Friday, August 29, 2014

The Long Life of "Tropical" Cyclone Cristobal

Living a long life typically requires hitting the genetic jackpot, living in a relatively safe and healthy environment, taking care of yourself, and then perhaps just being plain lucky.  Swiss mountain guide Ulrich Inderbinen provides such an example.  He climbed the Materhorn 390 times, summited it a final time when he was 90, climbed 13,000 foot peaks in his 90s, worked until he was 95, and passed away this summer at 103.  Not too shabby.  

Although not as far out there on the longevity limb as Ulrich Inderbinen, "Tropical" cyclone Cristobal, which moved poleward off the west coast of North America this week, lived a pretty good life, benefiting from a caterpillar-to-butterfly-like metamorphosis from a tropical cyclone into a midlatitude cyclone as it moved into the North Atlantic.  

At the beginning of the loop below, Cristobal is barely a glint in his parent's eye and just a weak cluster of thunderstorms associated with a tropical easterly wave between Africa and the Lesser Antilles, islands that form the eastern edge of the Caribbean Sea.  He moves eastward and eventually experiences a quick birth and adolescence, growing into Hurricane Cristobal near the Bahamas.


The poleward movement of a hurricane into the cool waters of the higher latitudes often results in cyclone death, but Cristobal pulled off the necessary metamorphosis to extend his life, transitioning into an extratropical cyclone off the coast of the northeast United States and southeast Canada.  Such a transition requires a favorable large-scale environment, and Cristobal was fortunate to find himself in that environment as he crested the hill of middle age.  

Reborn as an extratropical cyclone, Cristobal is enjoying a productive maturity and is expected to survive until he reaches Iceland (see lower panel below).  


That's a lifetime from easterly wave through tropical cyclone to extratropical cyclone that spans nearly 2 weeks and almost 60º of latitude, and a remarkable example of one type of tropical–extratropical interaction that occurs during late summer and fall in the Northern Hemisphere.  

Thursday, August 28, 2014

Regionally, Mother Nature Can Still Bring It

There is a nice article in the latest EOS, a publication of the American Geophysical Union, discussing the remarkable ice cover on the upper Great Lakes this past spring [See Cold Water and High Ice Cover on the Great Lakes in Spring 2014 by Clites et al. (2014), unfortunately paywalled unless you are an AGU member and login with your membership account].
Source: Clites et al. (2014)
Some tidbits from the paper:
  • Lake Superior wasn't completely ice free until June 6th.  Yeah, June!
  • At the end of April, 51% of Lake Superior, 23% of Lake Huron, and 10% of Lake Michigan were still ice covered. 
  • In the 40-year period of record at the end of April, the previous record on Lake Superior was 30%, in only a few years was significant ice observed on Lake Huron, and at no time was their significant ice on Lake Michigan.
A quick look at data from NCDC shows that this past Dec–Apr was the coldest in Michigan (which flanks Lakes Superior, Michigan and Huron) since 1920 and the 4th coldest on record.  The period is a dramatic outlier during the 40-year period of good ice-cover records.

Source: NCDC
During the same period, globally averaged temperatures were the 6th warmest on record, illustrating that Mother Nature can still bring it, but only regionally.

Source: NCDC

Wednesday, August 27, 2014

Wet, But How Wet?

What an August it has been.  Lots of rain and relatively cool days.  Nobody can complain this year.

Although it has been wet, a quick look at the weather records suggests that the area has seen wetter.  Let's start with the Salt Lake City International Airport.  Through yesterday, the accumulation for August 1–27 was 1.77 inches (green line), well above average (brown line).  That ties it for 8th amongst the wettest August 1–27 periods.  However, there have been similar periods in past years that were much wetter, including 1968 when 3.66 inches fell (blue line).

Source: NWS
Given the fickle nature of monsoon convection, however, observations at a point can sometimes be misleading.  Let's look at a few other stations.

Alta has been deluged this August with an accumulation of 5.33" so far, which puts it just behind 1983 (5.97").  There is some missing data for the period though (black dots), including yesterday, which will add to the total.  On the other hand, the data at this location is very spotty.  For instance, there is no data for August 1–27, 1968, which was the wettest such period at some nearby stations.  Thus, we can't make any definitive conclusions here, but we can say it's certainly been very wet.

Source: NWS
If we head a bit west, the situation at Tooele looks pretty similar to Salt Lake City.  This year's August 1–27 period is well above average with 1.99" of rain, but still behind the 1968 deluge year.


