Disc: The calendar may only say November, but the pattern looks like one you'd find out of a textbook mid-January. From the looks of teleconnections and pattern indicators going forward, there isn't anything to indicate that this pattern will break down any time soon.
Currently: Weak low pressure was located well off the Delmarva. There was just enough forcing available to produce light rain (and some frozen precipitation in the north) this morning into the early afternoon. It's a little ironic, because models got the track and strength of the low just about perfect, but underestimated forcing. Forcing is typically created from a temperature difference. The temperature difference can be between the ocean water and land, or a subtle boundary over land, or even mesoscale effects, such as a sea breeze boundary or an outflow boundary from a previous system. In this case, it was the difference between the ocean and Long Island Sound temperature versus the cool air advecting in on north winds. This, combined with the fact that there was just enough moisture in the air, generated light precipitation over the area. Fortunately, it did not create too many problems with the commute, since temperatures were marginal, and precipitation intensity was mostly light.
Rest of today into tonight: Lingering showers, now all in the form of rain, will exit stage right. Tonight's temperatures will largely depend on cloud cover. Given the fact that the ground is now wet and I am not expecting any sun today, evaporative processes should be able to generate low cloudiness tonight. So I'll go with the cloudier side of guidance. At night, cloudier conditions tend to mean warmer temperatures. Therefore, I'll go just a degree or so above guidance for tonight. This still yields a chilly night across the state, with low temperatures in the range of 30-35 degrees. There is a possibility that black ice could form on some surfaces. One mitigating factor is that it is still a bit windy, and this tends to help the ground dry, and you need water to create ice. However, it only takes a small patch of unseen ice at night to create problems, so do use a little extra caution when traveling tonight- especially if the ground is still wet in your area at sunset!
Tomorrow: There is a big disconnect in guidance temperatures, with the NAM 5 to 10 degrees colder than the GFS. The GFS says skies will be mostly cloudy- but with some breaks of sun- while the NAM has overcast conditions and even a few flurries in the NW hills. In the very short term, the GFS tends to be a superior model with regards to its temperature algorithm. However, there are also two factors that make me not entirely dismissive of the NAM temperatures... 1) The sun angle this time of year is very low, and it is harder to scour out low cloudiness, and 2) For the simple fact that when you're in a below normal temperature regime, the cooler solutions often work out. So what I'll do is go 60% of the way towards the GFS' temperatures, given that they're more accurate than the NAM's, without completely ignoring the NAM's temperatures. This yields high temperatures within a few degrees of 45 for most, except only around 40 in the NW Hills.
Tomorrow Night/Wed: Once again, the NAM's temperatures are cooler than those of the GFS. Getting more out into this range, the NAM tends to have more difficulty regarding individual features, and I think what it is doing here is rushing clouds and precipitation from the weak frontal system (which will be mentioned later), and therefore, this results in cooler temperatures. Moreover, with a SW wind flow setting up ahead of the cold front, temperatures should be able to rise even if clouds and sprinkles did develop earlier than predicted. Therefore, on Wednesday, I'll completely throw out the NAM guidance, and go with the GFS. This may actually not even be warm enough, but caution should still be used at this range. Anyway, all of this yields high temperatures around 50 degrees. As mentioned earlier, I'll keep the precipitation ahead of the next weak frontal system out of the forecast for now.
Longer Term: The main highlights of the long term period are a weak frontal system generating light precipitation Wednesday night and early Thursday morning, a much heavier rain event on Saturday, and then another Arctic blast with possible snow squalls, gusty winds, and very cold temperatures on Sunday.
First up, will be an approaching weak cold frontal system. Models, aside from the NAM, have trended slower with this system, and are starting to hint that it could be something similar to today- where precipitation falls, aided by a weak developing coastal low. This also slows down the ending of the precipitation, and could have implications in precipitation type during the latter part of the storm. With this in mind, I'll call for periods of light rain all day on Thursday, transitioning to and ending as snow from north to south, but not making it south of the Merritt Parkway. Guidance high temperatures in the low 50s look reasonable. However, there is a distinct possibility that those high temperatures occur during the morning hours, with temperatures falling thereafter. I am not expecting any accumulations of any snow that falls at this time, since temperatures will be at or above freezing the majority of the time, and precipitation amounts will be light.
Guidance looks decent for Friday's temperatures, but I'll go a degree or two cooler, since we'll have fresh cold air advection and a fairly strong N-NW wind. So I am expecting high temperatures in the mid to upper 40s on Friday.
