 6 PM:

As the storms moved to the southeast from Brainerd, the most intense storms were over Mille Lacs and Isanti Counties, where numerous funnel clouds were reported.  Here are radar summaries north of the Twin Cities from the National Weather Service.

Base reflectivity:

Base velocity:

Areas of the greatest rotation are indicated by the darker colors below.  Based on what I saw on radar, I wouldn’t be surprised if there was a brief tornado touchdown near the Mille Lacs and Kanabec County border, east of Milaca.  A storm survey is being conducted in this area to determine if there were tornadoes.

As day progressed into the night, I decided to make a play at the storms to the west of the “main event” after 10 PM.

I headed out west on Minnesota Highway 5 towards Carver County, and intercepted the storms in Norwood-Young America.  Saw a pretty good lightning display from these garden-variety storms.  I captured some video from my cell phone as I was driving around the town.  The audio is WCCO Radio.

Severe storm reports from the day were scattered, with the most concentrated area from the cell that tracked southeast from Brainerd into the northern Twin Cities metro with large hail, felled trees from strong winds, and funnel clouds.  One tornado was reported in the city of Johnson, Minnesota in far west-central Minnesota from a short-lived storm.

RS

Severe thunderstorm watch in effect

A Severe Thunderstorm Watch is in effect for the following counties in Minnesota until 9:00 PM CDT for Anoka, Blue Earth, Brown, Carver, Chippewa, Chisago, Dakota, Goodhue, Hennepin, Isanti, Kandiyohi, Lac qui Parle, Le Sueur, McLeod, Meeker, Nicollet, Pope, Ramsey, Redwood, Renville, Rice, Scott, Sherburne, Sibley, Stearns, Steele, Stevens, Swift, Waseca, Washington, Watonwan, Wright, and Yellow Medicine

Stay tuned!

RS

Severe thunderstorm watch for the Twin Cities and southern Minnesota

A severe thunderstorm watch was issued by the Storm Prediction Center until 6 AM Wednesday for Anoka, Benton, Blue Earth, Brown, Carver, Dakota, Faribault, Freeborn, Goodhue, Hennepin, Kandiyohi, Le Sueur, Martin, McLeod, Meeker, Nicollet, Ramsey, Redwood, Renville, Rice, Scott, Sherburne, Sibley, Stearns, Steele, Waseca, Washington, Watonwan, and Wright Counties.

Having said that, I believe that the biggest weather maker overnight will be torrential rains.  Radar estimates indicate one to two inches of rain per hour over far west-central Minnesota.  Some gusty winds may accompany these storms that approach severe levels, but overall the setup is marginal for severe thunderstorms.  You might be awaken to some claps of thunder, which may make for a shortage of sleep for some.

RS

Severe weather and heavy rains possible in next 24 hours

A bout of severe thunderstorms and heavy rain look to be on tap for Tuesday across Minnesota.

A warm front is slowly projected to move eastward from the Dakotas into the western part of Minnesota by the evening hours:

Along the southern periphery of the progressing warm front is where the greatest instability will be in place, setting the stage for isolated thunderstorms capable of producing large hail and damaging winds.  No widespread outbreaks expected, and the tornado risk is small, with the best chance across central Minnesota.  During the afternoon, northeast South Dakota will be in line for severe weather first in the vacinity of the warm front, and as the front shifts to the east, southwest Minnesota will see the chances for strong to severe storms after 7 PM.  The Twin Cities should see storms by around midnight, or shortly thereafter.

The models are also indicating heavy rain across northern Minnesota through Wednesday night.  Anywhere from one to two inches of rain may fall from the storms as they pass through the area.

Most of Minnesota is already near normal for precipitation.  It's areas across the southern United States that need the rain the most as a historic drought is ongoing. Texas is experiencing it’s third-worst drought since 1895.

Stay tuned to StormChaser Schwartz through the day for further developments!

RS

So what happened with the Saturday weather?

I can’t believe that I’m actually writing a blog entry on what went wrong (read: bust) with the severe weather set up on Saturday, considering that everything was in place going into the day for a potentially explosive event.  Instability was off the charts, there was a cold front, with good temperature contrast, moving through to provide lift, and favorable wind shear for some rotating supercells.

Don’t get wrong, I’m glad nothing major happened close to the Minneapolis-St. Paul metro area with the Twins game played during the afternoon and followed by the U2 concert at night.  Chalk it up to another goofy weather day in 2011.  I’ve never seen a spring/summer storm season as bizarre as this one.  You might as well throw out the textbooks this year, because the classic set ups for storms just don’t seem to work this year.  Many head-scratching moments.

I have two theories that prevented a severe weather outbreak yesterday:

1.  Morning convection

During the morning hours, a line of thunderstorms moved through central and southern Minnesota.  Some of the stronger storms produced hail up to 1.25-inches near Cold Spring in the St. Cloud area, and winds strong enough to down trees across the southeast part of the state.

