Rio Grande Valley:
Believe it or not, high temperatures today reached 67 in Brownsville, 62 in Harlingen, and 63 in McAllen, though these temperatures were reached around 1 a.m. Today was a very chilly day if you are living in the Rio Grande Valley. Temperatures remained in the lower 50s and upper 40s and are continuing to drop as we speak. For tonight, expect upper-level moisture from the Pacific to keep the skies overcast with lows in the mid-to-upper 30s. I expect temperatures to range from 34, in the upper Valley, to 38 near South Padre Island. Winds will be out of the north at 10 mph.
(1/12): Wednesday looks to be another chilly one, with highs in the mid-to-upper 40s, especially in the upper Valley. Pacific moisture in the upper-atmosphere will keep a slight chance of light precipitation, or drizzle. Winds will be out of the north at 10-15 mph. Wednesday night looks to be cold with lows in the upper 30s, with a slight chance of drizzle. Winds will remain out of the north at 5-10 mph. The main threat will be the wind chill factor. Wind chill values will range from 28-32 early Wednesday morning, depending where you live.
(1/13): Thursday will remain chilly with highs in the lower 50s, with a better shot of light rain (30%). Be aware of the wind chill early on in the day. The arctic high pressure, causing the low temperatures, will slowly move east and by Friday. Overcast skies will stick around. Winds out of the north at 10-15 mph. Thursday evening will be mostly cloudy with a slight chance of showers. Lows will be in the mid-40s.
(1/14): By Friday, the high pressure in the Central Plains will be moving east, shifting our winds out of the southeast at 5-10 mph, and increasing temperatures to the upper 60s/lower 70s, as afternoon highs. Rain chances (20%) continue, as increased moisture from the Gulf of Mexico will interact with the Pacific moisture aloft. Friday evening looks to be mostly cloudy with lows in the mid-50s.
Rest of the Nation:
The big weather story for the nation is the winter weather impacting the Northeast. Why is there so much snow occurring in the Northeast right now? The answer to that is simple to summarize but can be difficult to understand from a dynamical and thermodynamical point of view. Therefore, I will briefly try to explain both perspectives to you.
For the easy, simple answer: two surface lows are merging in the Northeast, causing heavy snow to fall.
But why? And why do low pressure systems cause precipitation?
I will try to not get really technical as to why and how lows form at the surface or in the upper atmosphere. Again, dynamics and thermodynamics play a HUGE role in the atmosphere, that not even I understand at times.
In brief, in order for precipitation to fall, there must be a lifting mechanism (air rising from the surface) and that air must have moisture in it. Depending on how much moisture there is and how far it lifts, will determine if precipitation will fall. In the synoptic scale (for this example, synoptic scale will mean atmosphere flow pattern over the lower 48 states as a whole), there are many ways to lift air up. A few examples would be: orographic lift (air rising over a mountain, for example), upward vertical velocity, low level surface convergence (air converging at the surface and rising), positive vorticity advection (occurs in the upper-atmosphere), and divergence in the upper atmosphere due to jet streaks. Point is, all of these cause the air to lift and saturate, creating clouds and precipitation.
Now that we have that out of the way, low pressures are usually associated with rain and snow because of every single way of lift that I listed. I won’t get into how the Coriolis Force plays a role with low and high pressures, but if you want to know, just leave a comment.
Back to the two surface lows. These merging lows are enhancing the lift from the ground, causing the heavy snow to fall over the Northeast. If you want to know how to determine precipitation type, feel free to ask me. As far as the motion of the lows, they tend to move towards areas of lower pressure. In a sense, the center of the low relocates to an area with lower pressure, but looks as if it is moving. This is pretty confusing to understand, especially if you don’t have a dynamical and thermodynamical knowledge background. The Northeast will continue seeing heavy snow for the next 2 or 3 days.
Click on image to increase quality. Notice another low coming on ashore off the west coast that will affect the Pacific Northwest over the next few days with rain and heavy snow.