Our next storm due up is a "Lakes Cutter" type storm on Saturday. This storm will have lots of Gulf moisture to work with, so rainfall amounts could be quite heavy, on the order of one to two inches. As for timing of the rain, expect rain to develop from SW to NE within a few hours of dawn. Rain should then end around dinnertime. As for Saturday's temperatures, with clouds, rain, and onshore flow, also combined with onshore flow and a tendency for this type of setup to favor cold air damming, I'll go a couple degrees under high temperature guidance, which would yield highs in the mid to upper 40s. With some lingering cold air in place, there is some possibility that a brief start as freezing rain or sleet is possible in the NW hills and the far NE reaches of the state (outside of HFD metro). I am not including it in the forecast at this time, but it is at least a possibility to be watched.
Behind this storm, on Sunday, much colder air will flow into the region on gusty N-NW winds. Many models are now showing widespread snow showers and possible imbedded snow squalls with this cold air advection. I'll add a chance of flurries or snow showers this cycle because of that. It is possible some heavier snow squalls could produce minor accumulations, or at least lower visibilities. As of now, it is impossible to pinpoint exactly where those would occur, but climatology favors the NW hills. To be blunt, guidance temperatures look completely clueless during the day on Sunday, and this is not unprecedented with this setup. With the aid of gridded data, and my knowledge of atmospheric synoptics, temperature guidance will be ignored, and I'll call for temperatures gradually falling through the lower 40s and into the 30s on Sunday.
A cold pattern looks to continue beyond there. For Monday, temperature guidance looks a little more from the same planet than it does for Sunday. However, even having said this, it is still a bit too warm, and maybe more than that, given the upper level profile. For now, I'll cool it down a bit, since we're at day 7, I don't want to go too crazy, but I'll go with highs of around 40 and then we can trend from there.
In the long range, the pattern still looks to greatly favor colder than normal temperatures rather than warmth. In fact, that could be an understatement. There also may be a snow threat somewhere around Thanksgiving that could be more widespread than these past few little events. Of course, we're way out at day 10 again, and I don't want to get too far ahead of myself, but if there was ever a pattern in November that would support a widespread snowfall and is identifiable from a long ways' out, it would be the pattern we are about to get into, or a reasonable facsimile thereof.
Now that we've gone through the worded portion of this discussion, let's take a look at some of the systems that will be affecting this area this week. First we'll look at the potential frontal wave for Thursday, and then we'll look at the cutter for Saturday and incoming cold air behind it. On the map below, you can see a very weak low organizing offshore, with a front moving through the state and just enough forcing to generate weak, but steady precipitation. An argument could be made that we may need to watch to see if that low trends any further west, but for now, that seems to be an invalid argument.
Currently: Weak low pressure was located well off the Delmarva. There was just enough forcing available to produce light rain (and some frozen precipitation in the north) this morning into the early afternoon. It's a little ironic, because models got the track and strength of the low just about perfect, but underestimated forcing. Forcing is typically created from a temperature difference. The temperature difference can be between the ocean water and land, or a subtle boundary over land, or even mesoscale effects, such as a sea breeze boundary or an outflow boundary from a previous system. In this case, it was the difference between the ocean and Long Island Sound temperature versus the cool air advecting in on north winds. This, combined with the fact that there was just enough moisture in the air, generated light precipitation over the area. Fortunately, it did not create too many problems with the commute, since temperatures were marginal, and precipitation intensity was mostly light.
Rest of today into tonight: Lingering showers, now all in the form of rain, will exit stage right. Tonight's temperatures will largely depend on cloud cover. Given the fact that the ground is now wet and I am not expecting any sun today, evaporative processes should be able to generate low cloudiness tonight. So I'll go with the cloudier side of guidance. At night, cloudier conditions tend to mean warmer temperatures. Therefore, I'll go just a degree or so above guidance for tonight. This still yields a chilly night across the state, with low temperatures in the range of 30-35 degrees. There is a possibility that black ice could form on some surfaces. One mitigating factor is that it is still a bit windy, and this tends to help the ground dry, and you need water to create ice. However, it only takes a small patch of unseen ice at night to create problems, so do use a little extra caution when traveling tonight- especially if the ground is still wet in your area at sunset!
Tomorrow: There is a big disconnect in guidance temperatures, with the NAM 5 to 10 degrees colder than the GFS. The GFS says skies will be mostly cloudy- but with some breaks of sun- while the NAM has overcast conditions and even a few flurries in the NW hills. In the very short term, the GFS tends to be a superior model with regards to its temperature algorithm. However, there are also two factors that make me not entirely dismissive of the NAM temperatures... 1) The sun angle this time of year is very low, and it is harder to scour out low cloudiness, and 2) For the simple fact that when you're in a below normal temperature regime, the cooler solutions often work out. So what I'll do is go 60% of the way towards the GFS' temperatures, given that they're more accurate than the NAM's, without completely ignoring the NAM's temperatures. This yields high temperatures within a few degrees of 45 for most, except only around 40 in the NW Hills.
