It has been since Sunday when I posted last here and it was to discuss the many possibilities of Fay. Well it is almost Friday as I write this and Fay is still an issue. The models that had Fay stalling and drifting back west across Florida were correct. To put in perspective, Fay has dropped rainfall amounts over 2 feet locally in east central Florida Fay is currently sitting along the coast of Florida and will begin to track westward across Florida into the panhandle. Eventually the remnants will move back into the SE states of Alabama, Georgia, and parts of Louisiana and Mississippi. The question then becomes does her remnant circulation and moisture move NE towards the drought stricken areas of North Carolina, South Carolina, and North Georgia. Stay Tuned..
Closer to home, we have had relatively quiet weather, except a few showers/storms that formed on Wednesday evening dropping close to a half inch of rain at RDU. Temperatures have been normal to slightly above normal as well since last Friday. (Normal high is 87 now). I expect temperatures to be near 63 in the morning with a low overcast developing to a the low level easterly flow. This should burn off quickly though and temperatures should reach the middle 80s tomorrow with a high near 86. A very similar day is in store for Saturday and a little bit warmer on Sunday with a high closer to 88. Friday and Saturday evenings look to be extremely comfortable for this time of year with temperatures hovering near 70 early dropping to the low and middle 60s overnight.
Thursday, August 21, 2008
Sunday, August 17, 2008
Fay Going Where?
Tropical Storm has been a disorganized tropical cyclone since Friday as it passed through the Dominican Republic and Haiti. Fay is now just south of Cuba and is projected to begin turning west north west and northwest towards Florida. The big question then becomes how strong does Fay get after it re-emerges in the Gulf of Mexico and where does she eventually make U.S. landfall. Computer model forecasts have been extremely unstable where one day they are pushing Fay up into the Appalachians after landfall near Tampa Florida. The next day they are showing a landfall on the panhandle of Florida then slowing down as Fay meanders up into the southeast. Oh and not to mention there are models showing Fay turning NE back into the Atlantic and then making a second landfall on the east coast of the U.S near South Carolina or Georgia.
If the remnants of Fay do in fact move up into GA, SC, and NC, and her remnant circulation is west or south west of NC, then a much needed rainfall event will set up for several days as the flow regime will remain slow due to a a strong surface high setting up off the NE coast of the US. So whatever is left of Fay will meander somewhere over the SE US. Let it be known rain her in NC is by no means guaranteed.
Ill have more on Fay this week as hopefully things become a little clearer but right now expect a lot of chaos is the coming days with regards to what exactly we will feel here in NC.
If the remnants of Fay do in fact move up into GA, SC, and NC, and her remnant circulation is west or south west of NC, then a much needed rainfall event will set up for several days as the flow regime will remain slow due to a a strong surface high setting up off the NE coast of the US. So whatever is left of Fay will meander somewhere over the SE US. Let it be known rain her in NC is by no means guaranteed.
Ill have more on Fay this week as hopefully things become a little clearer but right now expect a lot of chaos is the coming days with regards to what exactly we will feel here in NC.
Wednesday, August 13, 2008
Record Setting August 13
For a record low maximum temperature. In fact it tied the old record for low maximum for this day. Here is the report from the National Weather Service in Raleigh...
... Record low Max temperature tied at Raleigh-Durham international
Airport today...
As 500 PM EDT... a record low Max temperature of 74 degrees was set
at the Raleigh-Durham international Airport today. This ties the
previous record for August 13th for the coolest high temperature...
last set in 1996.
The normal high temperature for the Raleigh-Durham international
Airport for August 13th is 88 degrees
...
As far as the rainfall, my hunch on more rainfall further northwest was true but amounts were relatively light except in isolated spots that got under some slow moving showers or locations down south such as Fayetteville.
On August 13, 2007, RDU hit a temperature of 98. This was during the stretch of very warm temperatures that we had that included two 104 readings as well as a 105 on August 21. One of the meteorological fields I look at to get a feel for the general atmospheric flow is a 500mb height chart. The lines on the chart show the general wind flow as at this height winds blow parallel to the contours. These contours represent lines of equal 500 mb pressure level height. The barbs are showing the wind direction and speed and the color fill is where the strongest winds are located.
Below is last August 13, 2007 8am 500 mb chart.. Notice how the majority of the lines are to the north across the northern US and southern Canada. This means the majority of the country was under a ridge with very warm temperatures. The ridge is indicated by the large closed contour labeled 5940. This is a large anticyclone meaning high pressure and sinking air.
