Upper level lows are beasts that can keep the weather fairly cloudy and damp for days on end, especially when they cut off from the main branch of the jet stream. Basically an upper level low (ULL) is an body of positive vorticity that can be caused from a jet streak or upper level trough. Over time, if the ULL matures, some of its energy can be translated down to the surface and on some weather maps, two lows (or a double barreled low) will show up on a surface map.
ULLs can form in a few different ways:
1: From a developed surface low associated with a mid latitude cyclone.
2: From air flowing over mountains.
3: From a shortwave.
4: In association with a jet streak.
From these different scenarios always watch for the development of an upper level low because they can hold alot of weight in your forecast. During the analysis process during forecasting, upper level lows usually show up to the west or northwest of a surface low in association with a mid latitude cyclone. Additionally, during the forecasting process, models tend to forecast a surface low much better then a low above the ground, so be careful in the event that an upper level low is near your forecast area.
Additionally, since the ULL is usually to the west or northwest of the surface low, wintry precipitation is a concern. Below the ULL the air is cold (relatively speaking), therefore, when the ULL forms precip behind a surface low, in wintertime, there will be more wintry precipitation even behind a cold front.
Finally to check is a ULL is maturing, take a look at a satellite image. If the clouds are showing up brighter (thicker) during a loop, then the ULL is maturing.
Keep these things in mind during your forecast and hopefully you will pick up on some anomalies.
ULLs can form in a few different ways:
1: From a developed surface low associated with a mid latitude cyclone.
2: From air flowing over mountains.
3: From a shortwave.
4: In association with a jet streak.
From these different scenarios always watch for the development of an upper level low because they can hold alot of weight in your forecast. During the analysis process during forecasting, upper level lows usually show up to the west or northwest of a surface low in association with a mid latitude cyclone. Additionally, during the forecasting process, models tend to forecast a surface low much better then a low above the ground, so be careful in the event that an upper level low is near your forecast area.
Additionally, since the ULL is usually to the west or northwest of the surface low, wintry precipitation is a concern. Below the ULL the air is cold (relatively speaking), therefore, when the ULL forms precip behind a surface low, in wintertime, there will be more wintry precipitation even behind a cold front.
Finally to check is a ULL is maturing, take a look at a satellite image. If the clouds are showing up brighter (thicker) during a loop, then the ULL is maturing.
Keep these things in mind during your forecast and hopefully you will pick up on some anomalies.
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