Medium Transport
Flight Crew Air Transport Pilot (ATP)
Workload
Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Weather
Departed Runway 15R BWI. Familiar with weather as [departure airport]. Rain. Light to Moderate Turbulence on arrival. However; our departure would prove radically different. After a normal and uneventful takeoff; we encountered a layer of clouds at approximately 3;500 MSL. It appeared thin and clear above. The airborne weather radar was operating normally and ON. Also; the tilt function was thoroughly utilized. While passing through this altitude with instruction to climb FL 140 and to proceed direct to SWANN; we encountered what could be described as Severe Turbulence. Additionally; a significant updraft was encountered as well. As control of the aircraft became increasingly difficult; I am unable to estimate accurately our climb rate. My guess though; would 5-6000 FPM. During this encounter; we also experienced a reversal of this climb to level flight or slight descent. The level of turbulence is not something I have frequently encountered.The passengers and Flight Attendants (FA) were briefed prior to departure on the potential for turbulence. They were seated and the sterile light was on. It is safe to say; the amount encountered far exceeded my expectations. The duration of the encounter was 2-4 minutes. My sense of time however was distorted. We exited the conditions at approximately 7;000 MSL. There were no radar returns on our radar. NWS radar showed we were on the back edge of light to Moderate rain only. There was no lightning observed in our area. There were no Convective Sigmets. There were no Sigmets or Airmet for turbulence. There were no PIREPS of such. The winds aloft were not exceptional. I do not know of any Low-level Jet streams in the area. The aircraft was light; approximately 38-39;000 lbs GTOW. The aircraft was configured Flaps 0 by this time (3;500 MSL). Climb thrust was selected. No Cautions or Warnings were generated by the aircraft. No injuries were reported. There were significant speed variations. 240 kts to briefly below 200 kts. Overspeed on the order of 260 knots was achieved in an extreme climb rate.The Stall Protection System (SPS) did not activate. The Pilot Limit Indicator (PLI) did show Green. I do not recall further.Upon landing in; we discussed the matter and wrote the airplane up in accordance with SOP.The aircraft was in severe turbulence. It achieved overspeed in clean configuration and also lost 40 kts of airspeed (my estimate). The aircraft achieved extreme climb rate and slight descent in a short period of time. The relatively low altitude of this encounter was also bothersome.I do not believe myself or the First Officer made any errors. I believe we encountered a very unique area of non-convective turbulence. There were no indicators that this scale of turbulence was present. We did know the weather was marginal and did have reasonable expectations regarding the weather. But to be clear; this event far exceeded those expectations.As the Pilot Flying (PF); I allowed the airplane to climb. It should be noted; I was hand flying the entire time. I did nothing to force the aircraft one way or the other. My recollection is that my inputs were simply to 'steer' the general performance of the airplane. In my opinion; the benefit to this encounter was that it propelled us up; much further than it did down. Hence my technique of 'letting' the airplane do its thing.
Air Carrier Captain encountered severe turbulence during climbout.