Hannah Strong

This blog is about ALL things weather! Check in for updates on the science behind what you see outside everyday.

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Forecast for the last day of the Allen County Fair

There will be beautiful weather for the last day of the fair and plenty of deals! Carnival rides are $1 each, and it's Farmers Care Day.  That means if you bring a non-perishable food item you get $2 off admission!

Temperatures will climb into the lower 80s by afternoon, but the Muggy Meter will stay at Comfortable! 

Remember to pack the SPF, though, since the UV Index is Very High.

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The sun won't be around much longer. We've got clouds rolling in later this morning that are going to stick around all day, keeping our high temperature in the upper 60s #sun #clouds #warm #wind #spring #instacast

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It's looking like another soggy day for Starkville, so you probably want to grab some rain gear before heading out the door. Fair warning, you also may hear some thunder over the next few hours #rain #showers #aprilshowers #mayflowers #thursday #radar #update #instacast #forecast

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Prompted by my morning jog (4/21)

It’s such a beautiful morning in Starkville! The ground is finally starting to dry out, and don’t even get me started on the PERFECT temperature we have achieved outside at this exact moment. Needless to say, I thoroughly enjoyed my morning run today.  But it made me curious about when our next rain chance will come.  So today’s blog is a forecast of our next rain event in Starkville using the NAM.  I just scrolled through the precipitation product until I saw rain over Starkville at 1 AM Thursday. 

So let’s look at why the model thinks this is our next chance for rain.

We will be in the exit region of the jet streak, moving into the right rear quadrant.  That quadrant promotes a lot of uplift based on the upper-level convergence and divergence patterns that set up in a jet streak. All this uplift in the upper-levels will help the surface air to rise and create storms.

There’s also going to be lots of vorticity advection.  There are areas of strong positive vorticity right next to areas of negative vorticity. These advecting over each other will create a lot of positive vorticity advection (due to the greater difference between positive and negative numbers versus numbers that are all positive). DPVA creates uplift which promotes storms.

We see some weak warm air advection here with winds coming from the southwest, but it’s not as strong as we would like.  Though this still contributes to rising air at the surface, and warm, moist air is very important for uplift, this is probably the factor that is contributing least to our rain chances.  

Adding all these factors together, we see that there will be rising air over us very early Thursday morning. The jet streak is probably going to be the most influential factor, but all of these show us why it will rain Thursday. And as a bonus, at no extra charge, the rain will continue off and on most of the day Thursday until about 6 or 7 PM.

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There's not a cloud in the sky this morning! (Believe me, I looked) All that sunshine means today will be a little warmer than yesterday #sun #sky #warm #spring

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Nowcasting (4/20)

The sky above Starkville has gotten very gray over the past few hours, and the wind is picking up. To any normal person, that would suggest that rain is coming.  But if we check radar, it’s not showing any rain headed for Starkville.  In fact, I don’t see any rain any where near us (Mississippi, Louisiana, or Arkansas).  

So what’s happening in the sky?  That’s today’s blog.  I will use the RAP because it gives model output for every hour, and it gives data for all our levels of interest.  All images are for 17Z, which is noon in Starkville.

At 250 mb, there is a jet streak in east Texas courtesy of the subtropical jet.  You could argue that coastal Mississippi is in the entrance region of that jet, but definitely not Starkville.  The winds are diverging a little over the state (moving apart in difference directions), so that could be helping create our dark clouds, but it’s pretty minor.

At 500 mb, we look for strong positive vorticity advection to create rising motion.  We don’t see that here.  If anything we are getting advection of negative values of vorticity (blue colors).  This will lead to more sinking motion than rising, and rising is what we need for rain and storms.  

850 mb helps us see why it feels so much colder today, but doesn’t really help us with the dark clouds question.  We are definitely experiencing cold air advection in Mississippi.  The cold air (blue colors) is spilling further south, and our winds are coming out of the WNW bringing that cold air to us.  But to get rain, we need warm air advection to get the air to rise.  We obviously don’t have that.