And here is this morning at 8am. Wow what a difference as the ridge is placed over the SW part of the country and is weaker than last year and there is a deep trough for August standards across the eastern US. This has allowed the cooler air to filter towards our region and because we had little sun today and rain most of the day temperatures were held down. This trough was also responsible for the cool Tuesday morning when we hit 56, and for the development of the low pressure that caused a gloomy, cool fall like day here in NC.
Oh and if your out driving tomorrow morning around sunrise, please be careful of dense fog. There are very light winds, moisture left over from today's rain and dry air on top of the moisture that has allowed for the development of fog. Visibilities have decreased to as little as 3 miles at RDU and 2.5 miles at Chapel Hill. We could also see the mercury drop to 58 or 59 in the morning coming short of the record low for August 14 of 55 set back in 1964.
UPDATE 12:05 AM AUG 14:
RDU does not seem to be sending out its observation for midnight but at Chapel Hill visibilities are down to a half a mile. The fog is getting denser out there and I would not be surprised if Dense Fog Advisories are hoisted for the early morning commute.
... Record low Max temperature tied at Raleigh-Durham international
Airport today...
As 500 PM EDT... a record low Max temperature of 74 degrees was set
at the Raleigh-Durham international Airport today. This ties the
previous record for August 13th for the coolest high temperature...
last set in 1996.
The normal high temperature for the Raleigh-Durham international
Airport for August 13th is 88 degrees
...
As far as the rainfall, my hunch on more rainfall further northwest was true but amounts were relatively light except in isolated spots that got under some slow moving showers or locations down south such as Fayetteville.
On August 13, 2007, RDU hit a temperature of 98. This was during the stretch of very warm temperatures that we had that included two 104 readings as well as a 105 on August 21. One of the meteorological fields I look at to get a feel for the general atmospheric flow is a 500mb height chart. The lines on the chart show the general wind flow as at this height winds blow parallel to the contours. These contours represent lines of equal 500 mb pressure level height. The barbs are showing the wind direction and speed and the color fill is where the strongest winds are located.
Below is last August 13, 2007 8am 500 mb chart.. Notice how the majority of the lines are to the north across the northern US and southern Canada. This means the majority of the country was under a ridge with very warm temperatures. The ridge is indicated by the large closed contour labeled 5940. This is a large anticyclone meaning high pressure and sinking air.
And here is this morning at 8am. Wow what a difference as the ridge is placed over the SW part of the country and is weaker than last year and there is a deep trough for August standards across the eastern US. This has allowed the cooler air to filter towards our region and because we had little sun today and rain most of the day temperatures were held down. This trough was also responsible for the cool Tuesday morning when we hit 56, and for the development of the low pressure that caused a gloomy, cool fall like day here in NC.
Oh and if your out driving tomorrow morning around sunrise, please be careful of dense fog. There are very light winds, moisture left over from today's rain and dry air on top of the moisture that has allowed for the development of fog. Visibilities have decreased to as little as 3 miles at RDU and 2.5 miles at Chapel Hill. We could also see the mercury drop to 58 or 59 in the morning coming short of the record low for August 14 of 55 set back in 1964.
UPDATE 12:05 AM AUG 14:
RDU does not seem to be sending out its observation for midnight but at Chapel Hill visibilities are down to a half a mile. The fog is getting denser out there and I would not be surprised if Dense Fog Advisories are hoisted for the early morning commute.
Tuesday, August 12, 2008
Unseasonable Storm System Approaching
First, I just want to mention that this mornings low temperature hit 56 degrees. Another gorgeous day also!...Now onto more important issues, and if your not Meteorologically(Is this even a word) savvy, this post may not be for you.
There is a cool-season like low pressure system that is developing across the southeast bringing widespreads with it to MS,AL, and GA. Forecast models are predicting this low pressure to move south of central NC and off the coast on Wednesday. With this will come increased mid and upper level moisture as well as the chance for rain. Forecast models are predicting widespread 2-4 inch rain amounts across parts of GA,SC, and coastal NC. Areas further north are forecast to receive much less in the range just a trace to .50 with higher amounts in spots. There is a stationary boundary draped across SC and GA as well and it appears that the low will track across wherever this boundary lies. Heres the problem.. this is summertime.. why wouldnt the boundary start to move north once the warm air advection off the coast kicks in overnight. In the wintertime, stalled out boundaries to the south have a very hard time moving northward and a Cold Air Damming event sets up where warm air overrides the cool (or cold) air at the surface. A situation like this may occur tomorrow if precipitation begins to fall into the relatively dry air we have right now at the surface. But is it really going to stop the boundary from moving further north than staying over the coast? Something just does not make sense to me with the scenarios the models show. I realize there is a large vortex over the NE part of North America but its also retreating further north now also.
