DROUGHT WATCH IN EFFECT FOR NEW JERSEY

8:14 AM

In case you don’t know, the sustained cold pattern is here and it is not going to leave any time soon.  Temperatures this morning are in the mid to upper 20′s over the interior and lower to mid 30′s along the coast, and those temperatures will not be moving far to reach the afternoon highs in a few hours.  A northwesterly wind around 10 to 20 mph will make air temperatures fell like the 10′s and 20′s through the day.  Clearly a significant change from the lower to mid 50′s of yesterday afternoon.  Of course, while everyone freezes outside, all eyes are to the Gulf Coast as a potentially significant winter storm organizes over southern Texas.

This morning’s water vapor satellite image clearly illustrates the strength of the Sub Tropical jet stream and the ability for this feature to introduce plenty of high, mid, and low level moisture into a developing upper level pattern.  An area of low pressure is organizing off the Texas coast and is producing very heavy rain over Corpus Christi and Brownsville, Texas.  Keep in mind, this storm is in the infant stages and the precipitation shield is already more organized than guidance suggested 12 hours out in the forecast.

As with every winter storm in the past and for every winter storm in the future, a lot of talk about model trends, depictions, and lots of hand ringing.  This morning I’m going to break down the forecast of this storm down to one feature that will drive this whole event either south and east of the northern Mid Atlantic or over the New Jersey coastal waters leading to a significant snowfall.  That feature is the upper low over eastern Quebec that I discussed last night.  For this discussion I am using the 500 MB ECMWF maps, due to the better ability of the model to handle the 500 MB lifting parameters and surface features.  The 00Z GFS once again showed that the southeast bias issue has not been solved as the surface low was place south and east of the main 500 MB vorticity on Saturday night and then was trying to correct itself with a double barrel low thereafter.

Friday Night-ECMWF

On Friday night, the upper level pattern is very favorable for a potential winter storm over the Mid Atlantic.  A mature negative NAO pattern is in place with an upper low right where we want it at 50N/50W.  A perfect set up!  The trough axis over the United States can be found over the Mississippi Valley at a neutral state while a ridge builds over the Rockies with a ridge axis over Montana.  Almost text book if not for the retrograding upper low moving towards western Alaska.  Cold air is in place at all levels of the atmosphere and the Sub Tropical jet stream is interacting with the Polar jet stream as moisture streams north and east from the Gulf of Mexico.  However, there are some problems.  The 50/50 low is showing signs of splitting while another disturbance over the Hudson Bay is dropping south.  The 500 MB pattern is about to become much more complicated.

Saturday Night- ECMWF

By Saturday night, we start to see some changes in the 500 MB structure, however the potential is very real.  A negative NAO is still clearly in place, however a split in the 500 MB upper low is clear.  Also note that the disturbance that was over the Hudson Bay is dropping south into the neutral to slightly negative trough over the Tennessee Valley.  Here in lies the problem with this forecast.  The fact the upper low low that was the negative NAO splits is not a bad thing for snow lovers.  The issue is how fast does this feature splits from the new 50/50 low already forming.  The other problem is how does the upper low over Newfoundland interact with the upper level feature dropping south from the Hudson Bay.  The strong disturbance in the Sub Tropical jet stream (note the neutral axis over Gulf Coast) is set up perfectly for interaction, however the develops over Canada is a huge wild card.

Sunday Night-ECMWF

By Sunday night, the ECMWF’s solution is to pull the 500 MB features all together into a very strong phase and an impressively strong negative NAO.  Remember what I said in the winter forecast.  A strong negative NAO is basically too much of a good thing, the strength of the 500 MB low causes suppression and a storm track too far east.  That’s exactly what happens here.  The disturbance dropping south over Ontario, the 500 MB low over eastern Quebec, and the 500 MB low over 50N/50W all phase into a strong upper low over the Quebec/Newfoundland boarder and thus the coastal storm is forced to track east-northeast and south of the 40N/70W bench mark.  It should be noted that this storm track still produces a light to moderate snowfall over central and southern New Jersey and eastern Long Island, but causes much of the rest of the region to completely miss out.

Now, here is what is rattling in my head this morning as I poured over Northeast Snowstorms Volume 1 by Kocin and Uccellini for some wisdom.  The difference between this storm being a major winter storm or a miss is roughly 50 miles based on all the guidance I have available.  What the forecast comes down to is the forecast of a 500 MB feature we have little data on dropping south from the Hudson Bay and the slightly and brief split of the 50/50 low over Quebec.  There are several ways this pattern can work out for this weekend.

The first is obviously what is shown on the model guidance right now, which would lead to a light to moderate snow for southern and central New Jersey and eastern Long Island.  Much of the Philadelphia and New York City metropolitan areas would miss out.

The second possibility is that the feature over the Hudson Bay drops south fast enough to cause an upper low to form over the Tennessee Valley.  the result is the storm track is further north and snow builds into much of the northern Mid Atlantic with a strong focus of lifting along the immediate coast.  The 500 MB feature over Quebec continues to slide south and east, eventually capturing the storm.  However, the position of the upper low over Quebec forces the storm to move east-northeast from the Delaware coastal waters leading to a miss for much of the Hudson Valley and portions of Connecticut.

The third possibility would be a dream come true for snow lovers.  The chances of this solution working out is not great as I don’t like to go against all model guidance here.  However, this solution is physically reasonable given the forecasted jet stream structures on all guidance.  The solution starts out with the text book set up on Friday Night.  As the 50/50 low splits, the strong feature remains over 50N/50W, meaning the feature that is sliding south and east over Quebec is the weaker of the two.  With the stronger 500 MB feature further north, the influence of the trough axis over New England is limited and the long wave trough over the eastern United States has the potential to go into a negative tilt.  The feature over the Hudson Bay drops south.  An upper low develops over the Tennessee Valley and the interaction becomes a phase over the southern Mid Atlantic coast.  The storm moves north and the feature over Quebec becomes entrained to enhance rather than capture the surface low.  This leads to a major and significant snowfall over much of the northern Mid Atlantic and possibly even southern New England.  The truth is that based on past storms given the set up at 500 MB on Friday night, this solution has just as much chance of happening as the solution shown on the model guidance at this time.

Again, I stress that the outcome of this storm and how all these upper level features is very much an unknown and I do expect changes in the guidance one way or another.  Before we can get into issues like the influence of convective precipitation, latent heat influence, and other features; this question of these 500 MB features interacting must be solved.  I’m hoping by tonight or tomorrow that those questions will be answered.

Beyond this storm, there are plenty of questions too.  The pattern is certainly a cold one with a negative NAO and a negative EPO in place, driving Arctic air into the heart of the nation and keeping much of the northern Mid Atlantic cold.  A weak clipper will swing through the Mid Atlantic by the middle of the week with some light snowfall over the region, but nothing significant is expected at this time.  Of course with a negative NAO in place, it is best to keep an eye on these features.

Another major storm is strongly suggested in the model guidance for next Friday and Saturday.  I think it is best to hold off on details of this storm until this storm for this weekend is put to rest.  The issue for this period will be what position will the upper level features be in and how do those features develop through next week.  I should note that the model guidance, whether GFS or ECMWF, have not been stellar for the time period of 7 to 10 days out.  Therefore, I will leave this discussion saying that once again another storm threat is very real the players are on the field.  How the disturbances develop and interact during this time period will have a strong influence on storm track and boundary layer considerations.  Looks like I’m going to be pretty busy through the New Year!