Radar image of the storms just after 7 AM Saturday:

Radar summary of the line of storms moving across southern Minnesota during the morning hours:

These initial storms created boundaries – pockets of cooler air trapped in the atmosphere, which can be tapped for later storm development.  This would throw a wrench into forecasting the intensity and coverage of thunderstorms for later in the day.  Here’s the radar summary from the entire day.  Notice how storms develop late in the day near the metro in the area where the morning storms occurred:

2.  Cloud cover

After the storms had passed in the morning, I made the decision around 12:30 PM to drive west on US-212 towards Olivia, and north on US-71 to Willmar, thinking there would be some decent storm development during the afternoon with no cloud cover to interrupt diurnal heating.

It was looking so promising before 2 PM that even the Storm Prediction Center (SPC) was indicating the likelihood of a weather watch box being issued – probably a tornado watch, based on the red outline the SPC used for the southern half of Minnesota and portions of Iowa and South Dakota. In the world of weather, tornado watches are sometimes referred to as “red boxes” and severe thunderstorm watches are “blue boxes”.

My hopes of seeing a supercell and perhaps a tornado quickly vanished about an hour later as I could see a cloud layer, with no precipitation, off in the distance that formed and was moving to the east as I got closer to Olivia.  This pretty much killed any severe weather threat for the day as the clouds would cap any serious storms from firing.

That’s just a brief summary of what took place yesterday that nullified the severe weather threat.  It’s difficult to win over people when I was promoting the likelihood of severe weather during the day and nothing happened.  Hopefully, I didn’t alter your plans too much for nothing.  It’s just one of those frustrating days as to why things don’t work out the way they should have on paper.

RS

Saturday AM update

Thunderstorms are on-going this morning across central Minnesota out ahead of a trough.  This will be round one of a two part storm event for the state today.  These morning thunderstorms will leave boundaries of cooler air for the late day storms to work with as the cold front marches east during the evening hours.

Looking at the Rapid Update Cycle (RUC) model runs, it appears the greatest risk areas for severe thunderstorms are in the same general areas as I highlighted from my blog entry from late last night.  The greatest severe weather risk is highlighted below.

The tornado threat area is also in the same vicinity across north-central Minnesota, about 50 miles north/south of a Brainerd, Minnesota east/west line.

One of the high-resolution models puts the storms into the Twin Cities right around 7 PM tonight.  This is also in agreement with several of the various models out there.

You’ll want your NOAA Weather Radio alert to be set today as it does appear more and more likely that severe weather will be imminent into the latter part of the day.  I’ve been trying to bring attention to this weather event over the last couple days, so hopefully many people will be sky aware and paying attention to weather developments later on today.

RS

Severe Weather Saturday

Saturday is shaping up to be a stormy one across Minnesota during the afternoon and evening hours as a cold front will move through the state and be positioned in Wisconsin by early Sunday morning.  It will bring with it a drop in high temperatures between Saturday and Sunday by 10-degrees, and a noticeable dip in dew points into the comfortable 50s.  Unlike most of the weather setups during the late spring into the summer, this one will be more of a textbook setup.  Here is the surface analysis at 7 PM Saturday:

Ahead of the cold front, temperatures will be in the low to mid-90s with dew points in the mid-70s.  This will create a very unstable atmosphere for the cold front and associated low pressure area to work with during the day.  Highlighted below is the greatest risk area for severe thunderstorms.  It covers about the southern two-thirds of the state.  Large hail and damaging winds will be the primary threat in this area.

This is roughly the same outline where the Storm Prediction Center indicated a slight risk of severe weather for Saturday in it’s Day 2 outlook, issued at 12:30 PM Friday.

The strongest wind shear will be along the northern periphery of the severe risk area, roughly between Brainerd and St. Cloud, Minnesota.

That area in the north-central part of Minnesota will see the risk of tornadoes with wind shear values in the 60 to 70 knots range.  That’s a lot of speed, folks!

U2 concert goers heading to TCF Bank Stadium on the University of Minnesota campus should pay close attention to the skies Saturday night and head for shelter if skies appear threatening.  I have plans to attend another concert that night, but I will likely be out watching the storms as they approach the Twin Cities.  Having nearly 60,000 people packed into an outdoor stadium with severe weather looming is a worst nightmare to anyone associated with weather and public safety.  However, if spotters and chasers are able communicate and collaborate effectively with weather service and media personnel, then providing advanced warning should go off without a hitch.  One positive working in emergency managers’ favor is that the tornado threat appears to be away from the metropolitan area, and outdoor concert events.

Stay safe, and have a great weekend!

RS

Why no tornado with “hook echo” on Tuesday storms?

