Analysis on Fri-Sat storm system and,,,,long range.

[Allexpert Mike]

Analysis on Fri-Sat storm and beyond ----------


Saturday- Our next rain feature in the Middle Atlantic and Northeastern US as a upper level feature moves toward us.

Quick synopsis- A mid to upper level storm system associated with the s/w trough will be on a neutral axis as it comes eastward. As it comes closer it will form a secondary low off Virginia. As the transfer occurs it will then ride northward bringing heavy rains and severe storms.

Forecast track- As the s/w trough takes a turn from a pos. tilt to a neutral axis it will then take a slight neg. tilt as it triggers off the secondary low. The upper level jet will be rather weak but it should be drawn northward phasing with the northern stream therefore allowing a track northward from VA.

Severe WX threat for Friday-

I like the SPC threat area and in brief here it is:

Mississippi, Alabama, Georgia, Tennessee, Western NC, and Western South Carolina.

As the cold front progresses eastward associated with our upper level low will see some nice dynamics come together to produce some severe weather. Capping will be very weak and will easily erode with sufficient lift and strong instability. The question right now is after the warm front passes with moderate-heavy rains,,does the sun come out and we get some nice adiabatic and diurnal heating leading to nice thermodynamic instability. Or does it remain cloudy,,,and it will still lead to a nice outbreak of severe wx but the sunshine if any will only contribute to the threat. Lower levels are also looking ominous with strong LLJ between 35-45KTS with strong WAA and isentropic lifting. Upward Vertical Velocities will be very strong as the vortmax associated with our upper level low will extend moderate to significant PVA down to the threaten areas with a nice MLJ with wind speeds of 45-55KTS helping the growth of cumulous clouds. Upper level flow is in the weak range as the jet max will be around 60KTS. With the absence of a strong flow aloft all other levels will have strong wind fields. With that said there will also be nice speed shear and vertical shear to help in the aid of development with supercells. Directional shear will almost be non existent if models are right, but even with a little directional shear the steep mid level lapse rates could make for strong rotating updrafts and tornadoes will me a major threat, but right now isolated tornadoes, large hail, and damaging winds are the threats. Some model guidance shows lift indices as low as -9C. SFC dewpoints will be very high, mostly in the range of 60-65°F, however some areas especially in the southern sections of the threat areas were dew points could pass the 70°F mark. H8 dew points also high in the range of 12-15°C. Southern areas of the threat zone will again see the highest SBCAPE values between 2500-3500j/kg.

Saturday the severe threat will move into the Carolina's and possibly Southern Virginia. More detail on this later.

------------Back to rain event-------------

As the secondary low forms there will be a wide area of nice low level and surface speed convergence with the diffluent flow aloft. The low level and surface convergence will lead to upr air divergence and will intensify the area of low pressure. But the deepening process will be gradually and not rapidly. UVV's also will be strong as we get some nice PVA and where the low level convergence is strong. We will also see some nice overrunning precipitation as a cyclone form the north and a mid level ridge moves in from the West will produce some CAA and with the strong waa we could see a nice widespread area of rain, and RH fields will also be in support of a widespread event as values will range from 90-100%.

For rain totals I'm leaning towards the higher totals and right now the best guess would be probably (for major cities DCA-NYC) between 1.0-1.50". Rainfall amounts will probably be highest inn the major cities rather than the other areas to the south, with the exception of the areas who will receive strong to severe storms which will enhance totals. The reasoning for the higher totals to the north of Central VA is once our coastal gets kicking will see an increase of ATL advection. Severe threat for Saturday could extend as far nroth as extreme S. DE. And wouldn't be suprised to see isolated strong to severe cell north of S. DE. As the Low pressure system moves eastward it will run into some ridging in the ATL and will create a strong pressure gradient leading to strong winds particularly from SC-E NC-E VA. And as the Low moves on north will see a strong easterly flow out ahead fof it leading to some tidal flooding. Also with the -NAO sig. will see a north to south orientation making the track of the low more certain with northerly movement once it develops.

LONG RANGE-----8-15 days-------

With good ensemble agreement will see the return of the positive phase of the PNA with the nice ridging over the Western States and troughiness in the Eastern US. With the AO forecast by ensemble agreement will see a weak-mod negative meaning nice ridging over the poles and perhaps another period of below average temps. But we still have time to monitor it and it won't be too drastic. Like always GFS shows a slow moving cold front in the day 8-10 range, but looking at the NAO sig it looks positive therefore more of a W-E orientation therefore a normal-quick moving front. The GFS shows a cut off high pressure system in the ATL which is looking like an outlier as ensembles clearly go against it.

[Skywatch_NC]

Excellent forecast/analysis as always Mike! 8)

Keep up the great work, Wxbuddy!

