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30
Sep

Rainy/Cloudy Period South and East Coast First Part of Week

The month of September was another dry one around part of Ga, Al, and SC as the drought rages on there. The good news is the GFS has decent rain amounts finally around the Atlanta area, with long duration showers on the way. But this will come mostly in October.  So far only .73″ has fallen at Hartsfield-Jackson.  Some areas of eastern Alabama through central GA and up to Atlanta and the low country of SC has seen even less than a half an inch in September:

The GFS is adamant that over 2″ of total rains are on the way though, a large widespread rain event is on the doorstep. Most of the Southeast will get significant totals from this through early Wednesday before the system tapers off.  Strong southerly flow from the Gulf will keep feeding showers off and on through atleast early Wednesday as the upper trough that cuts off early in Arkansas will slowly fill in and dissipate.

There is a chance at severe with the actual front in the Gulf states. Already atleast one confirmed tornado in Mississippi and by Monday the front will be oriented north to south, with warm buoyant air being pulled north ahead of the surface low, so shear will be strong for October.  There will be a wedge-front in the Upstate of SC, so north of that boundary will be cooler, very stable air on Monday, before the warm front lifts through the Carolinas into Virginia.  By Tuesday all the East Coast will be in the warm sector, so severe can’t be ruled out.  The CAPE will be the question though and sunshine won’t be very prevalent.

There are big differences now in how and when the next front arrives.  This front will be of Polar Origin and have a near blizzard attached to it in Minnesota and northern Wisconsin on Friday.  Trailing from it will be the strong cold front that is aiming southbound with some unusually cold (for October ) air.  However the GFS and ECMWF are at odds now on when this front arrives.  The Euro wants to create a positive tilt trough, which would delay the front ‘s arrival. The GFS would barrel the front through the MidSouth by Saturday and clear the East Coast on Sunday.  I’m not sure which is going to be right yet. Usually this is the time frame GFS outpeforms ECMWF but yesterday I was questioning whether the front would clear the Southeast since the pattern all last Winter, Spring, Summer and now has been to leave a front stalled out in the Southeast, especially around TENN Valley….and the idea of the ECWMF certainly fits that bill. I’ll watch and see this week for trends.

29
Sep

Been Thinking About….Memphis Rain Chances and Why KMEG Isn’t Going For It

The unfolding weather event across the Deep and Mid-South is a classic example of what makes WxSouth so vastly different from the traditional forecasters out there.  I’ve seen some pretty warm surface temperatures being forecast on both sides of the Appalachians for Monday in particular.  As you know, damming whether in-situ or classic, is a very real phenomenon and we’ve dealt with a couple episodes already in VA and NC this season and another one is on the doorstep.   The GFS model has highs in upper 50’s to around 60 in Winston-Salem, Hickory, Galax and Roanoke, yet the respective forecast offices from NOAA and the TV markets are going for low to mid 70’s in those areas, atleast last I looked.  It makes you wonder, after so many advances in weather prediction, why are some forecasters still going 10 to 15 degrees too high in these situations. In my experience, you usually can’t go low enough in damming forecasts. The GFS the last 3 years has been very good in the damming regions, it’s hard to go far against it.  Probably what we’ll see now is a gradual “stepping down” temperature forecast, but almost always they still don’t go low enough.   This will be interesting this Winter especially when we get into stronger damming situations.

As for why the forecast office out of Memphis is going with mid 70’s on Monday, I think they are banking on the storm going to the south. Yet Thicknesses and the location of a closed 850 low and 5h low still argue for temps probably lower than that. Clouds alone with no precip would do the trick. Yet there too, I think the temps will be vastly lower than forecast.  For several days GFS has been showing a pocket of upper 50s to around 60 in northern Mississippi to the edge of the Memphis forecast county warning area.  So unless  there is strong subsidence and a massive change in storm track, it would be pretty amazing to see anywhere near 75 on Monday…again the forecast is only going with slight rain chances, but once again this is also another area where WxSouth is much different:  Using past patterns and micro-climate forecasting in the Southeast to base predictions in the overall pattern.  Look how often the Tenn. Valley has been ground zero for rain events. Many fronts have stopped around the MidSouth and offered up numerous severe chances and rain events since Spring, Summer and now the Fall.  That pattern continues, yet the forecasters at NOAA went with some models that were going too far south, and using those models explicitly , rather than taking into account just how “troughy” the Mid-South has (and will continue to be).  I’d be willing to bet that KMEG will change the forecast soon, since a major rain event looks poised right for the city and within 36 hours, so a previous forecast of partly cloudy and highs in mid 70’s will become “Flash Flood Watch and Highs mid 60s”.

***edit***just as I finished typing this, the models are coming more north and west, just as I thought they would for most of Tennessee.  It really pays to put some hindsight analogues and rain forecasting experience into the forecast.