During the morning hours of Tuesday, July 20th, a supercell thunderstorm tracked from the Brainerd area southeastward through the Twin Cities.

As the storm ascended on the Twin Cities metro, it began to show instances of hook echoes on radar.  A hook echo is an indicator of tornado development.  Here is a radar image that the National Weather Service in Chanhassen put together of a hook appendage in northwestern Anoka County at 10:45 AM.  No tornado reports with this, but there was a public report of a funnel cloud about 15 minutes later at 11:02 AM in Maple Grove near the Interstate 494 and 694 junction.

Radar was not picking up real strong rotation with this storm on the velocity scans that detect wind from different directions.  This may have been one of the reasons why a tornado warning was not issued:

At first, I believed the funnel report was legitimate based on what I was seeing on radar at the time. However, as I was able to analyze the storm dynamics later, and seeing the storm first hand over my lunch break at work, I began to discredit the report.  It appears the funnel was mistaken for the low, ragged clouds present with this storm.  These are called scud clouds, which are nothing more than scary looking “junk” clouds that pose no immediate threat.  This can often fool an untrained eye.

The sky also grew massively dark as the large cell completely covered the sunlight from the east, and it made people aware there was something brewing off in the distance.  Here is video I found on YouTube of the storm as it rolled through:

The supercell with another apparent hook, as it appeared on radar, tracking through the Minneapolis and St. Paul downtowns and southward towards the Minneapolis-St. Paul International Airport at 11:59 AM:

Again, radar was not showing any areas of tight rotation with this storm on the velocity image that detects wind from different directions.  The storm was a little better organized than earlier, but still no indicators of danger.  It’s difficult for National Weather Service personnel to issue a tornado warning when there is no real evidence of a developing tornado.  Although it’s best to err on the side of caution, you don’t want a “cry wolf” scenario to develop, and no one ends up heeding the warning.  When NEXRAD was installed in the mid-90s to replace archaic World War II basic radar technology, velocity scans were one of the radar products introduced that provided clues to meteorologists as to the areas of greatest rotation that could eventually lead to tornado development.

So we had the classic “hook” show up on radar, but why wasn’t there any rotation?  Wind shear was not particularly strong this day as values were 40 knots across the thunderstorm area.  For tornadoes to form, strong sheer must be present.  In terms of speed, typically wind shear in excess of 40 knots is a good starting point.  Although the image below is from later in the day at 5 PM, it is fairly representative of the wind shear present (noted in black) throughout the day on Tuesday.  Shear was between 30 and 40 knots during the day across most of Minnesota.

The Storm Prediction Center noted in it’s 7:30 AM outlook the primary threats as large hail and damaging winds across Minnesota, but veering winds brought an isolated tornado threat to the area.

DEEP-LAYER VERTICAL SHEAR WILL NOT BE PARTICULARLY STRONG /I.E. LESS THAN 35 KT/...HOWEVER VERTICALLY VEERING WINDS INVOF SURFACE BOUNDARY WILL SUPPORT ORGANIZED STORM STRUCTURES CAPABLE OF LARGE HAIL...DAMAGING WINDS AND PERHAPS A TORNADO.

Due to the weaker wind shear, the storm reports received throughout the day where primarily from damaging winds across central Minnesota and western Wisconsin, but some hail reports were mixed in as well:

Hopefully this post helps explain why the storm was more impressive on radar, and that it had more “bark than bite”.  Had better wind shear been present, a main ingredient for tornadoes, this could have been a very dangerous situation with perhaps a tornado near St. Paul and MSP airport.  I don’t believe Minneapolis and St. Paul proper have been hit by different tornadoes in the same year.  In my opinion, we dodged another close call for metropolitan storms in what would have been another bullet point in this whacky year of weather extremes that is 2011!

RS

Unbelievable heat!

Some of the most tropical air the state has ever seen is ongoing this week. Heat indices well over 110°F has been common place across a good chunk of the area. It's not been so much the temperature as it has been the humidity. At the 3 PM hour on Tuesday, July 19, 2011, a new dew point record was established at Minneapolis-St. Paul International Airport with a reading of 82°F! This breaks the old dew point record set back on July 30, 1999 of 81°F. This kind of humidity is very rare around here. Our dew point is typically 75°F or less. The heat indices should subside by Thursday.

Using my professional-calibrated handheld Kestrel weather unit, I went outside my home shortly after 7 PM, and took a heat index reading of nearly 118°F! Yes, even at that time of the day, it was still quite warm, thanks to a dew point reading around 81°F.

Tomorrow won't have 120°F heat indices, but you'll still want to exercise caution outdoors. Use some common sense and live for another day. Heat is nothing to mess with.

RS

Severe storms approaching the Twin Cities

A severe thunderstorm is rolling through western Minnesota, nearly parallel with Interstate 94, with large hail and strong winds associated with it.  This is a thunderstorm complex that moved from North Dakota earlier and the day.

