A big change is coming to southeast Ohio next week! (9/28 - 10/3)
The first day of Fall brings bad news to summer-lovers. The high 70s to low 80s the past month coupled with sunny skies (until the last few days) are rapidly coming to an end and that end is much sooner than most expect. A drastic weather pattern change is forecast to occur for much of the northern half of the United States. This will be split into two parts, the first explains the current weather situation while the second one will describe the sudden change that will be occuring in the coming days.
Current Weather Situation
The current pattern is very modest for late September and the lacking of upper level steering winds in the jetstream have kept any strong storm systems from sweeping across the country - this is called a blocking pattern. A common occurance with patterns similar to this is something called "cut-off" or "closed" low pressure system. These lows get literally cut off from the jetstream and have no push to move. They tend to sit over the same area for days on hand just rotating and dropping often very large amounts of precipitation. They also tend to bring very unseasonable temperatures for areas around it, either cold or warm depending on just where the system sets up.
Here is the current jetstream set up as of 2pm today:
The current jetstream pattern is represented by the purple line north of the United States and the cut-off low is represented by the red L. You can see just how weak the winds are by looking at the wind barbs (more flags mean stronger winds).
Here is the coinciding water vapor imagery from nearly the same time:
The water vapor imagery shows the water content of the clouds by colors. The grays and blues (usually areas of precipitation) have much more moisture in them while the reds and the blacks are very dry. Looking in the same region of the cut-off low from the map of the jetstream you can clearly see the counter-clockwise spin of the low pressure system.
One final map shows the warnings at the current moment for the United States:
The area circled in pink are winter storm warnings and winter weather advisories. Though it may be the mountains, it is still very early in the year to see frozen precipitation anywhere in the United States. The black circle represents the massive amounts of rain that have been occuring in the last few days for the southeast. The red counties are flash flood warnings while the greens are flood advisories and warnings. These drastic weather patterns, unusual for this time of year, are all thanks to the low centered in the Southern Plains.
The Big Change
The big story is the break down of the cut-off low on Friday. This system will slowly begin a movement towards the north-northeast in the next few days and slowly get closer to the area. This will allow for associated disturbances to move along it and effect the Ohio Valley region. These disturbances will act as cold fronts bringing cooler air with each shot along with the possibility of precipitation (thankfully not frozen...yet). The first of these fronts is forecasted to arrive on Saturday as you can see with the wind change on the 850mb map below from southerly to westerly:
The next of these is forecast to come on Monday, and it will be much stronger than the Saturday front. Here is the 850mb plot for 8am Monday, the 28th of September:
Notice with this map, though the wind shift along the green line (cold front) isn't nearly as strong that the front itself is much more significant. The wind barbs contain many more flags than before portraying strong wind speeds. This represents a very strong northerly wind flow that will help transport much colder air in from the artic. Another note of interest is the yellow line. It crosses many of the black lines on the map. These black lines connect areas of equal pressure and when they are packed tightly across an area like at the yellow line and completly around the low pressure system, is symbollic of a very tight pressure gradient and strong winds. So when it all boils down, this map is representative of a very cold weather pattern setting up for the Ohio Valley region along with very windy and cloudy conditions for the early part of the work week.
The European Northa America model is also in agreement with the GFS model (what all the forecast images have been from) in foretelling of a strong low pressure system with the above characteristics at the same timeframe. This helps in developing confidence that the event will actually occur this coming week. Here is the European model for 8am Monday the 28th:
This next image is for 8am Tuesday, the 29th.
The brown arrows are pointing to a faint purple line that is representing zero degrees celcius or thirty-two degrees farenheit. Granted, that is at the 850mb level and actually 5000 feet above the ground, it is still very cold for this time of the year. Over time and with strong winds this air will mix with that below it making it much colder on the surface than normal. This fortales that the coldest temperatures will be felt mid-week as the colder air makes it to the surface and could be the coldest we have seen since spring. Although a frost isn't expected yet, it should be monitored closely for Wednesday and maybe even Thursday.
