Ramblings of a Graduate Student

Day 3 of VORTEX II and it appears that all is still quiet in the V2 domain. The armada has “met up” and is itching to go…but where?

Above is Thursday’s severe weather outlook issued this morning by the Storm Prediction Center. As you can see, no area is highlighted for severe weather. However, there is a small “See Text” region.

Taking a look at the probabilities of experiencing severe weather within 25 miles of a given point, the maximum contour is a measly 5%. While this is isn’t much, it is the best thing that has been forecast in the VORTEX II domain during the course of the project. Hopefully somewhere in this general vicinity will be thunderstorms to chase to allow the armada to shake off the cobwebs and be ready for possible several chase opportunities next week.

More on this in the coming days…

For the past few weeks I’ve alluded to the fact I will have an extremely active spring.  I’m involved in both VORTEX II (although my role has continued to evolve over the last few days) and the Experimental Forecast Program (a joint experiment hosted by the National Severe Storms Laboratory [NSSL] and the Storm Prediction Center [SPC] and held in the Hazardous Weather Testbed [HWT; I’m the one in the blue shirt in the image on the upper right!)  This year’s experiment will have collaborators from the Aviation Weather Center (AWC) in Kansas City, MO and the Hydrometeorological Prediction Center (HPC) in the Washington D.C. / Silver Springs, MD area.

In preparation of this year’s experiment I was on a teleconference this morning with HPC and SPC so tonight I thought it appropriate to display a graphic produced by HPC.  Above is the forecast precipitation totals over the next 5 days.  As you can see, heavy rain is forecast for places that were hit hard by last weekend’s tornado outbreak.  This does not bode well for cleanup efforts.  This heavy precipitation is the result of another slow moving trough (#4 in last night’s post) that will move through the southeast late in the week into the weekend.

Last night I mentioned a possible high risk, high reward scenario for storm chasers on “the day before the day before”, also known as Wednesday.  Well, it turns out that the Storm Prediction Center is keeping an eye on the potential as well.  Above is this afternoon’s “Convective Outlook” for tomorrow (Wednesday).  Notice the words “See Text” over Oklahoma?  This means that while the threat of severe thunderstorms does not appear to be sufficient for a “Slight Risk” (there are spatial and frequency requirements for severe thunderstorms to justify a Slight Risk), the threat is certainly non-zero and the reader should read the outlook for more information.  The official text is below.

   DAY 2 CONVECTIVE OUTLOOK
   NWS STORM PREDICTION CENTER NORMAN OK
   1213 PM CDT TUE APR 20 2010

   VALID 211200Z - 221200Z

   ...NO SVR TSTM AREAS FORECAST...

   FAIRLY IMPRESSIVE UPPER TROUGH WILL MOVE ONSHORE ALONG THE CA COAST
   BEFORE MOVING INTO THE GREAT BASIN LATE WEDNESDAY.  DOWNSTREAM OF
   THIS FEATURE...UPPER RIDGING WILL GRADUALLY SHIFT EAST INTO THE
   CNTRL/SRN PLAINS AS HEIGHT FALLS SPREAD ACROSS THE SRN ROCKIES.  AT
   THE SURFACE...WEAK CYCLOGENESIS IN THE LEE OF THE SRN ROCKIES SHOULD
   DAMPEN OUT OVER THE TX PANHANDLE EARLY IN THE PERIOD AS LARGE SCALE
   FORCING BEGINS TO FOCUS ACROSS THE SRN ROCKIES IN ADVANCE OF UPPER
   TROUGH.  RESULTANT LEE TROUGH/DRY LINE SHOULD RETREAT INTO EXTREME
   ERN NM BY PEAK HEATING WITH AN E-W SURFACE TROUGH OR WARM FRONT-LIKE
   BOUNDARY EXPECTED TO EXTEND ALONG THE RED RIVER.  THE RED RIVER
   BOUNDARY WILL LIKELY SERVE AS THE DEMARCATION FOR EARLY-MID DAY
   CONVECTION DRIVEN IN LARGE PART BY WARM ADVECTION.  THIS
   ACTIVITY...POSSIBLY AN MCS-LIKE CLUSTER...SHOULD SPREAD ACROSS OK
   BEFORE WEAKENING OVER AR AS VEERED LLJ DECREASES AND BEGINS TO
   RESPOND TO WRN U.S. TROUGH OVER THE SRN HIGH PLAINS.  STRONG HEATING
   WILL LIKELY BE FOCUSED OVER THE PLAINS OF ERN NM/WEST TX SOUTH OF
   THE WARM FRONT AND FORECAST SOUNDINGS SUGGEST SFC-BASED PARCELS
   COULD REACH THEIR CONVECTIVE TEMPERATURES ACROSS UPSLOPE REGIONS OF
   THE HIGH PLAINS BY LATE AFTERNOON.  EVEN SO...DEEP LAYER SHEAR IS
   NOT EXPECTED TO BE PARTICULARLY STRONG...BUT VEERING PROFILES WITH
   HEIGHT DO FAVOR ROTATING UPDRAFTS...ESPECIALLY WHERE LOW LEVEL FLOW
   IS DECIDEDLY ELY ALONG/NORTH OF WARM FRONT.  AT THIS TIME WILL
   MAINTAIN 5% PROBABILITIES FOR PRIMARILY LARGE HAIL WITH ANY SLOW
   MOVING SUPERCELLS.  A SLIGHT RISK MAY NEED TO BE ADDED TO PORTIONS
   OF THE SRN HIGH PLAINS IN LATER OUTLOOKS IF IT APPEARS DIURNAL
   HEATING WILL CONTRIBUTE TO SUBSTANTIAL CONVECTIVE
   DEVELOPMENT...PRIMARILY ACROSS THE TX SOUTH PLAINS.