Eric

[cycloneye]

As Eric said excellent forecast and anaylisis.

[ColdFront77]

Very well in-depth forecast, Mike... the more analysis we get the better our learning of meteorology will be. The tend not to read long posts, but I try my best when they are interesting/worth reading.

Even with what we already know about meteorology, we are all still learning.

[Amanzi]

Great forecast Mike! Thanks

[VAWXWatcher6]

SPC has the 5% chance of severe storms all the way north to Central Virginia on both Friday and saturday but i see only a very small chance of storms in Virginia tommorow becuse we be north of the warm front most of the day with Highs in the 50s to mid 60s. Saturday looks like a better chance Highs mid 60s to mid 70s just depends on how much sun we get. I see best chance of any storms south of Virginia but that is just what i see right know. This is likely to change!!!!

[Rainband]

Great Job!!!!!!

[Allexpert Mike]

Thanks everyone!


SEVERE OUTLOOK FOR SATURDAY
AS our main area of Low pressure weakens a little it will trigger off a secondary low off the Middle Atlantic Coast around Virginia. A cold front will extend down from the secondary low and along the front several dynamics will come together to produce some severe weather. The best low level convergence will be around the secondary low and that will lead to upr air divergence allowing the low to deepen and organize and move north as the -nao sig. shows nice ATL ridging along with a return flow from a anticyclone off the Eastern Canada coast leading to a strong pressure gradient and basically just a mess for Northern Northeast into New England with mix precip and rain. And just rain, no thunderstorm development, the thunderstorm development will be along the cold front extending from the system moving along the coast.

Southeastern US-

The flow aloft will be diffluent and rather weak with a jet max around 70KTS. As the vort max moves eastward will see strong PVA with a strong MLJ. With a significant cool pool of air at H5 will see an increase threat of large hail and a decrease in CAPE values, SBCAPE will be between 500-1000j/kg through a good part of the threaten areas. The very weak cap will erode with strong instability, however instability won't be that impressive as cloud cover will come in early in the mid to late morning hours preventing diurnal heating. This event will take place around noontime through the early to mid afternoon hours. The TT index will be between 45-50dC and that will be one of the main contributors to the strong instability to erode the weak cap. Directional shear will be very weak and with weak shear and a rather weak lifting mechanism will see marginal size hail. Main threat is for damaging winds and isolated tornadoes. 1KM helicity values should be pretty sufficient for some weak tornadoes with values of 150-250m^2/s^2. Lower levels show nice low-level moisture with strong WAA and nice isentropic lifting.

Northeast-

As we've said before just looks like a heavy rain event with strong LLJ up to 60KTS and with nice low level moisture along with great wind fields throughout the levels will monitor it closely for the threat to be extended northward towards the major cities (DCA-PHL). As new model data comes in will continue to monitor the threat.

After day 3- As our upper level low in the PAC continues to come closer to the Coast it will move very slow as its associated with a Rex block. It will continue to pour in moisture and a organized area of low pressure will develop. Since will be in a split flow pattern it will ride the northern branch and will extend a cold front down through the Central-Eastern US and we could be looking at more severe weather.

[Stormsfury]

Allexpert Mike, I think you have my area of responsibility pretty much covered, good job...

[grentz7721]

It was raining all day today, Mike. No thunderstorms today though,
but was in today's forecast. One Question, Does Myrtle Beach have any
chance for severe weather?

[Allexpert Mike]

It was raining all day today, Mike. No thunderstorms today though,
but was in today's forecast. One Question, Does Myrtle Beach have any
chance for severe weather?

Severe weather is a pretty good bet in South Carolina,,,,Myrtle Beach, SC stands a descent chance of getting in on some severe weather. Flow alof twill be moderate,,,,the eta shows nice jet streak to enhance flow aloft over SC are to up to 70-80KTS. We will also see nice PVA as the vort max moves to the north of us allowing an increase of positive vorticity advection wiht nice mid level flow. UVV's will be moderate to strong along with the nice ll convergence along the frontal boundary. Capping willl erode by noon time as strong instibality and good lifting will allow for convection to fire up. Significant cool pool at H5 will increase the threat for some large hail. Main threats are for large hail, damaging winds, and I can't rule out a chance of a isolated tornadoe.

[grentz7721]

Myrtle Beach had a few thunderstorms Today, Mike. Myrtle Beach
was under a Severe Thunderstorm Watch Until 5PM today as well.

[VAWXWatcher6]

Too many low clouds and not enough sun keep us up here in central va from getting severe storms today and not many storms, most of the storms been south south of richmond in virginia...

[Stormsfury]

Quite a few hail reports today from South Carolina, and also while I was at work, a bolt struck just outside the James Island P.O. --- I mean, flash and boom .... glad I wasn't outside ATT ...