This final image once again shows the jetstream at 300mb on 8am Tuesday, September 29th:
Notice the purple line of the main jetstream and how it has changed since the first image of the jetstream at the top of this article. The jetstream has dropped south considerably in both the east and the west and the closed low is gone from the Plains. This represents the drastic weather pattern change that is likely to occur over the next week.
September 28th Update
A cloudy, drizzily morning greeted southeast Ohio this morning as the predicted cold front was passing. Sunny skies and very windy conditions will continue for the rest of the day bringing our first true taste of fall. The strong winds that shifted to the northwest will bring the colder Canadian air into the region. These weren't the only changes that occured with the fronts passing as dewpoints dropped significantly along with a pressure increase. These changes can be seen on the Scalia Lab conditions from this morning:
The highlighted region labeled 1 represents the increase in wind speed. The 2nd region shows how the pressure increased, the 3rd shows the rapid drying of the atmosphere with the lowering dewpoint, and finally the 4th shows how the drop in dewpoint related to the drop in humidity. These are all typical changes that occur with a cold front's passing, but take notice of the area highlighted in orange and labeled 5th. This represents the temperatures change, which was relatively none at all. This is because the cold front passed at the coldest part of the day, when the sun has been away the longest, just before sun-up. The surface of the earth still warms the as the day continues and therefore the temperature is still going to increase through the day even though it will be cooler than yesterday.
The following maps show the changes that are occurring with the passing of the front:
These are the surface conditions for the region. The blue line represents the front. Notice the wind change with the front depicted by the direction of the tails. The speeds increase greatly as you go farther to the west with more flags on the end of the tail as stronger winds wrap around the low pressure system located north of Michigan. The speed of which the wind is gusting is given by the numbers at the end of the tail with a 'G' before it. As the winds increase, colder air filters in as you can see with the temperatures (numbers in red). The dewpoint change across the front can also be seen with the green numbers.
The above image is the three hour temperature change ahead and behind the front from 7am to 10am this morning. Blue is temperature decrease and red is temperature increase.
This is the change in dewpoint over the same three hours. The orange represents decreases in dewpoint and drying in the atmosphere while the green represent increasing moisture in the atmosphere from 7am to 10am.
The cold front as seen from visible satellite this morning at 10am can be picked out by the narrow band of clouds sweeping from New York all the way to New Mexico:
Here is a zoom in to the southeast Ohio region. Notice how clear it is after the fronts passing this morning. This is thanks to cold air advection sinking the air behind the front. As cooler air filters in it stabilizes the atmosphere, increasing the pressure and clearing out the sky. This should give us a relatively sunny day this afternoon. With some afternoon heating, a few fair weather, puffy, harmless cumulus can be expected.
Here is a look at the current watches and warnings for 10am this morning:
The area circled in green highlights counties in brown. These counties are all under wind advisories for continuous winds in access of 25-25 mph and gusts up to 45 mph today. The area highlighted by blue surrounds counties that are highlighted by different shades of blue which represent frost warnings/advisories and freeze warnings and watches. The path of the colder temperatures and strong winds is shown by the pink arrow.
Finally, a current analysis of the jetstream (300mb) and 850mb level is shown. Compare these to the forecasted ones from above and see just how well the forecast models handled the big change!
So for the rest of the week, very fall-like temperatures and dry conditions will stick around. Highs today will make it into the mid-60s but the cooler air will funnel in for tomorrow and keep temperatures in the high 50s for the next several days even with sunny skies. A slow rebound will occur Thursday as highs will climb back into the 60s and perhaps by Friday forecasted temperatures are hinting at even near 70. Overnight lows will be another story. Clear evenings will allow all the heating from the day to escape into space and let temperatures fall very low. This week, the early mornings will be in the mid-to-low 40s with Wednesday night/Thursday morning dropping down to near the upper 30s as the coldes air moves in. This is most likely going to be the cool air the leaves need to change and the jump to fall has finally occured. Lets not forget either that winter will be knocking at the door in just a few months! So enjoy the dry, cool days while they last before it starts snowing!
Christopher Redmond
cr898005@ohio.edu
