midatlanticweather

I asked Chat GPT - Here is what it thinks (LOL) Waste of time, but I could not resist! ------------------------- I've noticed the same thing this warm season, especially across the Mid-Atlantic. The NAM (both 12 km and 3 km Nest) has had a habit of looking terrible beyond about 6–12 hours for convective days, then suddenly "finding" storms in the final few runs. A few reasons: It's heavily driven by its own physics The NAM tends to overmix the boundary layer during the day. That lowers dewpoints too much. CAPE gets underdone and convective initiation is delayed or suppressed. Small errors explode in summertime July convection in Virginia often depends on: a leftover outflow boundary a weak differential heating zone a tiny vorticity maximum terrain circulations along the Blue Ridge If the model is off by 20 miles or an hour on any of those, the entire simulated radar looks different. Data assimilation doesn't capture morning boundaries well Once radar, satellite, surface observations, and morning soundings are ingested, the 6–12 hour forecasts improve dramatically because the model finally "knows" where the atmosphere actually is. The FV3-based CAMs have generally been outperforming it This year I've found: RRFS HRRR WoFS (short range) even the HRDPS at times have handled scattered convection better than the NAM Nest. The pattern we've been in is especially unfriendly We've had a lot of: weak northwest flow pulse convection little synoptic forcing abundant moisture That's almost the worst-case scenario for deterministic CAMs. The difference between "nothing" and "10 storms" can literally be one county's outflow boundary. For Loudoun County specifically The NAM has repeatedly shown this sequence: 24–36 hr: mostly dry 18 hr: isolated showers 12 hr: scattered storms 6 hr: widespread afternoon convection Reality: the 6-hour run ends up being closest. For your forecasting, I'd probably trust the NAM mainly for: temperature trends dewpoint trends low-level winds large-scale forcing ...and lean much more on the HRRR/RRFS for actual storm placement once you're inside about 18 hours. The other thing I've noticed this summer is that the ECMWF AI (AIFS) has often had a better "feel" for whether the day would end up active than the NAM did 24–48 hours out. It obviously can't tell you exactly where a cell will pop, but its broader convective signal has been surprisingly consistent.

Slight risk Saturday. Guess it depends how much clearing we get and heating ahead of the energy and way too many unknowns. ZCZC SPCSWODY3 ALL ACUS03 KWNS 160734 SPC AC 160734 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0234 AM CDT Thu Jul 16 2026 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE OHIO VALLEY INTO THE MID-ATLANTIC... ...SUMMARY... Severe thunderstorms will be possible across portions of the Ohio Valley during the late afternoon and evening hours before moving southeast toward the Mid-Atlantic overnight. Additional strong-to-severe thunderstorms will be possible during the afternoon across portions of the Mid-Atlantic. ... Synopsis ... The CONUS-wide mid-level ridge centered over the north-central Plains for much of the past week will have retrograded west by Saturday and be located across the US and Canadian Rockies. Strong mid-level westerlies will persist on the ridge's northwest, north, and northeast periphery. Embedded within the westerlies, a series of short-wave troughs and smaller-scale vorticity/speed maxima will move across the Great Lakes and Northeast. At the start of the forecast period, the main short-wave trough will be located across central Ontario, with its associated jet streak located across the Upper Midwest. This feature will dig southeast on Saturday, ending up in the vicinity of northern New England by Sunday morning. Ahead of this main wave, the 20260716/00 UTC guidance suite shows multiple speed/vorticity maxima moving through the west-northwesterly flow, each of which will be capable of aiding the development of scattered elevated thunderstorms. At the surface, a weak surface low should develop Saturday morning across southern Ontario/the northern Great Lakes. This low will slowly deepen during the day as it digs southeast, reaching upstate New York by evening. Ahead of the surface low, southwesterly low-level flow will transport a very moist airmass northeast into the Lower Great lakes, with 70F surface dewpoints possible as far northeast as western New York. To the southwest of the surface low, a surface cold front will serve as an initiating boundary for thunderstorms during the afternoon. An unstable and strongly sheared airmass will be in place by later afternoon across Ohio northeast into western New York. As thunderstorms initiate along the front, large hail will be possible before thunderstorm outflows eventually congeal into one or more linear clusters posing a threat for damaging winds. This line of storms will push south and east during the evening and overnight with a continued threat of strong, damaging thunderstorm winds. Farther southeast across the Mid-Atlantic, most model guidance indicates the development of a surface trough to the east of the Appalachians during the late afternoon. To the east of this trough axis, temperatures will warm into the 90Fs, although there is some uncertainty how far north the hot boundary layer will extend. Given the presence of this surface trough and strong diurnal heating, several clusters of thunderstorms will be possible during the afternoon, especially if any of the previously discussed vorticity/speed maxima can interact with the low-level trough. Strong, damaging winds will be possible with any thunderstorm complex during the afternoon. Additional severe potential will also exist overnight as the remnants of the convection along the cold front approaches the region. Gusty thunderstorm winds will be the likely threat with these storms. ..Marsh.. 07/16/2026

