#vawx A Marginal Sunday

Of course the SPC has now spilled a Marginal Risk across Virginia for Sunday:VA_swody2

The Piedmont is covered by a 2% tornado risk tomorrow, giving rise to this Marginal outlook.

The SPC wording, however, fits with my reading of the setup in that “conditional potential” pretty much sums it up. Checking out the short range convective allowing models casts doubt on anything like certainty with only one or two models showing any robust convection. I can’t find much – if any – upper level support to fire storms over the Piedmont nor does the cold front itself seem do much with the available moisture.

So far nothing has changed my mind about staying home (or least very local) tomorrow. If storms do fire the forward speeds still favor a “watch and wave” vs. a true chase opportunity. Coupled with the wisdom of self-isolation during these trying times it’s likely that Sunday afternoon will only involve haunting the radar and peeking outside for glimpses of anvils.

#vawx Updates on Sunday

With the weekend forecast coming into better focus I doubt that I’ll go out chasing. “Da Wedge” will be fully entrenched on Saturday across Virginia so that’s a no-go. A cold front crossing the mountains on Sunday would seem to hold some potential for severe weather but here’s the NAM forecast sounding for Lynchburg at 18Z (2 pm EDT), just before the boundary reaches that location:

2020032706_NAM_060_37.32,-79.16_severe_ml

I’ve circled (in white) one problem area, an inversion just above the 850 mb level. That’s a pretty stout low-level cap to overcome. Also – as one might expect for late March – storm speeds are in the 60 mph range. So IF a storm goes up along the front it’ll be “watch it go by” vs. “let’s give chase”.

So at this juncture this setup isn’t ballistic enough to entice me to head out especially given the overall wisdom of self-isolation during these trying times. I’ve heard all sides of the chasing argument (“I’ll be in my car so I’ll maintain social distancing” vs. “Keep your body and its potential coronavirus infection out of my hometown”) and I’m coming down firmly on the side of staying home. IF there are storm setups in the next few weeks that pose a real threat to public safety I’ll certainly reconsider given that I provide ground truth to a local TV station. But hopefully by then the overall health situation will have improved.

#vawx Sunday now looks like a possibility

Saturday still looks capped but I’ll continue to keep an eye on it. Meanwhile given several more model runs it now looks as if Sunday will be this weekend’s chase day. More recent numerical model solutions have begun to analyze an approaching cold front crossing Virginia during the afternoon hours Sunday, several hours later than earlier runs had indicated. (BTW, models don’t “slow down” weather features…they scramble to keep up with the actual parameters Mother Nature throws at them.)

Here’s a GFS analysis of the 0-3 km EHI for 18Z (2 pm EDT) Sunday showing decent instability and shear along and east of the U.S. Route 29 corridor:

GFSMA_con_3kmehi_108

Now here’s the GEFS (ensemble) forecast of the supercell composite parameter at the same time:GEFSMA_con_meanscp_108

The forecast sounding at Danville at 18Z looks pretty linear with not a lot of directional shear which would indicate a squall line:2020032506_GFS_108_36.65,-79.21_severe_ml

However given the strength and direction of the 850 mb winds I’m anticipating a lee trough forming along or east of Rte 29. Here’s a representation of the surface conditions at 18Z with my interpretation of a lee trough:

Lee trough 21Z Sunday

Enter a caption

So Sunday is definitely on the chasing horizon. We’ll have to see how things look as more models come into range, especially the WRF and HRRR convective allowing models.

#vawx Could there be an end-of-March chase setup?

So here we go again with a late March chase potential. This upcoming weekend looks at first glance like it will have the parameters for severe weather here in the Virginia. Here is the 0-3 km EHI map per the GFS model at 21Z Saturday:GFS sfc map 21Z Saturday

A warm front (roughly aligned just north of the I-64 corridor as delineated by the black line) is forecast to drape across the Old Dominion with favorable shear and instability south of it. For comparison here’s the Euro forecast for surface temperature and wind three hours later (0Z Sunday):Euro sfc map 0Z Sunday

The Euro analyzes the warm front further south than the GFS’s solution, showing the boundary along the U.S. Route 460 corridor.