28
Sep

Rain Is On The Way

First just want to apologize for not being around the last few days. I got sick from, and this is ironic..the Weather!  and this one was  a doozy…feeling better now though :)  Fall allergies this year have been bad.

The first, of what will probably be many southern stream systems, is now organizing in Texas.  You can see signs of the El Nino by looking at the 200 mb maps, and for the last couple of weeks I’ve been noting it.  This is the southern subtropical jet, but it’s not strong yet, and we still don’t know how strong it gets.  If you’re looking for an action packed snow and ice type Winter, you want a relatively weak to maybe low moderate southern stream…anything stronger will work north with time and bring in warmer air.  Right now it’s too bad for snow lovers that once again, it’s not Winter yet. I’ve said this many times late last Spring and a couple times this late Summer/Early Fall.  Once again, we have a Wintery looking map, with western ridging and confluence in the northeast (50/50 Low) and a southerly displaced low pressure or cyclogenesis, and this one looks like a classic Autumn El Nino Rainmaker.  Below is the 5H Valid Monday Morning:

If this were Winter, a strong Arctic airmass would be located in the Ohio Valley and East Coast with strong damming east of the Apps and an inverted trough likely through the Tenn. Valley, so snow and ice problems would plague the upper Southeast, depending on exact temperatures.  No doubt about it, we’ve had some perfect scenarios several times (about 8 to be exact ) in the Spring and late Summer to now, we’ll just see if this keeps on happening.

Here’s a look at GFS rains through Tuesday morning.  The QPF should be plentiful in the cold sector of the storm, which will be just north of the center of the Low’s track.  The track of the surface low will be from Eastern Texas to northern Alabama and then up the spine of the Appalachians. I’m a little hesitant of the due northeast track so far inland by Monday but since all the models have that track, right now it’s hard to ignore.

The rain begins in Texas soon and slowly spreads east, and northeast reaching the Carolinas and western Virginia by early Monday, possibly Sunday night.  Again, the cold sector on the north side of the low combined with all the steady rains means temperatures on Sunday will struggle to reach 60 around Memphis and the MidSouth, where many areas stay under 65 degrees.

By Monday afternoon, GFS has temps in the 50’s in western Virginia and all of West Virginia as the low pulls north and weakens through the Apps.  This looks like a very beneficial rainmaker for many unfortunately, central to south Georgia and central and eastern Carolinas won’t be the recipients of the rain max, atleast the way it’s appearing now.  If the low pulls north into the Apps, a dry slot usually is quick to appear in SC and GA especially.

The weather looks to get active again right after this storm, by late next week a strong push of cold Canadian air will push strongly south and east, and the snow pack in Canada is (or will be) building rapidly.  There’s strong signs of a major snowstorm around central Canada to Hudson’s Bay.

 

 

25
Sep

Will Update On Weather When Sickness Passes

It’s that time of year, allergy season and I just got back up out of bed after 2 days of pretty hardcore knockout allergy/bronchitis.  Just wanted to post something here that I will be updating just as soon as I can stay up for more than 30 minutes at a time.  The last few Springs haven’t got me as far as allergies go, but the Fall season now does about every year. Hope everybody is keeping healthy and keep me in your thoughts so I can get back to forecasting soon!

Robert

 

24
Sep

Nice Fall Weather…Canada Turning Cold/Snowy Earlier Than Usual

There’s just not a lot going on for the Southeast or East Coast until later in the week. No surprises here as we looked for this kind of calm to follow the recent active pattern. We’re in the typical early Autumn pattern, and usually this is a quiet pattern.  The models do show a weak front that will stretch mostly to the north of the Southeast most of the week, so the baroclinic zone near the MidWest to Ohio Valley is where the rainfall will be this week, leaving the Southeast under high pressure and slowly rising temperature/height field.

Here’s the total precip forecast via GFS through next Sunday night:

 

But I’m looking for the possibility of an uptick in action starting next weekend. Both models show a fairly strong shortwave trough to cutoff near the Lakes or Northeast, and this would slowly bring clouds and rain chances back to the Southeast. It doesn’t look like much yet, but some of this moisture could come from the southern stream (Trop. Storm Miriam) off the Baja, which would get pulled into a southern stream flow.  In fact the flow looks sort of chaotic and murky in about  7 to 10 days, so I wouldn’t trust any models yet , and one of the rules of thumb in Fall Forecasting is not to trust models this time of year.  A “zonal” flow can quickly change to something else.

