wxmeddler

The 0z HRRR is the exact failure mode that seems most likely, the crapvection from the west hangs on and is enhanced east of the mountains by the synoptic lift. By the time the low ejects, the moisture is wiped.

The failure mode is for sure if the squall in the TN Valley right now stays together over the mountains and wipes our moisture at 11AM. And the associated low clouds hang around with it.

My thoughts align with Mark's (surprise surprise). Any cell that breaks out ahead of the line should be taken with caution, but the squall line damage should be fairly localized. This will NOT be a derecho situation where there is widespread 60-80 mph gusts. The 60-80 mph gusts will be localized into 1-3 mile wide swaths. Parameters I'll be watching is MLCAPE, 3CAPE, 0-2km SR Winds

I can see early dismissals for places in central VA, even far southern MD, but don't see it for the capitol region. The squall should be late enough in the day not to matter for places along I-95. Even so, the safest place for kids would be in schools. The issue is panicked parents rushing to pick up kids and getting caught up exposed in the parking lot.

Hi there, I got tagged that I was quoted up here; Yeah, the write up was for the Mid-Atlantic. I don't see the isolated pre-squall tornado threat getting up into Southeast PA. The hodographs are more linear compared to down in VA and So. MD. The squall will still be dangerous with embedded supercells.

When I bought my house, one of my asks for the realtor was no trees that could reach the house. Needless to say it was a hard find, but we did end up finding one! It also has a brand new metal roof, so the rain sounds fantastic! What I didn't notice is that a neighbors gutter goes right into a low spot near the house, so... that's my next worry.

FOLKS Exceptional Synoptics call for exceptional care, and in the equinox seasons if you've got big numbers on the cold side, you should be prepared for big numbers on the warm side. This system is no exception. CAM guidance from this morning's 12z runs show a variety of scenarios and evolutions. When in doubt about storm mode or coverage, falling back on the synoptics is usually the best forecast. In this scenario, the synoptic evolution is clear. A large mid-latitude trough exhibiting two distinct mid/high level wind-maxima rounding the base of the trough is creating a primary low through the upper mid-west while the secondary (later) wind maxima emerges over the southeast and quickly ejects through the Mid-Atlantic. Ahead of this second wind maxima large scale ascent through upper-level divergence will cause mass flux response from the Carolina's northward into southern PA. As the secondary wind maxima / embedded trough tilts negative an area of lower pressure will develop east of the blue ridge in the Piedmont region of North Carolina and quickly traverse northward. Along this embedded low, guidance that has taken this solution has backing wind vectors in the lowest 1km relative to the Bunkers right motion. This produces large curvature hodographs in the lowest 1-2km's followed by a storm relative weakening in the mid-levels, with exceptional ventilation in the upper levels. The kinematics from the Blue Ridge to about the US301 corridor from North Carolina to the M/D line in our region are exceptional. Storms that form ahead of the main pre-frontal line that exceed 30kft tops or start producing significant amounts of lightning will be capable and likely will produce long-tracked significant tornadoes. A violent (EF-4) level tornado cannot be ruled out either if instability increases due to pre-frontal warming / breakout sunshine. Storm motions will exceed 50kts and while potentially photogenic, will be un-chaseable except for those who position themselves ahead of the storm 20-30 miles in advance. The highest risk will be from about noon in North Carolina Piedmont to about 7pm in Southern Maryland. Storm coverage in this area ahead of the main pre-frontal trough / squall is uncertain and will have to wait till tomorrow morning to see what debris / storm outflow from the ongoing convection off-shore of South Carolina brings northward. For the pre-frontal squall line: Embedded supercells that produce narrow corridors of 60-80 mph winds seem likely in RFD regions. Especially storms that form ahead of the squall line and get absorbed / merged in with the squall line have the potential to produce strong gusts. Power outages in these narrow corridors (3-5 mi wide) could be substantial. The lack of leaf out on the trees up our way will be beneficial, still, the strengths of the gusts in the enhanced regions will be enough to down branches onto lines. Given the unseasonable cold of the airmass behind the cold front, warming shelters and means of finding warmth Monday into Tuesday as power is restored will be of concern. If I have time this evening, I'll do a historical perspective and get some analogs.

I'm fairly well convinced that the recent SPC changes have fundamentally altered the way higher percentages are given out. So much so that most of the SPC climatology is going to have to be tossed / step-changed. Arguably for the better though! SPC Forecasters have repeatedly said that the % were under-done due to the way the rubric was constructed. That's why things like NadoCast and PPF's were always markedly higher. New 30%D3 is the old 15%. And that's good! I think it better conveys the actual risk. It's just going to get some getting used to.

Not everyday you get a CONUS wide mid-latitude trough break in the center of the country. Exceptional synoptics call for exceptional caution.

Was outside in a wide open field helping a student setup her research project... felt like I was back in North Dakota today! Fun times!

Thundersnow reports confirmed by GOES GLM. Over NE AA Co at 1:56p EDT

Now 1/4mi Vis and +SN at BWI. NYG (Quantico) too!

Half-Mile Vis at BWI

If you're on the eastern shore the bay being 40 deg is killing you... was great yesterday when it was cooling you off by 20 deg!

Nice big flakes. Even sticking to the grasses in the lowlands of College Park.