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  • Sailing is all about the Weather.

    Big into the exploration of Atlantic Hurricanes since Katrina came uninvited into his world, James (Jim) Gurley (JamesG161) has followed every Tropical Storm birthed in Atlantic, Gulf and Caribbean waters since. Being a boater, he knows that we often need more time to prepare than we get from the TV weather folk. Jim relies on the science of storm development to share early warning info with friends and fellow boaters.

    Early in 2018, Jim and John Shepard, (JSSailem) started to chat about the weather data available. John asked Jim to help forecast Pacific NW storms, and this morphed into discussions on weather forecasting.

    For John, sailing in the PNW is sometimes hit and miss. One day is ugly, then a string of beautiful days but no wind, followed by a series of blue-sky days and 12 knot breezes. Being ready for those great sailing days means you need to look to the Pacific Ocean and what is brewing. John has been into Pacific NW Weather since the 1970’s when his first PNW November storm hit bringing more than 40 days and 40 nights of continual rain.

    Together we want to share information, new APPs, safety, and thoughts about letting the weather help you. Identify some of the resources for sailors and help prepare you for your next sailboat outing.

    It is far better to go out on the water knowing what to expect in weather terms, than to be out on the water and see dark ominous clouds suddenly appear, unprepared.

Low East Of Corpus Christi?

Nov 6, 2006
9,203
Hunter 34 Mandeville Louisiana
I don't hear any discussion about the low in the gulf east and south of CC Tx.? may be just upper, but it looks to be developing. No chance to be anything bad, but looks interesting.
Comments?
animate.png (1200×875) (w-x.co)
 
Oct 22, 2014
15,811
CAL 35 Cruiser moored EVERETT WA
Looking at Windy... there is nothing at the surface.
Kl1.jpg


A minor circular patterned low at 18000 ft.
Kl2.jpg


That get blown out in the next 24 hours.
Kl3.jpg
 
Jan 1, 2006
5,987
Slickcraft 26 Greenport, NY
I hear the term “Upper level low”. On the weather often. I have little idea what it means. What is a working definition? And what is it’s significance?
 
May 1, 2011
2,282
Pearson 37 Lusby MD
A cold-core low, also known as an upper level low or cold-core cyclone, is a cyclone aloft which has an associated cold pool of air residing at high altitude within the Earth's troposphere, without a frontal structure.

Hopefully @JamesG161 and @jssailem can put a better spin (pun intended) on this!
 
Oct 22, 2014
15,811
CAL 35 Cruiser moored EVERETT WA
Kappy caught the essence of the “Upper Level Low” definition in his post Low East Of Corpus Christi?. Let us try to spin my observations of the words and interpretations of the meaning.

First, from our sailing experiences, we know that the wind in our sails is not evenly distributed across the sail. Sometimes we can have wind low in the sail, near to the surface and at other times we are trying to capture the wind puffing at or near the top third of the sail.

Weather patterns are much the same. We recognize the weather at the surface as it contacts us. This weather is influenced by forces that play at different altitudes in the column of air above our heads.

We begin looking at cell development at or near the surface when we scan the skies or examine the reported weather patterns across the map. Generally, we start at less than 5000 feet. Often even closer, like right on the surface. With so much of the planet being water, we examine water temperatures. NOAA has chosen to focus on the 20 degree C Isotherm recording the depth of this in the ocean, giving us an observation of heat content.

We monitor the High and Low pressure cells. Based on winds around the cells. We observe circular wind fields and watch these for formation of cell cyclonic flow, wind patterns approaching the cell from around the compass. A Low pressure cell that begins to spin due to the winds at or near the surface catches out attention. There is an opportunity, if moisture and heat conditions are in alignment to build the cell in a vertical direction. The air in the center of a Low pressure cell rises as moisture and heat fuel the cells formation. If the winds aloft cooperate and they remain nonexistent or at the most moderate and in the same pattern, then we can see the cell formation grow both horizontal and vertical. We get excited and start to watch the surrounding conditions like thermal conditions, humidity, condensing, temperatures aloft, nearby High pressure cells etc. when this happens.

In the case presented near Corpus Christi on the Sunday, there was no circular movement at the surface. The air pressure was relatively high 1010hPa. This can be seen in the first image. The reports called for an “Upper Level Low”. When I adjusted Windy to look at above the surface (850hPa and 500hPa). Nothing really showed up. The 5,000 ft altitude is a good indicator of mid to upper level cell development. It was not until I looked at the 18,000 ft level that a small circular cell became evident, in the second image. You can see the Low with a counterclockwise rotation of the wind patterns. When I looked at the levels above 18,000 ft the cyclonic rotation disappeared. This led me to opine that the “Upper Level Low” was not going to form into anything that would cause caution.

Tools like Windy and the charts on the NOAA site let us observe (based on computer models) the possible effects of pressure, wind, moisture, temperature etc. through time. The science of the data and the art of applying previous observations to the dynamic data leads to the forecasting of possible outcomes.

When you hear the term “Upper Level Low”, then you need to start looking at the other levels and surrounding conditions to see what may come of that named condition in the air that surrounds us.

James and John
 
Jan 1, 2006
5,987
Slickcraft 26 Greenport, NY
Thank you for a detailed answer that obviously took time to compose. I am digesting it. I have other questions but don't want to pester asking bad questions. But, I wonder about a so called upper level low when I think of a typical thunderstorm which has atmospheric affects to as high as 60,000 ft. Does such a storm supersede the ULL or is it impeded by it?
 
Oct 22, 2014
15,811
CAL 35 Cruiser moored EVERETT WA
It is important to distinguish between area weather patterns and weather events. The thunderstorms you seek are events that can be embedded in the front of a Low Pressure cell be it Upper Level or Surface level.

Think about it this way. A Hurricane is a fully developed cyclonic low pressure cell. It can cover a large area. The motion of the air is counter clockwise around the center.

Embedded with in the cell, usually along the frontal edge where most of the action occurs can be events like thunder storms and tornadoes. These can be within the storm or spawn from the storm.

For more detail, UPPER LEVEL LOW - Weather Events
 
Feb 14, 2014
5,624
Hunter 430 Waveland, MS
Weather Radar shows you the Tops of Rain events. The higher the clouds the more likely the heaviest rains.

That is different from Satellite Infrared views. Both show high altitude clouds.

This thread shows you why they did not react fast enough.
Caught in a Storm

They saw the rain front, that was when they should have reacted, not minutes later.

Jim...