Tuesday, January 25, 2011

Day 2

Things have changed slightly for our forecast day, Sunday the 30th. The temperatures remain the same. In fact, the evening forecast kept the same numbers last night. The change in the forecast comes in an increased chance for rain. Let's take a look at what changed on the maps:

Let's start from the ground up.

Surface Map
Here is the latest 0Z update for the surface. We see the batch of precipitation spreading northward. Yesterday, this moisture was limited to southern Oregon. Now it has pushed its way a bit further north into our region. I have added some edits in order to highlight the areas that have undergone change.

850mb level (about 5,000 ft)

Using this map, I am looking to diagnose where areas of warm air invade areas of cool air and vice versa. Areas where warmer air is over-taking cooler air indicate instability and aid precipitation processes. Areas where cooler air is moving in will indicate stable conditions. In our situation, we aren't seeing any warm air coming in, nor is a significant amount of cool air coming in. All in all, today's map isn't all that impressive.

500mb level (18,000 ft)
As I mentioned in yesterday's post, the 500mb level is the steering mechanism for a majority of our weather systems. Yesterday, we saw a good ridge over our heads but to our south we saw a shortwave, cutoff low. In today's map, that cutoff low has weakened some. The energy is still there. The region is still centered in southern Oregon and has plenty of positive vorticity associated with it. This is a large area of uplift, which is a major part in aiding precipitation. This particular area still looks strong enough to produce some good uplift in our area, which is why I've upped the rain chance a bit. But the low was cutoff yesterday but not today. We look to the 300mb level to see why.

300mb level (30,000 ft)

This map shows the location of the jet stream as well as streaks within the jet flow. Yesterday, we saw a jet streak that was beginning to dig south. Today, it has flattened out a bit but increased in intensity. That is helping push the energy up our way. The southerly flow yesterday was a sign that the jet may dig south, allowing the cutoff low at the 500mb level to go south as well. Now that the jet has flattened out, that cutoff low will now begin to flow back up towards the north. The cutoff low itself has weakened but the jet has increased in intensity. This will be another aid to precipitation as an increase in the jet means an increase in uplift around the jet streak.

So the glaring change from yesterday to today was the intensity and location of that shortwave kink in the middle of the atmosphere. It will be interesting to watch the shortwave and see if any cold or warm air moves into the region. Also, the closer we get to our forecast day, we will have access to more model runs that will allow some comparison. I'll be back tomorrow with another look at the forecast!

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