It should come as no surprise that 700 mb doesn’t show us any real rising motion over Starkville or much of the state of Mississippi.  In fact, we will stay rain-free through at least early tomorrow morning.  This next map is for 4 AM tomorrow (Starkville time), and there’s still no rain near us.   So what’s with the clouds?

If you loop through the water vapor imagery from the last 12 hours, you will see the culprit.  It’s that sub-tropical jet we noticed at 250 mb. That is funneling in a lot of moisture from the southern Pacific, across Mexico.  All of that moisture is getting wrapped up in the low-pressure system that is currently near the Great Lakes.

So, while we lack our normal ingredients that we look for when forecasting rain, it is not outside the realm of possibility to see some sprinkles in Starkville today.  Rain isn’t’ the main threat, but the clouds will be here most of the day.   Since we won’t get much sun, our high temperature is going to stay in the mid- to upper-60’s for the Golden Triangle.  This probably isn’t a good day to try to hit the pool.  

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Not a speck of color on radar this morning now that last night's storms have moved out. It's pretty breezy this morning, so you may want to grab a light jacket as you head out the door because today's high will stay in the 60's #instacast

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The rain from last night isn't causing as many problems this morning! Some of you may even see some sun ⛅️

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Home Sweet Home (4/13)

Today’s blog is totally selfish; I will focus on the weekend forecast for Fort Wayne, Indiana.  My mommy and I are flying up there to pick out my new apartment!! So we will take a look at what she and I can expect for weekend weather in the summit city.  The only model that looks that far into the future is the GFS, so we will use that and the GFS ensemble.  Before we look into the future though, we need to look at now.  Let’s initialize the GFS with the short range, higher resolution models to see what the GFS’s shortcomings are with the current systems. That will help me know where to trust it and where not to trust it.  We start with current satellite and radar images and the HRRR and RAP models.  

 Clearly the GFS is on the heavier side as far as precipitation goes, but it’s dead on with timing in the Great Lakes region.  We need to keep that in mind as we look towards the weekend.  Next, we will see what kind of confidence we can put in the GFS this far out by look at the ensembles.  

Clearly the lines are all over the map.  Below is what this same map looks like at the start of this model (right now).

You can see much less variance in the lines, which translates into greater confidence.  While there is still a clear pattern in this map for the weekend (look big picture, it helps if you squint), there is not great confidence.

So, after I looked through all the GFS model data for our visit, here’s my forecast:

Friday: It’s going to rain during our travels; temperature when we arrive will be in the mid-50′s.

Saturday: It’s going to rain all day, which is a bummer since we will be outside all day. Temperatures will basically stay between 40 and 50 all day.

Sunday: The temperature will be in the upper-30′s when we leave, but at least the rain will have stopped! 

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Start of the week in Starkville (4/12)

Since it’s the start of the week, let’s take a look at the weather in Starkville tomorrow.  Today we will use satellite to initialize three models, use the best model, and compare that model to an ensemble.  So here’s the satellite image from around 21Z to which we will compare the models.

And a radar image for good measure.

Now we will compare the RAP, NAM, and GFS (in that order) to the satellite image and see which one is doing the best.

 CLEARLY the NAM and GFS are overdoing the precipitation.  So let’s go with the RAP.  If we need to look further than the RAP goes, we will use the NAM because it’s doing better with timing than the GFS (GFS is lagging a bit).  Looking ahead at tomorrow, rain chances hit Starkville around 7 AM.

The NAM shows the rain sticking around until Tuesday at 7 AM, and then we will only get a little break.  The rain returns Tuesday afternoon.  It looks like a soggy week for Starkville.  And the GFS ensemble agrees!

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That’s a big bubble... (4/8)

The Storm Prediction Center has put out an Enhanced risk for tomorrow, which is one step above Slight. The interesting thing here is the large area inside this Enhanced bubble.  So let’s go to the models and see why they may have done this.

The Short Range Ensemble Forecast shows a very large area of high CAPE values.  CAPE tells us how much energy that air will have; it’s a measure of the instability of the air parcels.  The air needs energy to rise to create thunderstorms.  