I learned last year that sometimes model over develop precipitation bulleyes forcing other issues to occur in its grids allowing for misplaced features. Could this be happening? One short-term model that has better resolution(NAM) does have some of these features moving further north than the model that does not have better resolution (GFS) but which will be right?? Normally CAD events have surface pressures 1025mb or higher... right now surface pressure are running 1010-1013 mb.. not that strong.. so that could also be a factor.
I guess what I am trying to say is that I am in no way confident that there will be these huge amounts confined to a region in GA,SC, and coastal NC. This could be totally wrong and be to high, or it can simply be correct and then we here in central and northern NC will not see much at all. I am no way confident in any of these scenarios and apart of me wants to believe there will be more significant rains across a larger area with this type of system. Oh and one more thing, the NAM is much slower with the progress of the low and its track than the GFS and this to me seems more reasonable as the flow right now in the jet stream is for slow progression.
Well thats that. we will see whos right. a computer or human knowledge of the meteorological setup. We will soon find out
There is a cool-season like low pressure system that is developing across the southeast bringing widespreads with it to MS,AL, and GA. Forecast models are predicting this low pressure to move south of central NC and off the coast on Wednesday. With this will come increased mid and upper level moisture as well as the chance for rain. Forecast models are predicting widespread 2-4 inch rain amounts across parts of GA,SC, and coastal NC. Areas further north are forecast to receive much less in the range just a trace to .50 with higher amounts in spots. There is a stationary boundary draped across SC and GA as well and it appears that the low will track across wherever this boundary lies. Heres the problem.. this is summertime.. why wouldnt the boundary start to move north once the warm air advection off the coast kicks in overnight. In the wintertime, stalled out boundaries to the south have a very hard time moving northward and a Cold Air Damming event sets up where warm air overrides the cool (or cold) air at the surface. A situation like this may occur tomorrow if precipitation begins to fall into the relatively dry air we have right now at the surface. But is it really going to stop the boundary from moving further north than staying over the coast? Something just does not make sense to me with the scenarios the models show. I realize there is a large vortex over the NE part of North America but its also retreating further north now also.
I learned last year that sometimes model over develop precipitation bulleyes forcing other issues to occur in its grids allowing for misplaced features. Could this be happening? One short-term model that has better resolution(NAM) does have some of these features moving further north than the model that does not have better resolution (GFS) but which will be right?? Normally CAD events have surface pressures 1025mb or higher... right now surface pressure are running 1010-1013 mb.. not that strong.. so that could also be a factor.
I guess what I am trying to say is that I am in no way confident that there will be these huge amounts confined to a region in GA,SC, and coastal NC. This could be totally wrong and be to high, or it can simply be correct and then we here in central and northern NC will not see much at all. I am no way confident in any of these scenarios and apart of me wants to believe there will be more significant rains across a larger area with this type of system. Oh and one more thing, the NAM is much slower with the progress of the low and its track than the GFS and this to me seems more reasonable as the flow right now in the jet stream is for slow progression.
Well thats that. we will see whos right. a computer or human knowledge of the meteorological setup. We will soon find out
Monday, August 11, 2008
Cannot Get Any Better Than Today
For the middle of August. Today's high temperature was 86, 2 degrees below the normal high of 88. Add the mild temperature to extremely low dewpoints, you get a glorious fall-like (or spring-like) day. So how about tonight.. with continued clear, dry and relatively calm conditions, I expect to see lows in the middle to upper 50s. Take note that the record low for August 12 is 54 set back in 1954 at RDU. We will probably not reach 54, but we could come very close if the winds go completely calm. This would allow the heat from the day to totally escape into space and the temperature drop towards the dewpoint as long as the sky is clear.
Tomorrow looks to be another glorious day with high temperatures around 87. There will be an increase in high cirrus clouds in the afternoon and evening with the approach of a storm system that should affect some folks in the SE Tuesday night into Wednesday. Right now it appears that the most widespread precipitation will occur along the NC/SC border area but this is not set in stone so stay tuned! I will have an update on this tomorrow evening as new data, current observations, and trends are assessed. Regardless, Wednesday may struggle to get above 80 with cloud cover from this system even if it does not rain.
