Mysterious E/ENE undercut in spite of solid W/SW’rlys around Duxbury 5/9
Tim Kent
5/16/16
A day like many other spring days with Low pressure spinning well to the North of the region scheduled rotate a short wave through the region late morning or early afternoon. High pressure set up in the Great Lakes, producing solid W’rly gradient over the New England region.
See forecast below:
As you can see I was anticipating the W’rly flow to back SW’rly and couple with Sea Breeze influences as the shortwave approached, a classic Canal Trough feature (a la Matt Corey) was likely to develop as full sun encouraged strong surface heating. Therefore, I bumped up tables beyond guidance in the early afternoon to reflect what I suspected would be a pretty solid afternoon of SW’rly flow. See Tables Below:
See AM guidance vs Observations for Duxbury:
As you can see AM guidance does not suggest a NE/ENE’rly turn with the exception of the hourly updating HRRR which doesnt count since it incorporates hourly observations into each new run and it still doesnt suggest that the turn happens until hours later anyway.
So what happened??? lets take a look at some urface analysis maps just to confirm the scenario.
The 12z Analysis from WPC shows exactly what we have described prior.
SPC’s surface objective analysis at 11AM does reveal more pronounced trough like feature at the surface right along the Mass. coast. Not unusual in and of itself especially considering the Upper Level shortwave that was in the area and the general pattern in place.
But why were pressures so low over just W of Duxbury as to induce a reversal within a solid W/SW’rly gradient????
See Wind Map:
So lets look into this further…..
Surface METARS for Mass.
Taunton
STN TIME PMSL ALTM TMP DEW RH DIR SPD GUS PEAK VIS CLOUDS Weather MIN MAX P01 PCP
DD/HHMM hPa inHg F F % deg kt kt ddfff mile F F in in
==== ======= ====== ====== === === === === === === ===== ==== ======= ======= ======= ============ === === ==== ====
TAN 09/1552 1013.5 29.93 66 36 33 260 9 17 10.0 SCT065
TAN 09/1452 1013.8 29.94 64 36 35 260 14 20 10.0 FEW060 FEW090
TAN 09/1352 1014.0 29.94 61 37 41 250 9 19 10.0 CLR
TAN 09/1252 1014.4 29.96 57 37 47 240 7 10.0 SCT100
TAN 09/1152 1014.3 29.95 51 35 54 230 4 10.0 SCT070 OVC090 46 51
TAN 09/1052 1013.8 29.94 51 34 52 240 3 10.0 BKN065 OVC090
Marshfield (Duxbury)
STN TIME ALTM TMP DEW RH DIR SPD GUS VIS CLOUDS Weather P01
DD/HHMM inHg F F % deg kt kt mile in
==== ======= ====== === === === === === === ==== ======= ======= ======= ============ ====
GHG 09/1555 29.93 52 41 66 60 9 10.0 FEW055 BKN070 BKN075
GHG 09/1535 29.94 52 41 66 60 9 10.0 FEW055 BKN065 BKN075
GHG 09/1515 29.94 52 39 62 60 11 10.0 FEW055 BKN065 OVC110
GHG 09/1455 29.94 54 39 58 50 7 13 10.0 SCT055 BKN065 BKN090
GHG 09/1435 29.92 59 36 41 260 9 19 10.0 FEW050 SCT070 SCT095
GHG 09/1415 29.93 59 37 44 270 10 18 10.0 CLR
GHG 09/1355 29.94 59 37 44 260 8 16 10.0 CLR
GHG 09/1335 29.94 57 37 47 250 10 17 10.0 CLR
GHG 09/1315 29.94 54 36 50 260 10 15 10.0 FEW055 SCT070 BKN080
GHG 09/1255 29.94 54 36 50 240 9 16 10.0 FEW060 BKN080
New Bedford
1453Z 8 May 2016 to 1553Z 9 May 2016
STN TIME PMSL ALTM TMP DEW RH DIR SPD GUS PEAK VIS CLOUDS Weather MIN MAX P01 PCP
DD/HHMM hPa inHg F F % deg kt kt ddfff mile F F in in
==== ======= ====== ====== === === === === === === ===== ==== ======= ======= ============ === === ==== ====
EWB 09/1553 1013.5 29.93 64 38 38 250 11 21 10.0 CLR
EWB 09/1453 1013.8 29.94 62 38 41 280 15 23 10.0 FEW095
EWB 09/1353 1014.0 29.95 59 38 45 240 9 10.0 BKN090
EWB 09/1253 29.95 55 39 54 240 9 10.0 BKN100
EWB 09/1153 1014.3 29.95 52 37 57 240 5 10.0 OVC070 44 52
EWB 09/1053 1013.7 29.94 50 35 56 230 5 10.0 OVC095
Based on these observations it is not clear that surface pressures were lower in the interior portion of Mass., than they were on the E or S facing shores. We do however, note a simultaneous appearance of overcast conditions or scattered clouds between early morning and 15z, suggesting, that the Shortwave was approaching. There is however no notable signature in the pressure charts:
Minor Sea Breeze front velocity signature on local radar
So what do we think?? It appears that surface pressures were more or less the same at the time of reversal and the only difference is surface temperature, which was nearly 10F between the beaches and the interior. Is this enough to overcome ~20mph of W/SW’rly gradient??? Ideas, thoughts, concerns, talk amongst yourselves….