Now, let’s look with a top-down approach to figure out why there’s so much energy using the RAP, NAM, and GFS in that order.

The GFS and NAM are a little more kinked than the RAP.  The upper-level flow on the RAP is slightly smoother, which means less disturbance. Also, notice the jet streak above the Great Lakes.  This will affect the northern parts of our risk area, causing some extra uplift.

 All the models show the strong vorticity maximum just west of our risk area.  That means it will be advected into our risk area, which makes sense. You also see over the risk area both positive and negative vorticity.  This will result in a lot of vorticity advection over our area.  All of that vorticity advection will increase the threat of severe weather.

All the models are in pretty good agreement with the location of the low at this time; on the border between Nebraska and Iowa.  That means the low-level flow pattern will be coming out of the southwest, which you can see in the wind barbs on these maps.  That also means we’re getting some warm air advection in our area, which further increases the risk of severe weather.

The RAP and GFS are fairly similar here showing areas of stronger uplift next to areas of sinking air. This circulation will strengthen storms that pop up in this area.  The NAM looks a little weaker because of the flow pattern it’s picking up on at this level. It’s also trying to show the same idea of both rising and sinking air.

When you add all this together, here’s the forecast: severe weather is likely tomorrow in the area highlighted in the SPC map (first picture).  The key will be to watch the surface winds tomorrow.  If they’re coming out of the southeast, watch out for tornados.  If they’re more out of the south/southwest, hail and strong wind will be the biggest threats.  

Another thing to keep an eye on is the dry line, which is exactly what it sounds like.  It’s a line between dry air and moist air.

 This dry line + the warm front attached to the low pressure system highlight the area we need to focus on. Storms will initiate ahead of the dry line in the warm, moist sector of the system.  

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#sww

My new hashtag is severe weather Wednesday.  This blog will look at where the chance for severe weather will set up on Wednesday.  Today in forecasting class, I learned about the dry line bulge! No, it has nothing to do with how you look in a bathing suit.  It has everything to do with forecasting severe weather.  The dry line is exactly what it sounds like, the line between dry and not dry on a dewpoint map.  We will look at the GFS and NAM, in that order.

The yellow line on the GFS map shows where the dry line is.  The yellow circle points out where the bulge is.  It’s the area that sticks out a little further than the rest of the line. This bulge tells us several things are going on here.  The wind in this area is a little stronger which pushes the moisture out a little further than the rest of the line.  Warm, moist air is a crucial ingredient for severe weather.  So the fact that the moisture reaches a little further out in this region shows this area has a better chance for severe weather.  It also tells us which direction the surface winds are blowing at this point which gives us a clue about the turning of the winds. You need good turning to have a better chance of severe weather.  You can also see where the warm front will likely be based on the moisture gradient going through Missouri, Illinois, Indiana, etc. Our area of interest will be between the bulge and the warm front.    

Next we will look at a widely accepted parameter of severe weather to see how the dry line bulge verifies. The first map is MUCAPE (Most Unstable CAPE) from the NAM 4 km.  This shows us exactly what it says, where the most unstable CAPE values are occurring on the map (not vertically).

You can see that these values line up well with the dry line bulge.  The highest CAPE values are a little ahead of the dry line, but that is to be expected.  The winds are blowing the warm, moist air into the area with the highest CAPE values. Next we will look at SREF (Short Range Ensemble Forecast) CAPE values greater than 2000.  

This map shows the CAPE a little further behind than in the map above it, a little closer to the dry line and bulge.  Both of these CAPE maps show what we expect earlier.  We said our area of interest would be between the warm front and dry line bulge, and it is!  These CAPE maps, though they show different evaluations of CAPE, validate our evaluation of the severe weather potential based on the dry line bulge. Here’s what the SPC has predicted for Wednesday:

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The Sun’ll Come Out Tomorrow (3/29)

Today’s blog will take a look at Fort Wayne, Indiana.  We will be looking at 12Z, which is 6 AMlocal time.  I picked this time because this is when most people are waking up to start their workweek.