 

ECMWF Saturday Night:

Comparing ECMWF /GFS for the 10 day average 5H flow here we can see that strong ridging is forecast to develop on both sides of North America. Atleast one of the effects of this type of flow is an increase in cold and snowfall in Canada. Again this is very early, even for central Canada.  By this time, the southern US might be in a stream of moisture from the Pacific or the Baja, but it’s too early to tell for sure.  And most likely as we start October, either a big trough will form in the West, or the East.  It depends on where the zonal flow buckles.  We’ll keep an eye on it and WxSouth will alert you which way it shakes out as early as I feel safe to make the call.

19
Sep

All Quiet On the Eastern Front

There’s not much going on after the big storm that raked the Southeast and East Coast.  Several daily rainfall records were set, as expected.  Now the cooler and drier air is here to stay.  There will be one more reinforcement coming later Saturday as a strong shortwave drops into the Eastern trough.  The best chance of showers will move across Kentucky, northern and eastern TN, western NC and much of VA by late Saturday night, followed by clearing.  The front will be moisture starved and won’t really be able to tap the Gulf.

By Sunday morning, high pressure (pretty strong at 1028 mb) will sprawl across the Midwest, Ohio Valley and start reaching into the Southeast.  So Sunday and Monday mornings will have very cool starts, some 30’s in the mountains, upper 40’s in TN, KY, VA, NC and low 50’s in much of Dixie.  With this kind of Fall-like weather, leaves will start changing soon…in fact, already are high in the mountains.

The next weather event looks like later next week, as east and southeast winds veer in from the Atlantic with time, producing warmer weather and more afternoon clouds.   Enjoy the break while we have it.

 

NAM Saturday Night:

16
Sep

First Gulf Storm of the Season

There’s a few things to note, in addition to my other updates on this event. One big one is how overall the models do agree on a big sizeable rain event, complete with a couple of lines of thunderstorms, possible meso-low somewhere, and another line of strong storms possible east of the Apps chain later Tuesday.  But right now the big question is exactly how this phases or if it doesnt’ quite fully phase.

I’m seeing signs of the Texas system remaining just out of phase by a fraction.  The northern stream might not completely 100% phase with the southern stream and if so, the storm would ride along the mountain chain directly, but there’s a chance the surface low goes immediately west of the Apps. It’s a tough call. Also, this slight difference in models could offer a later time of day for the frontal passage in VA and NC, SC GA, meaning there is a risk of more instability. At the same time, if it does phase, this would pull more of a severe threat further north in the MidAtlantic.  Either way, the big rains are definitely coming, sweeping up from the South, and pulling northeast.  One other fly in the ointment, or subtle change is just how slow the southern part of the front becomes.

Once again, how many times this season already have we seen the southern part of fronts nearly stall or slow down significantly this season (and Summer) in the Southeast. This time, the models are hinting at just that in an unusual location, eastern Georgia and eastern SC.  The NAM , GFS and ECMWF all hint at a secondary development on Wednesday, so this will have to be watched. Normally, this has happened in and around  the Tennessee Valley or Alabama, so we will see if this trends further west (or east ) with time. But the record cold air in TN Valley is most likely still on.  And for the eastern US, by Thursday morning the high should be settled, but once again, if the southern part of the front fails to push totally east of the coast, there could be a quick switch in wind directions, meaning low clouds banking inland for eastern GA and the Carolinas into Virginia.  Again, something to keep in mind for later this week.

By then, another strong front will be driving into the eastern Trough, and once again, more cool air comes south, possibly with showers in KY and TN/VA region. There is a big discrepancy on the modeling for how the western ridge and eastern trough aligns.  Let’s get past the first storm, first.  If this were Winter, this would be a classic “Clipper ” pattern.

Here’s a look at NAM totals, which resembles ECMWF totals. The GFS has an even higher amount in the TN Valley. Get ready for an active Monday through early Wednesday coming up, and I still believe Flash Flood Watches, and eventually warnings will come out of several Southeast states by early Tuesday.  Not just because of the totals listed below, but because of the actual rainfall rates.  The models are showing extremely strong omega and dynamics with a meriodonal flow. This almost always yields excessive rates of rainfall.  There’s a reason why some runs of GFS, NAM and ECMWF have had 5″ bullseyes in different regions.

15
Sep

Major Widespread Southeast Rain Event Looms Large

Lots going on…first, the ball is rolling now and soon the shortwave in Texas will amp up just enough to be a nice little low in its own right, but it’s going to merge with a larger long wave and become part of a powerful +PNA pattern…and this pattern will stick a while.

The GFS has shifted its heaviest of the heavy rains through the Tenn. Valley, and considering how last Winter, last Spring and this Summer played out, it’s very possible.  But this time there is excellent 850 wind advection right into north GA and the Southern Apps, so I expect a max of rainfall there from this event, where some areas will top 5″ when it finally ends later on Tuesday.  The front will sweep off the east coast by early Wednesday morning, setting the stage for a much cooler airmass, the coldest of the season (and since last Spring) to cover the Mid-South.