Tomorrow looks to be another glorious day with high temperatures around 87. There will be an increase in high cirrus clouds in the afternoon and evening with the approach of a storm system that should affect some folks in the SE Tuesday night into Wednesday. Right now it appears that the most widespread precipitation will occur along the NC/SC border area but this is not set in stone so stay tuned! I will have an update on this tomorrow evening as new data, current observations, and trends are assessed. Regardless, Wednesday may struggle to get above 80 with cloud cover from this system even if it does not rain.
Sunday, August 10, 2008
2008 Atlantic Hurricane Season Heating Up
Indications are that the next few weeks there will be an increase in tropical cyclone activity in the Atlantic Basin. The Intertropical Convergence Zone (ITCZ) has become quite active with wave after wave coming off the coast of Africa. This time of year also marks when systems, disturbances, or tropical waves (whatever you might want to call them) come off of Africa can make a full track across the Atlantic ocean and affect the Caribbean Islands, the Gulf of Mexico or even the U.S. mainland. The weather pattern is being predicted by several global computer models to begin shifting this week to a more favorable pattern for Atlantic tropical cyclones to develop and make this track across the Atlantic. It is impossible for computer models to predict exact tracks of these storms this far out in advance, but when 3 different computer models (American, European, UK) all hint at several waves becoming tropical cyclones its time to start paying attention. Computer models generally do a good job at sensing larger scale patterns and pattern shifts and the one being predicted is definitely one that supports hurricane development.
The National Hurricane Center already is keeping an eye of 2 of these waves over open waters of the Atlantic.
The National Hurricane Center already is keeping an eye of 2 of these waves over open waters of the Atlantic.
Thursday, August 7, 2008
So Now What?
Not much occurred today across the northern portion of the state, but south of Wake County there has been several rounds of showers and thunderstorms. The first few rounds were severe with large hail and damaging winds. Golf ball (1.75 inch diameter) hail occurred in Fayetteville with nickel to quarter sized hail (.88 - 1.00 inch) in other areas including Harnett County and Pope AFB. Several trees fell on homes in Fayetteville. The radar shown below shows this nasty thunderstorm cell. Apart of me believes it was a supercell and some of the parameters necessary for supercells were there across the southern part of the state. Supercell thunderstorms are capable of producing large damaging hail, damaging winds, and the stronger tornadoes. Image courtesy of WRAL's Fayetteville Doppler. The purple and black colors indicate hail being detected by the radar(High intensity signal).
Here is an picture of some the hail and a tree that hit a house. WRAL says this house was up for sale. Images courtesy of WRAL.
So how come we did not see any thunderstorms with such a big weather change coming? Our winds were coming from the NW direction which is down slope of the higher terrain of the Appalachian mountains. This wind flow tends to dry out the air so it is harder for storms to develop in such an environment. The southern part of the state was in a much more favorable environment with higher low level moisture and was also in a region of high instability.
Now.. the next several days should stay away from the 90 degree mark. Last August, we had one day that did not hit 90. It appears like the next several days (maybe even into the middle of next week) will stay below 90. That is significant because our normal high temperature is 88 for the next several days meaning we will actually have more normal or even below normal weather if we stay below 88 which is certainly possible. There are other variables to discuss that might play a role in sensible weather but I will not get into details. Oh and one more thing..Saturday mornings low temperature should be near 60 and just as a note.. the record low for August 9 is 58.. could come close!
Here is an picture of some the hail and a tree that hit a house. WRAL says this house was up for sale. Images courtesy of WRAL.
So how come we did not see any thunderstorms with such a big weather change coming? Our winds were coming from the NW direction which is down slope of the higher terrain of the Appalachian mountains. This wind flow tends to dry out the air so it is harder for storms to develop in such an environment. The southern part of the state was in a much more favorable environment with higher low level moisture and was also in a region of high instability.
Now.. the next several days should stay away from the 90 degree mark. Last August, we had one day that did not hit 90. It appears like the next several days (maybe even into the middle of next week) will stay below 90. That is significant because our normal high temperature is 88 for the next several days meaning we will actually have more normal or even below normal weather if we stay below 88 which is certainly possible. There are other variables to discuss that might play a role in sensible weather but I will not get into details. Oh and one more thing..Saturday mornings low temperature should be near 60 and just as a note.. the record low for August 9 is 58.. could come close!
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