250 NAM

250 GFS

250 RAP

At 250 mb, the NAM and GFS show a fairly similar flow pattern while the RAP amplifies the trough a little more.  That means the curve of the trough is a little stronger/more pronounced.  The deeper trough could mean stronger development of storms.  The trough axis is very close to Fort Wayne, but slightly east.  Let’s keep looking...

850 NAM

850 GFS

850 RAP

Again, at 850 mb, the RAP has the deepest trough.  The trough axis is east of Fort Wayne, so it has already moved through our area of interest by this time.   However, all the models agree that there will be cold air advection at this time. Cold air advection does not lead to rising motion, but sinking motion.

500 NAM

500 GFS

500 RAP

At 500 mb, we again see that the RAP has the trough amplified a little more.  It also has the strongest vorticity maximum followed by the NAM then the GFS.   We need to notice that Fort Wayne is just behind the strongest positive vorticity. This means that the storms and precipitation will likely take place before our time frame.  But let’s check with the GFS ensembles before we decide. 

The ensembles show, with pretty decent consistency, that the trough at 500 mb. will be east of Fort Wayne.  This gives us greater confidence in all the other models as far as timing.  So the forecast for 6 AM tomorrow in Fort Wayne is a clear, beautiful, and cold morning!  There is a chance for fog in the morning, especially areas that get heavier rainfall today.

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Severe Season (3/24)

In today’s blog we will inspect the threat of severe weather tomorrow using the NAM and GFS in that order every time.  All the maps are valid for 0z which is 7 PM Central time and is the time with the greatest upward vertical motion.

The RAP shows us where the low pressure system is right now.

In the upper-levels at 250 mb, here’s what the wind pattern looks like:

The NAM shows the trough a little deeper than the GFS, but other than that the models are in pretty good agreement.  Our focus area is just barely upstream of the trough based on the SPC map above.  The big factor in this particular system is vorticity, which we find at 500 mb.

The NAM shows stronger vorticity all around, but the timing in each model is very similar.  The GFS doesn’t have as good spatial resolution as the NAM which is probably why it appears to be underdoing the vorticity. Regardless, both models show areas of strong positive vorticity in prime locations to be advected over our region. Next, we need to check temperature advection at 850 mb.

The areas of warm air advection are basically in the same spot in both models.  The cold air advection behind it is shifted a little between models, but that isn’t contributing to our storm chances.  We focus on warm air advection, which lines up with the DPVA from the maps above.  Finally, we will check our ideas with the vertical velocities map from 700 mb.

There are very strong areas of uplift in our region, but the GFS is obviously much stronger. Either way, there is a good chance for severe weather tomorrow based solely on uplift in the atmosphere.  If the GFS is right, the chances for severe weather increase.  If the NAM is right, the chances are still moderate that we will see severe weather south of the Great Plains.

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Is it over yet? (3/22)

It’s been gloomy/rainy in Starkville for several days, so let’s check with the models to see when it will all end.

First let’s look at when each model expects the rain to be out of Starkville using the RAP, NAM, and GFS.

An important note: I pulled the first image where the rain was out of Starkville.  Then NAM and GFS produce maps for three hour intervals.  This means the previous image still had rain on in, but that rain could have stopped anytime during those past three hours.  For example, the NAM image is from 15Z.  That means the 12Z image still had rain in Starkville, but the 15Z didn’t.  That rain could stop at 1201Z or at 1459Z, the model doesn’t tell us.  The RAP produces an image for every hour; the same principle holds true but on a smaller scale.  The image I have here is the first one without rain in Starkville, but that rain could have stopped anytime in the last hour according to the model.

I have the RAP at 4Z, GFS at 6Z, and NAM at 15Z.  The RAP and GFS are predicting a similar time frame based on what we just discussed, but the NAM is much later.  Let’s see if we can figure out why this is happening.

At 250 mb, the wind pattern is totally different in the NAM than it is in the GFS or RAP (shown in that order).

Basically it looks like the NAM expects stronger winds aloft.  The area of strongest wind has shifted further east, but don’t forget this is 9 hours after the GFS and 11 hours after the RAP.  The stronger winds aloft (more green than the other two models) could be contributing to why the NAM things the rain will stick around longer.