Here’s a look at the latest GFS rain amounts. Overall, this looks like a good event, with a solid warm front developing across Ms, Al, GA early Monday and working north, before fully phasing (not to mention the possibility of a triple point low in western Maryland by later Tuesday).  This could be a very big deal with flood watches being posted soon in some areas of the Southeast and MidAtlantic.

Next up, the question will be just how cold will it get by Wednesday and Thursday mornings?  I have looked at some old records and upper maps, and one year that stood out was 1981.  So here’s a look at Sept 19, 1981, and the official records. You’ll notice the 850’s are very comparable, especially in Tn/Ky/Va where the models have it dropping to +3 or even +2 at 850..thats very cold for September. Both GFS and ECMWF have this.  Combined with surface high sitting over Memphis by Wednesday morning, I think the Tennessee Valley stands  a decent shot at achieving atleast a TIE on the records, and possibly a couple of sites actually breaking the record lows. 

Current Prog on Left, 1981 Prog on Right:

 

 

Just for kicks, this looked interesting from the ECMWF…so far, I’m doubting we’ll have quite this much troughing in the Southeast around days 8 through 10, but the models mostly keep a big trough in the East for a while.

If this verifies, September will end up above normal in rainfall over much of the Southeast…as Sept. is usually one of the drier months.

 

 

 

14
Sep

Possibly Record Cold in Ohio Valley/TN Valley/Southeast Next Wednesday

All models still agree on building a huge western ridge, thanks to a strong Aleutian low pumping up heights out west. This will aim the jet due south along the Rockies later Sunday and begin to scoop up the low in Texas.  This low will deepen and go negative tilt on Monday and into Tuesday as it rockets up the East Coast or Apps (possible severe from Alabama to New England), and then very cold air for September will rush in. As a matter of fact, some snow is still likely on the backside in the upper Midwest early next week.

Aloft, this setup looks pretty fascinating if the low in Texas fully phases with the northern stream, which is very possible to likely right now.  If this happens this will literally plow the cold front through the Southeast, beginning in the Tennessee Valley and crossing the Apps later Tuesday, which will set the stage for a possible record cold airmass early Wednesday over a large region of the East, including the South.  Right now I’d place the best chances of maximum radiational cooling in Tennessee as the High Pressure sits there by Wednesday morning.  Lows of 30s is possible in some areas.  The GFS is adamant on bringing down+3 at 850 all the way to central Kentucky…again, for September this is absolutely amazing. It would be a strong cold shot in October.

The active flow continues for a while, but eventually the models show a big closed high developing in the northwest part of Canada, and builds a nearly 1040 mb high there…again, pretty incredible for so early in the season, but by then, the flow could have changed to make the Southeast about average on temps, but remaining cold and snowy in Canada.  In fact, later next week and the weekend looks very cold and very snow in central, to southeast and east Canada thanks to a strong negative NAO and and airmasses that are well below normal.

A look at the developing low Monday night in the Southeast:

12
Sep

Been Thinking About…

I’ve been thinking about the subtle things that models sometimes show (or even don’t show but should!) and how run to run changes often prompt the National Weather Service, HPC and other Weather Forecasters to change their forecast. It happens often, as I’m sure you’ve noticed.  One such thing could be our Sunday Forecast.  GFS has some northeast winds at the surface, southeast winds aloft, and enough moisture to generate rain in east TN, west NC/SC and possibly northeast Georgia and southwest NC, basically the southern Appalachian region.  This rain could actually turn moderate late Sunday thanks to good divergence ahead of the Texas shortwave and since there is good confluence and a 1025 high in New England, this could equate to a decent Cold-Damming event for the lee side of the Apps.  Actually this is pretty common in October or any Fall month, given this 5H look, yet most forecasters are willing to wait until models explicitly begin showing some rain before pulling the trigger on forecasting rain.  Maybe I’m making a big deal over nothing, and to be honest it’s going to be localized, but still I think its worth a mention.

Also, I’m seeing differences now in the western ridge and its orientation for Sunday, in addition to seeing more strength shown in the southern stream split.  Just look at the GFS panels below.  The left panel is yesterdays run, the right is todays run.  Already a 120 to 130 knot jet is showing up in western Canada and is aimed due south. This will help dig the trough and s/w toward the Plains by next week, pulling in pretty cold air for September, and likely some snow in the Dakotas or Minnesota..which is quite early yet.  Also, the southern jet shows more energy than just 24 hours before.  Again, noticing little things like this could give clues to the all important Winter Forecasting.  Look how often the Southeast has had precip events show up, without much warning from the models. If you know how to read subtle cues and nuances rather than taken the models for explicit panel or even explicity ensembles, you can build a better, more accurate forecast. That’s always been my primary goal at WxSouth…to give plenty of notice and advance warning on the little as well as big events.

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