A couple of problems arise upon checking forecast soundings for Saturday afternoon. First, both models show warm temperatures aloft with the Euro’s solution being much stronger. As an example the Euro’s 700 mb temperatures are 10-11 degrees C south of the warm front, a decently strong cap for Plains chasing and almost insurmountable here in Virginia. The GFS shows weaker inversions at a couple of levels above the surface.

Secondly there is little indication of a lifting mechanism. The warm front certainly provides a shear zone but looks almost stationary with little lateral movement to provide lift. Moreover there is no definable upper level mechanism which could trigger convection late Saturday afternoon into the early evening hours.

So at this time Saturday’s setup doesn’t look enticing enough to plan a chase. That could change between now and then but the question still arises whether it is advisable to get out on the roads given current needs to restrict movement. That’s something I’ll be debating until the last moment before each and every potential chase this spring.

#vawx The “day before the day” may make another appearance

I’ve been focused on the chase potential for Friday, with a decaying squall line/outflow boundary due into the Virginia Piedmont in the late afternoon hours. At the moment there does appear to be a slim chance of some robust convection across Southside near the U.S. Route 58/U.S. Route 29 corridors before dark. But with a positively tilted upper trough enabling the main energy to slide well north of my chase area tomorrow may be an iffy proposition.

However…one mustn’t ignore the “day before the day”. This – Thursday – afternoon the tail end of a warm front will be creeping northward across western parts of the Old Dominion. Here’s the RAP model’s interpretation of MLCAPE (>1000 j/kg) and 0-6 km shear (40+ kts) at 5:00 pm today:RAPMA_con_cape180_012

Now for the sounding just south of Roanoke at the same time:2020031909_RAP_012_37.14,-80.03_severe_ml

And for comparison here’s the HRRR simulated reflectivity at 4:00 pm as the eastern edge of the warm front approaches that environment:HRRRMA_prec_radar_008

So perhaps today may offer a relatively local chase/spotting opportunity. Hmmm….

#vawx Potential for storms still exists on Friday

Here on St. Patrick’s Day the models are still hinting at a chance for severe weather on Friday March 20th. A check of the NAM, GFS, GEFS, GEM, and ECMWF solutions all seem to point to several common threads:

(1) Dew points in the 60s pushing into Virginia east of the mountains.

(2) A lee trough setting up along the U.S. Route 29 corridor which could provide the lift needed to fire storms.

(3) A moderate shear regime with CAPE values in the several hundred j/kg range.

With that in mind here’s a NAM forecast sounding near Danville:2020031712_NAM_081_36.78,-79.26_severe_ml

And here’s a Euro sounding from the same vicinity:ecmwf_full_2020031700_096_36.75--79.25

700 mb vertical velocities look better north of I-64 but the instability seems to be a bit stronger in Southside Virginia.

Given these parameters I’d expect the SPC to issue a Marginal Risk in their Day 2 convective outlook on Thursday for the Piedmont. The question will be whether it’s enough to tempt me to chase given the health concerns during these trying times.

#vawx A Pi Day peek ahead

Welcome to Pi Day 2020 (3/14). Per the last blogpost there was indeed severe weather across parts of KY/MO/AR on Thursday as shown on the SPC storm reports graphic:200312_rpts

However there were only two tornado reports – both in MO – and both surveyed at EF-0 strength. Fortunately the already traumatized folks in TN were spared damage from this system.

The long range SPC discussion centers around an upper level low tracking across the nation next week with the potential for severe stuff here in the Mid-Atlantic late in the period. Of course this far out the models don’t agree very well. However both the GFS and the GEM models show moisture return into Virginia on Friday March 20th with dew points exceeding 60 degrees (F). And if one can suspend incredulity somewhat a peek at GFS forecast soundings for Friday afternoon looks like the following:

Fri Mar 20 sounding near LYH

Near Appomattox VA

And this:

Fri Mar 20 sounding in Botetourt Co

Botetourt county, just north of Roanoke

Again, it’s waaayyyy too early to put any stock in these deterministic solutions but it’s worth keeping an eye on. After all, next Friday will be the first full day of astronomical spring!