Winter weather lesson

With the storm bearing down on the midwest and that being foremost on my mind right now, I thought I’d give those unfamiliar with winter weather a lesson :).  After the lesson, I’ll also post what our winter storm warning says (yes – we’re under a winter storm warning now, going into effect at noon tomorrow and expiring at 6am on Sunday).

First, there’s a big difference between how winter storm watches/warnings are issued as opposed to how severe t-storm & tornado watches/warnings are issued.  With t-storms and tornadoes, a watch simply means the conditions are favorable for development and they start as soon as they’re issued.  The warnings mean that it’s happening right then and will continue to affect the area until the time it expires.  Also, the watches tend to last anywhere from 3-7 (or 8) hours and the warnings usually last 45 minutes or so, unless the storms don’t move, in which case they might be extended.  However, by the time they issue a winter storm watch, they’re already pretty sure winter weather that will severely impact travel and the area is coming.  They’re usually issued about 48 hours before the storm is forecast to arrive.  For example, a winter storm watch was issued yesterday for my area – would go into effect from noon Saturday through 6am Sunday – well in advance of when it was actually issued.  It’s not uncommon for winter storm watches/warnings to last 24 hours or more.  A  winter storm warning is issued when the storm is less than 24 hours away and cancels out the winter storm watch.  Like a t-storm/tornado warning, a watch doesn’t have to happen first, though it usually does.  For example, last Feb we had a huge winter storm – had a winter storm watch for Saturday into Sunday that eventually turned into a winter storm warning by early Friday afternoon, but there were no alerts for Friday night.  9:30 Friday night rolls around and all of a sudden we’re under a winter storm warning until 9am the next morning (and later, our winter storm warning for Saturday into Sunday was turned into a blizzard warning).  The other main winter weather alert we see in this area of the country is a snow advisory.  It simply means 3-6 inches of snow in a 12 hour period – enough to cause travel issues.  A blizzard warning is issued when it’s snowing and sustained winds of 35mph or more are expected for at least 3 hours straight.  There are many other types of winter weather advisories, but we don’t see them often enough around here for me to understand any of them. 

Around here, we tend to see more snow than ice.  Actual accumulations of ice aren’t very common here.  Typically, the snowstorms we see here are in the neighborhood of 6 or 7 inches, though it’s not uncommon to have a 10 inch snowstorm in a season.  More than that, however, is uncommon.  Also, the vast majority of our snow falls from January – March, with very little of it falling in November and December.

Another term to know – "thundersnow" Think the heavy bursts of rain you see with your run of the mill thunderstorm, except in the form of snow.  Sometimes you can hear the thunder and see the lightning, but usually you can’t.  Usually the thunder is so muffled by the snow you can’t hear it and it’s usually snowingso hard you can’t see the lightning either.  Thundersnow doesn’t happen very often, but it does happen from time to time.  If you end up with thundersnow, you’re going to get quite a bit of snow in a short amount of time – it’s not uncommon to see obscene snowfall rates during bursts of thundersnow.

All that being said, here’s what our winter storm warning says:

.POLAR HIGH PRESSURE BUILDING INTO THE MIDWEST…IS BRINGING A FRESH SURGE OF COLDER AIR ON NORTHWEST WINDS INTO SOUTHERN WISCONSIN. MEANWHILE…A DEVELOPING LOW PRESSURE SYSTEM IN THE PLAINS ON SATURDAY WILL SPREAD RELATIVELY WARM AND MOIST AIR OVER THIS COLD DOME SATURDAY AFTERNOON AND SATURDAY NIGHT…RESULTING IN WINTRY PRECIPITATION.

SNOW IS EXPECTED TO DEVELOP ACROSS SOUTHERN WISCONSIN BY LATE SATURDAY MORNING AND BECOME HEAVY AT TIMES DURING THE AFTERNOON. THE SNOW WILL BECOME MIXED WITH…THEN CHANGE TO SLEET AND FREEZING RAIN FROM SOUTH TO NORTH DURING THE LATE AFTERNOON AND EARLY EVENING. SIGNIFICANT GLAZING IS POSSIBLE ON TOP OF SEVERAL INCHES OF SNOW…PERHAPS EXCEEDING ONE HALF INCH OF ICE.