Next we’re going to skip down to 850 mb to look at temperature advection (RAP, NAM, GFS).

The NAM has the low much further east than the other two models, but of the same strength.  Other than that, the temperature and wind flow generally look the same across all three models.  Next we go back to the mid-levels to look at vorticity at 500 mb (RAP, NAM, GFS).

 We see here what we saw at 250 mb; the pattern is totally different in the NAM.  The GFS and RAP look pretty similar, but the NAM has everything further east.  So, here’s my conclusion thus far: the NAM has rain trailing further behind this system than the other two models.  Both the RAP and GFS keep the rain close to the low pressure area, but the NAM trails rain off behind the low for several more hours.  This could be a result of the different upper-level flow pattern the NAM expects.  Maybe that will cause some extra disturbances behind the surface system.

Finally, we will check with an ensemble to see if any of the runs of the GFS agree with the NAM.  If they do, it might give us more confidence in the NAM’s interpretation of events.  If they don’t, it might give us more confidence in the GFS and RAP version.

These are all the different versions the GFS spit out with the average on the bottom.  Most of these look like the rain will clear out earlier rather than later because they have similar patterns to the RAP and GFS, not the NAM.  After looking at all of them, I’m leaning more towards the timing of the GFS and RAP, not the NAM.  So, here’s my forecast: expect the rain to stop coming down in Starkville overnight tonight.

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Second Chances (3/19)

Today is my second attempt at the new blog format, so we will stick with what we know and forecast for Starkville.  All maps are valid for 7 AM local time tomorrow (Friday).   Since we didn’t get any rain today, we will looking to see if we will get rain here tomorrow.

At 250 mb (the upper-levels), we see a strong jet streak just to the north of our area in all three models (RAP, NAM, GFS).  By the way, this is looking at wind speeds.

The jet streak is the strongest in the GFS and weakest in the RAP.  The RAP also has the streak a little less curved, which creates less wind disturbance in the upper-levels.  Less disturbance in the upper-levels means less of a rain chance for us at the surface.

Next we will look in the mid-levels at 500 mb for vorticity using the same three models (RAP, NAM, GFS). 

The NAM and RAP have the vorticity maximum in basically the same place (Eastern Colorado), but the RAP shows it being much stronger.  The GFS has the vorticity maximum lagging back in Southeastern Utah, but its intensity is in between what the NAM and RAP are showing.  Let’s keep this in mind as we continue analyzing.  In our neck of the woods, all three models show a vorticity minimum headed our way.  The NAM and GFS show it lagging a little bit behind the RAP.  Also, in the NAM the energy is much less organized.  That’s important to remember.

Next is the lower levels (850 mb) to look at temperature advection using the same three models (RAP, NAM, GFS).

For our area of interest, all three models look pretty consistent.  The flow is coming from the west and is converging over the state of Mississippi (coming together).  The flow is also pretty zonal and parallel to the isotherms (lines of constant temperature), so we aren’t getting much advection of either warm or cold air.

The last thing to evaluate is the ensemble.  Today we will use the GFS ensemble that shows us the average height of the 500 mb level and the anomalies.

Obviously some of the individual runs got cut off, but that just shows you how many different runs there are! The large one with lots of color is the model consensus, and the smaller ones are individual runs using slightly different physics and equations.  Higher heights means a warmer column of air. That’s why the warmer colors (orange and red) are positive anomalies (higher than average), and the cooler colors (blue and purple) are lower than average heights which corresponds to lower than average temperatures.  We are clearly in a warm area of the country during our time frame according to the ensemble.  

When we add all these factors together, it looks to me like the best chance for rain is to the north of us. There is the unorganized vorticity pattern plus the fact that we are lacking positive vorticity in our area added to the lack of temperature advection.  We will still get some decent chances at rain tomorrow, but there will be better chances for Tennessee and southern Kentucky.

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Return of the #instacast! We're a tad cooler today than yesterday or Monday, but still warm. The clouds are going to stick around, but the bulk of the rain isn't coming until tomorrow #rain #spring #warm