Tomorrow Night/Wed: Once again, the NAM's temperatures are cooler than those of the GFS. Getting more out into this range, the NAM tends to have more difficulty regarding individual features, and I think what it is doing here is rushing clouds and precipitation from the weak frontal system (which will be mentioned later), and therefore, this results in cooler temperatures. Moreover, with a SW wind flow setting up ahead of the cold front, temperatures should be able to rise even if clouds and sprinkles did develop earlier than predicted. Therefore, on Wednesday, I'll completely throw out the NAM guidance, and go with the GFS. This may actually not even be warm enough, but caution should still be used at this range. Anyway, all of this yields high temperatures around 50 degrees. As mentioned earlier, I'll keep the precipitation ahead of the next weak frontal system out of the forecast for now.
Longer Term: The main highlights of the long term period are a weak frontal system generating light precipitation Wednesday night and early Thursday morning, a much heavier rain event on Saturday, and then another Arctic blast with possible snow squalls, gusty winds, and very cold temperatures on Sunday.
First up, will be an approaching weak cold frontal system. Models, aside from the NAM, have trended slower with this system, and are starting to hint that it could be something similar to today- where precipitation falls, aided by a weak developing coastal low. This also slows down the ending of the precipitation, and could have implications in precipitation type during the latter part of the storm. With this in mind, I'll call for periods of light rain all day on Thursday, transitioning to and ending as snow from north to south, but not making it south of the Merritt Parkway. Guidance high temperatures in the low 50s look reasonable. However, there is a distinct possibility that those high temperatures occur during the morning hours, with temperatures falling thereafter. I am not expecting any accumulations of any snow that falls at this time, since temperatures will be at or above freezing the majority of the time, and precipitation amounts will be light.
Guidance looks decent for Friday's temperatures, but I'll go a degree or two cooler, since we'll have fresh cold air advection and a fairly strong N-NW wind. So I am expecting high temperatures in the mid to upper 40s on Friday.
Our next storm due up is a "Lakes Cutter" type storm on Saturday. This storm will have lots of Gulf moisture to work with, so rainfall amounts could be quite heavy, on the order of one to two inches. As for timing of the rain, expect rain to develop from SW to NE within a few hours of dawn. Rain should then end around dinnertime. As for Saturday's temperatures, with clouds, rain, and onshore flow, also combined with onshore flow and a tendency for this type of setup to favor cold air damming, I'll go a couple degrees under high temperature guidance, which would yield highs in the mid to upper 40s. With some lingering cold air in place, there is some possibility that a brief start as freezing rain or sleet is possible in the NW hills and the far NE reaches of the state (outside of HFD metro). I am not including it in the forecast at this time, but it is at least a possibility to be watched.
Behind this storm, on Sunday, much colder air will flow into the region on gusty N-NW winds. Many models are now showing widespread snow showers and possible imbedded snow squalls with this cold air advection. I'll add a chance of flurries or snow showers this cycle because of that. It is possible some heavier snow squalls could produce minor accumulations, or at least lower visibilities. As of now, it is impossible to pinpoint exactly where those would occur, but climatology favors the NW hills. To be blunt, guidance temperatures look completely clueless during the day on Sunday, and this is not unprecedented with this setup. With the aid of gridded data, and my knowledge of atmospheric synoptics, temperature guidance will be ignored, and I'll call for temperatures gradually falling through the lower 40s and into the 30s on Sunday.
A cold pattern looks to continue beyond there. For Monday, temperature guidance looks a little more from the same planet than it does for Sunday. However, even having said this, it is still a bit too warm, and maybe more than that, given the upper level profile. For now, I'll cool it down a bit, since we're at day 7, I don't want to go too crazy, but I'll go with highs of around 40 and then we can trend from there.
In the long range, the pattern still looks to greatly favor colder than normal temperatures rather than warmth. In fact, that could be an understatement. There also may be a snow threat somewhere around Thanksgiving that could be more widespread than these past few little events. Of course, we're way out at day 10 again, and I don't want to get too far ahead of myself, but if there was ever a pattern in November that would support a widespread snowfall and is identifiable from a long ways' out, it would be the pattern we are about to get into, or a reasonable facsimile thereof.
Now that we've gone through the worded portion of this discussion, let's take a look at some of the systems that will be affecting this area this week. First we'll look at the potential frontal wave for Thursday, and then we'll look at the cutter for Saturday and incoming cold air behind it. On the map below, you can see a very weak low organizing offshore, with a front moving through the state and just enough forcing to generate weak, but steady precipitation. An argument could be made that we may need to watch to see if that low trends any further west, but for now, that seems to be an invalid argument.
On the next map, you can see the low moving up into Canada producing heavy rain over the state. I also used a different map background, because I want to illustrate the cold air coming down from Canada, and I feel this map does a better job.
Anyway that's all for now! Have a great week!
-GP!
-GP!