   ..DARROW.. 04/20/2010

The “See Text” area is outlined by the 5% risk level contoured above.  Notice how it is shaped very similar to the areas I discussed yesterday.

Lastly, the local National Weather Service Forecast Office in Norman, Oklahoma is also watching the same scenario very closely.  The image above was taken from their enhanced weather and graphicast webpage.

With the chance of severe weather returning to the eastern two-thirds of the United States by mid-week, I thought tonight I’d post about this year’s severe weather to date.  If you’ve thought this year has been unusually devoid of severe weather, you’d be correct.

The image above was created by the Storm Prediction Center’s Warning Coordination Meteorologist, Greg Carbin.  It displays the 2010 tornadoes (in red) and 2005-2009 tornado averages in grey.  The vertical bars represent the daily occurrence of tornadoes (2005-2009 in grey; 2010 in red; axis on the left) and the more horizontal bars indicate the running totals (axis on the right).  A quick glance quickly captures how far below recent history we are, with less than 100 preliminary tornado reports through 15 April.  To put it into perspective, the recent average through 15 April is 415!  It isn’t very often that by mid April, January was is one of your bigger tornado producing months!  As we continue to head into peak tornado season, this gap continues to widen for each day that passes without tornado occurrences.

Late this week, the atmosphere may support tornadoes again through portions of the central United States.  I’ll have more on this throughout the week.

As some of you know, I’m heavily involved in the VORTEX II project, which this year begins on 1 May and runs until 15 June.  Additionally, I’m heavily involved in the National Severe Storms Laboratory (NSSL) and Storm Prediction Center (SPC) Experimental Forecast Program (EFP) which begins 17 May and runs through 18 June.  As you can imagine, I’m up to my eyeballs with respect to all the things that still have to get finished before the start of these projects.  Since the weather has been rather tranquil of late, I’ve tried to get a lot of work done for VORTEX II and the NSSL/SPC EFP.  This way, when the weather becomes active again, I can devote some attention to the blog.  (Yes, this is why the blog posts have been rather short of late.)

The image above is screenshot of one of the projects I’m working on for VORTEX II.  It takes some of the data feeds we have here at the NSSL and SPC (particularly the mesoanalysis data) and converts into an overlay for the Gibson Ridge radar viewer(s).  The image above depicts the amount of Convective Available Potential Energy (CAPE).  A simple way to understand CAPE is that the greater the amount of CAPE, the more energy thunderstorms have available to them.  Thus, they can become stronger. However, a large CAPE value does not mean a thunderstorm will develop (just look at the image above; the storms aren’t located in the maximum CAPE values!).  That’s an entirely different question altogether!  This tool will be one of many used by VORTEX II personnel in trying to identify where the strongest thunderstorms will develop, and differentiate between those that are more likely to produce tornadoes and those that are not.

If you have thought that this year has been unusually devoid of severe thunderstorms and tornadoes, you’d be correct.  This has been an incredibly quiet year.  In fact, based on the SPC Preliminary Storm Report page, up through today, 10 days did not have a single report of severe (convective) weather.  (Please note that these are preliminary reports.  Official numbers will be released in the publication Storm Data a couple months after the event.  Verification takes time…) The no severe weather report days are,

• 2 March 2010 to 6 March 2010 (5 days);
• 14 March 2010 to 18 March 2010 (5 days).

Also, there have been only 14 tornadoes reported in March, compared to an average of around 150.  March tornadoes were reported on

• 8 March 2010 (2 tornadoes);
• 10 March 2010 (7 tornadoes);
• 11 March 2010 (4 tornadoes);
• 12 March 2010 (1 tornado).

