May 2006 floods

 

Historical floods occurred in New England in May of 2006.  A description of the event from NWS Taunton, MA is below.

 

 

Figure 1.  Public Information Statement from NWS Taunton, MA.  Part 1 is left and part 2 is right.  Click on each for larger image.

 

a)b)

 

Figure 2.  SREF a) 11 May MSLP and Precipitable Water (PWAT) and b) 09Z 12 May MSLP spread, mean and anomaly.  Note the 2-3 SD above normal surface pressures from Maine into southeastern Canada and the axis of higher PWAT (1-2 SD above normal) oriented southeast to northwest into New England.  Also note the 3-4 SD below normal surface pressure that developed in the Great Lakes area.

 

a)b)

 

Figure 3.  SREF initialized at 21Z 12 May depicting forecasted MSLP spread and anomalies valid at a) 21Z 12 May and b) 15Z 13 May.  Note the persistent southeast-northwest oriented band of PWAT 1 SD to just over 2 SD above normal slowly shifting through New England.

 

a)b)

 

Figure 4.  SREF initialized at 21Z 12 May depicting forecasted MSLP spread and anomalies valid at a) 09Z 14 May and b) 03Z 15 May.  Note the persistent southeast-northwest oriented band of PWAT diminishes to just over 1 SD above normal as it continues to shift through New England.

 

a)b)c)

 

Figure 5.  850 hPa U and V wind anomalies from a) 09Z initialized 13 May SREF b) 09Z 12 May SREF valid 09Z 15 May and c) 12Z 12 May SREF valid 15Z 13 May.  Note the U winds that are 3-4 SD below normal and the V winds that are 3-4 SD above normal.  The southeast winds were registering as anomalously high within the high PWAT band seen in figure 3.  This persistent low-level forcing and moisture advection within the high PWAT band contributed to extreme rainfall.

 

 

 

a)b)

 

Figure 6.  Probability of 2 or more inches of rain in 36 hours from 09Z 12 May SREF valid a) 21Z 13 May and b) 15Z 14 May.  Note the small chances and little areal extent of the probabilities in New England.  However, also notice the spread showing virtually every member of the SREF is depicting an area of 2 inch rainfall, but due to a lack of overlap, the magnitude and area of probabilities is small.  This suggests that looking at the spread is at least as important as looking at the numerical and areal probabilities, as the spread suggested a much higher probability for 2 or more inches, but ambiguity with respect to the exact area of highest probability.

 

a)b)

 

Figure 7.  Probability of 2 or more inches of rain from 21Z 12 May SREF valid a) 09Z 14 May and b) 21Z 14 May.  Note the lack of probabilities in New England.  However, also notice the spread showing the majority of members of the SREF is depicting an area of 2 inch rainfall, but due to a lack of overlap, the magnitude and area of probabilities is small.  Similar to figure 6, this suggests that looking at the spread is at least as important as looking at the numerical and areal probabilities, as the spread suggested a much higher probability for 2 or more inches, but ambiguity with respect to the exact area of highest probability.

 

a)b)c)

 

Figure 8.  Plume diagrams for Boston, MA from a) 09z 10 May SREF, b) 09Z 11 May SREF and c) 09Z 12 May SREF.  Note the large spread, but more importantly, notice the clustering of members increasing to above 2 inches by the 09Z 12 May SREF with at least 7 SREF members suggesting 3.5 to 4.5 inches of rain.

 

 

Figure 9.  Observed precipitation.