The storm should be into the heart of the metro around 1 AM or soon after. Expect rumbles of thunder, gusty winds, and hail as it moves through. The atmosphere is still very unstable, so I don’t see the intensity letting up any time soon. It appears the southwest Twin Cities metro will get the brunt of it.

Stay alert for possible warnings shortly!

RS

Near record dew point today in MSP?

Looking at some of the projected dew point temperatures for Sunday, Minneapolis-St. Paul will be very close to hitting the all-time record of 81-degrees on July 30, 1999.  The short-term forecast model, the Rapid Update Cycle (RUC), has done a good job at projecting temperatures and dew points, and will use it's projections.  Earlier this morning, it was indicating an unbearable dew point value of 81-degrees just around sunset.

Looking at the latest data, the RUC has now indicates a dew point around 83-degrees around 10 PM!  The Global Forecast System (GFS) also hints at 80-plus degree dew points, but it’s generally not reliable in the short-term, and I don’t put much stock in it within 24 hours of an event.

Based on the 9 AM temperature and dew point observations around the Twin Cities, it is quite possible that there will be areas that see dew points in the low 80s later on today.  At MSP airport, the temperature is already 85-degrees, with a dew point at a very sticky 77-degrees!

CITY           SKY/WX    TMP DP
TWIN CITIES    MOSUNNY   85  77
ST PAUL        SUNNY     84  79
CRYSTAL        MOSUNNY   85  78
BLAINE         SUNNY     82  79
EDEN PRAIRIE   SUNNY     85  79
LAKEVILLE      SUNNY     82  77
SOUTH ST PAUL  SUNNY     84  77
LAKE ELMO      PTSUNNY   82  79

With the higher dew points, I’m going to knock my temperature forecast down a degree and go with a high temperature of 97-degrees for Sunday.  Heat indices will be in excess of 105-degrees for most of the day, so you’ll want to find a cool place quickly.  This type of weather leads to heat exhaustion quickly, and I don’t recommend ANY physical outdoor activity today.  Stay indoors.

RS

That’s hot!

A tremendous amount of heat will be arriving into Minnesota within 24 hours, and will last for several days.  Temperatures will be well into the 90s through Wednesday of next week with high humidity.  Dew points will above 70-degrees, making it feel quick sticky out there.  This combination will lead to dangerous heat index values above 100-degrees.  As a result, the National Weather Service in Chanhassen has issued an Excessive Heat Warning for the Minnesota counties and a few Wisconsin counties the office serves until 9 PM Wednesday.  Additional Wisconsin counties are expected to be added by this afternoon.

... Excessive heat warning remains in effect until 9 PM CDT
Wednesday...

An excessive heat warning remains in effect until 9 PM CDT
Wednesday.

* Temperature... afternoon highs in the lower to middle 90s with low temperatures in the middle to upper 70s

* heat index... 105 to 110 degrees in the afternoon and early
evening.

* Impacts... these hot and humid conditions will lead to a
heightened risk of heat related stress and illnesses.

Precautionary/preparedness actions...

Take extra precautions if you work or spend time outside. When possible... reschedule strenuous activities to early morning or evening. Know the signs and symptoms of heat exhaustion and heat
stroke. Wear light weight and loose fitting clothing when
possible and drink plenty of water.

To reduce risk during outdoor work... the occupational safety and health administration recommends scheduling frequent rest breaks
in shaded or air conditioned environments. Anyone overcome by heat should be moved to a cool and shaded location. Heat stroke is an emergency... call 9 1 1.

An excessive heat warning means that a prolonged period of
dangerously hot temperatures will occur. The combination of hot temperatures and high humidity will combine to create a dangerous situation in which heat illnesses are likely. Drink plenty of fluids... stay in an air-conditioned room... stay out of the sun...and check up on relatives and neighbors.

Looking at the overnight NAM models, here is the temperature map for Sunday showing the bulk of hot air surging northward.  Click the image below to enlarge.  Temperatures will be very close to 100-degrees for southern Minnesota.  For the Twin Cities, my thinking is that the high temperature will top off at around 98-degrees.  This will be dependent on the amount of cloud cover in the area, which can be difficult to predict days in advance.

Monday is looking quite steamy as well with another day of temperatures in the upper 90s.  Click the image below to enlarge.

The National Weather Service Hydrometeorological Prediction Center heat index forecast indicates heat index values hitting 110-degrees in Minneapolis-St. Paul (MSP) on Monday.

Interpreting forecast data, the Hydrometeorological Prediction Center believes MSP has a 62% chance of seeing heat index values in excess of 105-degrees during the day on Monday.

Make sure to drink plenty of water and your A/C is tuned and ready to go with the heat index likely in excess of 105-degrees!

RS