The image above was created by the Warning Coordination Meteorologist, Greg Carbin, of the Storm Prediction Center (SPC).  It is the inflation adjusted annual tornado running total and percentile rank.  Please click here to understand the inflation adjusted process.

• The red line was created by taking the maximum number of tornadoes reported on any given day.  In this regard, it can be thought of as the worst case scenario (if you don’t want tornadoes).
• The orange line was created by taking the 75th percentile number of tornadoes reported on any given day.  In this regard, it can be thought of as the upper-bound on “average”.
• The green line was created by taking the 50th percentile number of tornadoes reported on any given day.  In this regard, it can be thought of as the average.
• The blue line was created by taking the 25th percentile number of tornadoes reported on any given day.  In this regard, it can be thought of as the lower-bound on “average”.
• The magenta line was created by taking the minimum number of tornado reports on any given day.  In this regard, it is the best case scenario (if you don’t want tornadoes).
• The black line is the running total for the current year.

The current year, while below average, is still within the envelope of possibilities; although, edging very close the the minimum values.  In any event, the data shown in the graphs suggest that as we head into April, the number of tornado reports should begin to increase rather quickly.

So, what do the last days of March have in store?

The image above (and annotated below) is quickly becoming a staple on this blog.  It depicts the amount of moisture in the atmosphere, as derived by satellites, at 2300 UTC on 22 March 2010.  In the wake of this past weekend’s significant southern plains winter storm, northwest winds have swept dry, continental air out over most of the Gulf of Mexico.  Immediately ahead of this storm, southerly winds are drawing up moist air into the storm, but this moist air is continually being advected away from the Gulf of Mexico as the storm continues to move east.  Also of importance is the fact that numerous cold, dry air intrusions into the Atlantic Ocean has resulted in deep moisture being suppressed to areas south of the 10 degree North latitude.  In fact, the tropical easterlies across much of the Atlantic is transporting dry air, instead of the moist air typically contained in the tropical easterlies.  This is readily apparent when one compares the moisture values of the Atlantic to those in the Pacific at a given latitude.

Why do I pay so much attention to moisture?  Because it is one of the necessary ingredients for deep convection (thunderstorms), and deep convection is a necessary ingredient for (true) severe thunderstorms.  It also plays a crucial role in the development and evolution of surface pressure features, which help dictate our weather.  Check out my Day 79 post to get an idea of just how important rich moisture is to developing cyclones.

With repeated intrusions of cold, dry, continental air into the Gulf of Mexico and Caribbean, the atmosphere is unable to generate sustained areas of deep, rich moisture.  This is detrimental to the formation of long-lived thunderstorms which often go on to be the kind of thunderstorms to generate severe weather.  Unless the pattern changes sufficiently to limit the number of cold, dry air intrusions into the Gulf of Mexico, severe weather should remain quite hard to come by.

Over the past week, a series of storm systems have walloped the west coast of the United States with wind, rain, and even a rare southern California tornado!  So much rain has fallen in such a short amount of time, mudslides are becoming a worry.  Today’s set of  images attempts to put into context just how much rain has fallen in southern California in terms of the last six months rainfall total.  Please note that today’s rain is *not* included in these totals!

Also, continuing with the tornado watch theme from yesterday, a rare tornado watch for southeastern California and southern Arizona was issued by the Storm Prediction Center earlier today.  This is the eighth tornado watch this year (also the eighth tornado watch issued in the last 36 hours!).

The image above displays the “normal” expected rainfall for 14-21 January.

The image above displays the observed rainfall for 14-21 January of this year.

The image above displays the departure from normal rainfall for 14-21 January 2010 in terms of inches.  Several places have received more than 8 inches more than normal.

The image above displays the departure from normal rainfall for 14-21 January 2010 in terms of percent of “normal”.  Several places have received more than 600 percent of their normal rainfall.

The image above displays the departure from normal rainfall for the past 180 days, ending 21 January in terms of inches.  Even with the heavy rains of the last week, most places in the desert southwest still remain several inches below normal.  Places that are not significantly below normal are typically within 2 inches of normal.  When you consider how much rain has fallen over the past week, one begins to appreciate the drought that was plaguing the southwest.

The image above displays the departure from normal rainfall for the past 180 days, ending 21 January in terms of percent of normal.  Even though a lot of places are within 2 inches of normal, they have received only about half to maybe three-quarters of their normal rainfall.  This goes to show just how little rain the southwest receives – they can be within two inches of normal and still only have 50% of what they would expect.

Also, not everywhere in the last two images have below average rainfall over the last 180 days.  Places along the coasts and in the higher elevations of California are above normal – however, a significant portion of that has fallen this week!

And last, but not least, the outline and (color-filled) counties included in the desert southwest tornado watch!