TEMPERATURES WILL FINALLY RISE ABOVE FREEZING LATE SATURDAY NIGHT OR EARLY SUNDAY AS THE PRECIPITATION TAPERS OFF TO LIGHT RAIN AND DRIZZLE.

…WINTER STORM WARNING IN EFFECT FROM 12 PM SATURDAY TO 6 AM CST

SNOW IS EXPECTED TO DEVELOP SATURDAY MORNING ACROSS SOUTHERN WISCONSIN AND BECOME HEAVY AT TIMES BY AFTERNOON. SNOW AMOUNTS ARE EXPECTED TO RANGE FROM 2 TO 4 INCHES SOUTH OF INTERSTATE 94 WITH NEARLY 7 INCHES AROUND THE WISCONSIN DELLS…FOND DU LAC AND SHEBOYGAN AREAS WITH LOCALLY HIGHER AMOUNTS.

THE PRECIPITATION IS THEN EXPECTED TO MIX WITH…THEN CHANGE TO SLEET BY LATE AFTERNOON AND THEN TO FREEZING RAIN BY EARLY EVENING FROM SOUTH TO NORTH.

A SIGNIFICANT AMOUNT OF ICE COULD ACCUMULATE ON TOP OF THE SNOW BY LATE SATURDAY NIGHT. CURRENT INDICATIONS SHOW WIDESPREAD ACCUMULATIONS OF ICE TOTALING ONE QUARTER TO ONE THIRD OF AN INCH WILL FALL ON TOP OF THE SNOW…WITH LOCALLY HIGHER AMOUNTS POSSIBLE.

TRAVEL CONDITIONS WILL DETERIORATE QUICKLY WITH THE ONSET OF THE ACCUMULATING SNOW…AND MAY BECOME NEARLY IMPOSSIBLE WITH THE FREEZING RAIN DURING THE EVENING. ICE ACCUMULATIONS WILL END AS TEMPERATURES RISE ABOVE FREEZING LATE SATURDAY NIGHT…BUT RESIDUAL ICE ON ROADWAYS AND STRUCTURES WILL LIKELY PERSIST THROUGH AT LEAST EARLY SUNDAY MORNING.

ICE ACCUMULATIONS SUCH AS THESE MAY CAUSE CONSIDERABLE TREE AND POWER LINE DAMAGE WITH WIDESPREAD POWER OUTAGES. IN ADDITION…SOUTHEAST WINDS GUSTING TO 30 MPH WILL FURTHER STRESS ICE-LADEN STRUCTURES. ICE ACCUMULATIONS WOULD LIKELY BE HIGHEST AWAY FROM THE WARMER SHORES OF LAKE MICHIGAN. NOW IS THE TIME TO PREPARE FOR POSSIBLE POWER OUTAGES.

IN ADDITION TO THE WINTRY PRECIPITATION…ELEVATED INSTABILITY MAY PROMOTE THE DEVELOPMENT OF ISOLATED THUNDERSTORMS. ANY THUNDERSTORMS THAT OCCUR WOULD BRING VERY HEAVY PRECIPITATION.

A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW… SLEET…AND ICE ARE EXPECTED. STRONG WINDS WITH GUSTS TO 30 MPH ARE ALSO EXPECTED…WHICH WILL FURTHER REDUCE VISIBILITIES. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE…ESPECIALLY SATURDAY EVENING.

One of the main concerns is that those thunderstorms you see mentioned will happen when the precipitation is either changing to or in the form of freezing rain because that would cause more ice and more problems.  If it ends up as thundersnow, it’ll simply mean more snow than expected.  However, it doesn’t look like any possible thunderstorms will happen when it’s too warm to have frozen precipitation. By the time it’s that warm, the system will be far enough off that the bulk of the moisture will be out of the way.  All in all, a messy weekend!