Anyone have thoughts after 12z runs?

10:50 AM in Purcellville --> 89.9/79/106 --> It is thick outside - a wall of steamy madness!

LWX Discussion had some good Climate Summary data

https://x.com/bam_weather/status/2069093088639811884?s=20

Cell north of Culpepper looks interesting.

Mesoscale Discussion 1091 NWS Storm Prediction Center Norman OK 0202 PM CDT Thu Jun 11 2026 Areas affected...the Mid-Atlantic into southern New York and southwestern New England Concerning...Severe potential...Watch possible Valid 111902Z - 112100Z Probability of Watch Issuance...40 percent SUMMARY...Scattered thunderstorm development is expected this afternoon across the mid-Atlantic northward into southern New York and southwestern New England. Severe wind gusts and hail are possible with the strongest storms. DISCUSSION...Some deeper convective attempts are underway this afternoon across portions of the mid-Atlantic, particularly in southern New York as of 1900z. This development is occurring in a warm, unstable airmass with surface temperatures in the upper 80s and lower 90s F and MLCAPE values around 2000+ J/kg. The 18z ALB/Albany, NY sounding sampled the northern periphery of this airmass (along the CAPE gradient) with 0-6-km shear of 24 kts. This has supported some sporadic, more organized thunderstorm development recently. As the afternoon progresses, diurnal heating should support additional thunderstorm development across the region. Furthermore, a mid-level impulse in eastern OH -- influencing the ongoing convection in WW312 -- will continue moving eastward and should provide additional support for convective initiation and maturation. Bulk shear is expected to remain generally in the 15-25 kt range which, amidst forecast large MLCAPE around 2500-3000 J/kg, will promote strong updrafts capable of producing wind gusts and hail. Uncertainty remains as to how much convection will develop and coalesce/strengthen in the short term, but trends will continue to be monitored for possible watch issuance this afternoon. ..Flournoy/Gleason.. 06/11/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...OKX...ALY...PHI...BGM...AKQ...CTP...LWX... LAT...LON 39937855 42097738 42657579 42777436 42337326 41237290 40177310 37717495 37397648 37777765 38937842 39937855 MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

94 .. HI 108.. DP 78... Worst weather

Gfs wants to end the drought in the extended outlook. Tropical moisture could try.. I know it's way out and not right.

38.4 degrees for the low. No Frost but pretty cold

86.5 today was quite hot honestly. Not humid though. Watching the storms/rain progress slowly south.

Sleet and snow now in Purcellville. Mainly sleet Shall move to Discobs since it is not severe related from now on

That is impressive! almost 30 degrees in 2 hours!

Down to 36 here in Purcellville. Windy and rainy

Ominous temperature out right now!

24.4 for a low. 25.5 currently

Snow now and down to 36.

Basically, had a heavy shower that made things go to all sleet and even some slush balls, but as soon as it got lighter it went back to rain with some sleet and now just light rain with an occasional pinger. So, type of precip seems rate dependent which makes sense. Close to 38..was a bit cooler in the heavy precipitation

Rain mixing snow and sleet. 38.1

41.9 here in Purcellville. Temp dropped 2 degrees the last 20 mins. It was 72 around 4am. Pretty dramatic changes

You must record it and share

Spidy sense on that storm north of Luray.

84.7 for a high. That is crazy. Ac was tested today