Finally, if we go down to Utah County, records from the school that shall not be named show August 1–27 to be wet with 2.54", but not record setting.  Here, long-term records are also spotty (1968 is missing, for example).


I suspect if we had a dense and complete precipitation observing network covering 50 years we would find that August 1–27,  2014 ranks in the top 10 such periods at most locations in the Salt Lake area and perhaps near record levels at a few spots that have really gotten walloped by the thunderstorms.  During the past 50 years, August 1–27, 1968 may be the wettest such period on record, although I've only looked at a few stations and there could be some exceptions to this given the hit-and-miss nature of monsoon thunderstorms.

If you are interested in records for the month, we still have 4 days left.  Although there are no big monsoon surges in the offing, we have a chance of some showers and thunderstorms later today and perhaps we'll see something pop up later in the period.  Some sites could add to their totals.

Tuesday, August 26, 2014

Showers and Thunderstorms, But Where and When?

Where is the coldest air in the continental United States?  Well, if we go up to 500 mb, which sits about 18,000 feet above sea level at an area where the presence of cold air is frequently associated with thunderstorm formation, it's over northern Utah and eastern Nevada, with a close 2nd for the upper Dakotas (technically the analysis below is a 6-hour forecast, but let's call it good).

GFS Forecast 500-mb temperature at 1800 UTC 26 Aug 2014
Accompanying that pocket of cold air is a weak 500-mb trough centered over Nevada.


With the pocket of cold air, monsoon moisture, and surface heating, thunderstorms are likely across much of Utah this afternoon and are even possible overnight thanks to the dynamical forcing of the upper-level trough (you may have heard some last night).  When it comes to storms like these, however, their development and evolution occurs over periods of at most a couple of hours.  Therefore, forecasting the where and when is pretty much impossible until you see 'em on radar and even then the skill of predicting location and intensity declines rapidly after 30 minutes.  Sometimes the presence of an upper-level trough helps as it can organize the convection, but in this case, the trough is fairly weak and thus it's evolution also has low predictability.

Perhaps in the future we'll have pinpoint forecasts of thunderstorms at long lead times.  A new high-resolution forecast model known as the High Resolution Rapid Refresh (HRRR) may provide modest advancement and is featured in today's forecast discussion from the National Weather Service, although you get the gist of the uncertainty from the initial statements.
VARIOUS OVERNIGHT MODELS...12Z NAM...AND 12/13Z HRRR OFFER A WIDE VARIETY OF FORECASTS ON EXACT LOCATION OF TODAY`S PRECIPITATION...SO CONFIDENCE IS NOT HIGH ON DETAILS...BUT GENERAL IDEA IN HRRR SEEMS REASONABLE...AND THIS GENERAL IDEA IS FOR CONVECTION TO DEVELOP BENEATH THE JET FROM ABOUT KANAB TO LAKE POWELL AND THEN QUICKLY EXTEND NORTHWARD THIS AFTERNOON AND EVENING...WHILE ANOTHER AREA OF CONVECTION DEVELOPS IN THE VICINITY OF THE UPPER LOW OVER THE MOUNTAINS OF EAST CENTRAL NEVADA...AND THIS AREA MOVES INTO THE WESTERN UTAH DESERTS LATE THIS AFTERNOON. SOME OF THIS DESERT CONVECTION COULD EXTEND INTO THE WASATCH FRONT THIS EVENING.
The last I checked, the hRR was to become operational in late September.  I'm not sure if that schedule will hold.  I don't expect it will be a panacea for predicting convection of the type we have today, but I'm hoping it will be useful for forecasting mountain precipitation at short (≤18 hours) lead times this winter.

Monday, August 25, 2014

Freshman Orientation

Today is the first day of Fall Semester at the University of Utah.  Welcome to all the students, new and continuing.  Even those on double secret probation (you know who you are).

If you are new to Utah, consider yourself fortunate.  We have had a remarkably cool and wet August, especially over the past several days.  Average high temperatures for the month so far are 3.3ºF below average, and we've had 1.57" of rain at the Salt Lake City Airport compared with an average of 0.69".  It's been especially cool the past several days when many of you have arrived, moved into your dorms or apartments, and told the parents adios.  Over the past two days, we haven't even hit 80ºF!

Source: NWS
If you are coming from out of state, this weather is isn't normal.  The average high for today is 88ºF, with a record of 100ºF.  When you look for a new place for the next academic year, don't just find good roommates, find an air conditioned unit too.

Saturday, August 23, 2014

Freshies

Source: http://meso1.chpc.utah.edu/station_cameras/armstrong_cam/armstrong_cam_hour.mov